bluuebunny/crossref_metadata_2025 huggingface dataset:
Random root movements in weightlessness
Authors: Johnsson Anders , Karlsson Christina , Iversen Tor‐Henning , Chapman David K.
Published: May 2006

The dynamics of root growth was studied in weightlessness. In the absence of the gravitropic reference direction during weightlessness, root movements could be controlled by spontaneous growth processes, without any corrective growth induced by the gravitropic system. If truly random of nature, the bending behavior should follow socalled ‘random walk’ mathematics during weightlessness. Predictions from this hypothesis were critically tested.

In a Spacelab ESA‐experiment, denoted RANDOM and carried out during the IML‐2 Shuttle flight in July 1994, the growth of garden cress (Lepidium sativum) roots was followed by time lapse photography at 1‐h intervals.

The growth pattern was recorded for about 20 h. Root growth was significantly smaller in weightlessness as compared to gravity (control) conditions.

It was found that the roots performed spontaneous movements in weightlessness. The average direction of deviation of the plants consistently stayed equal to zero, despite these spontaneous movements. The average squared deviation increased linearly with time as predicted theoretically (but only for 8–10 h).

Autocorrelation calculations showed that bendings of the roots, as determined from the 1‐h photographs, were uncorrelated after about a 2‐h interval.

It is concluded that random processes play an important role in root growth. Predictions from a random walk hypothesis as to the growth dynamics could explain parts of the growth patterns recorded. This test of the hypothesis required microgravity conditions as provided for in a space experiment.
Changes in cellular osmotic potential and mechanical properties of cell walls during light‐induced inhibition of cell elongation in maize coleoptiles
Authors: Parvez Mohammad Masud , Wakabayashi Kazuyuki , Hoson Takayuki , Kamisaka Seiichiro
Published: May 2006

The growth rate of maize (Zea mays L. cv. Cross Bantam T51) coleoptiles in the dark was highest at the basal zone and decreased towards the tip. Growth was strongly inhibited by white fluorescent light (5 W m−2), especially in the basal zone of coleoptiles. Light irradiation caused an increase in the values of stress‐relaxation parameters, the minimum stress‐relaxation time and the relaxation rate and a decrease in the extensibility (strain/stress) of the cell walls at all zones. In addition, during growth, the accumulation of osmotic solutes was strongly inhibited by white light irradiation, resulting in an increased osmotic potential. The influences of white light on the mechanical properties of the cell wall and the osmotic potential of the tissue sap were most prominent in the basal zone. Significant correlations were observed between the increment of coleoptile length and the mechanical properties of the cell walls or the osmotic potential of the tissue sap and osmotic solutes content. Furthermore, light inhibited the outward bending of split coleoptile segments. These facts suggest that white light inhibits elongation of maize coleoptiles by modifying both the mechanical properties of the cell walls and cellular osmotic potential, which control the rate of water uptake.
Tubulin and actin protein patterns in Scots pine (Pinus sylvestris) roots and developing ectomycorrhiza with Suillus bovinus
Authors: Niini Sara S. , Tarkka Mika T. , Raudaskoski Marjatta
Published: May 2006

The role of tubulin and actin in the development of Scots pine (Pinus sylvestris) roots and in the formation of the ectomycorrhiza with the basidiomycete Suillus bovinus was studied by immunoblotting of 2D‐gels with anti‐tubulin and anti‐actin antibodies. In the short roots the α‐tubulin pattern was different from that in the other root types due to the more acidic pI of the two α‐tubulins. During the formation of the ectomycorrhiza, two new α‐tubulins were detected in the acidic α‐tubulin cluster. No such variation occurred in the plant β‐tubulin patterns. The fungal tubulins dominated in the ectomycorrhiza, but no changes in tubulin polypeptide patterns from those in the S. bovinus mycelium were observed. Contrary to the tubulins, plant actin dominated in the mycorrhiza. The specific α‐tubulin patterns of uninfected and infected short roots indicate that α‐tubulin is involved in the morphogenesis of Pinus sylvestris short roots. The high level of plant actin at early stage of the mycorrhiza formation suggests a significant role of this protein in the interaction between plant cells and fungal hyphae.
Lignin deposition induced by aluminum in wheat (Triticum aestivum) roots
Authors: Sasaki Masao , Yamamoto Yoko , Matsumoto Hideaki
Published: May 2006

We investigated the relation between the toxic effect of aluminum (Al) on root growth and the lignin deposition in wheat (Triticum aestivum L. cvs Atlas 66 and Scout 66). In the Al‐tolerant cultivar Atlas 66, control treatment without AlCl3 at pH 4.75, cell length increased dramatically in the portion of the root that was 0.6 to 3.2 mm from the root cap junction (approximately 1.0 to 3.6 mm from the root tip). However, treatment with 20 μM AlCl3 for 24 and 48 h completely inhibited root elongation and markedly decreased the length and increased the diameter of the cells in the same portion of the root. Moreover, marked deposition of lignin was observed in the cells that corresponded to the portion 1.5 to 4.5 mm from the root tip in Atlas 66 roots treated with 20 μM AlCl3, while no deposition of lignin was detected in control roots. Treatment with 5 μM AlCl3 slightly inhibited root growth and there was no deposition of lignin in the root. On the other hand, in roots of the Al‐sensitive cultivar Scout 66, treatment with 5 μM AlCl3 completely inhibited root growth and markedly induced deposition of lignin. These results suggest that lignification in the elongating region coincided with the extent of inhibition of root growth by Al in two wheat cultivars that differed in their sensitivity to Al.
Selection for mutants with low nitrate uptake ability in rice (Oryza sativa)
Authors: Hasegawa Hiroshi
Published: May 2006

