bluuebunny/crossref_metadata_2025 huggingface dataset:
Short‐term UV‐B radiation and ozone exposure effects on aromatic secondary metabolite accumulation and shoot growth of flavonoid‐deficient Arabidopsis mutants
Authors: Ormrod Douglas P. , Landry Laurie G. , Conklin Patricia L.
Published: May 2006

The presence of UV‐absorptive substances in the epidermal cells of leaves is thought to protect mesophyll tissues from the harmful effects of UV‐B radiation. We examined the influence of short‐term UV‐B exposures on UV‐absorptive (330 nm) sinapates and flavonols, and on shoot growth of the Arabidopsis wild type ecotype Landsberg erecta and two mutants. 114 deficient in chalcone synthase, and 115, deficient in chalcone/flavonone isomerase. Sequential ozone exposures were used to determine the effects of oxidative stress The levels of sinapates and flavonols on a leaf fresh weight basis increased substantially in the wild type and sinapates increased in the 114 mutant in vegetative vegetative/reproductive transitional and reproductive stage plants in response to short‐term (48h) UV‐B radiation. When UV‐B was discontinued the levels generally decreased lo pre‐exposure levels after 48 h in vegetative/reproductive but not in reproductive plants. Exposure to ozone before or alter UV‐B treatment did not consistently affect the levels of these UV‐absorptive compounds. Dry matter accumulation was less affected by UV‐B at the vegetative and reproductive stages than at the vegetative/reproductive stage. At the vegetative/reproductive stage, shoot growth of all 3 genotypes was retarded by UV‐B. Growth was not retarded by short‐term ozone exposure alone but when exposure to ozone followed UV‐B exposure, growth was reduced in all genotypes. Leaf cupping appeared on 115 plants exposed to UV‐B.
Uptake kinetics of iron‐phytosiderophores in two maize genotypes differing in iron efficiency
Authors: von Wirén Nicolaus , Marschner Horst , Römheld Volker
Published: May 2006

Iron inefficiency in the maize (Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe‐phytosiderophores. To characterize this defect further, the uptake kinetics of Fe‐phytosiderophores in ysl was compared to the Fe‐efficient maize cultivar Alice. Short‐term uptake of 59Fe‐labeled Fe‐deoxymugineic acid (Fe‐DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe‐deficient plants followed Michaelis‐Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe‐phytosiderophores. The saturable component had similar Km (∼ 10 μM) in both genotypes. In contrast. Vmax was 5.5 μmol Fe‐DMA g−1 dry weight [30 min]−1 in Alice, but only 0.6 μmol Fe‐DMA g−1 dry weight [30 min]−1 in ysl. Uptake experiments with double‐labeled 59Fe‐[14C]DMA suggest that in both cultivars Fe‐DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high‐affinity and a low‐affinity uptake system mediating Fe‐phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high‐affected uptake and led to a decrease in activity and/or number of Fe‐phytosiderophore transporters.
Regulation of plastid photosynthetic psbK‐I‐D‐C gene expression by light in rice plants
Authors: Chen Shu‐Chen Grace , Wu Sang‐Pin , Lo Pang‐Kuo , Mon Dir‐Pu , Chen Long‐Fang Oliver
Published: May 2006

The expression of the plastid photosynthetic psbK‐I‐D‐C gene cluster is closely regulated by light. The time courses of expression of the gene cluster in rice seedlings (Oryza sativa L. cv. Tainong 67) grown under various irradiation regimes were examined by northern and western blot analyses. The data indicated that the gene cluster is photoregulated at the transcriptional and post transcriptional levels. Blue light not only enhanced the accumulation of the overlapping transcripts present in the 7 to 8‐day dark‐grown seedlings, but also induced the accumulation of new class d transcripts encoding D2 protein and CP43. This observation confirms the conservation of blue‐light regulation of psbD‐psbC transcription in plants. In etiolated seedlings, the accumulation of class e transcript encoding CP43 increased most remarkably during development: irradiation further enhanced the transcript level. Although the transcripts encoding D2 protein and CP43 are present in etiolated plants, only D2 protein is accumulated, and CP43 was not detected unless the seedlings were exposed to light. The transcript levels of RNAs d1 and f2 in green seedlings grown under a 12‐h photoperiod exhibited fluctuating patterns over the 24‐h period. The levels o1 RNAs dl and f2 also exhibited significant fluctuation during the 36‐h exposure of the etiolated seedlings to light. These data imply that the circadian regulation of pshD‐psbC expression takes place at the transcriptional and post‐transcriptional levels.
Desiccation tolerance in developing soybean seeds: The role of stress proteins
Authors: Blackman S. A. , Obendorf R. L. , Leopold A. C.
Published: May 2006

The consistent correlation between desiccation tolerance in orthodox seed tissue and an accumulation of certain “late embryogenesis abundant” (LEA) proteins suggests that these proteins reduce desiccation‐induced cellular damage. The aim of the present work was to test this hypothesis. Exogenous abscisic acid (ABA) was used to elevate the level of heal‐soluble LEA‐like proteins in axes from immature (30 days after flowering: mid‐development) seeds of soybean (Glycine max [L.] Merrill cv. Chippewa 64). As the LEA‐like proteins accumulated in response to ABA, the leakage of all elements after desiccation and subsequent rehydration markedly declined. Both LEA‐like protein accumulation and the decline in desiccation‐induced electrolyte leakage were apparently dependent on the presence of ABA. Both effects of ABA were inhibited by cycloheximide. Light microscopy revealed a marked effect of the ABA on cellular integrity following desiccation. Osmotic stress also caused a decrease in desiccation‐induced electrolyte leakage and stimulated the accumulation of LEA‐like proteins. Our data are consistent with the hypothesis that the LEA‐like proteins contribute to the increase in desiccation tolerance in response to ABA, and are consistent with a general protective role for these proteins in desiccation tolerance.
Photoperiodic control of endogenous gibberellins in seedlings of Salix pentandra
Authors: Olsen J. E. , Jensen E. , Junttila O. , Moritz T.
Published: May 2006

