bluuebunny/crossref_metadata_2025 huggingface dataset:
Ubiquitination and ATP levels in garden pea seeds
Authors: Agustini V. , McIntosh T. , Malek L.
Published: May 2006

Developing and germinating pea seeds contain high levels of ubiquitin conjugated to proteins as detected on western blots. In contrast, the level of dry seed protein‐ubiquitin conjugates in vivo appears low, with mainly free ubiquitin present. The ubiquitination of endogenous dry pea seed proteins is observed in vitro, relying only on already present endogenous ubiquitin, suggesting the enzymatic machinery for ubiquitination is present in the dry seed. Energy source in the form of ATP increased the formation of large molecular mass conjugates, although some conjugation took place without added ATP. The usefulness of dry seeds, having low levels of ATP which can then be manipulated in the in vitro reaction is discussed. ATP and ubiquitin degrading activities are detected in the crude in vitro system, pointing to the need to purify the individual components, or to seek specific inhibitors of the undesirable secondary reactions.
Asparaginyl endopeptidase during maturation and germination of durum wheat
Authors: Bottari Andrea , Capocchi Antonella , Galleschi Luciano , Jopova Andrea , Saviozzi Franco
Published: May 2006

Asparaginyl‐endopeptidase activity was detected in endosperms of maturing and germinating wheat seeds. The highest activity was found during maturation before the maximal accumulation of storage proteins. The enzyme activity then decreased in the dry seeds and increased again during germination. The increase of activity during germination required the presence of the embryo. In fact, the activity found in detached endosperms was lower than that found in attached ones. The localization at tissue level of the enzyme reveals differences between maturation and germination: the enzyme was about equally located in the aleurone layer and starchy endosperm during maturation, but solely in the aleurone layer during germination. The asparaginyl enzymes from maturing and germinating seeds had many similar properties, such as pH optimum, pH stability, thermal stability and sensitivity to thiol reagents and to thiol compounds. The results suggest that asparaginyl endopeptidases may be involved in the modification of proproteins of storage proteins during seed maturation and in the degradation of storage proteins deposited in the aleurone layer during germination.
Changes in structure of starch and enzyme activities affected by sugary mutations in developing rice endosperm. Possible role of starch debranching enzyme (R‐enzyme) in amylopectin biosynthesis
Authors: Nakamura Yasunori , Umemoto Takayuki , Takahata Yasuhiro , Komae Kozo , Amano Etsuo , Satoh Hikaru
Published: May 2006

In maturing endosperms of a variety of sugary mutants of rice, phytoglycogen‐like polysaccharides with highly branched a‐glucans were accumulated instead of amylopectin. while the amylose content greatly decreased. Measurement of activities per endosperm of the 10 major enzymes involved in starch and sucrose metabolism revealed that the activity of starch debranching enzyme (R‐enzyme) was specifically reduced in the sugary mutants. The activity of starch branching enzyme I (Q‐enzyme I) was also significantly decreased, but less so than the R‐enzyme, in the mutants, suggesting some coordination of the expression of the genes coding for R‐enzyme and Q‐enzyme I. Western blot analysis showed that the sugary mutations of rice resulted in a decrease in the amount of R‐enzyme protein, but not in major modification of the enzyme. These findings strongly suggest that R‐enzyme plays a critical role in determining the amylopectin fine structure, since at the extremely low level of R‐enzyme activity as compared with Q‐enzyme activity, as found in sugary mutants, the rice endosperm produced phytoglycogen. We hypothesize that balance of activities or interaction between Q‐enzyme and R‐enzyme may be responsible for the fine structure of a‐polyglucans in plant tissues.
Multiple transcripts of a calcium‐binding protein gene from Atriplex nummularia are differentially regulated by developmental and environmental stimuli
Authors: Zhu Jian‐Kang , Hasegawa Paul M. , Bressan Ray A. , Niu Xiaomu
Published: May 2006

H6 is an Atriplex nummularia gene having high sequence homology with the algal caltractin (a basal‐body‐associated calcium‐binding protein) gene. Recombinant H6 was expressed at high levels in Escherichia coli. The recombinant protein exhibited an ethylene glycol‐bis(β‐aminoethyl ether)‐N,N,N′,N′‐tetraacetic acid‐induced mobility shift during sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, and it was able to bind 45Ca2‐. An H6 cDNA probe detected three RNA transcripts of 1.3, 2.2 and 2.4 kb, respectively. The levels of these transcripts were regulated by different environmental cues and during developmental stages. The steady state levels of the 1.3‐kb mRNA decreased after touch and heat treatments. Expression of the 2.2‐kb message correlated with cell proliferation activity. In cultured cells, the highest level of the 2.2‐kb message preceeded the peak of mitotic cell division activity. In plants, the 2.2‐kb message was detected only in shoot tips that contained meristematic tissues. The 2.4‐kb message was detected exclusively in heat‐shocked cells. The relationship among the three transcripts is discussed in the context of the possible role of H6 in mediating developmental and environmental signals.
Effects of water and nitrogen interaction on net photosynthesis, stomatal conductance, and water‐use efficiency in two hybrid poplar clones
Authors: Liu Zhijun , Dickmann Donald I.
Published: May 2006

