Intracellular Localization of Peptide Hydrolases in Wheat (Triticum aestivum L.) Leaves

Protoplasts from 8- to 9-day-old wheat (Triticum aestivum L.) leaves were used to isolate organelles which were examined for their contents of peptide hydrolase enzymes and, in the case of vacuoles, other acid hydrolases. High yields of intact chloroplasts were obtained using both equilibrium density gradient centrifugation and velocity sedimentation centrifugation on sucrose-sorbitol gradients. Aminopeptidase activity was found to be distributed, in approximately equal proportions, between the chloroplasts and cytoplasm. Leucyltyrosine dipeptidase was mainly found in the cytoplasm, although about 27% was associated with the chloroplasts. Vacuoles shown to be free from Cellulysin contamination contained all of the protoplast carboxypeptidase and hemoglobin-degrading activities. The acid hydrolases, phosphodiesterase, acid phosphatase, α-mannosidase, and β-N-acetylglucosamidase were found in the vacuole to varying degrees, but no β-glucosidase was localized in the vacuole.     

Free Polyamines in Senescing Wheat(Triticum aestivum L.)

The free polyamine content of flag leaves, peduncles, rachis,glumes, and grains of wheat (Triticum aestivum L., cv. Castell)plants, ripening under field conditions, has been investigatedduring three consecutive growing seasons. Putrescine was quantitativelythe most important of all polyamines detected in these organs.Concentrations were highest in the grains, glumes and flag leaves.No correlation was found between polyamine content and the onsetof senescence of flag leaves and other organs. Excised primaryleaves, however, showed a decrease in polyamine content in thedark and also in light/dark cycles, but in the latter case onlyafter an initial increase. Sink removal of otherwise intactwheat plants caused an accumulation of putrescine in flag leavesat the later stages of senescence, whereas removal of all otherleaves was without any significant effect. Putrescine was alsorecovered in phloem-exudate samples collected throughout theperiod of grain development. In both grains and glumes, peakconcentrations of polyamines were found early during seed development. Key words: Triticum aestivum, polyamines, ripening, senescence     

Nitrogen Metabolism in Senescent Flag Leaves of Wheat (Triticum aestivum L.) in the Light

Nitrogen metabolism was examined in senescent flag leaves of 90- to 93-day-old wheat (Triticum aestivum L. cv Yecora 70) plants. CO₂ assimilation and the levels of protein, chlorophyll, and nitrogen in the leaves decreased with age. Glutamine synthetase activity decreased to one-eighth of the level in young flag leaves. Detached leaves were incubated (with the cut base) in ¹⁵N-labeled NH₃, glutamate, or glycine in the light (1.8 millieinstein per square meter per second) at 25°C in an open gas exchange system under normal atmospheric conditions for up to 135 minutes. The ¹⁵N-enrichment of various amino acids derived from these ¹⁵N-substrates were examined. The amido-N of glutamine was the first ¹⁵N-labeled product in leaves incubated with ¹⁵NH₄Cl whereas serine, closely followed by the amido- and amino-N of glutamine, were the most highly ¹⁵N-labeled products during incubation with [¹⁵N]glycine. In contrast, aspartate and alanine were the first ¹⁵N-labeled products when [¹⁵N] glutamate was used. These results indicate that NH₃ was assimilated via glutamine synthetase and glutamate synthase activities and the photorespiratory nitrogen cycle remained functional in these senescent wheat flag leaves. In contrast, an involvement of glutamate dehydrogenase in the assimilation of ammonia could not be detected in these tissues.     

Biochemical Basis of Variability in Nitrate Reductase Activity in Wheat (Triticum aestivum L.) Genotypes

Significant differences in the activity of nitrate reductasein vivo and in vitro were observed among wheat genotypes, whenexpressed on a dry weight basis. The genotypes with high nitratereductase (HNR) activity exhibited an efficient nitrate inductionsystem. Availability of NADH seemed to be partially responsiblefor the low activities of the enzyme in genotypes categorizedas low nitrate reductase group (‘LNR). Biochemical analysisof the genotypes revealed that ‘HNR’ genotype hadmore active enzyme protein, high rates of enzyme protein synthesisand higher level of steady state nitrate reductase-mRNA relativeto those observed in ‘LNR’ genotype. ¹ Present address: Department of Botany, Faculty of Science,Hamdard University, Hamdard Nagar, New Delhi 110062, India. ² Present address: Institut für Botanik, UniversitätHannover, 3000 Hannover 21, F.R.G.     

