Effects of exogenous hormones on floret development and grain setin wheat

At specific stages during floret development, solutions of IAA,GA₃, zeatin and ABA were injected into the leaf sheath around theyoung spike of wheat (Triticum aestivum L.) to study theregulating effects of exogenous hormones on floret development. Zeatin promotedfloret development and significantly increased the number of fertile florets aswell as grain set, especially at the stage of anther-lobe formation. Zeatinalsoincreased the sugar concentrations in spikes at anthesis. In contrast, IAA,GA₃ and ABA inhibited floret development, with different patternsforeach of the hormones. IAA inhibited the development of the whole spike and allflorets in the spikelets such that grain loss occurred in all positions in thespikelets. GA₃ increased the number of fertile florets per spike,butdecreased grain set of the third floret in each spikelet, especially whenapplied at terminal spikelet formation. ABA inhibited floret development, anddecreased the number of fertile florets and grain set at almost all developmentstages, except at anther-lobe formation. The inhibitory effect of ABA wasmainlyon the first and third florets in each spikelet.     

糖蜜草（Melinis minutiflora Beauv．）幼穗分化发育．及花和果实形态的研究

本文对糖密草（ＭｅｌｉｎｉｓｍｉｎｕｔｉｆｌｏｒａＢｅａｕｖ．）的幼穗分化发育及花和果实的形态作了研究,将幼穗分化发育过程划分为以下九个时期：第一苞原基形成期;第一次枝梗原基形成期;第二、三次枝梗原基形成期;小穗及颖花原基形成期;雌、雄蕊原基形成期;花粉母细胞形成期;花粉母细胞减数分裂期;花粉充实期;花粉成熟期。全过程历时约需４２ｄ．从抽穗到颖果成熟约需５０ｄ。糖蜜草的花序为圆锥花序。每花序有可育花２０００—３０００朵．小穗是由小穗轴、内外颖片、不育花外稃和小花构成。小花包括有内外稃各一片、一鳞被、雄蕊三枚和一枚雌蕊,颖果千粒重为９１ｍｇ。     

Wheat floret survival as related to pre-anthesis spike growth

Further improvements to wheat yield potential will be essential to meet future food demand. As yield is related to the number of fertile florets and grains, an understanding of the basis of their generation is instrumental to raising yield. Based on (i) a strong positive association between the number of fertile florets or grains and spike dry weight at anthesis; and (ii) the finding that floret death occurs when spikes grow at maximum rate, it was always assumed that floret survival depends on the growth of the spike. However, this assumption was recently questioned, suggesting that assimilates diverted to the spike do not determine the number of florets and grains and that the onset of floret death may instead be a developmental process that is not associated with spike growth. In this study, the relationships between the fate of floret primordia and spike growth from six independent experiments that included different growing conditions (greenhouse/field experiments, growing seasons, photoperiod/shading treatments during the floret primordia phase) and diverse cultivar types (winter/spring, semi-dwarf/standard-height, photoperiod sensitive/insensitive) were re-analysed together. Onset of floret death was associated with the beginning of spike growth at the maximum rate in c. 80% of the cases analysed; and the rate of floret death (the main determinant of floret survival) showed a negative quantitative relationship with spike weight at anthesis. As floret death and survival were shown to be linked to pre-anthesis spike growth, the strategy of focusing on traits associated with pre-anthesis spike growth when breeding to increase wheat yield potential further is valuable.     

