bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetics and expression of two pectinesterase genes in Valencia orange
Authors: Joseph Nairn C. , Lewandowski Dennis J. , Burns Jacqueline K.
Published: March 2003

The genetics and expression of pectinesterase (PE) genes were examined in Valencia orange. Degenerate primers based on partial amino acid sequence of a 36 kDa PE protein isolated from juice vesicles were used to amplify a 350 bp DNA fragment from cDNA prepared from juice vesicle total RNA. Two groups of 350 bp PE clones with 66% sequence identity were isolated. A clone from each group was used to screen a Valencia orange genomic DNA λ library. Two different lambda clones that contained complete PE coding sequence (CsPME1 and CsPME3) and a third lambda clone that contained partial PE sequence (CsPME2) were characterized. The CsPME1 gene contained two exons (1063 and 689 bp) interrupted by a 1452 bp intron, whereas the CsPME3 gene had two exons (844 and 686 bp) interrupted by a 771 bp intron. CsPME1 shared significant sequence similarity with the partial clone CsPME2, including the entire cloned region of the first exon, a large region in the 5′ portion of the intron and the 3′ portion of the second exon, but the 3′ portion of the intron and the 5′ portion of the second exon were dissimilar. Southern blots suggested that Valencia orange has two genes within each PE group. Full‐length cDNA clones that shared 99% sequence identity with CsPME1 and CsPME3 were isolated. Both groups of PE genes were differentially expressed in tissues of Valencia orange, and in addition CsPME3 appeared to be ethylene‐regulated. The deduced proteins of PE cDNA clones CsPME1 (63.5 kDa) and CsPME3 (56.3 kDa) were considerably larger than the PE protein we isolated from Valencia orange juice vesicles and also other mature plant PE proteins. The estimated size of group I (2.2 kb) and group II (2.0 kb) PE mRNAs also predicted a larger protein than was isolated from juice vesicles. Alignment of the mature tomato and mung bean PE proteins, the most N‐terminal sequence we obtained from polypeptides derived from the 36 kDa PE isolated from juice vesicles and the deduced amino acid sequences of plant PE cDNA clones suggest that a post‐translational cleavage event separates the variable N‐terminus from the more conserved C‐terminal domain of the mature PE protein.
Distinct responses to copper stress in the halophyte Mesembryanthemum crystallinum
Authors: Thomas John C. , Malick Farah K. , Endreszl Charles , Davies Elizabeth C. , Murray Kent S.
Published: March 2003

Selective gene expression allows the halophyte Mesembryanthemum crystallinum to survive a salt stress. To broaden our understanding of the environmental cues initiating diverse stress responses in this higher plant, unstressed and 0.4 M NaCl‐stressed plants were compared to plants treated with several concentrations of copper (CuSO4), an increasingly relevant environmental heavy metal pollutant. Comparisons of control and copper‐stressed plants included germination, chlorophyll content, accumulation of proline, heat shock protein (HSP) 60 and a Crassulacean acid metabolism (CAM)‐specific marker enzyme, phosphoenolpyruvate carboxylase (PEPCase). In germination and whole plant tests, M. crystallinum was significantly more tolerant to copper than Arabidopsis thaliana. Mature M. crystallinum plants stressed with 50 ppm CuSO4 for 48 h became dehydrated. These plants produced a 4‐fold increase in proline concentration and accumulated both the CAM‐specific PEPCase and HSP 60 compared to controls. Higher levels of copper stress resulted in a 10‐fold increase in leaf proline content, 10‐fold HSP 60 accumulation but no detectable PEPCase protein compared to unstressed controls. HSP 60 did not accumulate under NaCl stress. Concurrent with copper‐induced genetic responses to stress, copper was accumulated and concentrated in leaves (3 500 ppm). Together, these results suggest that this halophyte copes with copper metal exposure through distinct genetic mechanisms.
Inhibitory effects of ambient levels of solar UV‐A and UV‐B radiation on growth of cv. New Red Fire lettuce
Authors: Krizek Donald T. , Britz Steven J. , Mirecki Roman M.
Published: March 2003

The influence of solar UV‐A and UV‐B radiation at Beltsville, MD, USA, on growth of Lactuca sativa L. (cv. New Red Fire lettuce) was examined during early summer of 1996 and 1997. Plants were grown from seed in plastic window boxes covered with Llumar to exclude UV‐A and UV‐B, polyester to exclude UV‐B, or tefzel (1996) or teflon (1997) to transmit UV‐A and UV‐B radiation. After 31–34 days, plants grown in the absence of solar UV‐B radiation (polyester) had 63 and 57% greater fresh weight and dry weight of tops, respectively, and 57, 72 and 47% greater dry weight of leaves, stems and roots, respectively, as compared to those grown under ambient UV‐B (tefzel or teflon). Plants protected from UV‐A radiation as well (Llumar) showed an additional 43 and 35% increase, respectively, in fresh and dry weight of tops and a 33 and 33% increase, respectively, in dry weight of leaves and stems, but no difference in root biomass over those grown under polyester. Excluding ambient UV‐B (polyester) significantly reduced the UV absorbance of leaf extracts at 270, 300 and 330 nm (presumptive flavonoids) and the concentration of anthocyanins at 550 nm as compared to those of leaf extracts from plants grown under ambient UV‐A and UV‐B. Additional removal of ambient UV‐A (Llumar) reduced the concentration of anthocyanins, but had no further effect on UV absorbance at 270, 300 or 330 nm. These findings provide evidence that UV‐B radiation is more important than UV‐A radiation for flavonoid induction in this red‐pigmented lettuce cultivar. Although previous workers have obtained decreases in lettuce yield under enhanced UV‐B, this is the first evidence for inhibitory effects of solar UV‐A and UV‐B radiation on lettuce growth.
The range of mobility of the non‐cellulosic polysaccharides is similar in primary cell walls with different polysaccharide compositions
Authors: Smith Bronwen G. , Harris Philip J. , Melton Laurence D. , Newman Roger H.
Published: March 2003