Screening for mutants deficient in the high affinity system of nitrate uptake was performed using mutagenized M2 population of rice (Oryza sativa, cv. Nipponbare or Kinmaze). For selecting mutants, M2 seedlings were transferred individually to 10 ml solution containing 250 μM potassium nitrate and 500 μM calcium sulphate at 20 or 28°C. After 6 or 24 h, nitrate concentration of the solution was determined with a nitrate selective electrode and the seedlings showing impaired nitrate uptake were selected as nitrate uptake deficient variants. Of 74 variants, three were confirmed to be mutants with low nitrate uptake ability in the M3 generation. Potassium uptake ability also decreased in the mutants. Three mutants were divided into two groups based on the analysis of nitrate reductase (NR, EC 1.6.6.1) activity and chlorate resistance. Two, NUE13 and NUE36, had a lower level of NR activity than the original cultivar and were not resistant to chlorate, while the seedlings of NUE50 had the same level of NR activity as the original cultivar and were more resistant to chlorate than the original cultivar. All mutants were resistant to cesium, a toxic ion analogue for potassium, suggesting that the decreased levels of both nitrate and potassium uptake were coupled to the change of plasma membrane H+‐ATPase activity.
Effect of synthetic and natural protein tyrosine kinase inhibitors on auxin efflux in zucchini (Cucurbita pepo) hypocotyls
Authors: Bernasconi Paul
Published: May 2006

Basipetal auxin transport along the zucchini hypocotyl requires the cell‐to‐cell translocation of this hormone. Several authors have demonstrated that naphthylphthalamic acid (NPA) blocks auxin efflux. It is believed that NPA binds to a regulatory protein that modulates the activity of the carrier rather than to the carrier itself. A few regulatory mechanisms have been suggested but all lack strong supporting experimental evidence. Four classes of protein tyrosine kinase inhibitors (PTKIs) have been used to investigate the NPA perception pathway. First, six synthetic tyrphostins, inhibitors of the epidermal growth factor receptor (EGF‐R), were shown to displace NPA on plasmalemma fractions. The most potent compound was (3,4‐dihydroxybenzylidene)‐thiocyanoacetamide (tyrphostin A47). The inactive counterpart of tyrphostin A47, (4‐methoxybenzylidene)‐malononitrile (tyrphostin A1), was unable to displace NPA. Tyrphostins did not inhibit auxin efflux but were antagonists of the inhibition of auxin efflux by NPA. Again, tyrphostin A47 was the most effective and tyrphostin A1 was inactive. Second, the flavonoid genistein, also an EGF‐R inhibitor, showed an effect on NPA binding and NPA antagonism similar to the one for the tyrphostins. Daidzein, the inactive counterpart of genistein, was ineffective in displacing NPA and in antagonizing its inhibition of auxin efflux. Two other PTKIs, curcumin and lavendustin A, displayed similar characteristics. Calmodulin antagonists, protein serine/threonine kinase inhibitors, and phosphatase inhibitors were inactive. These results suggest that the NPA binding protein may be related to mammalian tyrosine kinases and may regulate the auxin efflux carrier by phosphorylation.
Relationship between photosynthetic radiation‐use efficiency of barley canopies and the photochemical reflectance index (PRI)
Authors: Filella Iolanda , Amaro Teo , Araus Jose Luis , Peñuelas Josep
Published: May 2006

Some processes of excess radiation dissipation have been associated with changes in leaf reflectance near 531 nm. We aimed to study the relations between the photochemical reflectance index (PRI) derived from this signal, and photosynthetic radiation‐use efficiency (defined as net CO2 assimilation rate/incident photon flux density) in a cereal canopy. Measurements of reflectance, fluorescence, gas exchange and xanthophyll cycle pigments were made in the morning, midday and afternoon in barley canopies with two levels of nitrogen fertilization. The photosynthetic radiation‐use efficiency decreased at midday, mainly in the third leaf, in both treatments, with lower values for the nitrogen deficient leaves. The zeaxanthin content showed the inverse pattern, increasing at midday and in the nitrogen deficient treatment. The photosynthetic radiation‐use efficiency was well correlated with the epoxidation state, EPS (violaxanthin + 0.5 antheraxanthin)/(violaxanthin + antheraxanthin + zeaxanthin). The PRI [here defined as (R539 ‐ R570)/(R539+ R570)] was significantly correlated with epoxidation state and zeaxanthin and with photosynthetic radiation‐use efficiency. These results validate the utility of PRI in the assessment of radiation‐use efficiency at canopy level.
Sucrose accumulation in developing peach fruit
Authors: Vizzotto Giannina , Pinton Roberto , Varanini Zeno , Costa Guglielmo
Published: May 2006

Uptake of 14C‐sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring 14C‐sucrose and 14C‐glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 mM14C‐sucrose and 14C‐glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.

At 10 mM, glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanide m‐chlorophenylhydrazone (CCCP) at 25 μM. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.

Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly.
Priming of seeds with NaCl induces physiological changes in tomato plants grown under salt stress
Authors: Cayuela E. , Pérez‐Alfocea F. , Caro M. , Bolarín M. C.
Published: May 2006

The effects of seed priming with 6 M NaCl solution have been investigated with respect to growth and physiological responses of tomato plants (Lycopersicon esculentum Mill. cv. Pera) exposed to 70 and 140 mM NaCl nutrient solutions from 11 to 60 days after sowing. Tomato seedlings from primed seeds emerged earlier than from non‐primed seeds. At 70 mM, a lower shoot and root dry weight reduction was found in plants from primed seeds at the different harvests (30, 45 and 60 days after sowing), while at 140 mM the positive effect of seed priming was only shown in roots. Significant changes in Na+ and CI− accumulation with seed priming were only found in roots at 60 days after sowing, with ion accumulation in roots being higher in plants grown at 70 and 140 mM from primed seeds. In leaves of salt‐treated plants, significant increases in sugars and organic acids with seed priming were found from 30 days after sowing, and these increases were higher at longer treatment times. In roots, however, only the organic acids tended to increase in plants from primed seeds, although they increased less than in leaves, especially at 60 days after sowing. These results support the hypothesis that priming of seeds with NaCl induces physiological changes in the plants, changes which are shown more clearly at advanced growth stages.
Changing root and shoot architecture with the rolA gene from Agrobacterium rhizogenes: Interactions with gibberellic acid and polyamine metabolism
Authors: Ben‐Hayyim Gozal , Martin‐Tanguy Josette , Tepfer David
Published: May 2006

The effects of rolA on root and shoot architecture have been ascribed to a deficiency in gibberellic acid (GA3) and to changes in polyamine metabolism. Using tobacco, we examined interactions among GA3, a polyamine accumulation inhibitor (α‐DL‐difluoromethylornithine or DFMO) and the rolA gene controlled by the 35S CaMV promoter. We measured the effects of these three agents on architecture and polyamine accumulation in excised roots and whole plants grown in vitro. Previous work showed that DFMO or genetic transformation with the rolA gene from Agrobacterium rhizogenes, controlled by the 35S promoter (P35S‐rolA), caused excised tobacco roots to grow faster with altered root system architecture. We show that gibberellic acid (GA3) reversed the effects of DFMO on the architecture of excised root systems, but neither reversed the effects of DFMO on growth, nor the changes in growth and architecture associated with P35S‐rolA. GA3 treatment alone resulted in increased agmatine levels, suggesting that the inhibition of the effects of DFMO on architecture was through a stimulation of the arginine decarboxylase (ADC) pathway, GA3 alone also inhibited the accumulation of putrescine and tyramine conjugates in excised roots.

In tobacco plants growing in vitro DFMO and P35S‐rolA were associated with reduced shoot height, which was partially restored by GA3 treatment; however, GA3 also stimulated shoot height in the controls. GA3 did not lessen the leaf wrinkling associated with P35S‐rolA. P35S‐rolA increased root number in young seedlings in vitro, and increased root system length in seedlings grown in soil. As in excised roots, the developmental changes linked to DFMO and P35S‐rolA were accompanied by reductions in putrescine titers. GA3 treatment stimulated putrescine accumulation in stems and leaves, and partially reversed the negative effects of DFMO and P35S‐rolA on putrescine accumulation in roots, stems and leaves. Again, the restoration of putrescine pools appeared to be through a stimulation of the ADC pathway, since agmatine accumulated in plants exposed to GA3. In general, the effects of DFMO and P35S‐rolA on phenotype and polyamine metabolism were coordinated, and in many cases these effects were similarly modulated by GA3, reinforcing the previous conclusion that the phenotypic effects of rolA in roots and shoots occur through interference with polyamine metabolism and that the putrescine conjugates are particularly important in regulating root system growth and architecture. We were unable, however, to discem consistent evidence for a direct role for GA3 in establishing the RolA phenotype.
Antagonistic effects of abscisic acid and gibberellic acid on the breaking of dormancy of Fagus sylvatica seeds
Authors: Nicolás Carlos , Nicolás Gregorio , Rodríguez Dolores
Published: May 2006

Study of the factors involved in the dormancy of Fagus sylvatica seeds shows that such dormancy is due partly to the seed coats and partly to endogenous factors. Seed coat removal accelerates both the release from dormancy and the effects of the other treatments that abolish it. The dormancy of these seeds is eliminated by cold treatment at 4°C over a period longer than 8 weeks, and exogenous application of abscisic acid (ABA) reverses the effects of low temperature, the seeds remaining in an ungerminated state. Additionally, ABA reduces protein synthesis but slightly increases RNA synthesis, which suggests its involvement in the synthesis of RNAs related to this process. In vitro translation of the RNAs isolated from these seeds shows that ABA delays the disappearance of at least 2 polypeptides (of ca 22 and 24 kDa), which are abundant in dormant seeds and under conditions that prevent the release from dormancy, but which disappear under treatments that abolish it. Exogenous application of gibberellic acid (GA3) proved to be efficient in breaking the dormancy of these seeds and in substituting for cold treatment as well as in antagonizing the effects of ABA on the synthesis of both DNA and proteins. GA3 also accelerates the disappearance of the two polypeptides abundant in dormant seeds and in ABA‐treated seeds. These findings suggest that both ABA and GA3 could be involved in the regulation of nucleic acid and protein metabolism during dormancy, acting antagonistically in these processes and, specifically, in the regulation of the synthesis of the two proteins that appear to play a role in the maintenance of dormancy in these seeds.
Predominant expression of a peroxidase gene in staminate flowers of Mercurialis annua
Authors: Boissay E. , Delaigue M. , Sallaud C. , Esnault R. , Kahlem G.
Published: May 2006

