Light Induced Enhancement in Proline Levels Under Stress is Regulated by Non-Photosynthetic Events

Vigna radiata (L.) seedlings (5-d-old) were exposed to different concentrations of NaCl in light and in dark. The content of proline in the shoots increased with an increase in NaCl concentration, in light as well as in dark. But, irrespective of the concentration of NaCl, proline accumulation in the shoots was higher in light than in dark. Pretreatment of seedlings with dichlorophenyl dimethyl urea (DCMU) did not make any significant difference in light promoted stress induced proline accumulation. As DCMU is a potent inhibitor of photosynthetic electron transport, the light reaction of photosynthesis was not responsible for the observed light promotion of stress induced proline accumulation. In another set of experiments, 5-d-old green as well as etiolated seedlings were exposed to NaCl stress in the presence of different concentrations of sucrose. Irrespective of the concentration of sucrose used, proline content in shoots of stressed seedlings was higher in light than in dark. Although, sucrose enhanced NaCl stress induced increase in proline content in dark by about 32 %, this enhancement was not comparable to the 286 % increase in proline content brought about by light. These results showed that certain factors other than photosynthesis play a role in light promotion of stress induced proline accumulation.     

Genome organization in dicots. II. Arabidopsis as a ’bridging species’ to resolve genome evolution events among legumes

Analysis of molecular linkage groups within the soybean (Glycine max L. Merr.) genome reveals many homologous regions, reflecting the ancient polyploidy of soybean. The fragmented arrangement of the duplicated regions suggests that extensive rearrangements, as well as additional duplications, have occurred since the initial polyploidization event. In this study we used comparisons between homoeologous regions in soybean, and the homologous regions in the related diploids Phaseolus vulgaris and Vigna radiata, to elucidate the evolutionary history of the three legume genomes. Our results show that there is not only conservation of large regions of the genomes but that these conserved linkage blocks are also represented twice in the soybean genome. To gain a better understanding of the process of genome evolution in dicots, molecular comparisons have been extended to another well-studied species, Arabidopsis thaliana. Interestingly, the conserved regions we identified in the legume species are also relatively conserved in Arabidopsis. Our results suggest that there is conservation of blocks of DNA between species as distantly related as legumes and brassicas, representing 90 million years of divergence. We also present evidence for an additional, presumably earlier, genome duplication in soybean. These duplicated regions were only recognized by using Arabidopsis as a ’bridging’ species in the genome comparisons. Received: 10 October 2000 / Accepted: 13 January 2001     

Host suitability, respiration rate and the outcome of larval competition in strains of the cowpea weevil, Callosobruchus maculatus

Abstract.  Variation between strains of Callosobruchus maculatus in several life-history traits is well known. Differences in functional anatomy of egg pores and larval respiration rates have also been reported in strains from Brazil and Yemen. The response of five strains of C. maculatus to seeds of two host species, cowpea ( Vigna unguiculata ) and mung bean ( Vigna radiata ), was measured along with the larval respiration rates of the same strains on both hosts. There was significant variability of response to the two hosts. Strains with higher larval respiration rate (µL O₂/insect/day) showed higher seed consumption, which significantly affected adult emergence per seed on both hosts. This finding provides support for the hypothesis that differential feeding rate is an important mechanistic component of the larval competition outcome observed in strains of C. maculatus .     

A comparative developmental pattern of enzymes of carbon metabolism and pentose phosphate pathway in mungbean and lentil nodules

The activities of enzymes of pentose phosphate pathway (PPP) viz. glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and carbon metabolism viz. phosphoenol pyruvate carboxylase, NADP- isocitrate dehydrogenase and NADP-malic enzyme were measured in the plant and bacteroid fractions of mungbean (ureide exporter) and lentil (amide exporter) nodules along with the developing roots for comparison. The enzymes of pentose phosphate pathway in legume cytosol had higher activities at a stage of maximum nitrogenase activity and higher sucrose metabolism. However, bacteroids had only limited capacity for this pathway. The specific activities of these enzymes were greater in ureide than in amide exporter. CO₂ fixation via higher activity of phosphoenolpyruvate carboxylase in the plant part of the nodules in lentil might have been due to the greater synthesis of four carbon amino acids for amide export. The peak of NADP-isocitrate dehydrogenase in both legumes coincided with the pentose phosphate pathway enzymes at the time of high rates of sucrose metabolism and nitrogen fixation. Higher activities of NADP-malic enzyme were obtained in mungbean than in the lentil nodules. These findings are consistent with the role of these enzymes in providing reductant (NADPH) and substrates for energy yielding metabolism of bacteroids and carbon skeletons for ammonia assimilation.     