The molecular mobility of the non‐cellulosic polysaccharides in hydrated primary cell walls of three monocotyledons (Italian ryegrass, pineapple and onion) and one dicotyledon (cabbage) was studied using solid‐state 13C NMR spectroscopy. These cell walls were chosen as they have different non‐cellulosic polysaccharide compositions. By exploiting proton rotating‐frame and spin‐spin relaxation time constants three different cell wall domains which responded to cross‐polarization experiments were identified. Most of the non‐cellulosic polysaccharides occupied a mobile domain (C), but some occupied a partly rigid domain (B). Crystalline cellulose occupied a highly rigid domain (A). In the cell walls of Italian ryegrass and pineapple, domain C contained mainly glucuronoarabinoxylans and small amounts of rhamnogalacturonans; domain B contained small amounts of xyloglucans and galacturonans. However, in the cell walls of onion and cabbage, domain C contained mainly rhamnogalacturonans with galactans (in onion) or arabinans (in cabbage) as side chains; domain B contained galacturonans and xyloglucans. Single‐pulse excitation was used on Italian ryegrass and cabbage cell walls to reveal signals from a highly mobile fourth domain (D). In Italian ryegrass cell walls domain D contained glucuronoarabinoxylans and small amounts of rhamnogalacturonan, whereas in cabbage cell walls it contained arabinan side chains of rhamnogalacturonans. A novel feature of the research was the use of solid‐state 13C NMR spectroscopy to examine the molecular mobilities of the polysaccharides in monocotyledon cell walls that contain glucuronoarabinoxylans.
Blue light‐induced apoplastic acidification of Arabidopsis thaliana guard cells: Inhibition by ABA is mediated through protein phosphatases
Authors: Roelfsema M. Rob G. , Staal Marten , Prins Hidde B. A.
Published: March 2003

The phytohormone abscisic acid (ABA) inhibits blue light‐induced apoplastic acidification of guard cells. The signal transduction pathway of ABA, mediating this response, was studied using ABA‐insensitive (abi) mutants of Arabidopsis thaliana. Apoplastic acidification was monitored with a flat tipped pH‐electrode placed on epidermal strips, in which only guard cells were viable. Blue light‐induced apoplastic acidification was reduced by vanadate and diethylstilbestrol (DES), indicating involvement of plasma membrane‐bound H+‐ATPases. In wild type epidermal strips, ABA reduced blue light‐induced acidification to 63%. The inhibition did not result from an increased cytoplasmic free Ca2+ concentration in guard cells, since factors that increase the Ca2+ concentration stimulated apoplastic acidification. Apoplastic acidification was not inhibited by ABA in abi1 and abi2 mutants. In abi1 epidermal strips ABA had no effect on the acidification rate, while it stimulated apoplastic acidification in abi2. The ABA response in both mutants could be partially restored with protein kinase and phosphatase inhibitors. The abi1 guard cells became ABA responsive in the presence of okadaic acid, a protein phosphatase inhibitor. In abi2 guard cells the wild type ABA response was partially restored by K‐252a, a protein kinase inhibitor. Apoplastic inhibition is thus mediated through the protein phosphatases encoded by ABI1 and ABI2. The results with protein kinase and protein phosphatase inhibitors indicate that ABI1 and ABI2 are involved in separate signal transduction pathways.
Involvement of abscisic acid and ethylene in the responses of citrus seedlings to salt shock
Authors: Gómez‐Cadenas A. , Tadeo F. R. , Primo‐Millo E. , Talon M.
Published: March 2003

The responses of salt‐sensitive citrus rootstocks to 200 mM NaCl were periodically determined on seedlings of citrange Carrizo (Citrus sinensis[L.] Osbeck ×Poncirus trifoliata[L.] Raf) during 30 days. The stressed seedlings adjusted osmotically, reduced stomatal conductance, increased proline content and ethylene production, and showed massive leaf abscission (92%). The salt shock also increased abscisic acid (ABA) and aminocyclopropane‐1‐carboxylic acid (ACC) in roots, xylem fluid and leaves, and in addition promoted Cl− accumulation. The pattern of change of ABA, ACC and proline followed a two‐phase response: an initial transient increase (10‐12 days) overlapping with a gradual and continuous accumulation. This biphasic response appears to be compatible with the proposal that the transitory hormonal rises are induced by the osmotic component of salinity, whereas the Cl− increase determines the subsequent accumulations. During the second phase, Cl− levels correlated with abscission in leaves. Production of leaf ethylene was also concomitant with the increase in the abscission rate. Salt‐induced abscission was either reduced with CoCl2 (52%) or inhibited with silver thiosulphate (14%). The results suggest that in salt‐stressed citrus, leaf abscission is induced by the chloride build‐up through a mechanism that stimulates leaf ACC synthesis and further conversion to ethylene.
Genetic variation of stomatal conductance, blue light sensitivity and zeaxanthin content in guard cells of Pima cotton (Gossypium barbadense)
Authors: Quiñnes Miguel A. , Lu Zhenmin , Zeiger Eduardo
Published: March 2003

