Changes in the properties of cell wall pectin methylesterase along the Vigna radiata hypocotyl

The properties of cell wall pectinesterase (EC 3.1.1.11) from Vigna radiata (L.) Wilczek hypocotyl were investigated with immobilized and solubilized wall enzymes. Along the hypocotyl, the decrease of growth potential coincides with significant changes of the characteristics of the pectinesterase activities. As hypocotyl cells grow older, the proportion of ionically bound enzymes decreases and pH profile, sensitivity to cations and affinity for pectin change. The possible significance of these observations is discussed.     

Individual and interactive effects of temperature,carbon dioxide and abscisic acid on mung bean (Vigna radiata) plants

We studied the effects of temperature, carbon dioxide and abscisic acid on mung bean (Vigna radiata). Plants were grown under 26/22°C or 32/28°C (16?h?light/8?h?dark) at 400 or 700?μmol?mol^?1 CO₂ and received ABA application of 0 or 100?μl (10?μg) every other day for three weeks, after eight days of initial growth, in growth chambers. We measured 24 parameters. As individual factors, in 16 cases temperature; in 8 cases CO₂; in 9 cases ABA; and as interactive factors, in 4 cases, each of temperature?×?CO₂, and CO₂?×?ABA; and in 2 cases, temperature?×?ABA were significant. Higher temperatures increased growth, aboveground biomass, growth indices, photochemical quenching (qP) and nitrogen balance index (NBI). Elevated CO₂ increased growth and aboveground biomass. ABA decreased growth, belowground biomass, qP and flavonoids; increased shoot/root mass ratio, chlorophyll and NBI; and had little role in regulating temperature–CO₂ effects.

Abbreviations: A_N: net CO₂ assimilation; E: transpiration; F_v/F_m: maximum quantum yield of PSII; g_s: stomatal conductance; LAR: leaf area ratio; LMA: leaf mass per area; LMR: leaf mass ratio;φPSII: effective quantum yield of PSII; qNP: non-photochemical quenching; qP: photochemical quenching; SRMR: shoot to root mass ratio; WUE: water use efficiency     

绿豆子叶衰老期间核酸代谢的变化

萌发绿豆的子叶自然衰老期间,核酸含量降低,RNA降低的幅度比DNA大。电泳分析结果表明,子叶衰老期间细胞核主带DNA明显降低;而迁移慢的卫星带DNA变化不大。在RNA各组分中,18S rRNA从衰老前期就开始降低;25S rRNA和4～5S小分子RNA到衰老后期才缓慢下降。DNase和RNase活性在子叶整个衰老期间都明显升高,是导致核酸含量下降的主要原因。~3H-核苷掺入试验表明,核酸的合成速率在子叶衰老前期有所上升,到衰老后期又降低。poly(A)~ -mRNA含量在子叶开始衰老时明显上升。     

Effect of water stress on the enzymes of nitrogen metabolism in mung bean (Vigna radiata Wilczeck) nodules

Abstract. Water stress created by withholding irrigation in mung bean resulted in decreased leaf water potential and nodule moisture content. Decreased leaf water potential was associated with decreased activity of nitrogenase, glutamine synthetase (GS), asparagine synthetase (AS), aspartate amino transferase (AAT), xanthine dehydrogenase (XDH) and uricase. However, the activity of glutamate dehydrogenase increased three-fold under severe stress. The activity of allantoinase and allantoicase was not affected by moderate stress but decreased under severe stress. The in vitro production of allantoic acid from allantoin and uric acid in the cytosol fraction decreased more than its production from xanthine and hypoxanthine. The production of NADH also decreased under stress.
During recovery from severe stress, the activity of XDH and uricase further decreased, whilst that of allantoinase and allantoicase increased compared to the control. This corresponded with the higher content of ureides during recovery. The recovery in other enzymes was not complete although leaf water potential and nodule moisture content recovered fully within 24 h.     