QTL Mapping of Diffuse Reflectance Indices of Leaves in Hexaploid Bread Wheat (Triticum aestivum L.)

Russian Journal of Plant Physiology - Quantitative trait loci (QTL) mapping of diffuse reflectance indices of laminas in bread wheat (Triticum aestivum L.) has been first performed under controlled...     

Colchicine-induced Paracrystals in Root Cells of Wheat (Triticum aestivum L.)

Tubulin conformations other than microtubules in the meristematiccells of wheat roots grown in the presence of 2 mM colchicinesolution were investigated by immunofluorescence and electronmicroscopy. In the affected cells microtubules disappeared andwere replaced by tubulin fluorescent strands that occurred inthe cortical cytoplasm. With increasing time of exposure tocolchicine the tubulin strands became better organized and occurredalso in the subcortical cytoplasm and finally they were restrictedto the area around the nucleus. In prophase and preprophasecells thick strands occupied the cortical cytoplasmic zone wherein normal cells a preprophase microtubule band (PMB) was expectedto be assembled. In the colchicine-treated cells electron microscopy revealedan accumulation of paracrystalline aggregates, which initiallyoccurred along the cell wall and later deeper in the cytoplasm,in the perinuclear regions and the cytoplasmic invaginationsof the nucleus. In transverse planes the paracrystalline strandsappear to consist of hexagonal subunits in a 'honeycomb' arrangement,while in longitudinal and oblique sections they exhibit variableimages. Since their distribution coincides with that of thetubulin strands visualized by immunofluorescence, they are consideredto be the same structure. Therefore, the paracrystals consistof, or at least contain, tubulin. They are most likely to bepolymers of tubulin-colchicine complexes.Copyright 1995, 1999Academic Press Wheat roots, colchicine, immunofluorescence, electron microscopy, tubulin paracrystals, Triticum aestivum L     

Floret Initiation and Development in Spring Wheat (Triticum aestivum L.)

The number and developmental stages of florets were determinedin each spikelet of the spike in the main shoots of spring wheat.Samples were taken frequently from plants grown in a phytotronand in a nitrogen application field-test. Ten stages of development,from floret initiation until anthesis, were recognized and described. Inter-spikelet variation in the total number of initiated floretswas rather small. However, the number of florets at advancedstages of development, as well as the number of grains, washighest in the central spikelets in which florets initiatedfirst. Floret initiation did not proceed beyond spike emergence,whereafter the distal florets and the spikelet apex degenerated.Grain-set was restricted to florets which had developed at leastto the stage of visible anther lobes at spike emergence. Thenumber of these florets was increased significantly by nitrogenapplication. Wheat, Triticum aestivum L., spikelet, floret, grain set, nitrogen     

A Study of Floret Development in Wheat (Triticum aestivum L.)

Plants of wheat (Triticum aestlvum L.) cv. Aotea were grownat high or low nitrogen levels and in a natural photoperiodor continuous light. Starting 17–21 days from the double-ridgestage, eight plants from each treatment were sampled every 3days until anthesis, and the two basal, the sixth, and the terminalspikelets were sectioned longitudinally. A developmental scorewas assigned to each floret and rates of development calculated.Continuous light hastened development but reduced the numberof spikelets per ear, while high nitrogen delayed developmentbut increased spikelet numbers. The number of florets initiatedin each spikelet varied within narrow limits, but grain settingdepended strongly on spikelet position and on treatment. Althoughflorets were initiated in acropetal succession, the rate ofdevelopment tended to increase up to floret 4 but then declinedmarkedly. As a result grain setting was confined to basal floretpositions, although the two basal spikelets developed so slowlythat they contributed relatively little to grain yield. Distalflorets degenerated almost simultaneously at or before ear emergence,but those in intermediate positions continued to develop untilafter fertilization in the lower florets. It is argued thatthe spikelet is an integrated system in which correlative mechanismsplay a part throughout the development of the florets.     