We examined the interactions of water and nitrogen availability by subjecting two Populus clones. Tristis and Eugenei, to five soil moisture and three soil nitrogen levels. Nitrogen application significantly increased net photosynthesis and stomatal conductance of flooded Eugenei and Tristis. The onset of flooding caused partial stomatal closure. Net photosynthesis significantly declined after a longer flooding period. Emergence of adventitious roots on the submerged portions of stems in both clones seemingly helped net photosynthesis fully recover in Eugenei and partially recover in Tristis. Under the progressive drought conditions, stomatal conductance was more sensitive to drought than net photosynthesis in both clones. Addition of nitrogen to progressively drying soil induced more stomatal closure in both clones. The highest water‐use efficiency was found on the high‐N/severe drought zone for Eugenei, whereas it was found on the high‐N/mild to moderate drought zone for Tristis.
Isolation and cDNA cloning of an Em‐like protein from mung bean (Vigna radiata) axes
Authors: Manickam Ayyanar , Van Damme Els J. M. , Kalaiselvi Kandasamy , Verhaert Peter , Peumans Willy J.
Published: May 2006

Until now no ‘early‐methionine‐labelled’ (Em) proteins have been reported in the Fabaceae. To check whether a previously isolated low‐molecular mass albumin from dry mung bean embryonic axes possibly corresponded to an Em‐like protein, the protein was purified, sequenced and its cDNA clone isolated and characterized. N‐terminal sequencing of cyanogen bromide cleavage products of the protein revealed homology with previously described Em‐like proteins from other species. Analysis of cDNA clones encoding the mung bean Em protein revealed the presence of two classes of Em proteins and confirmed their homology to the previously characterized Em‐like proteins. In vivo labelling and northern blot analysis further demonstrated that the mung bean protein is synthesized during early germination of the axes and that abscisic acid (ABA) extends its synthesis. It appears, therefore, that legumes also contain maturation‐specific, ABA‐responsive Em‐like proteins.
Changes in mRNA populations during loblolly pine (Pinus taeda) seed stratification, germination and post‐germinative growth
Authors: Mullen Robert T. , King Janice E. , Gifford David J.
Published: May 2006

Changes in the patterns of gene expression were examined during loblolly pine (Pinus taeda L.) seed stratification, germination, and post‐germinative growth. In both the megagametophyte and the embryo, DNA contents remained relatively constant at all stages examined. RNA contents, however, increased in both tissues following seed germination, particularly in the embryo where a 7‐fold increase in the RNA content was observed 5 days after germination. Poly(A)+ RNA, extracted from megagametophytes and embryos, was translated in vitro in a rabbit reticulocyte lysate cell‐free system. Analysis of [35S]‐methionine‐labelled translation products by two‐dimensional electrophoresis/fluorography indicated that there were changes in the populations of mRNAs during all developmental stages examined. In both the megagametophyte and the embryo several distinct mRNA populations, including one constitutively present at all stages examined, were identified. One mRNA population, present in the mature seed, decreased during seed stratification. Another population, not present in the mature seed, rose during the period of stratification that coincided with an increase in seed germinability. A third population, which appeared during seed germination, increased steadily during post‐germinative growth. Besides these similarities, specific differences between megagametophyte and embryo were noted. For example, one mRNA population, which was present in the megagametophyte of the mature seed and remained constant during the stratification period, disappeared immediately following seed germination. In the embryo, one set of messages was germination specific. In total, these results show that mRNA populations change in a temporal fashion that is consistent with the patterns of de novo protein synthesis known to occur in loblolly pine during the same developmental periods.
Effects of changes in growth temperature on photosynthesis and carotenoid composition in Zea mays leaves
Authors: Haldimann Pierre
Published: May 2006

The effects of changes in growth temperature on photosynthesis and carotenoid composition were examined in Zea mays L. leaves of different age and different developmental history. The plants were first grown at sub‐optimal temperature (14°C) until the full development of the third leaf. At that time, the mature third leaf and the immature fourth leaf had a low chlorophyll (Chl) content, a low Chl a/b ratio, a high carotenoid/Chl a+b ratio, a high xanthophyll/β‐carotene ratio, and about 80% of the xanthophyll cycle pool (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was in the form of zeaxanthin and antheraxanthin. When the temperature was increased from 14°C to 24°C for three days, increased Chl synthesis, accompanied by an increase in the Chl a/b ratio, took place. The ratios of lutein, neoxanthin, and V+A+Z to Chl a+b decreased markedly, whereas no significant changes appeared in the β‐carotene/Chl a+b ratio. Furthermore, there was a sharp decrease in the xanthophyll/β‐carotene ratio and most of zeaxanthin was converted to violaxanthin in the xanthophyll cycle. The third leaf and the tip segment of the fourth leaf, both expanded at 14°C, showed little difference in their pigment contents. However, the rate of CO2 assimilation of the tip segment of the fourth leaf was nearly twice that of the third leaf on the third day at 24°C, while the photosynthetic activity was similar in both leaves before the transfer to 24°C. During the warm period at 24°C, new leaf tissue (basal segment of the fourth leaf and part of a fifth leaf) was formed. On the third day at 24°C, the pigment content of 24°C‐grown leaf tissue did not differ much from that of 14°C‐grown leaf tissue with the exception that the total carotenoid content was lower in the former as compared to the latter, mainly because of a lower V+A+Z content. The rate of CO2 assimilation of 24°C‐grown leaf tissue was comparable to that of the tip segment of the fourth leaf. Regardless of which leaf tissue is considered, reducing the temperature from 24°C to 14°C for 5 days slightly affected the pigment content, but violaxanthin was largely converted to zeaxanthin and antheraxanthin in the xanthophyll cycle. The results indicate that compared to old leaf tissue of mature leaves, physiologically younger leaf tissue of immature leaves is much more able to recover from depressions in the photosynthetic activity induced by growth at sub‐optimal temperature when the plants experience optimal growth temperatures, but that factors other than the pigment content must determine this capability.
The effect of source or sink temperature on photosynthesis and 14C‐partitioning in and export from a source leaf of Alstroemeria
Authors: Leonardos Evangelos D. , Tsujita M. James , Grodzinski Bernard
Published: May 2006