Pima S‐6 (Gossypium barbadense L.) is a modern line with high stomatal conductance, while B368 is a primitive cotton with low conductance. The blue light sensitivity of adaxial guard cells, probed as the blue light‐dependent enhancement of the red light‐induced chlorophyll a fluorescence quenching, was investigated in these two cotton lines with contrasting stomatal conductance. Adaxial guard cells isolated from Pima S‐6 cotton plants had a significantly higher carotenoid content and a higher blue light sensitivity than those isolated from B368 plants. In a growth chamber‐grown F2 population of a cross between these two lines, adaxial stomatal conductances of individual plants segregated over a range exceeding the average conductances of the parents. Carotenoid content and the blue light sensitivity of adaxial guard cells also segregated. The concentrations of xanthophylls and β‐carotene in the adaxial guard cells were poorly correlated with the blue light response, except for zeaxanthin. The co‐segregation of stomatal conductance and blue light sensitivity suggested that the stomatal response to blue light may play a role in the regulation of stomatal conductance in the intact leaf. Zeaxanthin content and blue light sensitivity also co‐segregated, suggesting that both parameters are under genetic control. The co‐segregation of zeaxanthin content, blue light sensitivity and stomatal conductance provides further evidence for a role of zeaxanthin in the blue light photoreception of guard cells.
Influence of nitrogen supply and growth irradiance on photoinhibition and recovery in Heuchera americana (Saxifragaceae)
Authors: Skillman John B. , Osmond C. Barry
Published: March 2003

Prior work demonstrated that Heuchera americana, an evergreen herb inhabiting the deciduous forest understory in the southeastern United States, has a 3‐4‐fold greater photosynthetic capacity under the low‐temperature, strong‐light, open canopies of winter compared to the high‐temperature, weak‐light, closed canopies of summer. Moreover, despite the reductions in soil nitrogen, the chilling temperatures, and the increased quantum flux associated with winter, chronic photoinhibition was not observed in this species at this time of the year. We were interested in the photosynthetic acclimation and photoinhibition characteristics of this species when grown under contrasting light and nitrogen regimes. Newly expanded shade‐acclimated leaves of forest‐grown plants exposed to strong light varying in intensity and duration at 25°C showed a reduction in Fv/Fm (the ratio of variable to maximum room temperature chlorophyll fluorescence measured after dark adaptation), which was correlated with a decline in øa (the intrinsic quantum yield of CO2‐saturated O2 evolution on an absorbed light basis). Plants grown in the glasshouse under contrasting light (high and low light; HL and LL, respectively) and nitrogen supply (high and low nitrogen; HN and LN, respectively) regimes showed that photosynthetic acclimation to HL was impaired in LN regimes. The HL‐LN plants also had the lowest values of Fv/Fm and of ø on both incident and absorbed light bases and had 50% less chlorophyll (per unit area) compared to plants from other growth regimes. Controlled exposure to bright light at low temperatures (2‐3°C) for 3 h resulted in a sharp decrease in Fv/Fm (and rise in Fo, the minimum fluorescence yield) in all plants. Shade‐grown plants from both N regimes were highly susceptible to chronic photoinhibition, as indicated by a greater reduction in Fv/Fm and incomplete recovery after 18 h in weak light at 25°C. The HL‐HN plants were the least susceptible to chronic photoinhibition, having the smallest decrease in Fv/Fm with near full recovery within 6 h. The decline in Fv/Fm in HL‐LN plants was comparable to that of shade‐acclimated plants, but recovered fully within 6 h. Low‐N plants from both light regimes displayed greater increases in Fo which did not return to pretreatment levels after 18 h of recovery. These studies indicate that HL‐LN plants were sensitive to chronic photoinhibition and, at the same time, had a high capacity for dynamic photoinhibition. Experimental garden studies showed that H. americana grown in an open field in summer were photoinhibited and did not fully recover overnight or during extended periods of weak light. These results are discussed in relation to the photosynthetic acclimation of H. americana under natural conditions.
Origin and dynamics of indoleacetic acid under polar transport in Pinus sylvestris
Authors: Sundberg Björn , Uggla Claes
Published: March 2003

Polarly‐transported IAA is regarded as a long distance correlative signal important in many aspects of plant physiology, including, for example, apical dominance and growth and development of vascular tissues. In this study, we investigated the importance of apical sources in supplying stem tissues with IAA. The current‐yearshoots of 4‐year‐old Pinus sylvestris L. saplings were replaced with a source of [13C6]IAA. Subsequent mass spectrometric analysis showed that most of the IAA present at two positions in the subjacent 1‐year‐old internode consisted of [13C6]IAA, while [12C]IAA of endogenous origin formed a minor pool. However, the pool of [13C6]IAA decreased from 90 to 80% of the total free IAA pool [13C6]IAA+[12C]IAA) while being transported down the shoot. This dilution with [12C]IAA indicates that de novo biosynthesis of IAA occurred. An additional defoliation experiment showed that the synthesis took place in stem tissues rather than in the mature leaves. The results confirm the role of apical shoots as the major source of polarly‐transported IAA, but also indicate that synthesis of IAA takes place in stem tissues. This is important when considering IAA balance at the whole plant level.
Diatom plastids: Secondary endocytobiosis, plastid genome and protein import
Authors: Kroth Peter , Strotmann Heinrich
Published: March 2003

Plastids of diatoms and other chromophytic algae have four surrounding membranes. In contrast to plastids of green algae, higher plants and red algae chromophytic cells are thought to have evolved by secondary endocytobiosis, i.e. by uptake of a eukaryotic photosynthetic organism by a eukaryotic host cell. This review gives a brief summary of the current views about the origin of diatom plastids and discusses possible mechanisms the cells might employ to transport nucleus‐encoded plastid proteins into these organelles.
Chilling‐induced leaf abscission of Ixora coccinea plants. I. Induction by oxidative stress via increased sensitivity to ethylene
Authors: Michaeli Rina , Philosoph‐Hadas Sonia , Riov Joseph , Meir Shimon
Published: March 2003