Interaction of paclobutrazol and indole-3-butyric acid in relation to rooting of mung bean (Vigna radiata) cuttings

Paclobutrazol (PB) only slightly stimulated the rooting of mung bean cuttings but, interestingly, the number of adventitious roots formed was dramatically increased when PB was used together with indole-3-butyric acid (IBA). Application of PB in the first phase of root formation, when root initials are induced, caused the greatest enhancement of the promotive effect of IBA on rooting. Investigation of the effect of PB on uptake, transport and metabolism of [5^-3H]-IBA in mung bean cuttings revealed some changes in the rate of metabolism of IBA in comparison with control cuttings. PB was found to be involved in the partitioning of carbohydrates along the cuttings. Application of sucrose, like PB to the base of IBA-treated cuttings enhanced the effect of IBA. The patterns of the effects of PB and IBA, separately and together, on rooting were similar in defoliated and intact cuttings, however the number of roots was much lower in the defoliated cuttings, which lacked a source of assimilates. PB counteracted the effect of GA₃ in the upper regions of the cuttings and seemed to increase the sink capacity at the base of the cuttings. The results of the present study clearly demonstrated the enhancing influence of PB on IBA stimulation of the rooting of mung bean cuttings. It is suggested that PB may affect the rate of metabolism of IBA during rooting and the status of the local sink, in the base of the cuttings, thus partially contributing to the enhancement of the rooting-promotive effect of IBA.     

Bradyrhizobium elkanii, Bradyrhizobium yuanmingense and Bradyrhizobium japonicum are the main rhizobia associated with Vigna unguiculata and Vigna radiata in the subtropical region of China

Cowpea (Vigna unguiculata) and mung bean (Vigna radiata) are important legume crops yet their rhizobia have not been well characterized. In the present study, 62 rhizobial strains isolated from the root nodules of these plants grown in the subtropical region of China were analyzed via a polyphasic approach. The results showed that 90% of the analyzed strains belonged to or were related to Bradyrhizobium japonicum, Bradyrhizobium liaoningense, Bradyrhizobium yuanmingense and Bradyrhizobium elkanii, while the remaining represented Rhizobium leguminosarum, Rhizobium etli and Sinorhizobium fredii. Diverse nifH and nodC genes were found in these strains and their symbiotic genes were mainly coevolved with the housekeeping genes, indicating that the symbiotic genes were mainly maintained by vertical transfer in the studied rhizobial populations.     

Characterization of new microsatellite markers in mung bean,Vigna radiata (L.)

The present work reports the isolation and characterization of new polymorphic microsatellites in mung bean (Vigna radiata L.). Of 93 designed primer pairs, seven were found to amplify polymorphic microsatellite loci, which were then characterized using 34 mung bean accessions. The number of alleles ranged from two to five alleles per locus with an average of three alleles. Observed and expected heterozygosity values ranged from 0 to 0.088 and from 0.275 to 0.683, respectively. All seven loci showed significant deviations from Hardy–Weinberg equilibrium, whereas only one pairwise combination (GBssr‐MB77 and GBssr‐MB91) exhibited significant departure from linkage disequilibrium. These newly developed markers are currently being utilized for diversity assessment within the mung bean germplasm collection of the Korean Gene Bank.     

Effect of Phytohormone Pretreatment on Nitrogen Metabolism in Vigna radiata Under Salt Stress

Application of NaCl (electrical conductivity 4.0 mS cm^–1) resulted in about 52, 50 and 55 % reduction in total nitrogen contents in mung bean [Vigna radiata (L.) Wilczek] leaf, root and nodule, respectively. In nodule, nitrogenase activity was reduced by about 84 % under stress as compared with the control set. Glutamine synthetase activity was reduced by about 31, 16 and 23 %, glutamate oxoglutarate aminotransferase activity was reduced by 78, 57 and 42 % and glutamate dehydrogenase activity was reduced by 9, 8 and 42 % in leaf, root and nodule, respectively, under salt stress. The pretreatment with indole-3-acetic acid, gibberellic acid and kinetin, each ranging from 0.1 to 10 µM, in restoring the metabolic alterations imposed by NaCl salinity was investigated in mung bean. The three phytohormones used were able to overcome to variable extents the adverse effects of stress imposed by NaCl solution.     