A direct correlation between the feminizing process of male plants of Mercurialis annua by benzylaminopurine and the disappearance of male‐specific peroxidases was established. In order to understand the process of hormonal regulation of the sexual differentiation and peroxidase activity, two peroxidase cDNA clones were selected from a male flower cDNA library with degenerated oligonucleotide probes encoding a peroxidase‐specific site. These clones contained three peroxidase‐specific sequences and an Eco RI restriction site. The two Eco RI fragments of one cDNA clone were subcloned and used as probes to analyse the expression of corresponding gene(s). The northern blot analysis showed hybridization on a single mRNA band with a predominant expression in male flowers. The feminizing treatment with a cytokinin induced the progressive disappearance of the hybridization signal in correlation with the disappearance of male specific isoperoxidases.
Fatty acid desaturation in monogalactosyldiacylglycerol of Brassica napus leaves during low temperature acclimation
Authors: Williams John P. , Khan Mobashsher U. , Wong Doris
Published: May 2006

Brassica napus plants grown at 5°C have the potential to desaturate fatty acids in the major membrane diacylglycerols of leaves at rates much higher than those of plants grown at 30°C. This low temperature‐induced desaturation (LTD) is rapidly deactivated if plants grown at 5°C are transferred to 30°C for several hours. By exposure to 14CO2 and a computer simulation program, we estimated the rate of desaturation of monogalactosyldiacylglycerol by (ω9‐, ω6‐ and ω3‐desaturases of plants grown at 5, 10, 20 and 30°C. Data show that LTD can be induced in mature leaves of plants grown at 20 and 30°C after transfer to 5°C. Full activation of LTD takes several weeks and occurs more rapidly in plants grown at 20°C than 30°C. This activation is largely due to the increased activity of ω9‐ and ω6‐desaturases on C16 fatty acids and ω6‐desaturase on C18 fatty acids.
Characterization of extracellular oxygen consumption by the green alga Selenastrum minutum
Authors: Weger Harold G. , Lynnes Jaret A. , Torkelson Joel D.
Published: May 2006

Cells of the green alga Selenastrum minutum display a high capacity for extra‐mitochondrial O2 consumption in the presence of effectors such as salicylhydroxamic acid and/or NADH. We provide evidence that this O2 consumption is mediated by extracellular peroxidase. Peroxidase capacity, measured as the potential for stimulation of O2 consumption by a combination of salicylhydroxamic acid and NADH, changed over a 10‐day time course. Maximal stimulation of O2 consumption occurred at day three, at which point the capacity for peroxidase‐mediated O2 consumption was three‐to four‐fold higher than that of the control O2 consumption rate. Peroxidase‐mediated O2 consumption was sensitive to inhibition by 50 mM ascorbate and by cyanide. Cyanide titration curves indicated that O2 consumption by peroxidase was much more sensitive to inhibition by cyanide than was O2 consumption by cytochrome oxidase (I50 < 1.6 μM and I50= 18.3 μM cyanide, respectively). By using evidence from a combination of cyanide titration curves and ascorbate inhibition, we concluded that despite a large capacity for peroxidase‐mediated O2 consumption, peroxidase did not measurably contribute to control rates of O2 consumption. In the absence of effectors, O2 consumption was mediated primarily by cytochrome oxidase.
Expression of a gene for plastid ω‐3 fatty acid desaturase and changes in lipid and fatty acid compositions in light‐ and dark‐ grown wheat leaves
Authors: Horiguchi Gorou , Iwakawa Hirotaka , Kodama Hiroaki , Kawakami Naoto , Nishimura Mitsuo , Iba Koh
Published: May 2006

The leaves of monocotyledonous plants create a developmental sequence of cells and plastids from the base to the apical portion. We investigated fatty‐acid and lipid compositions in successive leaf sections of light‐ and dark‐grown wheat (Triticum aestivum L. cv. Chihoku) seedlings. The most notable change in the fatty acid composition was the increase of linolenic acid (18:3) with maturation of leaf cells, which occurred both in light‐ and dark‐grown leaf tissues. In light‐grown leaves, the increase of 18:3 with maturation was mainly attributed to the increase of monogalactosyldiacylglycerol (MGD) and also to the increase of the 18:3 level of MGD. In dark‐grown leaves, the increase of 18:3 in the leaf apex was caused by the increase of the levels of MGD and digalactosyldiacylglycerol (DGD) and also by the increase of the 18:3 levels of within these two lipids. Since MGD and DGD are mainly found in plastid membranes, these findings indicate that both the synthesis of galactolipids and the formation of 18:3 these lipids take place during plastid development. The plastid ω‐3 fatty acid desaturase is responsible for the formation of 18:3 in plastid membrane lipids. To investigate the regulation of desaturation, we isolated a gene for wheat plastid ω‐3 fatty acid desaturase (TaFAD7). The mRNA level of TaFAD7 in light‐grown leaves was much higher than that in dark‐grown leaves. During the greening of etiolated leaves the level of TaFAD7 mRNA increased significantly, accompanied by an increase of the 18:3 level of total fatty acids. On the other hand, the levels of TaFAD7 mRNA were almost the same in all the leaf sections of both light‐ and dark‐grown leaf tissues. These results suggest that the effect of the expression of the TaFAD7 gene on the increase of the 18:3 level is different between the leaf development under continuous light‐ or dark‐conditions and the light‐induced greening process of etiolated leaves. The increase of 18:3 content of MGD (or MGD and DGD) with maturation is apparently regulated not solely by the level of TaFAD7 mRNA.
Effects of water stress on plant growth and root proteins in three cultivars of rice (Oryza sativa) with different levels of drought tolerance
Authors: Pérez‐Molphe‐Balch Eugenio , Gidekel Manuel , Segura‐Nieto Magdalena , Herrera‐Estrella Luís , Ochoa‐Alejo Neftalí
Published: May 2006