Exposing ixora (Ixora coccinea) plants to chilling temperatures (3–9°C for 3 days) resulted in increased leaf abscission, initiated 3 days after transfer to 20°C. Exposure to chilling also induced a 7‐fold increase in ethylene production rates of abscission zone (AZ) tissue during the initial 5 h after chilling. The ethylene burst resulted from the high levels of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) accumulated in the AZ during the chilling period. ACC levels following chilling decreased also due to enhanced conjugation to 1‐(malonylamino)cyclopropane‐1‐carboxylic acid (MACC). Treating plants prior to chilling with antioxidants, such as butylated hydroxyanisole (BHA), n‐propyl gallate (PG), and vitamin E, significantly reduced chilling‐induced leaf abscission. This effect was obtained despite the fact that ethylene production in the treated plants resembled that of chilled plants receiving no BHA. In addition, exposure of plants to ethylene (0.5–10 μl l−1) for 1–3 days significantly enhanced leaf abscission only when they had been pre‐chilled. These data imply that chilling‐induced leaf abscission was closely correlated with increased sensitivity of the AZ to ethylene rather than with the chilling‐induced ethylene burst. Based on the findings that the ethylene action inhibitor, 1‐methylcyclopropene (1‐MCP), and the antioxidant BHA inhibited both the chilling‐induced and the ethylene‐enhanced leaf abscission, it is concluded that: (1) although ethylene is essential for chilling‐induced abscission, it is not the triggering factor; (2) oxidative processes derived from the chilling stress seem to be the trigger of chilling‐induced leaf abscission, operating via increased sensitivity to ethylene.
Does root‐sourced ABA have a role in mediating growth and stomatal responses to soil compaction in tomato (Lycopersicon esculentum)?
Authors: Mulholland B. J. , Hussain A. , Black C. R. , Taylor I. B. , Roberts J. A.
Published: March 2003

Isogenic wild‐type (Ailsa Craig) and abscisic acid (ABA)‐deficient mutant (flacca) genotypes of tomato were used to examine the role of root‐sourced ABA in mediating growth and stomatal responses to compaction. Plants were grown in uniform soil columns providing low to moderate bulk densities (1.1–1.5 g cm−3), or in a split‐pot system, which allowed the roots to divide between soils of the same or differing bulk density (1.1/1.5 g cm−3). Root and shoot growth and leaf expansion were reduced when plants were grown in compacted soil (1.5 g cm−3) but leaf water status was not altered. However, stomatal conductance was affected, suggesting that non‐hydraulic signal(s) transported in the transpiration stream were responsible for the observed effects. Xylem sap and foliar ABA concentrations increased with bulk density for 10 and 15 days after emergence (DAE), respectively, but were thereafter poorly correlated with the observed growth responses. Growth was reduced to a similar extent in both genotypes in compacted soil (1.5 g cm−3), suggesting that ABA is not centrally involved in mediating growth in this severely limiting ‘critical’ compaction stress treatment. Growth performance in the 1.1/1.5 g cm−3 split‐pot treatment of Ailsa Craig was intermediate between the uniform 1.1 and 1.5 g cm−3 treatments, whereas stomatal conductance was comparable to the compacted 1.5 g cm−3 treatment. In contrast, shoot dry weight and leaf area in the split‐pot treatment of flacca were similar to the 1.5 g cm−3 treatment, but stomatal conductance was comparable to uncompacted control plants. These results suggest a role for root‐sourced ABA in regulating growth and stomatal conductance during ‘sub‐critical’ compaction stress, when genotypic differences in response are apparent. The observed genotypic differences are comparable to those previously reported for barley, but occurred at a much lower bulk density, reflecting the greater sensitivity of tomato to compaction. By alleviating the severe growth reductions induced when the entire root system encounters compacted soil, the split‐pot approach has important applications for studies of the role of root‐sourced signals in compaction‐sensitive species such as tomato.
Expression of ACC synthase is enhanced earlier than that of ACC oxidase during fruit ripening of mume (Prunus mume)
Authors: Mita Satoru , Kirita Chikako , Kato Masaya , Hyodo Hiroshi
Published: March 2003

Mume (Japanese apricot: Prunus mume Sieb. et Zucc.) is a climacteric fruit that produces large amounts of ethylene as it ripens. Ripening is accompanied by marked increases in the activities of two ethylene‐biosynthetic enzymes, namely, 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase and ACC oxidase. To study the molecular aspects of ripening of mume, we isolated cDNA clones for proteins that we considered likely to be involved in the biosynthesis and perception of ethylene during ripening, namely, ACC synthase, ACC oxidase and the ethylene receptor. Northern blotting analysis revealed the markedly increased expression of ACC synthase prior to that of ACC oxidase and the increase in ethylene production during ripening. Overall, the levels of the mRNAs for the genes corresponded closely to the levels of activity of the ethylene‐biosynthetic enzymes. Exposure of mature green mume fruit to ethylene for 12 h induced strong expression of ACC synthase, as well as of ACC oxidase. Wounding of the pericarp of mume fruit induced the expression of ACC synthase but not of ACC oxidase. The rate of ethylene production increased only slightly after wounding. These results suggest that expression of the genes for ACC synthase and ACC oxidase must be activated sequentially for maximum production of ethylene during ripening of mume fruit and that several mechanisms regulate the expression of ethylene‐biosynthetic genes during ripening.
Abscisic acid increases anaerobic tolerance in alfalfa seedlings
Authors: Kato‐Noguchi Hisashi
Published: March 2003

