Stem sensitivity and ethylene involvement in phototropism of mung bean

A system is described for the examination of phototropism in the epicotyl of a dicot seedling, mung bean (Phaseolus aureus Roxb.), under conditions approximating nature, including the use of intact, nonetiolated plants exposed to elevated, continuous, white, unilateral light. It is found that in this system perception of the phototropic stimulus by the leaves alone cannot account for the curvature, and that exposure of the stem is also necessary. The phototropic response was found to be strongly altered in nonintact plants. Hypobaric treatment indicates that ethylene may participate in phototropism, possibly by acting as an inhibitor of auxin transport.     

Heat shock proteins and chilling sensitivity of mung bean hypocotyls

Excised mung bean (Vigna radiata L.) hypocotyl sections wereexposed to 40 C for up to 4 h in the presence or absence of50 µM cycloheximide (CHX) before being held at a non-chilling(20 C) or chilling (2.5 C) temperature. Mung bean hypocotyltissue is chilling sensitive, and the rate of solute leakageis highly correlated with the extent of chilling injury. A 3h heat shock at 40 C reduced chilling-induced solute leakageby up to 40%, but leakage was similar to non-heat-shocked hypocotylswhen CHX was present. Specific proteins were labelled when hypocotylswere exposed to [³⁵S] methionine during the last hour of heatshock. The nine most intense bands on the autoradiographs ofSDS-PAGE gels of extracted protein corresponded to molecularweights of 114, 79, 73, 70, 60, 56, 51, 46, and 18 kDa. The18 kDa band reached a maximum after 1 h at 40 C and then rapidlydecreased in intensity as the heat shock continued, becomingundetectable at 4 h. The four most intense bands after 3 h at40 C corresponded to molecular weights of 79, 70, 51, and 46kDa. The synthesis of these four hsps was markedly reduced whenthe hypocotyl sections were exposed to CHX during heat shock.During chilling for 6 d, the levels of hsps 79 and 70 remainedsignificantly higher in tissue that was heat shocked prior tochilling than in tissue that was not heat shocked. In contrast,the levels of hsps 51 and 46 were similar in bothheat-shockedand control tissues. Heat-shock-induced chilling tolerance waslost between 6 and 9 d ofstorage at 2.5 C; this loss coincidedwith the decay of hsps 79 and 70 to control levels. These resultssuggest that heat shock induces an increase in both chillingtolerance and the de novo synthesis of specific heat shock proteins;namely hsps 79 and 70. This is the first report showing a relationshipbetween heat-shock-induced chilling tolerance and specific heat-shock-inducedproteins. Key words: Ion leakage, protein synthesis, Vigna radiata     

Induction of double-strand breaks by S1 nuclease, mung bean nuclease and nuclease P1 in DNA containing abasic sites and nicks.

Defined DNA substrates containing discrete abasic sites or paired abasic sites set 1, 3, 5 and 7 bases apart on opposite strands were constructed to examine the reactivity of S1, mung bean and P1 nucleases towards abasic sites. None of the enzymes acted on the substrate containing discrete abasic sites. Under conditions where little or no non-specific DNA degradation was observed, all three nucleases were able to generate double-strand breaks when the bistranded abasic sites were 1 and 3 base pairs apart. However, when the abasic sites were further apart, the enzymes again failed to cleave the DNA. These results indicate that single abasic sites do not cause sufficient denaturation of the DNA to allow incision by these single-strand specific endonucleases. The reactivity of these enzymes was also investigated on DNA substrates that were nicked by DNasel or more site-specifically by endonuclease III incision at the discrete abasic sites. The three nucleases readily induced a strand break opposite such nicks.     

次氯酸钠真空处理绿豆消毒效果评价及机理研究

本研究讨论了绿豆中微生物的分布规律及相关联的结构特征,次氯酸钠常规及真空处理绿豆全豆、表皮及内部消毒效果的评价及机理分析.结果证明,绿豆全豆、表皮及内部的菌落总数分别为8.41×105cfu/g、6.70×103 cfu/g及8.30×105cfu/g,经有效氯浓度为(3 000～33 000)mg/kg的次氯酸钠溶液,1h常规浸种处理后绿豆全豆、表皮及内部菌落总数分别下降(0.93～2.22) log cfu/g、(0.92 ～ 2.20) log cfu/g及(0.94 ～ 2.09) log cfu/g.真空度0.05 MPa下,经有效氯浓度(3 000 ～ 33 000) mg/kg的次氯酸钠溶液1h浸泡后,绿豆全豆、表皮及内部菌落总数分别下降(1.67 ～ 4.15) log cfu/g、(1.15 ～2.38)1og cfu/g及(1.62～4.11) log cfu/g.经分析,真空处理能使次氯酸钠克服绿豆表皮蜡质层及内部空腔结构的影响,有效接触微生物从而提高消毒效果.     