In the temperate‐zone woody species Salix pentandra elongation growth is regulated by the photoperiod. Long days sustain active growth, whereas short days induce cessation of apical growth, which is a prerequisite for winter hardening. It is shown that this is correlated to quantitative changes in levels of endogenous GA19 GA20, and GA1. Within two short days the amount of the active GA1 and its immediate precursor GA20, decreased markedly in young leaves us well as in stem tissue. Also, the amount of GA19, declined, but the decrease was delayed relative to that of GA1 and GA20. The ability of S. pentandra seedlings to respond to exogenous GA19, decreased with increasing numbers of short days. Observations that support the hypothesis that the level of GA1 in S. pentandra is regulated by the photoperiod in a quantitative mode with conversion of GA19, to GA20, being one target for control.

Different distribution of GAs in various plant parts was observed. The level of GA was higher in young leaves than in other plant parts, and the amount of GA19 was 5–10 times higher in stem tissue than in leaves and roots. The ratios of GA8 to GA1 and GA20, were higher in roots as compared with other parts, as rods contained very low levels of GA1 and GA20, but amounts of GA20 comparable with other parts.
Activity of cell wall‐associated enzymes in ripening olive fruit
Authors: Fernández‐Bolaños Juan , Rodríguez Rocio , Guillén Rafael , Jiménez Ana , Heredia Antonia
Published: May 2006

Enzymatically active cell wall isolaled from olive (Olea europaea) fruit was employed Hi investigate some hydrolytic enzymes bound to the cell wall and the changes in these during ripening. Seven glycosidases. β‐glucosidase (EC 3.2.1.21) α‐galactosidase (EC 3.2.1.22). β‐galactosidase (EC 3.2.1.23). α‐arabinosidase (EC 3.2.1.55), α‐mannosidase (EC 3.2.1,24). β‐xylosidase (EC 3.2.1.37) and β‐N‐acetylglucosamidase (EC 3.2.1.30). as well as Cx‐cellulase (EC 3.2.1.4) and endo‐polygalacturonase (EC 3.2.1.15). were identified in the cell wall preparation, at four stages of ripeness (mature green. changing colour, black and black‐ripe). Activities of all these cell wall‐associated enzymes fionicallv and covalently linked) were determined either by cell wall incubation with artificial substrate or after extraction from the cell wall with buffers of high salt concentration (Cx‐cellulase). and were compared to those of forms solubilized from acetone powders with 500 nM citrate buffer (cytoplasmic and/or apoplastic plus ionically hound to cell wall) In general, the activities of low ionic strength buffer‐soluble enzymes were found to be much higher than those of the bound enzymes. The bound enzymes are present in the fruit at the green colour stage, whereas the activities of the soluble enzymes only increased from the changing colour stage onwards. The tenacity of binding of enzymes to the wall was investigated by treating the walls with high salt and measuring residual activity. The nature of the ionic and covalent binding and the changes during ripening were also established for wall‐hound glycosidase During ripening there was a marked change in the percentages of covalently‐ and tonically linked activities of β‐glucosidase and β‐galaclosidase: al the changing colour stages about 75–80% of the bound active in was present in high ionic strength buffer while al the black‐ripe stage it was only 15–20. A possible role for these cell wall degradative enzymes in olive softening is discussed.
Arabidopsis mutants with reduced response to NaCl and osmotic stress
Authors: Werner Joanna E. , Finkelstein Ruth R.
Published: May 2006

We isolated 6 mutant lines of Arabidopsis thaliana that expressed reduced sensitivity to salt and osmotic stress during germination. All 6 lines cum recessive mutations in a single gene, designated reduced salt sensitivity (rss), linked to the ADH marker on chromosome 1. The rss mutants are less sensitive than wild type for NaCl and osmotic stress inhibition of germination, tolerating approximately 150 mM higher concentrations of NaCl and about 250 mM higher concentrations of sorbitol in the media. Germination assays on media containing various salts indicate that the rss mutations reduce sensitivity lo Na+ and Rh+ but also, to a much lesser degree, to K+ and Css+. However, the rss mutation does not improve plant growth when plantlets are transferred to high salt or high osmotic pressure media after germination. The rss plantlets accumulate praline to a significantly lesser degree than wild type when they are exposed to either salt or osmotic stress. Thus, the rss mutants differ from wild type both at germination and during vegetative growth indicating that the rss mutations are pleiotropic and might affect perception of solutes or some aspect of stress‐induced signaling. The rss mutations do not alter ABA sensitivity and therefore probably do not affect ABA‐mediated signaling.
Distribution of nitrate reductase activity in Vicia faba: Effect of nitrate and plant genotype
Authors: Caba Juan Manuel , Lluch Carmen , Ligero Francisco
Published: May 2006