Rice (Oryza sativa L.) is considered a drought‐sensitive crop species; however, within this species, there are considerable varietal differences in sensitivity to this environmental stress. In the present work, the effect of water stress on germination, plant growth and root proteins in three rice cultivars (Sinaloa, IR10120 and Chiapas) was analyzed. Seed germination and plant growth were found to be significantly inhibited by polyethylene glycol (PEG)‐imposed water deficit in cv. Sinaloa; cvs IR10120 and Chiapas were more tolerant to water stress. Fluorographs of two‐dimensional electropherograms of in vivo‐labeled polypeptides were analyzed to identify changes in the root protein patterns that resulted when plants were grown in the presence of 10% PEG for 10 days. The treatment induced or increased the synthesis of eight polypeptides or groups of polypeptides in cv. Sinaloa, seven in cv, IR10120 and four in cv. Chiapas. The synthesis of several polypeptides was decreased by the PEG treatment in cv. Sinaloa and cv. IR10120. Most of these PEG‐induced changes in the root protein patterns were cultivar‐specific and only one 26‐kDa protein with a pI of 6.0 was induced by water deficit in the two cultivars Sinaloa and IR10120.
The rate of development of water deficits affects Saxifraga cernua leaf respiration
Authors: Collier Donald E. , Cummins W. Raymond
Published: May 2006

We allowed plant water deficits to develop at two different rates following the cessation of watering in order to investigate the effects of water stress on cytochrome pathway and alternative pathway respiration in the leaves of the arctic herb Saxifraga cernua. Plants were pretreated by growth in either a commercial organic (CO) mixture or a vermiculite‐perlite (VP) mixture, which allowed the complete development of water deficits in 19 and 8 days, respectively. The rate of water potential reduction was approximately 0.11 MPa day−1 in the leaves of CO plants, compared to a reduction of 0.21 MPa day−1 in leaves of VP plants. Osmotic adjustment occurred to a greater extent in leaves of CO plants and corresponded with an increase in ethanol‐soluble sugars. In leaves of CO plants, cytochrome pathway activity gradually declined from that of control rates until day 11, and then declined more rapidly. In contrast, cytochrome pathway activity significantly increased in response to water deficits in leaves of VP plants. In leaves of both CO and VP plants, alternative pathway activity declined as water stress progressed. Relatively severe water deficits reduced alternative pathway capacity in leaves of both CO and VP plants. We also investigated the effect of previous exposure to water deficits on leaf respiration. In plants that had previously experienced three cycles of water stress, the increase in cytochrome pathway activity during the fourth water stress cycle was small compared to the increase observed in leaves of plants experiencing water stress for the first time. These results suggest that cytochrome pathway activity is differentially sensitive to the rate of development of plant water deficits and that respiratory responses to acute water stress are not necessarily similar to the responses to chronic water stress.
Relationship between cavitation and water uptake in rose stems
Authors: van Doorn Wouter G. , Suiro Véronique
Published: May 2006

Cavitation in rose stems (Rosa hybrida L.) was assessed in both intact plants and excised flowers, by measurement of ultrasonic acoustic emissions at the stem surface and determination of the air‐conductivity of 2.5‐cm segments that were attached at one end to air at low pressure (0.01 MPa). On sunny days the stems of intact rose plants showed acoustic emissions and conductivity to air, starting early in the morning. In Cara Mia and Sonia rose plants the cavitations were repaired during the late afternoon; in Madelon plants this repair only occurred overnight. Water flow was seriously impaired in stems of Cara Mia roses cut around midday, on sunny days.

During dehydration of cut roses in air the onset of a high rate of acoustic emissions coincided with a low rate of water uptake when stems were subsequently placed in water. High emission frequency occurred after 2.4 ± 0.7 h, 6.8 ± 4.3 h and 19.8 ± 9.0 h of exposure to air in Cara Mia, Madelon and Sonia roses, respectively. A low rate of water uptake in excised stems placed in water was found after 3–4, 9–12 and 24–36 h of desiccation in air, respectively. The onset of the high emission frequency corresponded with a water potential of −1.7, −2.9 and −3.8 MPa in the three cultivars, respectively.