Autophagy regulated by day length determines the number of fertile florets in wheat

SUMMARY: The wheat spikelet meristem differentiates into up to 12 floret primordia, but many of them fail to reach the fertile floret stage at anthesis. We combined microarray, biochemical and anatomical studies to investigate floret development in wheat plants grown in the field under short or long days (short days extended with low-fluence light) after all the spikelets had already differentiated. Long days accelerated spike and floret development and greening, and the expression of genes involved in photosynthesis, photoprotection and carbohydrate metabolism. These changes started while the spike was in the light-depleted environment created by the surrounding leaf sheaths. Cell division ceased in the tissues of distal florets, which interrupted their normal developmental progression and initiated autophagy, thus decreasing the number of fertile florets at anthesis. A massive decrease in the expression of genes involved in cell proliferation, a decrease in soluble carbohydrate levels, and an increase in the expression of genes involved in programmed cell death accompanied anatomical signs of cell death, and these effects were stronger under long days. We propose a model in which developmentally generated sugar starvation triggers floret autophagy, and long days intensify these processes due to the increased carbohydrate consumption caused by the accelerated plant development.     

Endogenous Plant Hormone Contents in Relation to FlowerBud Differentiation in Ficus carica (Moraceae)

Based on the morphological results of the flower bud differentiation in Ficus carica L.‘Brunswick', we quantified certain plant hormones, including ZR, ABA, GA1₊₃ and IAA, in the developing flower bud at the differentiation stageon the seventh or the eighth node of the new shoots, and found that at the stage of floral receptacle and floscule formation, the buds contained high level of ZR and ABA, and low level of GA1₊₃ and IAA, leading to a high ratio of ABA to IAA, ABA to GA1₊₃ ZR to GA1₊₃ , and ZR to IAA, respectively.     

ABA and IAA control microsporogenesis in <Emphasis Type="Italic">Petunia hybrida</Emphasis> L.

The formation of fertile male gametophyte is known to require timely degeneration of polyfunctional tapetum tissue. The last process caused by the programmed cell death (PCD) is a part of the anther program maturation which leads to sequential anther tissue destruction coordinated with pollen differentiation. In the present work, distribution of abscisic acid (ABA) and indole-3-acetic acid (IAA) in developing anthers of male-fertile and male-sterile lines of petunia (Petunia hybrida L.) was analyzed by using the immunohistochemical method. It was established that the development of fertile male gametophyte was accompanied by monotonous elevation of ABA and IAA levels in reproductive cells and, in contrast, their monotonous lowering in tapetum cells and the middle layers. Abortion of microsporocytes in the meiosis prophase in the sterile line caused by premature tapetum degeneration along with complete maintenance of the middle layers was accompanied by dramatic, twofold elevation in the levels of both the phytohormones in reproductive cells. The data obtained allowed us to conclude that at the meiosis stage ABA and IAA are involved in the PCD of microsporocytes.     

Characterization of the common wheat (Triticum aestivum L.) mutation line producing three pistils in a floret

In a normal wheat (Triticum ssp.L.) spike, one floret carries only one pistil that will further develop into one grain after fertilization. The cultivated common wheat (T. aestivum L.) mutation line Three Pistils (TP) carried three pistils in a floret. Although one or two of the pistils died out before seed set in some florets, there were exist many florets that set three seeds. Normally, it was observed that there were one to three seeds in different florets of the same spike. Therefore, this mutation trait could raise considerably the number of grains per spike. The weight of 100 grains in three seeds set florets was lower than that of in one seed set florets. But three seeds set florets were significantly to surpass the one seed set florets in grain(s) weight per floret. Based on these results, the three pistils trait was suggested to be an interesting germplasm resource. Localisation of the gene controlling the three pistils trait was carried out by the method of crossing TP with the Chinese Spring disomic substitutions. F2 population segregation analysis revealed that only the 5B F2 population did not show homogeneity to control population. chi2-test analysis indicated that 5B F2 population, and only this population, was deviated from the Mendelian segregation ratio (3:1). As a conclusion, the gene for three pistils trait was located on chromosome 5B. According to the Recommended rules for gene symbolization in wheat, the name of the dominant gene for three pistils trait in the line TP was suggested as Pis1.     