The short term effect of NO3− (12 mM) on nitrate reductase (NR. EC 1.6.6.1) activity has been studied in the roots, nodules and leaves of different genotypes of Vicia faba L. at the end of vegetative growth. Root and leaf NR activity responded positively to NO3− while nodule activity, where detected, proved to he strongly inhibited. The withdraw of this NO3− from the solution consistently reduced activity in the roots and leaves but surprising, promoted a significant increase in nodule activity, which matched or surpassed that of control plants On the other hand, nodules developed in the presence of 8 mM NO3− expressed an on average 141% higher level of NR activity than did controls. This effect was observed even in nodules with negligible control activity. In any case, a naturally occurring mutant (VF17) lacking root and nodule NR activity is described. The results indicate that in V. faba. the effects of NO3− and plant genotype on NR activity depended on plant organ and time of NO3− application, hut the distribution of NO3− reduction through the plain was mainly dependent on plant genotype, and to a lesser extent on NO: supply and plant age.
Lipid changes in mature‐green bell pepper fruit during chilling at 2°C and after transfer to 20°C subsequent to chilling
Authors: Whitaker Bruce D.
Published: May 2006

Lipid composition and pigment content in bell pepper (Capsicum annuum L. cv. Bell Tower) fruit that were freshly harvested, chilled 14 days at 2° C. or chilled and then transferred to 20 °C for 3 days (“rewarmed”) were determined. There was slight to moderate loss of membrane glycerolipids during chilling, with much greater losses after chilled fruit was rewarmed. Galactolipid (GL) loss exceeded that of phospholipid (PL). The ratio of monogalactosyl ‐to digalactosyl‐diacylglycerol did not change in chilled or in rewarmed fruit, and there was no chlorophyll loss, but the amount of neutral carotenes declined during chilling and dropped further alter rewarming. Only minor changes in total membrane sterols (TMS = free sterols + steryl glycosides + acylated steryl glycosides) were noted in chilled and in rewarmed fruit (a small increase followed by a small decrease), but major changes occurred in sterol glycosylation and esterification. The ratio of stigmasterol to sitosterol increased during chilling and rose further after rewarming. Due to PL loss, the ratios of TMS and free sterols to PL increased in rewarmed fruit. The ratio of linolenate (18:3) to linoleate (18:2) rose during chilling and after rewarming in all fatty‐acyl lipids (GL. PL. and acylated steryl glycosides), but the unsaturation index increased only in GL. These results indicate that most membrane damage occurs after rewarming of chilled fruit and that the chloroplasts are especially chilling sensitive.
Induction of glutathione S‐transferase activity and glutathione level in plants exposed to glyphosate
Authors: Uotila M. , Gullner G. , Kömives T.
Published: May 2006

Treatment with the herbicide glyphosate led to significantly increased activities of the enzyme gluiathione S‐transferase (GST, EC 2.5.1.18) in wheat (Triticum aestivum L. cv. Kadett and cv. Satu), pea (Pisum sativum L. ev. Debreceni Világoszöld) and in maize (Zea mays. L. Pioneer 3839 hybrid) tissues. GST activities in wheat seedlings (cv. Kadett) exposed to 960 μM glyphosate for 4 days were ca 6‐fold and 3‐fold higher in shoots and roots, respectively, than in the controls. Glyphosate increased the GST activity to a lesser extent in pea and maize than in wheat. In wheat seedlings (cv. Satu) exposed let 120 μM glyphosate gradual increases in the content of non‐protein thiols were observed. After 7 days exposure to glyphosate the thiol levels rose to about 360% and 220% of the controls in wheal shoots and roots, respectively. The elevation of thiol content in glyphosate‐treated plants was shown to be primarily due increases of glutathione level. These results suggest that the enhanced glutathione metabolism may have a role in the mode of action or degradation of this herbicide.
Drought stress of apple trees alters leaf emissions of volatile compounds
Authors: Ebel Robert C. , Mattheis James P. , Buchanan David A.
Published: May 2006

Actively growing potted apple trees (Malus domestica [L.] Borkh. ev. Delicious) unacclimated to drought stress were subjected to drought to determine changes in emissions of leaf volatile compounds. Drought stress was imposed over a 2‐week period by weighing pots every 2 or 3 days and adding water hack to an arbitrary and decreasing traction of the original pot weight. Stem water potential was ‐2.7. ‐2.0 and ‐0.8 MPa for the severely stressed, moderately stressed and control trees, respectively. 13 days alter watering treatments were begun. Water use the last 4 days of the experiment was about one‐half for the moderately and severely stressed trees compared to that of the controls Twenty‐nine volatile compounds were identified by using gas chromatography and mass spectroscopy. Emission rates of hexanal, (E)‐2‐hexenal, (E)‐2‐hexen‐1‐ol, 1‐hexenol, hexyl acetate and (E)‐2‐hexenyl acetate were 5 to 310 times higher for severely stressed trees compared to those of the controls with the moderately stressed trees intermediate. The large increases in hexanal. (E)‐2‐hexenal and l‐hexanol may be related. In enhanced lipoxygenase activity. Volatile compounds are products of metabolism and measurement of their changes after biotic or abiotic stresses will increase understanding of the relationship of changes in plant metabolism by those stresses.
Effects of UV‐B on flavonoids, ferulic acid, growth and photosynthesis in barley primary leaves
Authors: Liu Lan , Gitz Dennis C. , McClure Jerry W.
Published: May 2006

