Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Effects of Drought Conditioning on Abscisic Acid Accumulation in the Leaf and Stomatal Response

The effects of a period of water stress (drought conditioning)on responses to a second (challenge) stress were examined inyoung vegetative rice (Oryza sativa L.) plants. Drought conditioningdid not affect the rate of subsequent stress development, nor,in a first experiment, did it influence relations between turgor(_p) and total () leaf water potential. However, conditioningdid extend the range of _p over which stomata remained open andsignificantly reduced the amount of ABA which accumulated inthe leaf at a given _p. The change in stomatal behaviour (stomataladjustment) was quantitatively accounted for by the change inleaf ABA accumulation. The reduction in ABA accumulation due to conditioning did notinvolve a change in the potential capacity to produce ABA, asABA accumulation in partially dehydrated detached leaves wasnot reduced by conditioning. It is suggested that effects ofconditioning on leaf ABA content in the intact plant involvechanges in the rate of ABA export from the leaf. Oryza sativa L, rice, drought conditioning, stomata, water stress, abscisic acid     

Abscisic Acid Accumulation in Detached Leaves of Rice (Oryza sativa L.) in Response to Water Stress: A Correlation with Leaf Size

When water stress was imposed on detached leaves of two rice(Oryza sativa L.) cultivars, more ABA per unit fresh weightaccumulated in IR20, a small-leaved cultivar, than in 63–83,a large-leaved cultivar; the difference being up to threefold.In an F₂ population of a cross between the two cultivars ABAaccumulation was found to be significantly negatively correlatedwith leaf fresh weight. This correlation persisted in the F₃generation. Such a correlation was not evident, however, whena number of rice cultivars, which varied widely in leaf size,were examined. The difference in ABA accumulation between IR20 and 63–83was not accounted for by different spatial patterns of waterloss or ABA accumulation within a leaf, and cultivar differencesin ABA content were maintained both across, and at various positionsalong the leaf. No major differences in leaf anatomy were observed between thetwo cultivars. Differences found in leaf water relations characteristicswere few and generally minor. It therefore seems unlikely thatthese properties account for the difference between the cultivarsin the ability to accumulate ABA or for the correlation withleaf size. Oryza sativa L, rice, water stress, abscisic acid, leaf size     

Modification of Leaf Size in Rice (Oryza sativa L.) and its Effects on Water Stress-induced Abscisic Acid Accumulation

The ability of detached leaves of the rice cultivars IR20 and63–83 and their F₂ progeny to accumulate ABA in responseto water stress is negatively correlated with leaf size. Itwas shown that this association was not an artifact of incubationconditions following the imposition of stress. Also, it waspossible to break the correlation by selecting plants in segregatingpopulations which differed in ABA yet had similar leaf size. In further experiments, leaf size was altered phenotypicallyby various treatments; either being increased by gibberellinapplication or periodic removal of tillers, or reduced by priorexposure to water stress or ABA. Although responses to thesetreatments were complex, the results demonstrated that leafsize and accumulation capacity were at least partially independent.It is suggested that the correlations observed previously inF₂ populations from the cross IR20 x 63–83 were a resultof genetic linkage. Oryza saliva L., rice, leaf size, abscisic acid, water stress     

Effects of Atmospheric Humidity on Abscisic Acid Accumulation and Water Status in Leaves of Rice (Oryza sativa L.)

Rice (Oryza sativa L ) plants were grown in controlled environmentcabinets with either low (c 0 4 kPa) or high (c 1 6 kPa) atmosphericwater vapour pressure deficit (v p d) The capacity of detachedleaves to accumulate ABA in response to rapidly induced waterstress was increased when plants were grown at high v p d Highv p d significantly lowered solute potential (     

Ethylene-Induced Inhibition of Root Growth Requires Abscisic Acid Function in Rice (Oryza sativa L.) Seedlings