水稻细胞质雄性不育系及其保持系幼穗发育过程中内源激素的变化

利用酶联免疫测定技术研究了水稻细胞质雄性不育系珍汕97A及其保持系珍汕97B在幼穗发育过程中叶片、幼穗和花药中内源IAA、GA1＋4、ABA和iPAs含量的动态变化。结果表明,1）从幼穗发育的雌雄蕊形成期到三核花粉期,保持系叶片中IAA水平高于不育系,并在二核花粉期最高;在幼穗和花药中也以保持系为高。2）保持系与不育系叶片中GA1＋4含量变化趋势相似,均为先升后降,但从单核到三核花粉期以保持系为高;在幼穗和花药中也都以保持系为高。3）不育系叶片中ABA水平在幼穗发育早期明显高于保持系,中期与保持系相近,后期又高于保持系;在幼穗和花药中也都以不育系为高。4）保持系叶片、幼穗和花药中iPAs含量始终显著高于不育系。5）保持系叶片中IAA＋GA1＋4＋iPAs与ABA之比值也始终高于不育系。提示不育系叶片、幼穗和花药中IAA、GA1＋4、iPAs和ABA含量出现了异常,且IAA、GA1＋4和iPAs亏缺以及ABA盈积可能与水稻细胞质雄性不育发生有关。     

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     

Grain number determination in durum wheat as affected by drought stress: An analysis at spike and spikelet level

Yield studies show that increases in grain yield are always accompanied by an increase in grain number and, hence, further increases in yield potential may require additional improvements in grain number. The improvement of modern durum wheat was mainly based on the introduction of semidwarf genes. A 2‐year field drought stress experiment, concerning two different genotype groups (landraces vs modern cultivars), was carried out under a rainout shelter in order (a) to assess the effect of water deficit on floret dynamics and grain number determination, (b) to explore the relationship between plant water status with grain number per spike and its components (i.e., spikelets per spike, fertile florets per spikelet and grain set) and (c) to quantify the importance of several plant traits in determining the final number of grains per spike and fertile florets per spike when the main source of variation is water availability. Compared to control (well irrigated), grain number per spike was reduced, depending on year, genotype and water availability level, by 12.4–58.7% and this reduction was evident almost in all spikelet positions along the spike. Although there were some doubts in the past about the increased sensitivity of semidwarf cultivars to drought stress, they were not confirmed from our results. In most of the cases, the variation in plant water status (by means of water potential index [WPI]) during floret primordia phase (FPP) explained most of the variance in grain number per spike, fertile florets per spikelet, grain set and fertile spikelets per spike. In general, increasing water stress intensity decreased grain number per spike by an average rate of 13.5 and 9.4 grains per 0.2 MPa decrease in WPI, in modern cultivars and landraces, respectively. However, seasonal and genotypic effects were evident by modifying the slopes of the linear regressions between WPI and the studied plant traits. Commonality analysis revealed that the number of fertile florets per spikelet was the best predictor of grain number per spike, indicating that there is still much space for further improvement for this trait in landraces. However, this trait has been clearly improved in modern cultivars, especially at the basal and central spikelets. Although the number of spikelets per spike was the best unique predictor of the number of grains per spike in modern cultivars, grain set presented the highest total effect.     

Class II tassel seed mutations provide evidence for multiple types of inflorescence meristems in maize (Poaceae)

The tassel seed mutations ts4 and Ts6 of maize cause irregular branching in its inflorescences, tassels, and ears, in addition to feminization of the tassel due to the failure to abort pistils. A comparison of the development of mutant and wild-type tassels and ears using scanning electron microscopy reveals that at least four reproductive meristem types can be identified in maize: the inflorescence meristem, the spikelet pair meristem, the spikelet meristem, and the floret meristem. ts4 and Ts6 mutations affect the fate of specific reproductive meristems in both tassels and ears. ts4 mutants fail to form spikelet meristems from spikelet pair meristems. Ts6 mutants are delayed in the conversion of certain spikelet meristems into floret meristems. Once floret meristems are established in both of these mutants, they form florets that appear normal but fail to undergo pistil abortion in the tassel. The abnormal branching associated with each mutant is suppressed at the base of ears, permitting the formation of normal, fertile spikelets. The classification of the different types of reproductive meristems will be useful in interpretation of gene expression patterns in maize. It also provides a framework for understanding meristem functions that can be varied to diversify inflorescence architectures in the Gramineae.     