Barley (Hordeum vulgare L.) was grown with UV‐B (280–320 nm) at levels simulating 25 nr 5% ozone depletion on the date of the summer solstice al 40°N latitude, with UV‐A (320–400 nm), or with no supplemental irradiation. In plant growth chambers providing 300 μmol m−2 s−1 photosynthetically active radiation (PAR). UV‐B‐grown leaves elongated more slowly than controls but reached the same final length 1 day later. Leal specific fresh weight (mass leaf area−1) was significantly increased by UV‐B after the 7th day of growth. IV‐B did not significantly affect leaf area, fresh weight, dry weight, total chlorophylls, total carotenoids or photosynthetic quantum efficiency. CO2 assimilation was decreased by UV‐B only at internal CO2 levels above 250 μl l−1. By the 8th day of growth, UV‐B increased flavonoid (saponarin and lutonarin) accumulation in both the lower epidermis and the mesophyll: about 40% of the saponarin and 20% of the lutonarin were in the lower epidermis under all experimental conditions. Glasshouse conditions proved too variable for reproducible determination of growth and photosynthesis but were reliable for determining developmental changes in flavonoid (saponarin and lutonarin) accumulation and provided up to 800 μmol m−2 s−1 PAR. In the glasshouse UV‐B‐grown leaves had more flavonoids than controls al all stages from 5 to 30 days after planting: ca 509 more saponarin and 100% more lutonarin. Levels of soluble (vacuolar) ferulic acid esters were similar under all conditions on day 5. and on day 20 or later, but were significantly higher in UV‐B‐grown plants on days 10 and 15. UV‐B decreased insoluble (cell‐wall‐bound) ferulic acid esters on a whole leaf basis but significantly increased this fraction in the lower epidermis. UV‐A had no significant effects on growth, photosynthesis or ferulic acid, but it slightly increased flavonoid accumulation. The results are discussed in terms of secondary phenolics as a tissue‐specific, developmentally regulated adaptive response to UV‐B.
Effects of UV‐B on activities of enzymes of secondary phenolic metabolism in barley primary leaves
Authors: Liu Lan , McClure Jerry W.
Published: May 2006

Barley (Hordeum vulgare L.) was grown in a glasshouse with 13.56 or 8.84 kJ m−2: biologically effective UV‐B (280–320 nm: UV‐BBE) simulating levels predicted to occur with 25 or 5% ozone depletion at 40°N latitude, with UV‐A (320–400 mm), or with no supplemental irradiation. Activities of L‐phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5). chalcone‐flavanone isomerase (CFI, EC 5.5.1.6) and peroxidase (EC 1.11.1.7) were determined from the 5th through the 30th day after planting. PAL regulates diversion of L‐phenylalanine into precursors for secondary phenolics. CFI regulates an early step of flavonoid biosynthesis, and peroxidase activates phenolic precursors for cross‐linking and rigidifying cell walls. At all ages UV‐B decreased soluble protein leaf−1 but had little effect on fresh weight or CFI activity. Exposure to UV‐B decreased peroxidase activity only slightly in early growth stages but decreased it about 40% by day 30. PAL activity was highest 5 days after planting under all treatments, decreased thereafter, and was not detectable in control plants after day 10. UV‐B prolonged PAL activity through day 15 in plants given the highest level of UV‐B. This UV‐B prolongation of PAL activity is correlated with, and is a likely underlying mechanism to explain, the UV‐B‐ enhanced accumulation of flavonoids and ferulic acid in barley primary leaves. The results are discussed in terms of barley leaf adaptation to UV‐B as developmental response dependent on conditions of plant growth.
Effect of glutamine on the induction of nitrate reductase
Authors: Li Xiu‐Zhen , Larson Dawn E. , Glibetic Marija , Oaks Ann
Published: May 2006

Nitrate reductase (NR. EC 1.6.6.1/2) is a substrate inducible enzyme that could be repressed by its end product glutamine or amino acids. To test this hypothesis, 6‐day‐old maize seedlings (Zea mayscv. W64A × W182E) were grown hydroponically in a 1/10 strength Hougland's salt solution modified to contain no nitrogen. Previous experiments had established that after a 24‐h induction with NO3−(5 mM KNO3−) the level of NR activity and protein had reached a constant level. In the present experiments when glutamine (5 mM) was included together with NO3−, there was a significant reduction in NR activity (34% of the control values). NR protein and NR mRNA accumulation in the root. In the shoot, on the other hand, glutamine additions had little or no effect on the levels of either NR activity (81% of control) or NR protein. Inhibition of glutamine synthetase by methionine sulfoximine (MSX) resulted in reduced levels of glutamine in both root and shoot tissues. Contrary in our prediction, however, it had no effect on NR activity and mRNA content in roots. In the shoot, on the other hand, there was a marked reduction of NR activity (34% of the control value) and NR protein, but no apparent effect on NR mRNA. When detached shoots were treated with MSX and other inhibitors of glutamine synthetase (tabtoxinine‐β‐lactam or phosphinothricin) the induction of NR activity by NO3−was also inhibited. Glutamine additions 15 or 50 mM to detached shoots had essentially no effect on the induction of NR activity (90% of control). These results demonstrate that the influence of glutamine and MSX on the induction of NR in maize root and shoot tissues, respectively, is very different.
Purification of intact chloroplasts from spruce (Picea abies) by free‐flow electrophoresis
Authors: Afif Dany , Canut Hervé , Dizengremel Pierre
Published: May 2006

Highly purified chloroplasts were isolated from spruce (Picea abies [L.] Karst.) needles by free‐flow electrophoresis. The chloroplast crude suspension was separated into two structurally different populations. The two populations could not be distinguished according to their protein/chlorophyll ratios and protein patterns from two‐dimensional gel electrophoresis. The O2 evolution, however, showed differences: the chloroplast population deflected towards the cathode contained a major part of structurally intact chloroplasts in contrast to the population deflected towards the anode. The two populations were not contaminated by endoplasmatic membranes or mitochondria.
Effect of auxin on cell wall glycanhydrolytic enzymes in epicotyls of Cicer arietinum
Authors: Valero Pilar , Labrador Emilia
Published: May 2006