Ethylene and abscisic acid (ABA) have a complicated interplay in many developmental processes. Their interaction in rice is largely unclear. Here, we characterized a rice ethylene-response mutant mhz4, which exhibited reduced ethylene-response in roots but enhanced ethylene-response in coleoptiles of etiolated seedlings. MHZ4 was identified through map-based cloning and encoded a chloroplast-localized membrane protein homologous to Arabidopsis thaliana (Arabidopsis) ABA4, which is responsible for a branch of ABA biosynthesis. MHZ4 mutation reduced ABA level, but promoted ethylene production. Ethylene induced MHZ4 expression and promoted ABA accumulation in roots. MHZ4 overexpression resulted in enhanced and reduced ethylene response in roots and coleoptiles, respectively. In root, MHZ4-dependent ABA pathway acts at or downstream of ethylene receptors and positively regulates root ethylene response. This ethylene-ABA interaction mode is different from that reported in Arabidopsis, where ethylene-mediated root inhibition is independent of ABA function. In coleoptile, MHZ4-dependent ABA pathway acts at or upstream of OsEIN2 to negatively regulate coleoptile ethylene response, possibly by affecting OsEIN2 expression. At mature stage, mhz4 mutation affects branching and adventitious root formation on stem nodes of higher positions, as well as yield-related traits. Together, our findings reveal a novel mode of interplay between ethylene and ABA in control of rice growth and development.     

栽培稻旱胁迫叶片相关性状的遗传解析

利用籼稻窄叶青8号(ZYQ8)和粳稻京系17(JX17)衍生的加倍单倍体(DH)群体127个株系,2002年在杭州采用田间断水法栽培,在水分胁迫下,对叶片的卷叶、相对含水量和电导率3个性状进行了评价和QTL分析。结果表明,3个性状在DH群体中均存在双向超亲分离,接近正态分布,受数量性状基因的控制;检测到影响这些性状的6个QTL,其中卷叶3个(qLR—1,qLR—5和qLR—11)、相对含水量2个(qRWC—1和qRWC—6和电导率1个(qERC—6）。旱胁迫时,目测卷叶方便易行,适于对大批品种或资源筛选,对抗旱栽培稻品种的筛选和利用具有一定的指导意义。     

Alteration of Leaf Metabolism in Bt-Transgenic Rice (Oryza sativa L.) and Its Wild Type under Insecticide Stress

Insecticide is always used to control the damage from pests, while the potential influence on plants is rarely known. Time-course metabolic changes of wild and Bacillus thuringiensis (Bt) transgenic rice (Oryza sativa L.) plants after insecticide treatment were investigated by using gas chromatography-mass spectrometry (GC-MS). A combined statistical strategy of 2-way ANOVA and multivariate analyses (principal component analysis and hierarchal cluster analysis) was performed to find the stress-associated effects. The results reveal that a wide range of metabolites were dynamically varied in both varieties as a response to insecticide, in multiple metabolic pathways, such as biosynthesis and metabolism of amino acids, carbohydrates, fatty acids, TCA cycle, and the shikimate/phenylpropanoid pathway, and most of the changes were correlated with the exposure time and dependent on the variety. A set of stress defenses were activated, including phytohormone signaling pathway, antioxidant defense system, shikimate-mediated secondary metabolism, and so on. In particular, insecticide led to much stronger regulations of signaling molecules (salicylate and the precursor of jasmonate) and antioxidants (α-tocopherol and dehydroascorbate/ascorbate) in Bt-transgenic variety at the early stage. Our results demonstrated that the Bt-transgenic rice had a more acute and drastic response to insecticide stress than its non-transgenic counterpart in antioxidant system and signaling regulation.     

水稻体细胞无性系变异

水稻体细胞无性系变异研究取得了很大进展 ,获得了大量抗病、抗逆、优质、矮杆等突变体。对这些突变体遗传分析表明 ,大多数突变性状由 1对或 2对基因控制。水稻体细胞无性系变异的发生与基因型、性状、继代时间、培养方式等有关 ,并具有内在的机制 ,点突变和反转录转座子插入可能是引起水稻无性系变异的两个重要原因。     