Multiple Forms of the Constitutive Wheat Cinnamyl Alcohol Dehydrogenase

Three cinnamyl alcohol dehydrogenase (CAD) isoenzymes were separatedfrom etiolated wheat seedlings (Triticum aestivum L.) and examinedby native gel electrophoresis. Two of these enzymes (CAD-1 andCAD-2) were purified to apparent homogeneity. They exhibiteda marked difference in substrate affinity. On sodium dodecylsulphate-acrylamide gel the isolated isoenzymes showed onlyone protein band each with an M_r 45000 and 40000 daltons, respectively,whereas on native gel two bands were identified for each protein.Isoenzymes from a variety of diploid, tetraploid, and hexaploidwheats were compared. The results indicated that the CAD polymorphismcould be genetically determined. Key words: Cinnamyl alcohol dehydrogenase, lignin, Triticum aestivum L     

The Morphology and Development of Cross Veins in the Leaves of Bread Wheat (Triticum aestivum L.)

In the leaves of bread wheat Triticum aestivum L. the longitudinalvascular bundles are linked by small transverse bundles Pairsof similar small vascular bundles also link the upper ends ofminor longitudinal bundles to their neighbours in a Y-shapedarrangement The cross-vein procambial strands arise from unexpanded cellsof one layer of the mesophyll tissue. Lines of these cells connectone longitudinal procambial strand to the next The procambialcells subsequently undergo two tangential divisions to producecells which differentiate to form the conducting and parenchymatouselements of the mature cross veins. Anomalous cross veins are sometimes found. possible modes oforigin of these anomalous cross veins are considered.     

Nitrate Uptake and the Induction of Nitrate Reductase Activity in Wheat (Triticum aestivum L.) Seedlings

Nitrate uptake and the subsequent induction of in vivo nitratereductase activity in wheat were studied by investigating aeuploid and certain ditelosomic stocks which exhibited in vivoactivity significantly greater than that of the euploid. Thekinetics of nitrate uptake were investigated, but the high activitiesof the ditelosomics were not caused by increased uptake of nitrate,although ditelo-7B^L exhibited unusual uptake dynamics. Analysisof the induction of nitrate reductase activity revealed a biphasicgeneral pattern, with an initial rapid phase being followedby a slower but longer period of induction. The induction rateover the second period, although responsible for only a minorproportion of the total activity induced, was positively correlatedwith the final nitrate reductase level, unlike the rate overthe first induction period. Several stocks exhibited high inductionrates over one or other of the two phases, while ditelo- 1 A^sshowed an abnormal monophasic induction pattern. At the endof the second period of induction, nitrate reductase activitybecame more or less steady, except for activity fluctuationsassociated with the time of application of induction stimuli.     

外源水杨酸对光抑制条件下小麦叶片光合作用的影响

以浓度为50、100、200 mg·kg-1的水杨酸(SA)预先处理灌浆期的小麦叶片,可有效防护强光所致的氧化损伤,维持较高的超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性,减轻丙二醛(MDA)积累.叶片在光抑制条件下,可维持较高的通过PSⅡ电子传递速率(Fm/Fo)、PSⅡ原初光化学效率(Fv/Fm)、PSⅡ量子效率(ΦPSⅡ)、光化学猝灭系数(qP)、净光合速率(Pn)和较低的非光化学猝灭系数(qNP).其中,以较低浓度SA(50 mg·kg-1)的效果较好.     

Gibberellic Acid Regulates Cell Wall Extensibility in Wheat (Triticum aestivum L.)

Mutations (Rht genes) blocking sensitivity to gibberellic acid (GA) were used to examine phytohormone mediated cell wall expansion in wheat (Triticum aestivum L.). Irreversible extensibility of immature leaf segments, as determined by stress/strain (instron) measurements, declined with Rht gene dose. Exogenous GA₃ significantly increased wall extensibility in the nonmutant controls but had no effect on the near-isogenic GA-insensitive genotypes. Furthermore, ancymidol, an inhibitor of gibberellin biosynthesis, diminished wall extensibility in the nonmutant control. Extensibility of immature segments was highly correlated with mature leaf sheath length (R = +0.95). The results indicate that wall yielding properties of expanding wheat leaves are associated with leaf cell expansion potential and that GA is involved in the determination of those properties.     