Characterization and developmental expression of single-stranded telomeric DNA-binding proteins from mung bean (Vigna radiata)

We have identified and characterized protein factors from mung bean (Vigna radiata) nuclear extracts that specifically bind the single-stranded G-rich telomeric DNA repeats. Nuclear extracts were prepared from three different types of plant tissue, radicle, hypocotyl, and root, in order to examine changes in the expression patterns of telomere-binding proteins during the development of mung bean. At least three types of specific complexes (A, B, and C) were detected by gel retardation assays with synthetic telomere and nuclear extract from radicle tissue, whereas the two major faster-migrating complexes (A and B) were formed with nuclear extracts from hypocotyl and root tissues. Gel retardation assays also revealed differences in relative amount of each complex forming activity in radicle, hypocotyl, and root nuclear extracts. These data suggest that the expression of telomere-binding proteins is developmentally regulated in plants, and that the factor involved in the formation of complex C may be required during the early stages of development. The binding factors have properties of proteins and are hence designated as mung bean G-rich telomere-binding proteins (MGBP). MGBPs bind DNA substrates with three or more single-stranded TTTAGGG repeats, while none of them show binding affinity to either double-stranded or single-stranded C-rich telomeric DNA. These proteins have a lower affinity to human telomeric sequences than to plant telomeric sequences and do not exhibit a significant binding activity to Tetrahymena telomeric sequence or mutated plant telomeric sequences, indicating that their binding activities are specific to plant telomere. Furthermore, RNase treatment of the nuclear extracts did not affect the complex formation activities. This result indicates that the single-stranded telomere-binding activities may be attributed to a simple protein but not a ribonucleoprotein. The ability of MGBPs to bind specifically the single-stranded TTTAGGG repeats may suggest their in vivo functions in the chromosome ends of plants.     

Effect of abscisic acid on endogenous IAA, auxin protector levels and peroxidase activity during adventitious root initiation in Vigna radiata cuttings

Endogenous levels of free and conjugated IAA, auxin protectors (Prs) and peroxidase (PER) activity and their relation to adventitious root initiation (ARI) were investigated at the potential sites of adventitious rooting in relation to exogenous application of 250 μM ABA during the first 120 h after treatment. Cuttings from 7-day-old mung bean [Vigna radiata (L.) Wilcz.] seedlings were treated with 125, 250, and 500 μM ABA for 24 h. ABA significantly stimulated ARI but extremely inhibited epicotyl growth as compared to control. Free and conjugated IAA were measured by reversed-phase high performance liquid chromatography while Prs and PER activities were measured spectrophotometrically. The present results also indicate that endogenous free IAA levels peaked later in ABA-treated cuttings than that in control, suggesting that ABA extended the length of the induction phase of rooting process in treated cuttings and that might explain the significant delay of the appearance of roots at the treated cuttings. Higher level of IAA conjugates was found in ABA-treated cuttings than that in untreated ones. Pr level also peaked later in ABA-treated cuttings than that in control, indicating that ABA extended the period of Pr activity. An initial temporary decrease of PER activity was found in associating with high levels of free IAA and Prs during most of the primary events, while the opposite occurred during the secondary events of adventitious rooting process in both treated and untreated cuttings. Thus, ABA may stimulate ARI in mung bean Vigna radiata cuttings by regulating the concentration and /or activities of endogenous IAA, Prs, and PER activity in favor of inducing a large number of adventitious roots at their potential sites of adventitious rooting.     

Purification and regulation of aspartate transcarbamylase from germinated mung bean (Vigna radiata) seedlings

Aspartate transcarbamylase (EC 2.1.3.2) was purified to homogeniety from germinated mung bean seedlings by treatment with carbamyl phosphate. The purified enzyme was a hexamer with a subunit molecular weight of 20,600. The enzyme exhibited multiple activity bands on Polyacrylamide gel electrophoresis, which could be altered by treatment with carbamyl phosphate or UMP indicating that the enzyme was probably undergoing reversible association or dissociation in the presence of these effectors. The carbamyl phosphate stabilized enzyme did not exhibit positive homotropic interactions with carbamyl phosphate and hysteresis. The enzyme which had not been exposed to carbamyl phosphate showed a decrease in specific activity with a change in the concentration of both carbamyl phosphate and protein. The carbamyl phosphate saturation and UMP inhibition patterns were complex with a maximum and a plateau region. The partially purified enzyme also exhibited hysteresis and the hysteretic response, a function of protein concentration, was abolished by preincubation with carbamyl phosphate and enhanced by preincubation with UMP. All these observations are compatible with a postulation that the enzyme activity may be regulated by slow reversible association-dissociation dependent on the interaction with allosteric ligands     