The influence of source and sink temperature on leaf net C exchange rate (NCER), export, and partitioning in the C3 monocotyledon Alstroemeria sp. cv. Jacqueline were examined. Leaf (i.e. source) temperature was varied between 12 and 35°C while source leaves were exposed to photorespiratory and nonphotorespiratory conditions during a 2‐h steady‐state 14CO2 labelling period. Between 12 and 20°C, at ambient CO2 and O2, leaf NCER and export were similar with maximum rates of 9.71 ± 0.51 and 3.06 ± 0.36 μmol C m‐2 s‐1, respectively. Both NCER and export decreased above 20°C. At 35°C NCER was 30% of the rate at 20°C, but export was totally inhibited. Between 12 and 35°C, at the end of the 2‐h feeding period, 14C was partitioned in the leaf as ethanol insolubles (3–10%), H2O solubles (88–92%), and chloroform solubles (2–8%). However, above 25°C, less 14C was recovered in the starch fraction and more in the sugar fractions. At all temperatures, 86 to 94% of the labelled sugars was 14C‐sucrose. In nonphotorespiratory conditions (i.e. 1 800 μI I‐1 CO2 and 2% O2). NCER and export were higher than the rates obtained at ambient CO2 and O2 at each temperature. Carbon dioxide enrichment sustained high NCER and export rates even at 35°C, Although CO2 enrichment increased partitioning of 14C into starch, starch synthesis at 35°C was markedly reduced.

Cooling the root‐zone mass (i.e. a dominant sink) to 10°C, which simulated the commercial practice used to induce flowering, had no significant effect on source leaf NCER and export rates either during a 2‐h steady‐state labelling period or subsequently during a 21‐h light‐dark chase period. Furthermore, partitioning of 14C among leaf products at the end of the feed‐chase period was not affected. Additional pulse and chase experiments using 11CO2 fed to source leaves of control and root‐cooled plants showed that there was no difference in the direction of movement of 11C‐assimilates towards the flower or the root zone as a consequence of root cooling. Together, the data indicate that changing source strength, by manipulating photosynthesis and photorespiration, by varying the leaf temperature had a more profound effect on leaf export than manipulating sink activity.
Expression of glutamine synthetase genes during natural senescence of tomato leaves
Authors: Pérez‐Rodríguez Josefa , Valpuesta Victoriano
Published: May 2006

Changes in the expression of cytosolic glutamine synthetase (GS1; EC 6.3, 1.2) and chloroplastic glutamine synthetase (GS2) were examined in tomato (Lycopersicon esculentum Mill.) leaves during natural senescence. Total GS activity during this process declined to 4% of the highest value reached at the time of maximum leaf growth rate. Changes of activity were probably caused by a decrease in the amount of GS2 polypeptides. The presence of GS1 polypeptides was evident during the late senescence stage of the leaf despite the low content of total soluble protein. The differential expression of GS genes during leaf senescence in tomato plants was followed using gene‐specific homologous probes synthesized from cloned cDNAs encoding cytosolic and chloroplastic GS polypeptides. Northern blot analysis showed that the level of GS2 transcripts decreased during leaf senescence as did the amounts of GS2 polypeptide, but messengers for GS2 were undetectable in the very late senescence stage when a small amount of polypeptides was still present. The content of mRNA detected with the 3’non‐coding region of the GS1 probe dramatically increased with leaf senescence, thus explaining the presence of GS1 polypeptides at this stage, although there was no correspondence between the amount of GS protein and the high abundancy of GS1 mRNA. The presence of both GS1 polypeptide and messenger in the leaf, and their increase during natural leaf senescence, support a role for GS1 in this process.
Fluxes of Na+, K+ and Cl‐, and osmotic adjustment in Lycopersicon pimpinellifolium and L. esculentum during short‐ and long‐term exposures to NaCl
Authors: Guerrier Gilles
Published: May 2006