水稻对叶瘟和穗瘟部分抗性的遗传分析

在一个水稻籼籼交重组自交系群体中,选用由感病株系构成的2个亚群体和2个不同的稻瘟病菌小种,进行了水稻对叶瘟部分抗性的QTL定位,还选用由感病而且抽穗期相近的株系构成的亚群体和另一个病菌小种,进行了水稻对穗瘟部分抗性的QTL定位,将病叶面积百分比(DLA)、病斑大小(LS)和病斑数(LN)作为对叶瘟部分抗性的性状,将病斑长度(LL)和孢子量(CA)作为对穗瘟部分抗性的性状。所构建的图谱包含168个标记。应用QTLMapper 1．01b,共检测到11个表现主效应的QTL和28对双因子互作,有3个表现主效应的QTL参与对同一性状的互作。QTL的主效应对单一性状的贡献率为4．7％～38．8％,而上位性效应对单一性状的贡献率为16．0％～51．7％,QTL的主效应对大多数性状的贡献率小于互作效应,表明互作效应对于部分抗性的重要作用。对穗瘟部分抗性的两个性状LL和CA,所检测到QTL总效应的贡献率分别达到70．6％和82．6％,表明由排除了主效抗病基因的感病株系组成的亚群体适合于进行部分抗性QTL定位。     

Relation between Leaf Age and Nitrogen Incorporation in the Leaf of the Rice Plant (Oryza sativa L.)

The relation between leaf age and the incorporation of nitrogeninto the leaf was examined in the 13th leaf blade of the riceplant, Oryza sativa L., after feeding it ¹⁵N-labelled ammoniumsulfate. The incorporation of nitrogen into the leaf was activeup to the maximum leaf nitrogen content; thereafter it decreasedquickly. At the beginning of senescence, when the nitrogen contentof the leaf had begun to decrease, the incorporation of ¹⁵Ndecreased to 28% of the value during development. At the middlestage of senescence, when the nitrogen content had decreasedto half the maximum, the incorporation was 13%. The incorporation of ¹⁵N into soluble proteins was examinedby gel filtration on Sephadex G-200. During development, largeamounts of ¹⁵N were incorporated into the ribulose bisphosphatecarboxylase-rich fraction. As the leaf aged, the incroporationof ¹⁵N into this fraction decreased more sharply than it didin other fractions. This tendency was more pronounced at thelate stage of senescence. We concluded that the amounts andkinds of protein synthesized in a leaf are closely related toleaf age. (Received November 24, 1981; Accepted June 17, 1982)     

Coleoptile Senescence in Rice (Oryza sativa L.)

We investigated the cellular events associated with cell deathin the coleoptile of rice plants (Oryza sativa L.). Seeds germinatedunder submergence produced coleoptiles that were more elongatedthan those grown under aerobic conditions. Transfer of seedlingsto aerobic conditions was associated with coleoptile opening(i.e. splitting) due to death of specific cells in the sideof the organ. Another type of cell death occurred in the formationof lysigenous aerenchyma. Senescence of the coleoptile was alsonoted, during which discolouration of the chlorophyll and tissuebrowning were apparent. DNA fragmentation was observed by deoxynucleotidyltransferase-mediateddUTP nick end labelling (TUNEL) assay, and further confirmedby the appearance of oligonucleosomal DNA ladders in senescentcoleoptile cells. Two nucleases (Nuc-a and Nuc-b) were detectedby in-gel-assay from proteins isolated from coleoptiles. Nuc-a,commonly observed in three cell death phases required eitherCa²⁺or Mg²⁺, whereas Nuc-b which appeared during senescencerequired both Ca²⁺and Mg²⁺. Both nucleases were strongly inhibitedby Zn²⁺. Copyright 2000 Annals of Botany Company Aerenchyma, rice, cell death, coleoptile, fragmentation, nuclease, Oryza sativa, senescence, split, submergence, TUNEL     

Release of Nitrogen From Chloroplasts During Leaf Senescence in Rice (Oryza sativa L.)