Plasmalemmasomes in cotyledon leaves of germinating Vigna radiata L. (mung beans)

Abstract. Storage parenchyma, vascular parenchyma and phloem companion cells are found adjacent to sieve tubes in the vascular bundles of cotyledon leaves of mung bean ( Vigna radiata L.) seedlings. The paramural bodies of storage parenchyma cells are characterized by flask shaped invaginations of the plasmalemma whereas the plasmalemmasomes of the adjacent vascular parenchyma and companion cells consist of numerous finger-like evaginations which are not enclosed in plasmalemma pockets. Phloem associated transfer cells are not present and it is suggested that the fine tubular plasmalemmasomes may act as the interface between apoplast and symplast in the transport of rapidly mobilized reserves during germination. Tubular structures observed within the protoplasts of storage cells close to vascular tissue were also observed in vascular parenchyma and companion cells between the plasmalemmae and cell walls.     

Bio-activity of fungal culture filtrates against root-knot nematode egg hatch and juvenile motility and their effects on growth of mung bean (Vigna radiata L. Wilczek) infected with the root-knot nematode,Meloidogyne incognita

Culture filtrates of selected soil fungi, namely Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Fusarium oxysporum, Penicillium vermiculatum and Rhizopus nigricans exhibited variable response to egg hatching and mortality of the root-knot nematode, Meloidogyne incognita. Higher concentrations of the culture filtrates of all the fungi inhibited egg hatching and proved to be toxic to the juveniles of M. incognita. In addition, development of the gall and multiplication of M. incognita were also found adversely affected in varying degrees on all the plants of Vigna radiata treated with the filtrates. The culture filtrate of A. niger showed highest toxicity to the nematode than those of any other fungus tested. Soil drench application of the culture filtrates gave better seedling growth and least nematode multiplication in comparison to seed soaking treatment.     

Responses of Vigna radiata to Foliar Application of 28-Homobrassinolide and Kinetin

Effects of 28-homobrassinolide (HBR) and kinetin (KIN) on photosynthesis, nitrogen metabolism, and the seed yield were studied. The leaves of 25-d-old plants of Vigna radiata (L.) Wilczek were sprayed with 0.01, 1.0 or 100 M aqueous solution of KIN, or 0.0001, 0.01 or 1.0 M that of HBR. KIN and especially HBR increased the activities of nitrate reductase and carbonic anhydrase, chlorophyll and total protein contents and net photosynthetic rate in the leaves, and pod number and seed yield, at harvest.     

Isolation and Characterization of Ty1/copia-like Reverse Transcriptase Sequences from Mung Bean (Vigna radiata)

Ty1/copia-like sequences were amplified from mung bean (Vigna radiata (L.) Wilczek) genomic DNA, by PCR with degenerate oligonucleotide primers corresponding to highly conserved domains in the Ty1/copia-like retrotransposons. PCR fragments of roughly 270 bp were isolated and cloned, and forty clones were sequenced. Thirty-six of the forty clones had unique nucleotide sequences, and eighteen clones had a frameshift, a stop codon, or both. Alignment of the nucleotide sequences indicated that these clones, denoted Tvr, fell into nine subgroups and nine ungrouped sequences. The nucleotide sequence similarity between these elements ranged from 8% to 100%, which indicates high level of sequence heterogeneity among these clones. A phylogenetic analysis comparing these clones with corresponding sequences from other plant species showed that some of the Tvr clones are more closely related to Ty1/copia-like retrotransposons from other species than to other Tvr clones. Dot blot analysis revealed that Ty1/copia-like retrotransposons comprise about 9.3% of the mung bean genome.     