NaCl (140 mM) was applied to 14‐day‐old plants of salt‐sensitive Lycopersicon esculentum Mill. cv. Volgogradskij and its wild relative L. pimpinellifolium Mill. accession PE‐2. Changes in the relative growth rate of whole plant, and in the levels of inorganic and organic solutes in leaves, stems and roots were followed for 15 days after the application. Short‐term salt exposure (4–6 days of salinization) resulted in enhanced relative growth rates for L. pimpinellifolium, but did not affect growth of L. esculentum, After 6 days of salinization, the relative growth rates of both species decreased significantly; leading to practically comparable growth rates for them by day 15. In all parts of both species, the contribution of organic solutes to the osmotic potential (Ψs) gradually decreased from 30% on day 0 to a value lower than 5% on day 4. In L. pimpinellifolium, compared to L. esculentum, short‐term salt exposure resulted in (1) a higher percentage of adjustment of Ψs; and (2) increases in Na+ and K+ uptake rates, and in the levels of organic acids and proline (the level of which reached that of sugars, i.e., 10 μmol g‐1 dry weight. Conversely, in L. esculentum, drastic reductions of K+ uptake rates and organic acid levels occurred already on day 1. During long‐term salt exposure, both species were able to adjust osmotically and both exhibited decreases in organic acid levels as well as in K+ uptake and accumulation rates in all parts. The results are discussed in an attempt to explain the adaptive responses during short‐term salt exposure and the metabolic dysfunctions that lead to growth decrease after long‐term exposure to salt.
Protein targeting and import into plant peroxisomes
Authors: Gietl Christine
Published: May 2006

A main characteristic of the eucaryotic cell is the compartmentalization of different metabolic processes into membrane‐enclosed organelles. Each organelle contains a characteristic set of proteins to accomplish specific metabolic functions that are often essential for the cell's viability. The most recently discovered class of organelles includes the microbodies that encompass a group of organelles which have some morphological properties in common. Microbodies are ubiquitous in eucaryotic cells and can be subdivided into different types of organelles according to their metabolic functions (e.g. peroxisomes and glyoxysomes). The size and number of microbodies per cell is often related to the developmental stage and/or the organism in which they occur. This implies that microbody proliferation is inductible in nature. This review summarizes the progress made in recent years in understanding how proteins are targeted to and imported into microbodies. Major breakthroughs were the identification of the two main peroxisomal protein targeting signals (PTS1 and PTS2), protein receptors for the signals and the isolation of yeast mutants defective in the biogenesis of microbodies. Especially the availability of these mutants has opened new ways to identify proteins involved in microbody protein import in plants as well as animals.
The ubiquitin system in plants
Authors: von Kampen Jan , Wettern Michael , Schulz Margot
Published: May 2006

The small polypeptide ubiquitin participates in a variety of fundamental cellular events, such as cell differentiation, stress response, determination of steady state levels of regulatory proteins, cell cycle control, regulation of transcription, and programmed cell death. Although the complex mechanisms of these processes are not fully understood, ubiquitinylation of regulatory proteins involved in those events is obviously essential. Target proteins can be covalently coupled with one or a few ubiquitin molecules, which is supposed to present a (reversible) post‐translational modification. Polyubiquitinylation, however, marks proteins selectively for degradation by the 26S proteasome. The ubiquitin system has been studied mostly with animal systems or yeast, but all basic reactions of ubiquitin appear in plants as well.

The scope of this review is to summarize several implications of recent studies directed towards the plant ubiquitin system.
Two classes of pollen‐specific, heat‐stable proteins in Lilium longiflorum
Authors: Wang Co‐Shine , Wu Tzong‐Daw , Chung Chi‐Keung Wilson , Lord Elizabeth M.
Published: May 2006

Several floral organ‐specific proteins in lily anthers do not accumulate to detectable levels until just before anthesis. Antisera were raised against three of these proteins. designated LLA, in pollen of Lilium longiflorum Thunb. cv. Snow Queen. Monospecific antibodies were further prepared from antisera to investigate the specificity and distribution of these proteins during development. In an effort to study the function of these gene products, pollen protein was heat‐treated at 90°C for 10 min. Monospecific anti‐LLA‐32 and ‐23 antibodies recognized two of these heat‐stable proteins with molecular masses of 32 and 23 kDa. Accumulation of the two proteins in anther development was correlated with desiccation that occurred naturally in the pollen. Immunob‐lot analyses of total protein from floral and vegetative organs confirmed that both LLA‐32 and ‐23 proteins were pollen‐specific. The proteins showed consistent patterns of expression during development and their levels decreased when pollen germinated. The properties of the two proteins differed in responsiveness to both polyethylene glycol 8000 and abscisic acid, and in solubility characteristics. Analysis of amino acid composition indicates that both LLA‐32 and ‐23 proteins are rich in glutamic acid/glutamine and glycine, a characteristic of heat‐stable proteins. However, LLA‐23 has more polar amino acid residues with a polarity of 57%, two‐fold higher than that of the LLA‐32. Immunoblot analyses showed that LLA‐32 and ‐23 proteins were immunologically unrelated to the dehydrin‐like protein in lily seeds. It concluded that the two classes of pollen‐specific proteins have some features in common with each other and with dehydrins. but that each is distinct.
Cut‐shoot vs root rehydration: Effects on pressure‐volume analysis of shoots and fascicles ofPinus resinosaseedlings
Authors: Parker W. C. , Colombo S. J.
Published: May 2006

Two methods of rehydrating red pine (Pinus resinosaAit.) shoots for pressure‐volume (PV) analysis were compared to clarify the effects of rehydration on estimated tissue water relations of shoots and fascicles. The commonly employed cut‐shoot method was compared to rehydration by means of water uptake through the roots of intact plants. Cut‐shoot rehydration and increased duration of rehydration significantly decreased estimates of tissue elasticity and relative water content at zero turgor for both shoots and fascicles. Rehydration of cut shoots for 2 days significantly increased the slope of the linear region of shoot pressure‐volume (PV) curves and decreased estimates of the apoplastic water fraction. Changes in these and estimates of other water relations attributes were correlated with increased initial water content during rehydration. Estimated apoplastic water fraction was higher for needle fascicles than shoots despite the large amount of woody stem tissue contained in shoots. Fascicle water status strongly influenced shoot water relations, in part due to apparent apoplastic loading with water of fascicles during rehydration.
Jasmonic acid promotes division of fern protoplasts, elongation of rhizoids and early development of gametophytes
Authors: Camloh Marjana , Ravnikar Maja , Zel Jana
Published: May 2006