小麦抗倒性研究进展

倒伏是严重影响小麦子粒产量和品质的一个重要因素。本文系统阐述了小麦茎秆形态和结构特性、茎秆化学成分与抗倒伏关系以及抗倒性的遗传和分子标记等方面的最新研究进展。株高、基部节间长度与抗倒性呈负相关;而基部节间粗度、秆壁厚、单位长度干重与抗倒性呈正相关。茎秆机械组织细胞层数、厚度,维管束数目、面积以及髓腔大小与抗倒性密切相关。茎秆化学成分中纤维素、木质素以及碳水化合物含量和硅、钾元素含量与抗倒性呈正相关。小麦抗倒性呈数量性状遗传特征,除受多对主基因控制外,可能还受微效修饰基因作用。采用分子标记技术已将抗倒性以及与抗倒性相关的茎秆形态性状进行了QTL定位。     

Effect of Water Deficit on Sporogenesis in Wheat (Triticum aestivum L.)

Plants of Triticum aestivum L., cv. Gabo, were grown in a glasshousefor 4 weeks and then transferred to a controlled environmentwith 20±1 °C temperature and 16 h photoperiod. Theywere subjected to water deficit by withholding the water supplyduring various stages of floral development, including thoseimmediately before meiosis and all stages until just after anthesis. The proportion of apparently normal florets which produced grainwas reduced when water deficit occurred during and immediatelyafter meiosis in the generative tissues. The effect of thisreduced grain set on total grain yield was partially compensatedby an increase in the weight of the remaining grains. Cross-pollinationbetween stressed and well-watered plants showed that grain setwas reduced as a direct consequence of the induction of malesterility by water stress, whereas female fertility was unaffected.A large proportion of the anthers on water-stressed plants weresmall and shrivelled, did not dehisce normally and containedpollen which was devoid of normal cytoplasmic constituents andshowed no staining reaction with triphenyl tetrazolium chloride.This effect on male fertility was not a result of desiccationof the sporogenous tissue, but an indirect outcome of the decreasein water potential elsewhere in the plant. Water stress, Triticum aestivum L., wheat, pollen, sporogenesis, grain set, male sterility     

In Vitro Synthesis of Wheat (Triticum aestivum L.) Storage Proteins

Free and membrane-associated polysomes were isolated in approximately equal amounts from endosperm of wheat kernels harvested 20 days after anthesis. The presence of heparin in the homogenizing buffer minimized polysome degradation. Ribonucleic acid from the isolated polysomes, when translated in vitro in a wheat germ system, yielded products ranging in size from about 12,000 to about 80,000 daltons, including at least two polypeptides that co-migrated with seed extract proteins in sodium dodecyl sulfate polyacrylamide gel electrophoresis. The nature of the translation products of free and membrane-associated RNA are distinctly different, with membrane-associated RNA yielding a higher proportion of polypeptides in the size range of 30,000 to 37,000 daltons. Analysis of membrane-associated 3′-terminal polyadenylyl-containing RNA in vitro translation products, by solubility in 70% ethanol and by immunoprecipitation, indicates that the 33,000- to 37,000-dalton polypeptides contain gliadins, and the analysis provides evidence that these proteins are synthesized in association with membranous cell organelles. Gliadin polypeptides synthesized in vitro are larger than authentic gliadins and probably are precursors which, in vivo, undergo modification to yield the smaller final products.     