Cell wall glycanhydrolytic enzymes have been related to cell wall loosening and cell growth, although the mechanism of this relationship has not been clarified. Since auxins are plant hormones that stimulate growth in elongating organs, in the present work we studied the effect of auxin on cell wall glycanhydrolytic enzymes, which were extracted with LiCl. Our results show that incubation of sections of Cicer arietinum epicotyls with indoleacetic acid elicit some minor changes in electrophoretic patterns of cell wall proteins when compared with control sections. This indicates that there is no appearance of a specific polypeptide synthesized de novo in response to the hormone, although there are increases in the intensity of some of the polypeptides, which could indicate an enhancement of wall protein biosynthesis. Brief incubation with IAA led to a general increase in the specific activities of these different cell wall enzyme fractions separated by chromatography, with the exception of the α‐fraction, with α‐galactosidase activity. Longer incubation resulted in an increase in the amount of protein associated with some of the enzyme fractions. In particular, it induced a large increase in the amount of protein associated with the β111‐galactosidase fraction that is involved in the autolytic process of cell walls of chick‐pea epicotyls. Our results indicate that auxin‐enhanced growth could be the result of the action of the hormone al the level of the cell wall glycanhydrolytic proteins that have been related to the wall‐loosening process.
Effects of water stress on photochemical function and protein metabolism of photosystem II in wheat leaves
Authors: He Jun Xian , Wang Jun , Liang Hou Guo
Published: May 2006

The effects of osmotic dehydration in wheat leaves (Triticum aestivum L. cv. Longchun No. 10) on the photochemical function and protein metabolism of PSII were studied with isolated thylakoid and PSII membranes. The results indicated that PSII was rather resistant to water stress as mild water deficit in leaves did nut significantly affect its activity. However, extreme stress conditions such as 40% decrease in relative water content (RWC) or 1.8 MPa in water potential (Ψ) caused ca 50% reduction in O2 evolution and ca 25% inhibition of DCIP (2.6‐dichlorophenol indophenol) photoreduction of PSII. In addition, it was found that the inhibited DCIP photoreduction of PSII could not be reversed by DPC (2.2‐diphenylcarbazide), a typical electron donor to PSII, suggesting that water stress did not affect electron donation to PSII. Urea‐SDS‐PAGE and western blot analysis showed that the steady slate levels of major PSII proteins, including the D1 and D2 proteins in the PSII reaction center, declined on a chlorophyll basis with increasing water stress, possibly as a result of increased degradation. In vitro translation experiments and quantitative analysis of chloroplast RNAs indicated that the potential synthesis of chloroplast proteins from their mRNAs was impaired by water stress. From the results it is concluded that the effects of water stress on PSII protein metabolism, especially on the reaction center proteins, may account for the damage to PSII photochemistry.
Chromosaponin I stimulates the growth of lettuce roots
Authors: Tsurumi Seiji , Tsujino Yoshio
Published: May 2006

A γ‐pyronyl triterpenoid saponin termed chromosaponin 1 (CSI), a conjugate of soyasaponin I and γ‐pyrone, was found at 3 mM to stimulate the growth of lettuce root (Lactuca sativa L. ev. Grand Rapids) to about 190% of the control. Since CSI is an amphipathic reductant, the stimulating effect of this saponin was compared with other reductants and other surface‐active compounds. Trolox (2‐carboxy‐2.5.7.8‐tetraamethyl‐6‐chromanol). another amphipathic reductant, also stimulated root growth, while other hydrophilic reductants including ascorbate. NADPH, NADH and glutathione did not. Some surfactants promoted root growth but their stimulating effects were smaller than the optimum effect of CSI. These results suggest a possible Function of CSI as an amphipathic reductant in root growth regulation.
A novel root gravitropism mutant of Arabidopsis thaliana exhibiting altered auxin physiology
Authors: Simmons Carl , Migliaccio Fernando , Masson Patrick , Caspar Timothy , Söll Dieter
Published: May 2006

A root gravitropism mutant was isolated from the DuPont Arabidopsis thaliana T‐DNA insertional mutagenesis collection. This mutant has reduced root gravitropism, hence the name rgrl. Roots of rgrl are shorter than those of wild‐type, and they have reduced lateral root formation. In addition, roots of rgrl coil clockwise on inclined agar plates, unlike wild‐type roots which grow in a wavy pattern. The rgrl mutant has increased resistance, as measured by root elongation, to exogenously applied auxins (6‐fold to indole‐3‐acetic acid, 3‐fold to 2,4‐dichlorophenoxyacetic acid, and 2‐fold to napthyleneacetic acid). It is also resistant to polar auxin transport inhibitors (2‐fold to triiodobenzoic acid and 3‐ to 5‐fold lo napthyleneacetic acid). The rgrl mutant does not appear to be resistant to other plant hormone classes. When grown in the presence of 10−2 M 2.4‐dichlorophenoxyacetic acid, rgrl roots have fewer root hairs than wild type. All these rgrl phenotypes are Mendelian recessives. Complementation tests indicate that rgrl is not allelic to previously characterized agravitropic or auxin‐resistant mutants. The rgrl locus was mapped using visible markers to 1.4 ± 0.6 map units from the CHI locus at 1–65.4. The rgrl mutation and the T‐DNA cosegregate, suggesting that rgrl was caused by insertional gene inactivation.
Responses to sucrose and glutamine by soybean embryos grown in vitro
Authors: Saravitz Carole H. , Raper C. David
Published: May 2006