The effects of jasmonic acid (JA) on spore germination, early gametophyte development and sporophytic protoplast culture of the fern Platycerium bifurcalum (Cav.) C. Chr. were investigated. JA and no influence on spore germination and primary rhizoid initiation, but significantly promoted early gametophyte development, which was evident from the longer primary rhizoids as well as the higher number of rhizoids and cells per gametophyte. Jasmonic acid (1 μM) also promoted the transition of gametophytes from a filamentous to a planar growth. Optimal primary rhizoid elongation and highest cell division activities in the gametophytes were observed at 0.01–1 μM JA, while the highest number of rhizoids on gametophytes was obtained at 0.1–1 μM JA. Jasmonic acid (0.01 μM) also stimulated initial protoplast divisions. Except for the experiment in which the effect of JA on germination was tested. JA concentrations exceeding 1 μM did not promote cell elongation or cell division but were instead inhibitory. On the basis of these findings, we propose that JA may be involved in early stages of P. bifurcatum development.
BT1, a protein critical for in vivo starch accumulation in maize endosperm, is not detected in maize endosperm suspension cultures
Authors: Cao Heping , Shannon Jack C.
Published: May 2006

MaizeBt1is a structural gene for the major 39–44‐kDa amyloplast membrane polypeptides. Loss of BT1 in thebrittle1(bt1) mutant results in an 80% reduction in kernel starch. As an initial step toward the understanding of BT1 function, we investigated the relation of BT1 to starch accumulation in the two well‐characterized maize endosperm suspension‐cultured cell lines which were derived from 10 days post pollination (DPP) kernels of inbred A636 and 12‐DPP kernels of thewaxymutant in the A636 background. Starch in A636 endosperm cultures accounted for about 1.5% of the fresh weight of cells but BT1 was not detectable in amyloplast membranes or in microsomal membranes isolated from the cultured cells.Bt1transcripts were detected in 10‐ and 20‐DPP A636 kernels, but only a trace ofBt1transcripts was detected in the suspension‐cultured cells. Southern blotting indicated that theBt1gene was present in the genome of the cultured cells. TheBt1gene products in A636 endosperm cultures were not increased by treatments which enhance starch accumulation such as sucrose supplementation, chlorocholine chloride (CCC) addition to the medium, or both. A similar pattern of differentialBt1gene expression was found in thewaxyendosperm cultures. These results indicate that starch accumulation in the cultured cells is not correlated withBt1gene expression. The significance of these findings is discussed.
Aluminum stress and protein synthesis in near isogenic lines of Triticum aestivum differing in aluminum tolerance
Authors: Somers Daryl J. , Briggs Keith G. , Gustafson J. Perry
Published: May 2006

Aluminum (Al) stress was examined in three lines of wheat (Triticum aestivum L.) by measuring root lengths, protein synthesis and protein accumulation in seedling root tips grown in a hydroponic system. An Al‐sensitive, recurrent wheat parent (cv. Katepwa) showed very little root growth in low Al concentrations. In contrast, an Al‐tolerant near isogenic line (Alikat) and Al‐tolerant donor (cv. Maringa) had much greater root growth. Segregation data from an F2 population (Katepwa × Alikat) showed that one major gene controlled Al tolerance based on root growth (X2= 0.651). All three lines showed an approximately 2‐fold increase in [35S]‐Met incorporation in root tips after 3 days in Al and a comparable increase in root‐tip dry weight. Maringa and Alikat root tips showed an increased total protein content while Katepwa root tips showed no increase in total protein content during the Al stress. Based on higher specific activities, insoluble proteins were preferentially translated in all three lines during Al stress. Proteinase activity in Katepwa root tips was 1.7‐fold higher during Al stress, with Maringa and Alikat showing no change in proteinase activity. The Al‐induced, increased proteinase activity in Katepwa appeared to inhibit soluble protein accumulation.
Immunolocalization of extensin and potato tuber lectin in carrot, tomato and potato
Authors: Li Shu‐xia , Showalter Allan M.
Published: May 2006

Tissue‐specific expression of two members of the cell wall hydroxyproline‐rich glycoprotein (HRGP) family, extensin and potato tuber lectin, was examined by immunolocalization at the light microscope level in various organs (leaves, stems, roots, fruit, tuber) of carrot (Daucus carota cv. Thumbelina), tomato (Lycopersicon esclentum cv. Pixie Hybrid II), and potato (Solanum tuberosum cv. Kennebec). Extensin was prominently expressed in vascular tissue, particularly xylem and also phloem, although virtually all cells displayed some degree of staining which varied as a function of the tissue, organ, and plant under study. Antibodies against potato tuber lectin (PTL) displayed a localization pattern similar to that observed for extensin; notably PTL did not stain cambium but did stain epithelial cells lining secretory cavities. These distribution patterns are consistent with a role for extensin, and possibly PTL, in providing mechanical support in tissues subjected to compression or torsional stress imparted by vascular growth, or by similar stress brought about by transport of vascular fluids.
Flowering in Pisum: Identification of a new ppd allele and its physiological action as revealed by grafting
Authors: Taylor Scott A. , Murfet Ian C.
Published: May 2006