It is concluded that a high number of cavitations may occur in noncut stems of rose plants, leading to low water uptake immediately after excision, depending on the weather and the cultivar, and that the low rate of water uptake after a period of dry storage, among the three rose cultivars investigated, is correlated with the presence of a high number of cavitated xylem elements.
NAD(P)+‐dependent isocitrate dehydrogenases in mitochondria purified from Picea abies seedlings
Authors: Cornu Sylvie , Pireaux Jean‐Claude , Gerard Joëlle , Dizengremel Pierre
Published: May 2006

Isocitrate dehydrogenase (IDH) activities were measured in mitochondria isolated from aerial parts of 21‐day‐old spruce (Picea abies L. Karst.) seedlings. Mitochondria were purified by two methods, involving continuous and discontinuous Percoll gradients. Whatever the method of purification, the mitochondrial outer membrane was about 69% intact, and the mitochondria contained very low cytosolic, chloroplastic and peroxisomal contaminations. Nevertheless, as judged by the recovery of fumarase activity, purification on a continuous 28% Percoll gradient gave the best yield in mitochondria, which exhibited a high degree of inner membrane intactness (91%). The purified mitochondria oxidized succinate and malate with good respiratory control and ADP/O ratios. The highest oxidation rate was obtained with succinate as substrate, and malate oxidation was improved (+ 60%) by addition of exogenous NAD+. Experiments using standard respiratory chain inhibitors indicated that, in spruce mitochondria, the alternative pathway was present. Both NAD+‐isocitrate dehydrogenase (EC 1.1.1.41) and NADP+‐isocitrate dehydrogenase (EC 1.1.1.42) were present in the mitochondrial matrix fraction, and NAD+‐IDH activity was about 2‐fold higher than NADP+‐IDH activity. The NAD+‐IDH showed sigmoidal kinetics in response to isocitrate and standard Michaelis‐Menten kinetics for NAD+ and Mg2+. The NADP+‐IDH, in contrast, displayed lower Km values. For NAD+‐IDH the pH optimum was at 7.4, whereas NADP+‐IDH exhibited a broad pH optimum between 8.3 and 9. In addition, NAD+‐IDH was more thermolabile. Adenine nucleotides and 2‐oxoglutarate were found to inhibit NAD(P)+‐IDH activities only at high concentrations.
Changes in distribution of chloroplast adenylate kinase isoforms during floral induction
Authors: Schlattner Uwe , Wagner Edgar , Greppin Hubert , Bonzon Marc
Published: May 2006

In the short day plant Chenopodium rubrum and the long day plant Nicotiana tabacum cv. Havana 425, adenylate kinase (EC 2.7.4.3) occurs as a family of isoforms, with at least two members localized in the chloroplast representing the main isoforms. In this work, isoforms were separated by anion exchange chromatography and relative isoform activities were compared between vegetative plants and plants induced to flowering. In both species examined, a light regime leading to floral induction resulted in a significant decrease in the activity of one chloroplast isoform. This decrease modified considerably the relative distribution of isoform activities, especially that between the two chloroplast activities.
The effect of cell turgor on sugar uptake in strawberry fruit cortex tissue
Authors: Pomper K. W. , Breen P. J.
Published: May 2006

A reduction in cell turgor has been shown to stimulate sugar uptake in several plant sink tissues and it may regulate the import of assimilate into the sink apoplast, as well as maintain cell turgor. To determine whether cell turgor influences sugar uptake by strawberry (Fragaria x ananassa Duch. cv. Brighton) fruit cortex tissue, disks were cut from greenhouse‐grown primary fruit at the green‐white stage of development and placed in buffered incubation solutions containing either mannitol or ethylene glycol as an osmoticum. Cell turgor of fruit disks was calculated from the difference between the water potential of bathing solution and tissue solute potential after incubation at various osmolarities. Cell turgor increased when tissue disks were placed into mannitol incubation solutions more dilute than the water potential of fresh tissue (about 415 mOsmol kg−1). The rate of uptake of [14C]‐sucrose or [14C]‐glucose decreased as osmolarity of the incubation solution increased, i.e. as cell turgor declined. Cell turgor and the rate of [14C]‐sucrose uptake were unaffected when rapidly permeating ethylene glycol was used as an osmoticum. A decrease in cell turgor reduced both the Vmax of the saturable (carrier mediated) kinetic component of sucrose uptake, and the slope of the linear (diffusional) component. The sulfhydryl binding reagent p‐chloromercuibenzenesulfonic acid, an inhibitor of the plasma membrane sucrose carrier, strongly inhibited only the saturable component of sucrose uptake. Increased uptake of the nonmetabolizable sugar, O‐methyl‐glucose, at high turgor was similar to that of glucose, indicating that carrier activity was influenced by cell turgor, not cell metabolism. Turgor did not influence efflux of [14C]‐sucrose from disks and had no effect on cell viability. Strawberry fruit cells do not possess a sugar uptake system that is stimulated by a reduction in turgor.
Herbicidal activity of 4‐chloroindoleacetic acid and other auxins on pea, barley and mustard
Authors: Engvild Kjeld C.
Published: May 2006

The natural auxins, 4‐chloroindoleacetic acid and its methyl ester have strong herbicidal effects on pea, Pisum sativum, a plant in which they occur naturally. The standard herbicide, 2,4‐dichlorophenoxyacetic acid (2,4‐D) is only 5 times more effective than 4‐chloroindoleacetic acid. The I50, the dose inhibiting yield by 50%, for 4‐chloroindoleacetic acid and its methyl ester is 0.5 kg ha−1 or 15 mg kg−1 fresh weight, close to the concentration of 4‐chloroindoleacetic acid methyl ester in maturing pea seeds. Naphthaleneacetic acid and indoleacetic acid are also inhibitory, but at much higher concentrations. In its inhibiting effect on white mustard, Sinapis alba, 4‐chloroindoleacetic acid approximates that of 2,4‐D, whereas in barley, Hordeum vulgare, it is a stronger herbicide than 2,4‐D. All auxins tested killed white mustard at low doses, but none killed barley. Both 4‐chloroindoleacetic acid and 2,4‐D killed pea. The chloroindole auxins of pea may be the hypothetic death hormones or senescence factors that are secreted from the developing seeds into the parent plant which is strongly inhibited or killed and from which the nutrients are mobilized and translocated to the seeds. The action mechanism of auxin type herbicides may be to simulate the action of endogenous herbicides.
Effect of planting date on flowering time in wheat
Authors: Johansson Eva , Oscarson Petter , Lundborg Tomas
Published: May 2006