In order to clarify the effect of abscisic acid (ABA) on anaerobic tolerance in alfalfa (Medicago sativa L.), the seedlings were subjected to anaerobic stress after pretreatment with ABA. At concentrations> 1 μM, ABA pretreatment increased the root viability of the seedlings to anaerobic stress and the viability increased with increasing ABA doses. At 100 μM ABA, the viability was 2.5‐fold greater as compared with that of control seedlings. Roots of the seedlings rapidly lost ATP under the anaerobic stress; however, the decrease in ATP was much slower in the ABA‐pretreated seedlings than the control seedlings. At 12 h after onset of the stress, ATP concentrations in the roots of 100 and 10 μM ABA‐pretreated seedlings were 2.7‐ and 2.0‐fold that of the control seedlings, respectively. During the period of ABA pretreatment under aerobic condition, ABA increased alcohol dehydrogenase (ADH, EC 1.1.1.1) activity in the roots until 12 h and then leveled off. The maximum ADH activities were 4.3‐ and 2.8‐fold that in the roots of the control seedlings for 100 and 10 μM ABA‐pretreated seedlings, respectively. After being subjected to the anaerobic stress, both ADH activities in the roots of the ABA‐pretreated and the control seedlings increased but the differences in their activity remained. These results suggest that ABA pretreatment may maintain ATP level due to induction of ADH activity, which may be one of the causes of increasing anaerobic tolerance in the seedlings.
Carbon fixation in Pinus halepensis submitted to ozone. Opposite response of ribulose‐1,5‐bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase
Authors: Fontaine V. , Pelloux J. , Podor M. , Afif D. , Gérant D. , Grieu P. , Dizengremel P.
Published: March 2003

The effects of ozone exposure on carbon‐fixation‐related processes in Pinus halepensis Mill. needles were assessed over 3 months under controlled conditions. Ozone fumigation (200 ppb) did not induce a modification of either net CO2 assimilation or stomatal conductance in 1‐year‐old needles, whereas ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activity was shown to be reduced by a half. Moreover, this ozone‐induced reduction in Rubisco activity was associated with a decrease in the quantity of Rubisco, as determined by the decrease in the large subunit (LSU). On the other hand, 200‐ppb ozone fumigation induced a strong increase in both activity and quantity of another carboxylating enzyme, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), generally considered in C3 plants to participate in carbon catabolism processes. Ozone induced a significant decrease in the Rubisco/PEPC activity ratio which promotes the role of PEPC in trees under ozone stress. The role of this carboxylase will be discussed.
Reinitiation of cell division and polyamine and aromatic monoamine levels in alfalfa explants during the induction of somatic embryogenesis
Authors: Cvikrová Milena , Binarová Pavla , Cenklová Věra , Eder Josef , Macháčková Ivana
Published: March 2003

The early cellular events in leaf explants of Medicago sativa L. cultured on somatic embryogenesis‐ and callogenesis‐inducing media (EIM and CIM, respectively) were correlated with the endogenous contents of polyamines (PAs) and aromatic monoamines (AMs). On the second day of culture, replication of DNA occurred in epidermal and subepidermal cells on the edges of explants on EIM and was a prerequisite for proembryonal mass and, later, globular proembryo formation. In explants cultured on CIM, replication occurred at least one day later and in fewer cells, which were randomly spread all over the explant. Transition of leaf explant cells to rapidly dividing meristematic‐like cells on EIM or to enlarged, highly vacuolated cells on CIM was observed. The increase in total PA levels in cultured explants was primarily a consequence of increases in putrescine (Put) and spermidine (Spd) contents and was much more pronounced on EIM than on CIM. High Spd levels were characteristic of meristematic cells and might be essential for the development of globular structures. The higher amount of insoluble PA conjugates was determined in explant cells on EIM, as compared with CIM. Proembryogenic cell mass formation was positively correlated with free tyramine and negatively correlated with free phenylethylamine contents.
Photoinactivation of photosystem II in leaves of Capsicum annuum
Authors: Lee Hae‐Yeon , Chow Wah Soon , Hong Young‐Nam
Published: March 2003

Leaf discs of Capsicum annuum L. were illuminated in air enriched with 1% CO2 in the absence or presence of lincomycin, an inhibitor of chloroplast‐encoded protein synthesis. The loss of functional photosystem (PS) II complexes with increase in cumulative light dose (photon exposure), assessed by the O2 yield per single‐turnover flash, was greater in leaves of plants grown in low light than those in high light; it was also exacerbated in the presence of lincomycin. A single exponential decay can describe the relationship between the loss of functional PSII and increase in cumulative photon exposure. From this relationship we obtained both the maximum quantum yield of photoinactivation of PSII at limiting photon exposures and the coefficient k, interpreted as the probability of photoinactivation of PSII per unit photon exposure. Parallel measurements of chlorophyll fluorescence after light treatment showed that 1/Fo−1/Fm was linearly correlated with the functionality of PSII, where Fo and Fm are the chlorophyll fluorescence yields corresponding to open and closed PSII reaction centers, respectively. Using 1/Fo−1/Fm as a convenient indicator of PSII functionality, it was found that PSII is present in excess; only after the loss of about 40% functional PSII complexes did PSII begin to limit photosynthetic capacity in capsicum leaves.
Carbohydrate availability modifies sorbitol dehydrogenase activity of apple fruit
Authors: Archbold Douglas D.
Published: March 2003