Complexes of DNA hairpins and a single-stranded oligonucleotide detected by affinity chromatography and mung bean nuclease cleavage

The emergence of a simple translation device consisting of an assembler strand (primordial mRNA) and RNA hairpins (primordial tRNA) is presumed to be an important step leading to the origin of life. The assumption of a non-enzymatic interaction of primordial tRNA and mRNA is experimentally approached. DNA hairpins containing five or more adenosine residues in the loop are able to bind to complementary oligonucleotides covalently bound to cellulose. The exact number of base pairs formed between the hairpins and the assembler strand is determined by two methods applied to DNA hairpin/assembler complexes. The melting temperature of a complex is measured and the cleavage pattern by nuclease from mung bean is determined. The loop of the smallest hairpin able to bind consists of five adenosine residues and only three base pairs are formed. This supports the idea of a primordial recognition similar to the contemporary codon-anticodon interaction.     

Changes in mitochondrial activity during enlargement of mung bean root cells

A mitochondrial fraction was separately prepared from two differentregions of mung bean roots; from root-tips which contained mainlyimmature cells and from tissue, other than the root-tips, whichwas composed of mature and fully vacuolated cells. The malatedehydrogenase, fumarase and aconitase activities per cell didnot increase or did so only slightly during cell growth. Respiratoryactivity of both tissue sections and the crude mitochondrialfraction also seemed to increase slightly as cells matured.However, the cytochrome oxidase and succinate cytochrome c reductaseactivities per cell increased significantly during cell enlargement.There was no difference in the distribution-profiles of thecytochrome oxidase and malate dehydrogenase activities aftersucrose density gradient centrifugation, between mitochondrialfractions prepared from two regions of the. roots. The malatedehydrogenase activity per unit of cytochrome oxidase activityin purified mitochondria of immature cells was much higher thanthat of mature cells. The results suggest that enzymes in mitochondrialmatrix are mainly synthesized in immature cells or during celldivision. In contrast, enzymes in the cristae seem to be formedduring cell maturation, as well as being formed in immaturecells. (Received January 26, 1973; )     

Changes in the forms of invertase during germination of mung bean seeds

High levels of ‘alkaline’ invertase activity occur in dormant mung bean seeds. During germination this activity decreases rapidly and is replaced by high ‘acid’ invertase activity. Cycloheximide prevented the formation of the latter activity and also inhibited germination. It is suggested that de novo synthesis of ‘acid’ invertase occurs during germination. Both enzymes bind to concanavalin A and, hence, are presumed to be glycoproteins. Affinity-purified enzyme samples show similar ratios of ‘acid’ and ‘alkaline’ invertase activities to the crude preparations indicating that specific enzyme inhibitors or activators are probably not involved in controlling the activities in vivo.     

Specific cleavage of kinetoplast minicircle DNA from Leishmania tarentolae by mung bean nuclease and identification of several additional minicircle sequence classes

Multiple sequence classes of kinetoplast minicircle DNA from Leishmania tarentolae were cleaved by mung bean nuclease in the presence of formamide, yielding unit length linear molecules which retained the anomalous electrophoretic mobility in acrylamide characteristic of minicircle DNA. No specific cleavage site sequence common to all minicircle sequence classes was apparent, although the main region of nuclease cleavage was localized approximately 350 bp from the unique SmaI restriction site of the conserved region found in all minicircle sequence classes. Covalent closure of the minicircle substrate was not a requirement for cleavage, as linearized network-derived or cloned minicircles were also cleaved by mung bean nuclease at similar locations. The partial sequences of several new minicircle sequence classes released from the network by mung bean nuclease are also reported.     

Salt sensitivity and low discrimination between potassium and sodium in bean plants

Bean plants (Phaseolus vulgaris) were very sensitive to moderate concentrations of NaCl, showing a dramatic decrease in their K⁺ content in the presence of this salt. Increasing the KCl content of the nutrient medium released the inhibitory effect of NaCl by increasing the K⁺ content of the plants. Likewise moderate concentrations of KCl were toxic for bean plants because they produced a large K⁺ loading. NaCl partially released this toxicity by inhibiting the K⁺ loading. When compared to the moderately salt tolerant sunflower plants (Helianthus annuus), bean plants showed a lower capacity to discriminate between K⁺ and Na⁺, at high Na⁺ levels, and an uncontrolled K⁺ uptake at moderate concentrations of K⁺. It is concluded that this low capacity of discrimination of the K⁺ uptake system of bean plants in presence of Na⁺ can account for by the NaCl sensitivity of bean plants.     

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.     

DNA hairpin loops in solution. Correlation between primary structure, thermostability and reactivity with single-strand-specific nuclease from mung bean.