The time from seed germination to anthesis varied for spring wheat in experiments in climate chambers with plants grown hydroponically at different nitrogen regimes. Time to anthesis was related to the time of seed germination during the calendar year. Seed germinating earlier in the calendar year required a shorter time to anthesis compared to seed germinating later in the year, a pattern found for all the spring wheat cultivars investigated. Time to anthesis was also found to be independent of factors such as year in which the seed was produced, nitrogen regime used, or year or site of cultivation. We suggest the existence of an annual rhythm for flowering in spring wheat. This variation in time to flowering can be due either to external factors or more likely to an endogenous rhythm in the plant. When investigating plant processes, it is of importance to be aware of such a rhythm, since it may influence the results depending on when during the year the experiments are performed.
On the functional significance of substrate accessibility in the photosynthetic water oxidation mechanism
Authors: Wydrzynski Tom , Hillier Warwick , Messinger Johannes
Published: May 2006

Recent evidence suggests that after selective perturbation of the protein structure in photosystem II, hydrogen peroxide is formed at the water oxidation catalytic site instead of molecular oxygen. In this communication, we review the interpretation of these observations and elaborate on the hypothesis that an essential factor in determining the end‐product of photosynthetic water oxidation is one of substrate accessibility. It is argued that normally the access of water to the catalytic site is controlled by a hydrophobic domain in the surrounding protein matrix and that the production of O2 is optimized by an ordered binding of the two substrate water molecules. It is proposed that upon perturbation of the hydrophobic domain (for example, through the removal of various extrinsic proteins) the catalytic site becomes exposed to excess water from the external solvent phase. As a consequence, additional water binds at the catalytic site during intermediate oxidation steps and undergoes a partial oxidation reaction to form hydrogen peroxide. The importance of water accessibility to the structure/function relationships of photosystem II is discussed, particularly with respect to photoinhibitory damage through the formation of hydrogen peroxide.
Function of the ascorbate‐glutathione cycle in aged sunflower seeds
Authors: De Paula M. , Perez‐Otaola M. , Darder M. , Torres M. , Frutos G. , Martimez‐Honduvilla C. J.
Published: May 2006

The function of the ascorbate‐glutathione (AsA/GSH) cycle was analyzed in seeds of sunflower (Helianthus annuus L. cv. Peredovik) subjected to accelerated ageing at 43°C and 75% relative humidity for 1 to 11 days. The study was performed using dry seeds and seeds hydrated by imbibition in distilled water for 4 h at 25 °C. Lipid peroxidation was also determined by measuring the malondialdehyde (MDA) level. As the ageing period increased, a progressive loss of seed viability became increasingly evident. Even though high levels of MDA were delected, the MDA level did not change during accelerated ageing, suggesting that lipid peroxidation might occur to some extent. The study of the ascorbate/glutathione (AsA/GSH) cycle revealed that the GSH system is the major detoxifying mechanism in both dry and imbibed sunflower seeds. The GSH system is mainly located in the embryo, and its protective role is mediated by reactions that consume the GSH pool and, thereby, minimize the increase of the oxidized form (GSSG). Seed imbibition activates cellular metabolism and allows some antioxidant enzymes like glutathione reductase (EC 1,6,4,2) to act upon toxic agents. These reactions provide a reducing status, so that repair of damage becomes possible. However, prolonged ageing conditions (11 days) result in an irreversible damage, as evidenced by the appearance of dead seeds when the germination period ended. Multiple regression analysis revealed the effectiveness of the GSH system in aged seeds, especially upon imbibition and until the AsA/GSH cycle became completely functional.
Alternative oxidase from Arum and soybean: Its stabilization during purification
Authors: Zhang Qisen , Hoefnagel Marcel H. N. , Wiskich Joseph T.
Published: May 2006

Complete purification of the alternative oxidase from plant mitochondria has not been achieved successfully, because of its instability on solubilization. We report here that the addition of pyruvate to the isolation medium stabilizes the activity of the solubilized enzyme. A procedure is described for the rapid isolation and partial purification of the cyanide‐insensitive alternative oxidase from both Arum maculatum and soybean cotyledon (Glycine max) mitochondria. The degree of purification was 16‐ and 74‐fold for Arum and soybean enzyme, respectively. The specific activities increased from 1 300 to 20 300 nmol oxygen consumed mg−1 protein min−1 (using duroquinol as substrate) after purification for the Arum erizyme and from 6 to 445 nmol oxygen consumed mg−1 protein min−1 for the soybean enzyme. A turnover for the partially purified Arum enzyme was estimated to be 47 electrons s−1.