The late flowering, quantitative long day habit of wild type pea (Pisum sativum L.) is conferred by the joint presence of dominant genes Sn, Dne and Ppd. Grafting studies have shown that flowering in wild type plants is delayed under short days by formation of a graft‐transmissible inhibitor and that the early flowering, day neutral mutants sn and dne are deficient in this inhibitor. However, the physiological action of the Ppd gene has not been examined by grafting and the possibility exists that the ppd mutation causes early flowering and a day neutral habit by blocking response to, rather than synthesis of, the inhibitor. We here identify a second, more severe (probably null) mutant allele (ppd‐2) at the Ppd locus and show that flowering was delayed by 4 nodes in a ppd‐2 shoot grafted to a wild type stock, and promoted by 13 nodes in a wild type shoot grafted to a ppd‐2 stock. Thus a ppd‐2 shoot can respond to inhibitor donated by a wild type stock but a ppd‐2 stock is unable to provide sufficient inhibitor to prevent early flower initiation in a wild type shoot. We conclude genes Sn, Dne and Ppd each control steps in the synthesis of the flower inhibitor. Grafts among the sn, dne and ppd mutants gave an indication that the three genes may act in the sequence Sn, Ppd, Dne, but possible cases of physiological complementation need to be tested using null mutants in the same genetic background.
Phosphoenolpyruvate carboxylase in root nodules of Vicia faba: Partial purification and properties
Authors: Ocaña Antonio , Cordovilla María del Pilar , Ligero Francisco , Lluch Carmen
Published: May 2006

Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) was purified 56‐fold from Vicia faba root nodules to a specific activity of 24.8 units mg‐1 protein. Native molecular mass was determined to be 443 kDa by gel permeation chromatography, whereas a molecular mass of 113 kDa was obtained for the subunit by means of SDS‐PAGE, indicating that the enzyme is a homotetramer. One peak of activity was obtained by ion‐exchange chromatography or gel filtration, and thus there was no evidence of isoenzymes. The effect of pH on PEPC activity was studied, the pH optimum found at 8.25. The effect of substrate (phosphoenolpyruvate, PEP) on the enzyme activity was studied at five different pH values from 6.5 to 9.5. The Km(PEP) at pH 8.25 proved to be 0.064 mM. Inhibition by malate or activation by glucose‐6‐phosphate was dependent on the pH of the reaction mixture. Malate behaved as a non‐competitive mixed‐type inhibitor with a Ki of 0.76 mM, a Ki(s) of 1.15 mM and a Ki(i) of 0.72 mM, at pH 7.0 while at pH 8.25 Ki was about 140 mM. Activation by glucose‐6‐P was 70% with 4 mM PEP at pH 7, whereas no effect was found at pH 8.25. Experiments with mixed effectors at pH 7 and 1 mM PEP, showed that glucose‐6‐P can reverse the inhibition caused by L‐malate on the PEPC activity.
Chromosaponin I increases mechanical extensibility of lettuce root cell walls
Authors: Tsurumi Seiji , Watanabe Ryugo , Kamisaka Seiichiro
Published: May 2006

Chromosaponin I (CSI), at 3 mM, stimulates the growth of lettuce roots (Lactuca sativa L. cv. Grand Rapids) with increasing fresh weight and decreasing root diameter compared with control. To analyze the mechanism of action of CSI, mechanical properties of lettuce root cell walls were examined with a tensiometer and the osmotic potential of the cell sap was measured with a vapor pressure osmometer. The mechanical extensibility of the cell wall was increased by CSI treatment, while the osmotic potential remained constant. Under osmotic stress, through addition of 0.225 M mannitol, the mechanical extensibility of the cell wall was increased before stimulation of growth was observed. These results suggest that cell wall‐loosening is involved in the growth stimulation induced by CSI.
Photosynthesis, growth and nutrient changes in non‐nodulated Phaseolus vulgaris grown under atmospheric and elevated carbon dioxide conditions
Authors: Mjwara Jabulani M. , Botha C. Edward J. , Radloff Sarah E.
Published: May 2006

The response of Phaseolus vulgaris L. cv. Contender grown under controlled environment at either ambient or elevated (360 and 700 μmol mol‐1, respectively) CO2 concentrations ([CO2]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO2 had a pronounced effect on total plant height (TPH), leaf area (LA), leaf dry weight (LD), total plant biomass (TB) accumulation and specific leaf area (SLA). All of these were significantly increased under elevated carbon dioxide with the exception of SLA which was significantly reduced. Other than high initial growth rates in CO2‐enriched plants, relative growth rates remained relatively unchanged throughout the growth period. While the trends in growth parameters were clearly different between [CO2], some physiological processes were largely transient, in particular, net assimilation rate (NAR) and foliar nutrient concentrations of N, Mg and Cu. CO2 enrichment significantly increased NAR, but from 20 DAG, a steady decline to almost similar levels to those measured in plants grown under ambient CO2 occurred. A similar trend was observed for leaf N content where the loss of leaf nitrogen in CO2‐enriched plants after 20 DAG, was significantly greater than that observed for ambient‐CO2 plants. Under enhanced CO2, the foliar concentrations of K and Mn were increased significantly whilst P, Ca, Fe and Zn were reduced significantly. Changes in Mg and Cu concentrations were insignificant. In addition. high CO2 grown plants exhibited a pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity.
Desiccation tolerance in vegetative plant cells
Authors: Oliver Melvin J.
Published: May 2006