Enzymic changes in response to zinc nutrition

With a view to evaluating the suitability of Zn induced changes in enzyme activities and for assessing Zn nutrient status, black gram (Vigna mungo L. cv. IPU 94) was grown under controlled sand culture at five levels of Zn supply ranging from 0.01 to 10 μmol/L. Leaves of 60 d old plants were examined for Zn concentration and activities of fructose 1,6 biphosphate aldolase, carbonic anhydrase, total superoxide dismutase, Cu-Zn SOD, acid phosphatase and ribonuclease, which have been shown to be activated/inhibited by Zn deficiency. Sub-optimal supply of Zn decreased the activities of FBPAse, CA, total SOD and Cu-Zn SOD and increased the activities of APase and RNAse. Activities of the Zn enzymes CA and Cu-Zn SOD, are highly correlated with Zn supply, and suitable as indicators of Zn nutrient status of plants. Activation of APase and RNAse by other micronutrient deficiencies and stress conditions does not favour their use as indicators of Zn nutrient stress.     

超干对种子活力及水分热力学特性的影响

以耐干的菜心种子和不耐干的豇豆种子为材料,研究了超干对其活力和水分吸附等温线及热力学参数（△S、△H、△G）的影响。超干使红豇豆种子活力下降,SOD、POD活性降低,膜结构受损,这些变化即发生在水分降低的干燥过程中又发生在眼干状态下的贮藏过程中,菜心种子的活力和SOD,POD的活性受超干的影响小,超干对细胞膜的轻微损伤可在萌发吸胀时得到修复,超干种子水分吸附等温线上区段1和区段2的含水量明显下降;超干种子除－△S和－△H在区段1略有所升高外,－△S、－△H在区段和2和区段3和－△G在各区段均有程度不同的下降;这些改变尤以豇豆种子较显著,说明豇豆种子的水分束缚能力低,较易失去水分吸附等温线上的强吸附水,继而引起大分子结构的改变,降低种子活力;而菜心种子则相反,能在超干状态下较好地保持酶的活性和细胞膜的结构,故适宜超干贮藏。     

Genotypic response of cowpea Vigna unguiculata (L.) to in vitro regeneration from cotyledon explants

Summary A plant regeneration system applicable to 17 cowpea genotypes was developed. Cotyledons were initiated on 1/3 MS medium containing 15 to 35 mg N⁶-benzyladenine (BA) per 1 (66.6 to 155.3 μM) for 5 to 15 d. For shoot regeneration, the explants were transferred to a medium containing 1 mg BA per 1 (4.4 μM). Within 1 wk, shoot formation was visible at the proximal end of the cotyledons. Regeneration percentages (1% to 11%) and the numbers of shoots (4 to 12 per explant) were significantly influenced by genotype. Culture duration and BA concentration in the initiation stage significantly affected regeneration capacity. Explants initiated on media containing 15 mg BA per 1 for 5 d resulted in the highest percentage of explants capable of regeneration. Conversely, the highest number of shoots was obtained from explants initiated on media supplemented with 35 mg BA per 1. Whole plants were obtained on a plant growth regulator-free medium. To our knowledge, this is the first report of plant regeneration from U.S. commercial cowpea cultivars and breeding lines. This system is adaptable to diverse cowpea genotypes and will facilitate cowpea genetic transformation. Published with the approval of the Director of the Arkansas Agricultural Experiment Station.     

Influence of calcium chloride and benzyladenine on lipoxygenase of Vigna unguiculata leaf discs during senescence

Cowpea ( Vigna unguiculata L.) leaf discs incubated in the dark in CaCl₂ and benzyladenine maintained higher levels of chlorophyll and protein than controls. The CaCl₂ or benzyladenine treatments reduced lipoxygenase activity, and the effect of these compounds in combination was additive. HPLC analysis of the product profile of lipoxygenase activity with arachidonic acid as a substrate showed a single peak comigrating with standard 15-hydroperoxyeicosatetraenoic acid. There appears to be a strong temporal correlation between the CaCl₂+ benzyladenine delay of senescence and lipoxygenase activity.     

Immunochemical identification of mung bean actin like protein and its cellular involvement during germination

Actin like protein, extracted and purified fromVigna radiata (mung bean) seedling, has been found to give positive enzyme-linked immunosorbent assay with mouse monoclonal antiactin antibody. In vivo studies show that cytochalasin B at sublethal dose inhibits the chromosomal movement at metaphase stage during germination. Fromin vitro studies it is found that the actin like protein isolated from mung bean seedling has a cytochalasin B binding property with a Kd value 1.2 × 10⁻⁵ M. From these two specific observations it appears probable that the biological function of mung bean actin like protein is to take part in cell division process directly or indirectly during the time of seedling development.