Recalcitrant Grain Legume Vigna radiata, Mung Bean, Made to Regenerate on Change of Hormonal and Cultural Conditions

Induction of shoots is possible from cotyledonary node of Vigna radiata seedlings by culturing them on a low concentration of thidiazuron (TDZ 1.0 μM). Interestingly, flooding the seedlings with the same concentration of TDZ considerably enhanced this effect and also led to the induction of shoots from the epicotyl – an unexpected and significant finding. Even plain mineral medium evoked this response on flooding. But seedlings raised on TDZ and flooding with mineral medium was not so effective. Instead seedlings raised on TDZ (1.0 μM) medium as well as flooding with it had synergistic effect. In a comparative study TDZ (1.0 μM) was found to be more effective than BAP (10 μM). Marked repression of root formation and expansion of shoot–apex were noted in seedlings raised on TDZ or BAP, particularly in cultures that were flooded.     

芦丁对绿豆幼苗营养生长的影响及其与IAA的相互作用

观察了植物体内的天然黄酮芦丁和吲哚乙酸(IAA)对绿豆幼苗营养生长的影响并测定胚轴中的芦丁和IAA含量.光照条件下芦丁(60μg/mL以下)处理对绿豆幼苗生长有一定促进作用,表现为胚轴和主根伸长加快、侧根数目增多、鲜重或干重增加;而光照条件下更高浓度芦丁(80μg/mL以上)处理及黑暗条件下芦丁(20～100μg/mL)处理对绿豆幼苗生长有抑制作用.当培养基中的芦丁浓度为60～80 μg/mL时,光照下的幼苗比暗处理的幼苗在胚轴中积累更多的芦丁;而芦丁浓度为40μg/mL以下和接近100μg/mL时幼苗在光照下累积的芦丁较暗处理的幼苗更少.0.1μg/mL以上的IAA促进芦丁的累积而进一步抑制幼苗胚轴和主根的伸长.当培养基中含有40 μg/mL的芦丁和0.5μg/mL的IAA时,胚轴中累积的芦丁达到高峰.芦丁降低黄化幼苗内源性IAA在胚轴中的累积,并抑制幼苗对IAA的吸收.     

Physiological basis of the synergistic effects of IBA and triadimefon on rooting of mung bean hypocotyls

Mixtures of 1–3 × 20.32 mg L^-1 IBA and 1–3 × 289.5 µg L^-1 triadimefon (TRI) significantly increased the formation of adventitious roots in mung bean hypocotyl cuttings compared to application of either IBA or TRI alone. The physiological basis of the synergistic effects of the mixture is likely to be due to a combination of increased endogenous IAA content and peroxidase activity. It is suggested that a mixture of IBA with TRI at appropriate concentrations is an effective and simple method for promoting adventitious root formation.     

Effect of NaCI on nitrate reductase,glutamate dehydrogenase and glutamate synthase inVigna radiata calli

The effect of NaCI stress on the activities of nitrate reductase (NR), glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) in callus lines ofVigna radiata which differ in salt resistance, was studied at weekly intervals upto 28 d of growth. After 28 d, the NaCI resistant callus (selected at 300 mM NaCI) at NaCI concentrations higher than 200 mM maintained higher NR activity than non-selected line. NaCI stress also affects aminating and deaminating activities of GDH. The NADH-GDH activity in the presence of NaCI was higher in the resistant than non-selected line. On the other hand, NAD-GDH activity in both the lines was completely inhibited after 7 d of growth. The increased activity of NADH-GDH in resistant calli may play a vital role in protecting the cells from toxic effect of increased endogenous level of ammonia which probably accumulates due to efficient NO₃ ⁻ reduction. NADH-GOGAT activity was found to decrease under salt stress in both the callus lines. Nitrogen assimilation in salt-resistant calli under salt stress was found to be characterized by high NR and NADH-GDH activities, concomitantly with low GOGAT activity. The authors are grateful to DST and CSIR for financial assistance.     

Influence of extremely low-frequency electric fields on the growth of Vigna radiata seedlings

The biological effects of extremely low-frequency electric fields (ELF) on living organisms have been explored in many studies, but the results are controversial and only a few studies investigated the influence of the intensity of the applied field on seedling growth. Here we assess the effects of a 50 Hz sinusoidal electric field on the early growth of Vigna radiata seedlings while varying the field intensity. Experiments performed in a dark, constant-climate chamber on several thousands of seedlings show that the field produces an inhibitory effect at a low field intensity and an enhancing one at a higher intensity. The maximum negative effect occurs at about 450 V/m, which is an intensity much lower than the exposure limits currently in force in the safety regulations.