Plants that can withstand desiccation of their vegetative tissues represent all but one class (the gymnosperms) within the kingdom Plantae. Phylogenetic evidence suggests that this trait has evolved a minimum of twelve separate occasions. Nevertheless desiccation‐tolerant plants can be grouped into two categories: (1) the desiccation‐tolerant plants whose internal water content rapidly equilibrates to the water potential of the environment and (2) the modified desiccation‐tolerant plants that all employ mechanisms to retard and control the rate of water loss. Desiccation tolerance can be achieved by mechanisms that incorporate one of two alternatives, viz, cellular protection or cellular recovery (repair). The majority of plants probably utilize aspects of both. Studies to date indicate that modified desiccation‐tolerant plants (angiosperms and pteridophytes) appear to rely more heavily upon drying‐induced (abscisic acid controlled) cellular protection strategies for survival. Desiccation‐tolerant species, in particular the moss Tortula ruralis, appear to utilize a tolerance strategy that combines a constitutive protection system and a rehydration‐inducible recovery mechanism. The moss is capable of storing mRNAs during slow drying that are rapidly utilized upon rehydration. Rapidly dried moss has to rely on rapid synthesis of the same mRNAs upon rehydration. Analysis of protein profiles upon rehydration has facilitated the identification of several “rehydrins,” proteins whose synthesis is specific to the rehydration phase. Northern analysis of rehydrin cDNAs confirm the importance of translational controls in producing rehydrin proteins and an additional role of transcription and/or mRNA stability in the response of Tortula to desiccation. These studies indicate that there is more to desiccation tolerance mechanisms than protection of the cells from drying, but rather rehydration‐induced events are important in the overall manifestation of desiccation tolerance.
The anhydrobiotic cyanobacterial cell
Authors: Potts Malcolm
Published: May 2006

The cyanobacterium Nostoc commune has been developed as the prokaryotic model for the anhydrobiotic cell and it provides the means to answer fundamental questions about desiccation tolerance. The anhydrobiotic cell is characterized by its singular lack of water — with contents as low as 0.02 g H2O g‐1 dry weight. These levels are orders of magnitude lower than those found either in bacterial spores or in cells subjected to acute salt (osmotic) stress. Mechanisms that contribute to the desiccation tolerance of N. commune include the selective stabilization of anhydrous proteins, the secretion of water‐ and lipid‐soluble UV‐absorbing pigments, and the secretion of a complex glycan that immobilizes the cells, immobilizes water stress proteins and the UV‐absorbing pigments, and which may confer the properties of a mechanical glass upon colonies. Rehydration of desiccated cells induces an instantaneous resumption of metabolic activities, including membrane transport and global lipid biosynthesis. These initial recoveries may not follow classical Arrhenius‐based kinetics. The rehydrating cell exhibits a stringent, stepwise recovery of physiological capacities beginning with respiration, then photosynthesis and finally nitrogen fixation. Protein turnover, de novo protein synthesis and a rapid rise in the intracellular ATP pool accompany these recoveries. During the early stages of rehydration, the de novo transcription of one gene set (rpoC1C2) is achieved using an extant DNA‐dependent RNA polymerase holoenzyme that remains stable in desiccated cells. These properties of desiccation‐tolerant cyanobacleria, present in extant forms such as N. commune and Chroococcidiopsis spp., may have been utilized by the eoanhydrobiotes. However, it is the desiccation‐tolerant cyanobacterium as a whole, and not some collection of disparate properties, that must be considered as the primary strategy for the achievement of desiccation tolerance.
Dehydrins: Emergence of a biochemical role of a family of plant dehydration proteins
Authors: Close Timothy J.
Published: May 2006

A number of proteins have been identified that typically accumulate in plants in response to any environmental stimulus that has a dehydrative component or is temporally associated with dehydration. This includes drought, low temperature, salinity and seed maturation. Among the induced proteins, dehydrins (late embryogenesis abundant [LEA] D‐II family) have been the most commonly observed, yet we still have an incomplete knowledge of their fundamental biochemical role in the cell. Current research trends are changing this situation: immunolocalization and in vitro biochemical analyses are, through analogies to other more fully characterized proteins and molecules, shaping our understanding. In brief, dehydrins may be structure stabilizers with detergent and chaperone‐like properties and an array of nuclear and cytoplasmic targets. Recent progress on the mapping of dhn genes and the inheritance of freezing tolerance in barley and other Triticeae species tentatively points to dehydrins as key components of dehydration tolerance.
Physiological aspects of Taxus brevifolia seeds in relation to seed storage characteristics
Authors: Walters‐Vertucci Christina , Crane Jennifer , Vance Nan C.
Published: May 2006