Immature soybean (Glycine max [L.] Merr. cv. Ransom) embryos were grown in vitro in the presence of different concentrations of sucrose and glutamine to examine how availability of carbohydrate and nitrogen affects dry matter accumulation and embryo composition. Embryos were transferred to fresh medium every 4 days to maintain sucrose and glutamine concentrations of the culture medium. In all experiments, accumulation of dry matter and protein content increased when the sucrose concentration of the culture medium was increased from 1.5 to 150 mM: however, a relatively greater enhancement of dry matter than of protein accumulation resulted in a lower protein concentration at 150 than at 1.5 mM sucrose. Both content and concentration of protein were increased by the increases in glutamine supply to concentrations exceeding 68% protein at 120 mM glutamine. In combination with 150 mM sucrose, however, oil increased as glutamine supply was increased from 0.6 to 6 mM and then decreased as glutamine supply was increased from 6 lo 120 mM. Varying the concentration of sucrose available during seed development also affected embryo composition. Decreased availability of sucrose during either the early or late portion of the culture period resulted in lower accumulation of dry mailer as well as oil. Protein concentration was actually higher for embryos transferred from 150 to 1.5 nM sucrose than for those remaining in 150 mM throughout the culture period: however, the greater percentage of protein was due lo a decrease in accumulation of dry weight. In addition, embryo composition was affected by altering the availability of glutamine during culture, indicating that variation in the level of nitrogen assimilate delivered during seed development can change embryo composition. Decreasing the glutamine concentration of the medium lowered both protein and oil content. In contrast, increasing the glutamine concentration of the medium from 0.6 to 6 mM 8 days after initiation of culture increased the protein content and concentration of the embryo while oil content was not affected.
Phytochrome effects on stem carbon gain in light‐grown mustard seedlings are not simply the result of stem extension‐growth responses
Authors: Casal J. J. , Sánchez R. A. , Paganelli‐Blau A. R. , Izaguirre M.
Published: May 2006

Carbon allocation and partitioning were investigated in the first internode of light‐grown Sinapís alba L. seedlings exposed to white light (WL) with or without supplementary far‐red light (FR). In the internode, supplementary FR increased the rates of extension‐growth and the accumulation of radiolabeled carbon (fed through the leaves), reducing sugars (even per unit volume), starch, hemicellulose and cellulose, but had no effect on the levels of sucrose and ammonium oxalate‐solubilised cell wall carbohydrates, on invertase activity or on the use of additional sucrose fed through the leaves. In source leaves, supplementary FR had no effect on photosynthesis rates and reduced the accumulation of radiolabeled carbon. Mechanical reduction of stem extension‐growth responses to supplementary FR did not affect internode carbohydrate or carbon accumulation responses. Supplementary FR provided only to one leaf had no effect on internode extension growth but increased carbon accumulation in the internode. provided that supplementary FR and radiolabeled carbon were both given to the same leaf. Phytochrome‐mediated effects on carbon partitioning are not the mere consequence of internode extension‐growth responses. Some additional control point(s) (e.g. leaf‐source strength) must be under the direct influence of phytochrome.
High level histone H2A gene expression during early stages of adventitious bud formation in Norway spruce (Picea abies)
Authors: Sundås A. , Engström P.
Published: May 2006

We have demonstrated the correlation between cell division and the expression of a histone H2A‐encoding gene, His2A, in Norway spruce. Picea abies (L.) Karst and used a cDNA clone in in situ hybridization experiments to monitor the cytokinin‐induced cell division during early stages of adventitious bud development. A general stimulation of division of epidermal and cortical cells followed upon the cytokinin treatment. After two weeks in culture a high mitotic activity was detected only in single cells or small groups of cells in the epidermis and subepidermal cell layers. These cells presumably constitute the early stages of meristem primordia. The small clusters of dividing cells enlarge and subsequently form adventitious buds. Cells of the meristem and needle primordia of adventitious buds divide frequently as do the corresponding cells in vegetative buds. A quiescent center is distinguished within the apical meristem of vegetative buds. These cells, in the summit of the domed meristem, divide with a considerably lower frequency than cells in the flanking region. Differences in the temporal expression pattern of the histone H2A gene in cells of the vascular tissue, detected between embryos germinating in vitro and bud‐induced embryos, suggest that the cytokinin treatment affects the timing of cell divisions in the differentiating procambium.
Examination of the possible involvement of lipoxygenase and jasmonates in pollination‐induced senescence of Phalaenopsis and Dendrobium orchid flowers
Authors: Porat R. , Reiss N. , Atzorn R. , Halevy A. H. , Borochov A.
Published: May 2006

Application of linoleic and linolenic acids to Phalaenopsis and Dendrobium flowers enhanced their senescence and promoted ethylene production. This effect was specific to unsaturated fatty acids which serve as substrates for lipoxygenase action, and did not occur following similar treatments with saturated fatty acids. Several major lipoxygenase pathway metabolites including jasmonic acid methyl ester, traumatic acid, trans‐2‐hexenal and cis‐3‐hexenol also enhanced flower senescence. Jasmonic acid methyl ester promoted ethylene production by Phalaenopsis flowers. In contrast, treating flowers with the lipoxygenase inhibitors salicylhydroxamic acid and n‐propyl gallate. which inhibite(d) lipoxygenase activity in vitro, had no effect on pollination‐induced senescence of the flowers. Furthermore, during the 50‐h period following pollination, there was no increase in lipoxygenase activity in Phalaenopsis flowers. During the 10‐h period from pollination of Dendrobium flowers until the initiation of ethylene production, there was no effect of pollination on jasmonate levels in either the perianth or the columns. These results suggest that lipoxygenase activity and jasmonates are not directly involved in pollination‐induced Phalaenopsis and Dendrobium flower senescence.
The expression of desiccation‐induced damage in orthodox seeds is a function of oxygen and temperature
Authors: Leprince Olivier , Vertucci Christina W. , Hendry George A. F. , Atherton Neil M.
Published: May 2006