The partially purified enzyme from both Arum and soybean cotyledon mitochondria was sensitive to alternative oxidase inhibitors such as salicylhydroxamic acid, n‐propyl gallate and octyl gallate, but not to myxottriazol, KCN or antimycin A. The activity of the enzyme could be stimulated by pyruvate, but not by malate and suceinate. The stability of the purified enzyme was also dependent on the continued presence of pyruvate. In the absence of pyruvace, the enzyme activity was lost in a time‐dependent manner and the ability of pyruvate to recover the activity was also irreversibly lost.
Fibre length and gibberellins A1 and A20 are decreased in Eucalyptus globules by acylcyclohexanedione injected into the stem
Authors: Ridoutt Brad G. , Pharis Richard P. , Sands Roger
Published: May 2006

Trinexapacethyl (TriEt), an acylcyclohexanedionetype inhibitor of gibberellin (GA) biosynthesis, was applied to 3‐year‐old Eucalyptus globules saplings by localised injection near the base of each stem. The objective was to alter cambial region GA levels and to study the effects on secondary xylem fibre development. Seven weeks later wood samples, with bark and cambial region intact, were removed 10 and 30 cm above the point of injection. Fusiform cambial cell dimensions were compared with those of fibre‐tracheids in the most recently formed 100 um of secondary xylem. Increasing TriEt applications from 5 to 5 000 mg active ingredient significantly reduced average fibre length, and to a lesser extent average fusiform cambial cell length. Also reduced was the number of cells in the cambial zone and the number of differentiating fibres with primary walls. However, no trends were evident for changes in fibre diameter, the proportion of vessel elements or the ratio of cambial ray cells to fusiform cambial cells. Two gibberellins (GA1 and GA20), indole‐3‐acetic acid (IAA) and abscisic acid (ABA) were quantified in cambial region tissues by gas chromatographymass spectrometry using stable isotope labelled internal standards. Increasing TriEt application reduced both GA1 and GA20 levels. Effects on IAA and ABA were not significant, although their levels tended to be lower at the highest TriEt application rate. The elongation of secondary xylem fibres was positively correlated with higher levels of endogenous GA1 (rs= 0.74, P < 0.01) and GA20 (rs= 0.72, P < 0.01). These results support a causal role for GA1 in cambial cell division. They are also consistent with the hypothesis that the elongation of differentiating secondary xylem fibres in woody an–giosperms is dependent on GA1 levels in the cambial region.
Close relationship between the state of the xanthophyll cycle pigments and photosystem II efficiency during recovery from winter stress
Authors: Verhoeven Amy S. , Adams William W. , Demmig‐Adams Barbara
Published: May 2006

The potential involvement of the xanthophyll cycle in photoprotection of overwintering evergreen plants was investigated. Leaves from five evergreen species. Pseudotsuga menziesii, Pinus panderosa, Euonyums kiautschovicus. Mahonia repens and Malva neglecta, were collected from the field predawn during winter and transferred to the laboratory where chlorophyll fluorescence emission as well as the chlorophyll and carotenoid composition were ascertained periodically for 4.5 days. Leaves and needles from all species were found to have retained large amounts of the xanthophyll cycle pigments zeaxanthin and antheraxanthin, and they exhibited sustained low values of the intrinsic efficiency of photosystem II (PSII; measured as the ratio of variable to maximal fluorescence, Fv/Fm) upon collection. The increase in PSII efficiency was biphasic, with a rapid phase (requiring several hours) and a slow phase (requiring several days). Changes in the conversion state of the xanthophyll cycle were found to correlate with increases in PSII efficiency in both phases, with the latter phase involving large increases in both Fm (maximal fluorescence) and Fo (minimal fluorescence) throughout the period of recovery. The relationship between Fm quenching (expressed as nonphotochemical or Stern‐Volmer quenching [NPQ] of Fm, i.e. Fm/ Fm–1) and Fo quenching (Fo/Fo–1) was linear, as expected for changes in xanthophyll cycle‐dependent energy dissipation in the antenna complexes. Furthermore, the relationship between Fv/Fm and NPQ during recovery followed the theoretical relationship predicted for changes in the rate constant for energy dissipation in the antenna complexes. This fit between the theoretical relationship and the actual data indicates that all changes in NPQ or Fv/Fm can be accounted for by changes in this rate constant. The results suggest a role for the photoprotective xanthophyll cycle‐dependent dissipation process in the lowered efficiency of PSII observed in coldstressed evergreen plants in the field.
Characterization of embryogenesis‐related proteins in alfalfa (Medicago sativa)
Authors: Giroux Randal W. , Pauls K. Peter
Published: May 2006

Large samples of embryogenic cells can be obtained from tetraploid alfalfa (Medicago sativa L.) suspension cultures following induction by auxin and culture on growth regulator‐free medium. A one–dimensional sodium dodecyl sulphate‐polyacrylarnide gel electrophoresis (SDS‐PAGE) comparison of the polypeptides synthesized by embryogenic and nonembryogenic alfalfa genotypes during inductive conditions identified a 50‐kDa polypeptide band that was specific to embryogenic genotypes. Two‐dimensional (iso electric focusing SDS‐PAGE) electrophoretic separations resolved the 50–kDa band into three 50‐kDa polypeptides with different isolectric points. A comparison of the polypeptides in the soluble and microsomal membrane fractions from embryogenic cell masses of an embryogenic genotype suggested that the 50‐kDa pep‐tides are membrane associated. The in vitro translation products from RNAs of an embryogenic genotype had a 50‐kDa band that was absent from the in vitro translation products obtained from RNAs of a nonernbryogenic genotype. Therefore, we concluded that the membrane‐localized 50‐kDa proteins are involved in somatic embryo–genesis in alfalfa and that their expression is transcriptionally determined.