Acid Carboxypeptidases in Grains and Leaves of Wheat, Triticum aestivum L

Extracts of resting and germinating (3 days at 20°C) wheat (Triticum aestivum L. cv Ruso) grains rapidly hydrolyzed various benzyloxycarbonyldipeptides (Z-dipeptides) at pH 4 to 6. Similar activities were present in extracts of mature flag leaves. Fractionation by chromatography on CM-cellulose and on Sephadex G-200 showed that the activities in germinating grains were due to five acid carboxypeptidases with different and complementary substrate specificities. The wheat enzymes appeared to correspond to the five acid carboxypeptidases present in germinating barley (L Mikola 1983 Biochim Biophys Acta 747: 241-252). The enzymes were designated wheat carboxypeptidases I to V and their best or most characteristic substrates and approximate molecular weights were: I, Z-Phe-Ala, 120,000; II, Z-Ala-Arg, 120,000; III, Z-Ala-Phe, 40,000; IV, Z-Pro-Ala, 165,000; and V, Z-Pro-Ala, 150,000. Resting grains contained carboxypeptidase II as a series of three isoenzymes and low activities of carboxypeptidases IV and V. During germination the activity of carboxypeptidase II decreased, those of carboxypeptidases IV and V increased, and high activities of carboxypeptidases I and III appeared. The flag leaves contained high activity of carboxypeptidase I and lower activities of carboxypeptidases II, IV, and V, whereas carboxypeptidase III was absent.     

Purification and Characterization of Lipase from Wheat (Triticum aestivum L.) Germ

A method of isolation and purification of lipase (EC 3.1.1.3) from the germ of wheat (Triticum aestivumL.) is described. An electrophoretically homogeneous preparation of the enzyme (specific activity, 622.5 × 10^–3 mol/min per mg protein) was obtained after 61-fold purification. The molecular weight of the enzyme, determined by gel chromatography, was 143 ± 2 kDa. The optimal conditions for the enzyme were 37°C and pH 8.0. The homogeneous preparation of the lipase exhibited high thermal stability: over 20% of the original activity was retained after incubation of the preparation at high temperatures (60–90°C) for 1 h at pH 8.0.     

Light-dependent Proton Excretion of Wheat (Triticum aestivum L.) and Maize (Zea mays L.) Roots

We investigated the change of root net proton excretion of seedlings of Triticum aestivum L. and Zea mays L. with daily variation of illumination using a multi-channel pH-stat system. We found an increase of net proton excretion during darkness and a drop after the beginning of illumination. Inhibition of carotenoid biosynthesis by norflurazone and photooxidation of chlorophylls did not change the periodicity or its induction. The induction of diurnal periodicity was possible with blue, green and red light. After induction the oscillation of net proton excretion continued for at least two cycles under constant light. We conclude that net H⁺ excretion of wheat and maize roots may be regulated by an endogenous clock or by a signal from the leaves. The nature of such a hypothetical signal remains unknown.     

DNA Synthesis in Microspores in Anther Culture of Wheat (Triticum aestivum L.)

Anthers with mid-unlnucleate microspores were cultured on W5 medium supplemented with 0.5 mg/l kinetin, 2 mg/l 2,4-D and 9% or 3% sucrose. At a series of interval (0, 1, 1.5, 2, 14 days) after cultured, the anthers were labelled with 3H-thymidine (4 MCi/mi) for 24 h, fixed, and then performed autoradiography according to conventional method. Results show that after cultured for 24 h, 3H-thymidine was incorporated into some late-uninucleate microspores (see Plate I, 3), and after for 2.5 days, vegetative nuclei in pollen grains were la- belled (see Plate I, 4). Usually, vegetative nuclei were labelled frequently and generative ones were labelled rarely. Sometimes generative cell which could synthesis DNA might develop suspensor-like structure individually (see Plate I, 13). During early stage of development of a multicellular pollen grain, the DNA synthesis in the cells were synchronized. With pollen development, the synchronism of DNA synthesis was destroyed. When anthers cultured on medium with 3% sucrose, DNA in microspores could be synthesized normally, and the number of labelled microspores was more than that of anthers cultured on medium with 9% sucrose. However, on medium with 3% sucrose, the nuclei in microspores stopped dividing after one or two divisions and the cell wall of them could not be formed and multicellular pollen was not observed. It seems that the absence of multicellular pollen on medium with 3% sucrose was primarily due to the block of cell division and cell wall formation, not due to the interruption of DNA synthesis.