Water relations, desiccation tolerance and longevity of Taxus brevifolia (Nutt.) seeds were studied to determine the optimal stage of development and storage conditions for seeds of this species. Seeds equilibrated to a range of relative humidities (RHs) had unusually low water contents which can be accounted for by the high lipid content of gametophyte tissues (71% of the dry mass). Water relations of embryonic tissue were more typical of those reported for other seed species. The water content below which freezing transitions were not observable in the embryo was ca 0.24 g H2O (g dry weight)−1 (g g−1) for all maturity classes studied. Embryos did not achieve significant levels of desiccation tolerance (survival to water contents less than 0.5 g g−1) until the latter stages of development when dry matter was maximal. Mature embryos could be dried to 0.025 g g−1 (seed water content of 0.010 g g−1) with no loss of viability. Thus, at the latter stages of development, embryo water content could be optimized to avoid both desiccation and freezing damage. Survival of mature seeds declined over a 2‐year period when seeds were stored at temperatures between 5 and 35°C and RHs between 14 and 75%, corresponding to seed water contents between 0.015 and 0.07 g g−1. The deterioration rate was slowest for seeds stored at the lowest RH and temperature. Our data indicate that seeds of Taxus brevifolia show orthodox rather than recalcitrant storage characteristics, but that the optimum water content for storage was extremely low. The results suggest that even if stored at optimal water contents and low temperatures, T. brevifolia seeds will be relatively short lived. The high quantity of lipids or reducing sugars may be contributing factors in the poor storage characteristics.
Focusing of light by leaf epidermal cells
Authors: Vogelmann Thomas C. , Bornman Janet F. , Yates David J.
Published: May 2006

Leaf epidermal cells from a wide variety of plants focus light to surprisingly high levels. Using image analysis, the concentration and distribution of light was measured after it passed through epidermal cells within peels and epidermal cells attached to palisade cells in partially dissected leaves. In peels taken from Medicago sativa, Zea mays, and Impatiens sp., light was concentrated 15‐ to 20‐fold by individual epidermal cells. When left attached to the mesophyll, which attenuated focusing by absorption and scattering, light was focused up to 5 times. The position of the focal spot beneath each epidermal cell was affected by the direction at which the light struck the cell. When the light was perpendicular to the leaf surface, individual focal spots fell beneath each epidermal cell. When the incident light was oblique, the focal spot shifted laterally and was positioned closer to the anticlinal cell wall. Focusing was observed when leaves were irradiated with collimated light but not with diffuse light. Focal lengths were relatively independent of wavelength within the visible region of the spectrum and there were only slight differences between focusing of blue vs red light. Epidermal lens properties can affect chlorophyll fluorescence and the photosynthetic performance of leaves. A survey of 47 species collected from a wide variety of habitats indicates that many plants have leaf epidermal cells with lens properties. The ability to measure epidermal focusing makes it possible to examine the adaptive and physiological significance of epidermal lens effects in plants.
Photochemical response to drought acclimation in two sunflower genotypes
Authors: Maury Pierre , Mojayad Fahima , Berger Monique , Planchon Claude
Published: May 2006

The effects of drought acclimation on CO2 assimilation and light utilization were investigated in two sunflower genotypes (Helianthus annuus L., T32 and Viki) in relation to water deficit and/or high light conditions. Drought interaction with PSII efficiency was observed in the genotype T32 with a sustained decrease in the potential photochemical efficiency of PSII, Fn/Fm. In response to drought acclimation, T32 displayed some tendency to accumulate closed PSII traps (higher value of 1‐qp) without an enhancement of thermal deactivation (Stem‐Volmer non‐photochemical quenching, NPQ). Irrespective of the growth conditions (growth chamber or greenhouse), only Viki was responsive to drought acclimation, with (1) increased net photosynthesis in well‐watered plants, (2) higher maintenance of photochemical electron transfer under water deficit and/or high light, (3) limited PSII inactivation (lower value of 1‐qp) through increased non‐photochemical energy dissipation (Stern‐Volmer NPQ) which was readily reversible even at low leaf water potentials, and (4) higher Fv/Fm recovery after high light treatment. Additionally, drought acclimation delayed turgor loss during subsequent water stress in Viki. Thus, the response to drought acclimation, with an adjustment of water relations and of energy utilization by PSII, was observed under both growth conditions and was mainly genotype dependent.
Acquisition and within‐plant allocation of 13C and 15N in CO2‐enriched Quercus robur plants
Authors: Vivin Philippe , Martin Francis , Guehl Jean‐Marc
Published: May 2006

We assessed the effects of doubling atmospheric CO2 concentration, [CO2], on C and N allocation within pedunculate oak plants (Quercus robur L.) grown in containers under optimal water supply. A short‐term dual 13CO2 and 15NO3− labelling experiment was carried out when the plants had formed their third growing flush. The 22‐week exposure to 700 μl l−1 [CO2] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l−1 [CO2] treatment) but decreased the root/shoot biomass ratio (‐23%) and specific leaf area (‐18%). Moreover, there was an increase in net CO2 assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above‐ and below‐ground CO2 respiration rates (‐32 and ‐26%, respectively, on a dry mass basis) under elevated [CO2]. 13C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO2] both after the 12‐h 13CO2 pulse phase and after the 60‐h chase phase. Plant N content was increased under elevated CO2 (+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (‐11%). There was no effect of elevated [CO2] on fine root‐specific 15N uptake (amount of recently assimilated 15N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO2] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO2]. These results are consistent with the short‐term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60‐h 13C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent 13C under ambient [CO2], whereas these leaves retained important amounts of recently assimilated 13C (carbohydrate reserves?) under elevated [CO2].