Complete defoliation of the stem or spur and girdling the phloem (D/G) subtending a single apple (Malusdomestica Borkh.) fruit at 70 or more days after bloom resulted in reduction of fruit growth. Extractable sorbitol dehydrogenase (SDH) (enzyme code, 1.1.1.14) activity and sorbitol and starch content of the cortex tissue of fruit receiving D/G treatment subsequently declined. Co‐extraction of control and D/G cortex tissues yielded expected levels of SDH activity, indicating that the loss of extractable SDH activity in D/G fruit was not due to presence of an inhibitor or proteolytic activity. Incubating cortex sections from D/G fruit in a buffered 200 mM sorbitol or glucose solution increased extractable SDH activity, and incubating cortex sections from control fruit in the sorbitol solution maintained the activity. However, neither 200 mM fructose or 27 mM PEG, the latter with the same osmotic potential as the sorbitol solution, affected extractable SDH activity of D/G fruit. The results indicate that carbohydrate availability may affect extractable SDH activity of apple fruit, and that specific carbohydrates such as sorbitol and glucose may be signals for modulating this activity.
Effects of root restriction on the growth and physiology of cucumber plants
Authors: Kharkina T. G. , Ottosen C.‐O. , Rosenqvist E.
Published: March 2003

Cucumber plants (Cucumis sativus L. cv. Athene F1) were grown with four treatments: unrestricted root volume fruiting (UF); unrestricted root volume non‐fruiting (UN); restricted root volume fruiting (RF); and restricted root volume non‐fruiting (RN). Restricting root volume to 40 ml reduced leaf area, and by day 60 leaf area was only 20% that of unrestricted plants. Leaf area reduction in restricted plants was due to a combination of smaller and fewer leaves. Root restriction strongly depressed total dry matter production in both root and shoot. Significant differences of treatments in shoot and root growth rates were akpparent 30 days after sowing. RN plants had a 70% lower net photosynthesis (Pn), stomatal conductance (gs) and transpiration rate (E) measured on day 50, while root restriction had no effect on Pn in fruiting plants, although gs and E were significantly decreased due to restriction. Respiration capacity of restricted roots decreased sharply after day 24 compared with unrestricted root systems. Initially, O2 may have been the limiting resource and root respiration capacity a major factor involved in root restriction, since it causes imbalances in root growth substances and related hormones that alter the plant's morphology.
The role of Ca2+ ions in modulating changes induced in bean plants by an excess of Cu2+ ions. Chlorophyll fluorescence measurements
Authors: Maksymiec Waldemar , Baszyński Tadeusz
Published: March 2003

Ca2+‐dependent influence of excess Cu2+ on the photosynthetic akpparatus monitored through chlorophyll fluorescence measurements was investigated in runner bean plants (Phaseolus coccineus L. cv. Pie

kny Jaś) at three different growth stages. It was observed that the toxic effect of excess Cu2+ on plants depends both on their growth stages and the Ca2+ content in the medium. Increased Ca2+ content limits Cu2+ action on plants at their initial growth stage (I) through: stabilization of the PSII complex (increase of the ratio of variable to minimal fluorescence [Fv/F0]), improved electron flow and reoxidative processes of the quinone primary electron acceptor of PSII (QA) (increase of quantum yield of PSII electron transport [φe] and photochemical quenching of fluorescence [qP] values) and elimination of nonphotochemical energy dissipation (decrease of nonphotochemical fluorescence quenching from the Stern‐Volmer equation [NPQ] and fraction of the absorbed light energy not used for photochemistry [LNU] values). At this growth stage excess Cu2+ decreases the rates of QA reduction as a result of decreased PSII activity at its donor side only at lower Ca2+ level. At the intermediate growth stage (II) the plants were less sensitive to Cu2+ treatment and also to changed Ca2+ content. A weakening of some photochemical processes by excess Cu2+ could be observed only at a higher Ca2+ dose. At the final growth stage of plants (III) Ca2+ ions exerted a decisively different effect on the mechanism of excess Cu2+ action on bean plants, visualized by decreased PSII stabilization and utilization of absorbed light energy at increased Ca2+ content in the medium.
Plant aspartic proteinases: enzymes on the way to a function
Authors: Mutlu Asuman , Gal Susannah
Published: March 2003

Plant aspartic proteinases have been characterized from seeds, flowers and leaves of a number of different species. The enzymes are generally either monomeric or heterodimeric, containing two peptides processed from the same precursor protein. The plant enzymes, like their mammalian and microbial counterparts, are active at acidic pH and inhibited by a class specific inhibitor pepstatin A. Plant aspartic proteinases are generally either secreted or targeted to the vacuolar/protein storage body compartment. The primary sequences of many of these enzymes have been determined and are very homologous with each other as well as with enzymes from mammalian and microbial origins. Plant aspartic proteinases, however, have a very unique plant specific region, which is not found in mammalian, microbial, or viral aspartic proteinases. The function of this region has not been elucidated. A role for these plant enzymes in protein processing or degradation has been proposed, however, more studies are required to confirm their in vivo functions. Recent intriguing results suggest possible roles for these enzymes in programmed cell‐death of tissues and in pathogen resistance.
A 23‐kDa, root exudate polypeptide co‐segregates with aluminum resistance in Triticum aestivum
Authors: Basu Urmila , Good Allen G. , Aung Taing , Slaski Jan J. , Basu Atanu , Briggs Keith G. , Taylor Gregory J.
Published: March 2003