Hairpin structures formed by seven DNA inverted repeats have been studied by PAGE, UV(CD)-spectroscopy and nuclease cleavage. The hairpins consisted of (CG)3 stems and loops of 2, 3 and 4 residues. Thermal stabilities (Tm) have been determined in low and high ionic strength buffers, where the hairpins were structured in the B- and Z-DNA form respectively. The thermodynamic parameters of hairpin formation have been obtained by a two-state analysis of the hairpin-coil transitions. It is found that, on increasing the number of bases in the loop from 2 to 3 and 4, the Tms of the B-hairpins decrease, whereas the Tms of the same hairpins in the Z-form increase. This confirms previous evidence (1,2) that in a hairpin molecule the size and structure of the loop are modulated by the conformation of the helical stem. Moreover, B-hairpins with loops comprising 2, 3 and 4 bases have been digested with the single-strand-specific nuclease from mung bean. In our experimental conditions (0 degrees C) the nuclease preferentially cleaves the unbonded nucleotides of the loops. However, the rates of loop hydrolysis, which roughly follow a first-order kinetics, markedly depend on the size of the loop. At a ratio of 3 enzyme units/micrograms DNA, the half-lives of hairpins which are expected to form loops of 4, 3 and 2 residues are 90, 145 and 440 minutes respectively. Thermostability and enzymatic digestion data suggest that two-membered loops can be formed in B-hairpins but not in Z-hairpins.     

Studies on energy status and mitochondrial respiration during growth and senescence of mung bean cotyledons

Several characteristics of mitochondrial respiration and energy status have been studied during growth and senescence of mung bean ( Phaseolus radiatus L.) cotyledons. The results showed that mitochondrial oxygen consumption, respiratory control, ADP:O ratios, and energy charge changed in the cotyledons during germination and growth of the seedlings. The respiration rate of intact cotyledons approximately reflected the trend of the oxidative activities of the isolated mitochondria. An increase was observed in both whole cotyledon respiration and mitochondrial oxygen uptake at the onset of senescence of mung bean cotyledons (day 3 after germination), which thereafter declined gradually. The capacity and activity of the alternative pathway increased markedly in mitochondria isolated from senescent cotyledons. After the onset of senescence, the mung bean cotyledon mitochondria exhibited a decrease both in the respiratory control ratios and ADP:O ratios, and the cotyledons exhibited a gradual decline in energy charge. All these results showed an irreversible deterioration of energy conservation in mung bean cotyledons. The role(s) of the alternative pathway in senescent mung bean cotyledons is discussed.     

Purification to homogeneity and properties of mannosidase II from mung bean seedlings

Mannosidase II was purified from mung bean seedlings to apparent homogeneity by using a combination of techniques including DEAE-cellulose and hydroxyapatite chromatography, gel filtration, lectin affinity chromatography, and preparative gel electrophoresis. The release of radioactive mannose from GlcNAc[3H]Man5GlcNAc was linear with time and protein concentration with the purified protein, did not show any metal ion requirement, and had a pH optimum of 6.0. The purified enzyme showed a single band on SDS gels that migrated with the Mr 125K standard. The enzyme was very active on GlcNAcMan5GlcNAc but had no activity toward Man5GlcNAc, Man9GlcNAc, Glc3Man9GlcNAc, or other high-mannose oligosaccharides. It did show slight activity toward Man3GlcNAc. The first product of the reaction of enzyme with GlcNAcMan5GlcNAc, i.e., GlcNAcMan4GlcNAc, was isolated by gel filtration and subjected to digestion with endoglucosaminidase H to determine which mannose residue had been removed. This GlcNAcMan4GlcNAc was about 60% susceptible to Endo H indicating that the mannosidase II preferred to remove the alpha 1,6-linked mannose first, but 40% of the time removed the alpha 1,3-linked mannose first. The final product of the reaction, GlcNAcMan3GlcNAc, was characterized by gel filtration and various enzymatic digestions. Mannosidase II was very strongly inhibited by swainsonine and less strongly by 1,4-dideoxy-1,4-imino-D-mannitol. It was not inhibited by deoxymannojirimycin.     

绿豆尖镰孢枯萎病抗性鉴定方法

绿豆是我国的主要食用豆类之一。由尖镰孢引起的绿豆枯萎病是一种严重的土传病害,病原菌从根部侵入,引起植株矮化,叶片黄化、枯萎,根茎部维管束变褐,严重时导致植株死亡。防治枯萎病最经济、有效的方法是培育利用抗病品种。本研究在控制条件下以具有不同抗性表型绿豆品种为材料,分别对接种方法、植株生育期、接种体浓度、接种体处理时间及接种后植株培养温度等影响绿豆抗性表型的因素进行比较研究,以期建立一个快速、准确和高效的绿豆枯萎病抗性鉴定方法,为抗病资源的筛选和抗病育种提供技术支持。结果表明,绿豆枯萎病苗期抗性鉴定最适宜的接种方法为剪根浸根法,最适宜接种体浓度为105~106孢子/m L,接种最佳植株生育期为2叶期,最短有效接种体浸根时间为2 min,最适宜发病温度为25℃,接种后14 d调查病情。     

Prostaglandin inhibitors and the development of mung bean seedlings

The effect of cortisol and prostaglandin inhibitors on the growth and development of germinating mung bean, Vigna radiata L. Wilzek, cv. Jumbo was investigated. Cortisol, indomethacin, and a mixture of cortisol with aspirin, or benoxaprofen significantly increased radicle length and the number of lateral roots as compared with non-treated controls. A mixture of cortisol and indomethacin significantly increased growth of hypocotyls.