In order to ascertain the possibility that nitrogen associatedwith chloroplasts serves as a major source of nitrogen redistributedfrom senescent leaves, chloroplasts were isolated from riceleaves and changes with leaf age in total leaf nitrogen andchloroplast nitrogen were examined. Results presented here showthat decrease in total leaf nitrogen during leaf senescencewas closely correlated with decrease of chloroplast nitrogenand roughly 85–95 per cent of leaf nitrogen released fromsenescent leaves during the experimental period could be accountedfor by a loss of chloroplast nitrogen. By dividing chloroplastnitrogen into two fractions, i.e. lamellar and stroma fractions,the question of which fraction was more deeply concerned withthe loss of leaf nitrogen was clarified. Results suggested thatin the vegetative stage of plant growth the stroma was mainlyresponsible for the loss of leaf nitrogen. On the other hand,nitrogen was released from lamellar and stromal fractions atalmost the same rate during the reproductive stage. Oryza sativa L., rice, chloroplasts, nitrogen, leaf senescence     

Cyclic AMP Promotion and Abscisic Acid Inhibition of {alpha}-Amylase Activity in the Seeds of Rice (Oryza sativa L.)

Cyclic AMP and GA₃ stimulated both -amylase activity in riceendosperm and the germination of the seed. In combination theyalso induced germination of ABA-treated seeds but cyclic AMPalone failed to neutralize the inhibitory effect of ABA; withadded kinetin, however, it promoted the -amylase activity ofthe dormant seeds. The enzyme activity decreased as the storageperiod of seeds increased. Cyclic AMP and GA     

Short- and Long-Term Effects of Salinity on Leaf Growth in Rice (Oryza sativa L.)

Addition of 50 mM NaCl to Oryza sativa L. had little effectupon the time of leaf initiation, but leaf mortality prior tothe normal phase of senescence was increased and the onset ofsenescence was advanced. There was no significant effect uponthe day-to-day pattern of growth, nor upon the ultimate length,of leaves that were developing at the time of, or shortly after,salinization with 50 mM NaCI. Leaves that developed after prolongedexposure of the plants to salinity were shorter. Addition ofNaCl, KC₁ or mannitol to the root medium brought about a cessationof leaf elongation within one minute. Growth at a reduced raterestarted abruptly after a lag period that depended upon theexternal concentration. Elongation rate recovered its originalvalue within 24 h after exposure to 50 mM NaCl, though not athigher concentrations. Addition of NaCl at concentrations upto 100 mM elicited no short-term effects upon photosyntheticgas exchange. Na uptake contributed to osmotic adjustment ofthe growing zone. When plants were rapidly exposed to 50 mMNaCl, no change in turgor pressure was detectable in the growingzone with the resolution of the miniature pressure probe used(about 70 kPa). It is concluded that the initial growth reductionin rice caused by salinization is due to a limitation of watersupply. A clear distinction is made between the initial effectsof low salinity which are recoverable and the long-term effectswhich result from the accumulation of salt within expanded leaves. Key words: Leaf elongation, gas exchange, photosynthesis, water relations     

The Remobilization of Nitrogen Related to Leaf Growth and Senescence in Rice Plants (Oryza sativa L.)

Rice plants (Oryzae sativa L.) grown in a nutrient solutionwere fed with (¹⁵NH₄)₂SO₄ during the 5 days of their young panicleformation. At the end of that time in the youngest leaf blade, which hadstarted to emerge during the labelling, absorbed-nitrogen accountedfor 37% of the increased nitrogen of the tissue; in the nextdeveloping leaf blade it accounted for 55%. Thus, remobilized-nitrogenoriginating from older patrs of the plant made up 63 and 45%,respectively, of their total nitrogen. The important contributionof the remobilized-nitrogen to the development of a leaf isevident. The remobilization of nitrogen in the 12th leaf blade on themain stem was examined in detail after labelling during itsdeveloping stage. The ¹⁵N level started to decrease soon afterthe end of the labelling period and continued to decrease untilfull senescence, although the total nitrogen in the same leafincreased until just after its complete expansion, suggestingthat even a young leaf plays a role as a supplier of remobilized-nitrogen. During the rapid decrease in the total nitrogen after its peakat full expansion of the leaf, the actual proportion of labelledabsorbed nitrogen remained nearly the same, indicating thatinflux of new nitrogen into a senescing leaf is very limited. (Received March 13, 1981; Accepted July 13, 1981)     

Proteomic Analysis of Upland Rice (Oryza sativa L.) Exposed to Intermittent Water Deficit