We previously reported that treatment with aluminum (Al) leads to the accumulation of several polypeptides (12‐, 23‐, and 43.5‐kDa) in root exudates of an Al‐resistant cultivar of Triticum aestivum. In this report, we examine the segregation of the 23‐kDa, Al‐induced polypeptide and the Al‐resistant phenotype in single F2 plants arising from a cross between Al‐resistant and Al‐sensitive doubled‐haploid (DH) lines. Single plants and plant populations were screened for sensitivity/resistance to Al using synthesis of 1,3‐β‐glucans (callose) as a sensitive marker for Al injury. Callose production in the Al‐sensitive cv. Katepwa was approximately 3‐fold higher than observed in the Al‐resistant cv. Maringa, or a near‐isogenic line derived from Katepwa and Maringa (Alikat), over a broad range of Al concentrations (0–100 μM). Similar results were observed with DH lines developed from cv. Katepwa, which produced two–four times more callose than DH lines developed from cv. Alikat. When single plants from F1 and F2 populations derived from a cross between DH Katepwa and DH Alikat were scored for Al‐induced callose production after 4 days exposure to 100 μM Al, all F1 plants were Al‐resistant and F2 plants segregated approximately 3:1 for Al‐resistance/sensitivity. A backcross population derived from crossing Al‐resistant F1 with Al‐sensitive Katepwa, segregated 1:1 for Al‐resistance/sensitivity. Thus, the Al‐resistant phenotype is inherited in a monogenic, dominant fashion in our DH lines. Enhanced accumulation of the Al‐induced, 23‐kDa polypeptide in root exudates was a trait which co‐segregated with the Al‐resistant phenotype in F2 populations. This polypeptide was strongly labeled with S‐methionine after 3 days of Al exposure and 6 h labeling. When root exudate polypeptides were separated by immobilized metal ion affinity chromatography, the 23‐kDa polypeptide demonstrated significant Al‐binding capacity. This polypeptide has been purified to near‐homogeneity, providing an opportunity to isolate the gene(s) encoding this polypeptide.
Purification and properties of an aspartic protease from potato tuber that is inhibited by a basic chitinase
Authors: Guevara María G. , Oliva Claudia R. , Machinandiarena Milagros , Daleo Gustavo R.
Published: March 2003

A protease was isolated from potato (Solanum tuberosum L. cv. Huinkul) tuber disks after 24 h of aeration when proteolysis is markedly increased. Purification was performed by ammonium sulfate precipitation, ion exchange chromatography, and affinity chromatography. A size of 40 kDa was estimated by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and gel filtration, it is monomeric and its properties are consistent with those of aspartic proteinases (EC 3.4.23): it had a pH optimum between 4 and 5 and it was inhibited by pepstatin. Partial homology with other plant aspartic proteinases was observed in two sequenced tryptic fragments. It binds to Sepharose‐concanavalin A and can be eluted with α‐methyl mannoside, indicating that it is possibly glycosylated. Unlike other aspartic proteinases from Solanaceae that degrade pathogenesis‐related proteins, it is unable to cleave a basic chitinase from potato. Moreover, this aspartic protease is strongly inhibited by the basic chitinase; the 50% inhibition is obtained when the molar ratio approaches 1, the same as with pepstatin. The interaction between this aspartic protease and a new type of endogenous inhibitor may be an interesting starting point to study the regulation of these aspartic proteases during stress.
Pectolytic enzyme treatment of sunflower explants prior to wounding and cocultivation with Agrobacterium tumefaciens, enhances efficiency of transient β‐glucuronidase expression
Authors: Alibert Bénédicte , Lucas Olivier , Le Gall Valerie , Kallerhoff Jean , Alibert Gilbert
Published: March 2003

The genetic transformation of sunflower is very difficult. The protocols published so far combined wounding of meristematic axes by microprojectils or glass beads and gene transfer by Agrobacterium tumefaciens. The yields of transgenic plants were well below 0.1% in all cases. Treatment of meristematic explants of germinating seedlings by a pectinase, before wounding, followed immediately by Agrobacterium tumefaciens cocultivation, enhanced β‐glucuronidase (GUS) gene expression in 14‐day‐old in vitro cultivated explants. Moreover, pectinase‐treated explants showed a significant increase in interaction with bacteria compared to non‐treated ones. This result suggests facilitated access of the bacteria to competent sunflower cells, due to cell‐wall digestion by the pectinases. Furthermore, we show here, using competition experiments, that integrin‐like proteins do not seem to be involved in the enhancement of bacterial binding to the cell explants.
Ethylene‐induced putrescine accumulation modulates K+ partitioning between roots and shoots in barley seedlings
Authors: Tamai Tesshu , Inoue Miwako , Sugimoto Toshio , Sueyoshi Kuni , Shiraishi Naomasa , Oji Yoshikiyo
Published: March 2003

We investigated the cause and effect relationships among ethylene, polyamines, and K+ in barley (Hordeum vulgare L. cv. Amagi) seedlings. Application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), a precursor of ethylene, to the growth medium caused a decrease in K+ concentration in roots and an increase in shoots. Addition of ACC induced putrescine accumulation in roots, while spermidine and spermine levels remained unchanged. Exogenous supply of putrescine led to putrescine accumulation and reduced K+ concentration. Application of Co2+, an inhibitor of ethylene biosynthesis, together with ACC, inhibited putrescine accumulation with a decrease in K+ concentration in roots. ACC‐treated roots showed K+ uptake capacity equivalent to that of control roots, implying that the majority of K+ is translocated to shoots. These results suggest that ethylene regulates K+ partitioning between roots and shoots through the level of accumulation of putrescine in barley seedlings.
Amines of the subantarctic crucifer Pringlea antiscorbutica are responsive to temperature conditions
Authors: Hennion Françoise , Martin‐Tanguy Josette
Published: March 2003