From the premise that desiccation‐induced damage is associated with a free‐radical mechanism of injury, we address the hypothesis that expression of desiccation damage is dependent on metabolism. The effects of temperature and O2 concentration on the expression of damage were studied in germinating bean (Phaseolus vulgaris L. cv. Pole Kentucky Wonder) axes and maize (Zea mays L. cv. Kelvedon Glory) radicles submitted to flash drying. Damage in desiccation‐tolerant and ‐intolerant material was assessed by measurements of electrolyte leakage and accumulation of a stable free radical. In desiccation‐tolerant material leakage rates remained low during water removal. In contrast, in desiccation‐intolerant tissues, leakage profiles revealed the presence of a critical moisture content below which leakage rates increased sharply. In the desiccation‐intolerant stage, a highly significant correlation was found between critical moisture contents and temperatures of drying. The concentration of the stable radical was lower if tissues were dried below 15°C and higher when tissues were dried at 30°C and above. Both leakage and build up of free radicals were highly sensitive to O2 concentrations: damage was lower when tissues were dried in the presence of N2, but increased several‐fold when tissues were exposed to O2 concentrations between 2 and 100%. In contrast, neither temperature nor O2 concentrations affected electrolyte leakage in desiccation‐tolerant samples. Treatment with a respiration inhibitor (KCN) prior to drying reduced the desiccation sensitivity of tissues, as noted by a reduction of the critical moisture content. We conclude that the expression of desiccation damage depends on the drying history and that factors that limit metabolism also reduce the incidence of desiccation injury.
Active glutamine synthetase is required for ammonium‐ or glutamine‐promoted prevention of nitrate and nitrite reduction in the cyanobacterium Phormidium laminosum
Authors: Tapia María I. , Liama María J. , Serra Juan L.
Published: May 2006

The filamentous non‐N2‐fixing cyanobacterium Phormidium laminosum (strain OH‐1‐p.Cl1) was able to utilize glutamine as the sole nitrogen source. The addition to ammonium‐grown cultures of the irreversible inhibitor of glutamine synthetase activity L‐methionine‐D, L‐sulfoximine (MSX) inhibited cell growth. Supplying glutamine to the culture restored cell growth. This re‐established growth was not due to interference by glutamine of MSX uptake by the cells, since glutamine synthetase (GS, EC 6.3.1.2) activity remained completely inhibited by MSX even when glutamine was simultaneously present. Both glutamine and ammonium exerted a negative effect on nitrate reductase (NR. EC 1.7.7.2) and nitrite reductase (NiR, EC 1.7.7.1) in vivo. This negative effect was reversed by MSX. When glutamine was added to MSX‐treated cells, intracellular glutamine level was high, but the activity of both reductases remained at a high level. These results suggest that the presence of the active form of glutamine synthetase is required for the in vivo prevention of nitrate assimilation caused by ammonium and glutamine.
Thiols of Cu‐treated maize plants inoculated with the arbuscular‐mycorrhizal fungus Glomus intraradices
Authors: Galli Ulrich , Schüepp Hannes , Brunold Christian
Published: May 2006

Mycorrhizal colonization of roots, fresh weight, content of cysteine, γ‐glutamylcysteine (γEC). glutathione (GSH), thiol groups in Cu‐binding peptides (CuBP), and the uptake of Cu were measured in roots and shoots of maize (Zea mays L., cv. Honeycomb F‐1) grown in quartz sand, with Cu at 0, 4.5, 9, 15 and 30 μg g−1 added with or without inoculum of the arbuscular‐mycorrhizal fungus (AMF) Glomus intraradices. In control plants (no Cu added) AMF significantly reduced shoot growth, but did not affect root growth. At an external Cu supply of 9 μg (g quartz sand)−1 or higher, both mycorrhizal colonization and growth of roots and shoots of mycorrhizal and non‐mycorrhizal plants were significantly reduced.

With up to 9 μg Cu g−1, mycorrhizal colonization increased the content of cysteine, γEC and GSH in the roots. However, the amount of thiols in CuBPs was not increased by mycorrhizal colonization in Cu‐treated plants and no differences in Cu uptake were detected between non‐mycorrhizal and mycorrhizal plants. A CuBP‐complex with a relative molecular mass of 7300 and a SH:Cu ratio of 1.77:1 was separated on a Sephadex G‐50 column from both non‐inoculated and inoculated roots of Cu‐treated plants. HPLC chromatography of the CuBPs of both non‐inoculated and inoculated roots resulted in a similar peak pattern, indicating that no additional CuBPs were formed by the fungus. In conclusion, our results do not support the idea that AMF protects maize from Cu‐toxicity.
Nitrate regulation of nitrate uptake and nitrate reductase expression in barley grown at different nitrate:ammonium ratios at constant relative nitrogen addition rate
Authors: Samuelson Mariann E. , Öhlén Elisabeth , Lind Maria , Larsson Carl‐Magnus
Published: May 2006

Barley (Hordeum vulgareL. cv. Golf) was cultured using the relative addition rate technique, where nitrogen is added in a fixed relation to the nitrogen already bound in biomass. The relative rate of total nitrogen addition was 0.09 day−1(growth limiting by 35%), while the nitrate addition was varied by means of different nitrate: ammonium ratios. In 3‐ to 4‐week‐old plants, these ratios of nitrate to ammonium supported nitrate fluxes ranging from 0 to 22 μmol g−1root dry weight h−1, whereas the total N flux was 21.8 ± 0.25 μmol g−1root dry weight h−1for all treatments. The external nitrate concentrations varied between 0.18 and 1.5 μM. The relative growth rate, root to total biomass dry weight ratios, as well as Kjeldahl nitrogen in roots and shoots were unaffected by the nitrate:ammonium ratio. Tissue nitrate concentration in roots were comparable in all treatments. Shoot nitrate concentration increased with increasing nitrate supply, indicating increased translocation of nitrate to the shoot.