Rice is the most important crop consumed all over the world. In Brazil, irrigated rice covers 50 % of the rice producing area and is responsible for 75 % of the national production. Upland rice covers most of the remaining area, and is therefore, a very important production system in the country. In the present study, we have used the drought tolerant upland rice variety Três Meses Antigo to investigate the proteomic changes that occur during drought stress. Plants were submitted to drought by the reposition of 50 % of the water lost daily. Twenty days after the beginning of the drought stress period, leaves were harvested and used for protein extraction. The 2D maps obtained from treated and control plants revealed 408 reproducible spots, 44 of which were identified by mass spectrometry, including 15 differential proteins. Several unaltered proteins were also identified (39 spots) and were mainly involved in photosynthesis. Taken together, the results obtained suggest that the tolerant upland rice up-regulates anti-oxidant and energy production related proteins in order to cope with water deficit.     

Influence of Osmotic Adjustment on Leaf Rolling and Tissue Death in Rice (Oryza sativa L.)

Osmotic adjustment, measured by the lowering of the osmotic potential at full turgor, and its influence on leaf rolling and leaf death was assessed in the lowland rice (Oryza sativa L.) cultivar IR36 in both the greenhouse and field. The degree of osmotic adjustment varied with the degree and duration of stress, but was usually 0.5 to 0.6 megapascal (maximally 0.8 to 0.9 megapascal) under severe stress conditions. In leaves in which osmotic adjustment was 0.5 to 0.6 megapascal, leaf rolling and leaf death occurred at lower leaf water potentials in adjusted than in nonadjusted leaves. We conclude that osmotic adjustment aids in the drought resistance of rice by delaying leaf rolling, thereby maintaining gas exchange, and by delaying leaf death.     

Stomatal Responses of Pearl Millet (Pennisetum americanum (L.) Leeke) Genotypes, in Relation to Abscisic Acid and Water Stress

Stomatal responses to water stress and to applied (±)-abscisicacid (ABA) were examined in genotypes of pearl millet (Pennisetumamericanum (L.) Leeke) known to differ in amounts of endogenousABA accumulating during drought. In both a pot and a field experiment,Serere 39, a genotype with a high capacity to accumulate ABA,showed a higher stomatal sensitivity to water stress than didthe ‘low’ ABA accumulator, BJ 104. In the fieldexperiment, a third genotype, B282, accumulating least amountsof ABA, also had the lowest stomatal sensitivity to water stress. There were no significant differences between these genotypesin stomatal response to applied (±)-ABA, or in the relationshipsbetween leaf conductance and levels of endogenous ABA. It isconcluded that the differences in accumulation of endogenousABA by these genotypes of pearl millet are of functional significance,and that endogenous ABA generated during a water stress whichdevelops over days or weeks mediates stomatal responses to suchstress.     

应用微卫星标记鉴别水稻籼粳亚种

应用70个微卫星标记分析了3个籼稻测验种和3个粳稻测验种的多态性,发现其中36个标记可以区分籼粳测验种。再以18个籼粳品种进一步筛选,找到了分布于12条染色体的21个籼粳特异性微卫星标记。在这21个标记中,20个在籼粳亚种间带型相异,其中7个在亚种内带型一致,13个在亚种内带型不一致;1个标记在12个籼稻品种和1个粳稻品种检测到相同的带型,其余11个粳稻品种具有另一种带型。微卫星标记和RFLP标记检测籼粳亚种不仅具有一致性,而且还有互补性。 Abstract:Six indica and japonica testers were assayed using 70 microsatellite markers.Thirty-six markers distinguishing indicas from japonicas were detected.By further-screening among 18 indica and japonica varieties,21 markers distributed on 12 rice chromosomes were found to be indica-japonica differentiated.No indica varieties shared same patterns with any japonica varieties at 20 marker loci,of which identical patterns were observed within subspecies at 7 loci while within-subspecies variations were observed at 13 loci.At the remaining locus,12 indica and 1 japonica varieties had the same allele,while other 11 japonica varieties had another allele.It also showed that SSLP was not only consistent,but also complementary,to RFLP for the subspecies identification.