Different polyamine and aromatic amine compositions and contents were observed in the leaves and the roots of plants from the subantarctic crucifer Pringlea antiscorbutica growing in the field and collected during the austral summer in Kerguelen and those grown under controlled conditions mimicking the thermoperiod and photoperiod conditions in summer in Kerguelen. In controlled conditions, the plants grew more slowly than in the field and did not flower. In roots, this was associated with an increase of agmatine (Agm). In contrast, acetylated putrescine (Put) disappeared while dopamine (Dop) and tryptamine (Try) were strongly reduced. In leaves, cultivation under controlled conditions led to an accumulation of Agm, acetylated Put, tyramine (Tyr) and Try. A complete depletion of acetylated spermidine (Spd) and spermine (Spm) and a strong decrease of Dop occurred. Cultivation of plants at constant 25°C was lethal after a few weeks. Before the external symptoms of heat challenge became acute, leaves and roots showed a different amine content and composition. In roots, and to a lesser extent in leaves, heat treatment was associated with an apparent impairment in the ability to accumulate Agm, acetylated Put and Try. Strong increases in Put, Spd and Tyr and accumulation of hydroxycinnamoyl amines as feruloylputrescine, feruloylspermidine and feruloyltyramine were observed in leaves. Aminoguanidine, a potent and specific inhibitor of diamine oxidase activities, caused phenotypic alterations and changes in amine composition and content in roots and leaves of Pringlea plants similar to those observed under the heat treatment. Our results highlight possible roles of amine catabolism, acetylated polyamines and hydroxycinnamoyl amines in plant responses to external conditions.
Population differences in water‐use efficiency of Eucalyptus microtheca seedlings under different watering regimes
Authors: Li Chunyang
Published: March 2003

Gas exchange, water‐use efficiency (WUE), carbon isotope composition (Δ13C) and growth traits were compared among 5 populations of Eucalyptus microtheca F. Muell. Seedlings grown from seed collected across the natural distribution of the species were maintained under water‐stressed and well‐watered conditions. Gas exchange was measured in terms of net photosynthesis (A) and transpiration (E); WUE was measured in terms of instantaneous water‐use efficiency (WUEi) and transpiration efficiency (WUET); growth traits were measured in terms of total biomass (TB), root/shoot ratio (RS), and specific leaf area density (DEN). Significant differences in all traits were detected among the populations. Overall population variation was 1.68–2.50 and 1.48–2.26 μmol CO2 uptake per mmol H2O transpired (WUEi), 1.97–3.04 and 1.64–2.36 g dry matter accumulation per kg water transpired (WUET), and Δ13C was −28.81 to −26.75‰ and −30.56 to −30.04‰ under the water‐stressed and well‐watered conditions, respectively. In addition, WUEi, WUET and Δ13C were significantly correlated with A, E, RS, DEN and TB. The study indicated that measurement of WUE may be a useful trait for selecting genotypes with improved drought adaptation and biomass productivity under different environmental conditions.
Utilizable water in leaves of 8 arid species as derived from pressure‐volume curves and chlorophyll fluorescence
Authors: Lamont Byron B. , Lamont Heather C.
Published: March 2003

The water‐storage properties of leaves from 8 co‐occurring arid species, ranging from 4 to 36 in turgid weight/dry weight ratio, were studied. Total water content at saturation varied from 75 to 97%, with 65–93% of this utilizable when bound water (B) was subtracted, and 72–93% when water content at a critical level of optimal fluorescence (Fc) was subtracted. Fc represented the turning point from slight to substantial impairment of chlorophyll fluorescence, and either coincided with B (two species) or was slightly below B (6 species). An incipient level of fluorescence was also recognized, corresponding to the lowest water content before any effect on maximum variable fluorescence/maximum fluorescence could be detected. This lay closer to B than to water content at turgor loss point (TLP), rendering TLP of no significance in dictating the fraction of stored water utilizable (UWC). Under laboratory conditions, turgid branchlets of the 8 species were estimated to take from 1.5 days to 15 weeks to reach Fc. The rate of water loss was almost completely explained by variations in leaf thickness. Under field conditions in mid‐spring, UWC at Fc on a harvest weight basis ranged from 51 to 87% predawn and from 45 to 86% by early afternoon (EA). The UWC of plants severed from their root systems 6 weeks earlier ranged from 0 to 63% during the EA. Overall, two groups of species could be recognized: thick‐leaved species whose UWC is high and varies little during the day and which use their stored water conservatively and have limited reliance on their root system for replenishment after winter; and thinner leaved species whose UWC is moderate and fluctuates daily, and whose stored water falls rapidly unless replenished continuously from the soil.
The influence of a reduced gibberellin biosynthesis and nitrogen supply on the morphology and anatomy of leaves and roots of tomato (Solanum lycopersicum)
Authors: Nagel Oscar W. , Konings Henk , Lambers Hans
Published: March 2003

We investigated how the differences in growth and morphology, between fast‐growing wildtype (Wt) tomato (Solanum lycopersicum L.) plants and slow‐growing gibberellin (GA) deficient W335 mutants, were reflected in cell numbers and cell sizes. We also studied whether the differences between the Wt and the low‐GA mutant would persist at a growth‐limiting supply of nitrate. Both a low endogenous GA concentration and a low supply of nitrate reduced the number and size of leaf cells, whereas they increased the size and number of root cortex cells. The effects of low N‐supply on the size and number of leaf and root cells did not depend on endogenous GA concentrations. The mutant's higher allocation to roots seemed to be the result of the strongly reduced growth of the shoot.