The apparent Vmaxfor net nitrate uptake increased with increased nitrate fluxes. Uptake activity was recorded also after growth at zero nitrate addition. This activity may have been induced by the small, but detectable, nitrate concentration in the medium under these conditions. In contrast, nitrate reductase (NR) activity in roots was unaffected by different nitrate fluxes, whereas NR activity in the shoot increased with increased nitrate supply. NR‐mRNA was detected in roots from all cultures and showed no significant response to the nitrate flux, corroborating the data for NR activity. The data show that an extremely low amount of nitrate is required to elicit expression of NR and uptake activity. However, the uptake system and root NR respond differentially to increased nitrate flux at constant total N nutrition. It appears that root NR expression under these conditions is additionally controlled by factors related to the total N flux or the internal N status of the root and/or plant. The method used in this study may facilitate separation of nitrate‐specific responses from the nutritional effect of nitrate.
Chlorsulfuron influence on garden pea reproduction
Authors: Fletcher John S. , Pfleeger Thomas G. , Ratsch Hilman C.
Published: May 2006

The influence of chlorsulfuron on the reproduction of green pea (Pisum sativum) was examined by exposing plants at 3 different stages of development to 3 different exposure levels (46, 92, and 180 mg ha−1; corresponding to 2 × 10−3, 4 × 10−3, and 8 × 10−3 of the recommended field application rates for small grain crops). Reproduction was only influenced by the two higher rates. The most susceptible stage of development was when plants possessed 6 expanded leaves and one visible flower bud. At that stage, an application rate of 180 mg ha−1 (0.8% of the recommended field rate) reduced the seed yield of treated plants to 1% of that of the control plants without severely altering the height or appearance of mature plants. When correspondingly low application rates of atrazine. glyphosate, and 2.4‐D were administered at this same developmental stage there were no effects on either growth or reproduction. Thus, chlorsulfuron had an influence on plant reproduction that was not produced by other herbicides administered at low levels.
Importance of dormancy and sink strength in sprouting of onions (Allium cepa) during storage
Authors: Pak Caroline , van der Plas Linus H. W. , de Boer A. Douwe
Published: May 2006

In onion (Allium cepa L.) postponement of sprouting is necessary to achieve long term storage. We studied the factors determining sprouting during dry storage at 16°C. The period to visible sprouting depends on the length of the dormancy period, if present, and on the growth rate of the sprout. In the three cultivars tested, sprouts were initiated within 2 weeks after harvest indicating the absence of a real dormancy period. Sprout length increased linearly during storage. The mitotic activity of the apex decreased before harvest, was low at the transition from scale to leaf formation, and increased again when the sprout was initiated. From a few weeks before harvest, the initially high fructan content of the scales decreased, leading to a large increase in fructose. The sprout always contained enough carbohydrates for growth (between 50 and 60 mg g−1 dry weight, of which 30% was fructan). The activity of sucrose synthase (EC 2.4.1.13) increased as the sprout grew, indicating an increase in sink strength. Invertase (EC 3.2.1.26) was absent in all bulb organs, during the various developmental stages. Although carbohydrates and enzymes were available for fast sprouting, sprout growth was still linear instead of exponential during dry storage at temperatures favorable for growth (16°C). The relative importance of factors determining sprouting are discussed.
Effects of W‐7, W‐5, Verapamil and Diltiazem on vacuolar proton transport. Comparison of vacuolar H+‐ATPase and H+‐PPase from roots of Zea mays
Authors: Pfeiffer Wolfgang
Published: May 2006

The vacuolar membrane of plant cells is characterized by two proton pumps: the vacuolar H+‐ATPase (V‐ATPase; EC 3.6.1.3) and the vacuolar H+‐PPase (V‐PPase; EC 3.6.1.1). Recently, Du Pont and Morrissey reported that Ca2+ stimulates hydrolytic activity of purified V‐ATPase (Arch. Biochim. Biophys., 1992. 294: 341–346). Since this effect may be due to degradation during purification further investigation of Ca2+ regulation of native V‐ATPase was done. However, native tonoplast membranes contain a Ca2+/H+ antiport activity, which interferes with effects of calcium ions on proton transport activity of vacuolar ATPase. Therefore, the effects of anti‐calmodulin drugs (W‐7, W‐5, calmidazolium), and calcium channel antagonists (Verapamil, Diltiazem) on proton transport activities of the vacuolar‐type H+‐ATPase and H+‐PPase in tonoplast enriched membrane vesicle preparations from roots of Zea mays L. were studied. The concentrations for half maximal inhibition of vacuolar H+‐ATPase (H+‐PPase) were: 71 (191) μM W‐7, 470 (> 800) μM W‐5, 26 (24) μM calmidazolium (= compound R 24571). 398 (700) μM Verapamil, and 500 (1 330) μM Diltiazem. Estimation of Hill coefficients (nH) for the inhibition by Verapamil showed a further difference between the two vacuolar proton pumps (H+‐ATPase, nH= 2.02; H+‐PPase, nn= 0.96). The data indicate that the vacuolar H+‐ATPase itself is affected by these chemicals. It is suggested that some biological activities of W‐7, W‐5, Verapamil, and Diltiazem are due to their effects on proton translocation by the vacuolar‐type H+‐ATPase.