外源信号物质对肉苁蓉种子萌发与吸器形成内源激素水平变化的影响

利用外源信号物质氟草敏（norflurazon）和2,6-二甲氧基对苯醌（2,6-DMBQ）分别诱导肉苁蓉种子萌发与吸器形成,研究它们在此过程中对内源激素脱落酸（ABA）、赤霉素（GA3）、吲哚乙酸（IAA）、玉米素核苷（ZR）水平变化的影响。结果表明：在诱导肉苁蓉种子萌发时,经norflurazon处理0～168h后,种子中ABA水平呈现显著降低的变化趋势,GA3、IAA、ZR水平呈现显著升高的变化趋势。在诱导肉苁蓉种子萌发体吸器形成时,经2,6-DMBQ处理0～72h后,肉苁蓉种子萌发体ABA水平变化不显著,GA3、IAA、ZR水平均呈现显著升高的变化趋势。表明在肉苁蓉种子萌发与吸器形成中外源信号物质nor-flurazon和2,6-DMBQ能影响内源激素水平的变化。     

Relationship Between Male Fertility and Endogenous Phytohormones in Photoperiod-Sensitive Genic Male-Sterile Rice

A spontaneous male sterile rice plant (Oryza sativa L. cv. Nongken 58S) "Photoperiod-sensitive Genic Male-sterile Rice has been found to be male sterile under long day cycles (LD) and fertile in short day cycles (SD). The period from secondary rachis-branch and spikelet primodia to pollen mother cell formation in the process of panical development was the photoperiod-sensitive stage for fertility alternation. The phenotype of this mutant was reported to be controlled by two pairs of recessive alleles. The research on relationship between the fertility alternation and phytohormone action in this mutant have been performed by Chinese scientists since 1985. In order to study the mechanism of fertility alternation in Nongken 58S, endogenous IAA, ABA, GA1 and GA4 in apical leaves and reproductive organs in different development stages under LD and SD conditions have been quantiatvely and qualitatively identified by GC-MS-SIM method. It was found that endogenous IAA in apical leaves at the stage of pistil and stamen primodia formation and in panicles at pollen mother cell stage of Nongken 58S with LD condition was deficient comparing with those in SD. Endogenous ABA level in panicles at pollen mother cell stage, in spikelets at uninucleate stage and in anthers at anthesis stage of Nongken 58S-LD were lower than those in SD. ABA levels in corresponding organs and developmental stages of wild type of rice, "Nongken 58" were always higher in LD treatment than those in SD. Endogenous IAA, GA1 and GA4 levels in anthers at anthesis stasge of "Nongken 58"-LD were increased obviously. Thus it appeared that "Nongken 58" possess stronger resistance to LD stress than Nongken 58S. It is concluded that IAA deficiency of reproductive organs at early developmental stage, ABA decrease implying poor resistance to LD stress and reduction of GAs in late developmental stages were the factors causing the anther sterility in Nongken 58S-LD.     

Effect of abscisic and gibberellic acid on grain set in wheat

When abscisic acid was applied to wheat ears at or just before anthesis, it prevented grain set in the third floret of each spikelet but not in the lower florets. It had no effect on semi-dwarf cultivars in pot experiments, but there was a small response in a field experiment. Gibberellic acid inhibited anthesis in all florets of all cultivars.     

无花果花芽分化过程中内源激素含量的变化

无花果花芽分化过程中的花托和小花形成阶段,新梢第7或第8节位芽中,脱落酸（ABA）和玉米素核苷（ZRs）含量先升高,后保持高水平：生长素（IAA）和赤霉素（GA1＋3）含量先下降,后保持低水平。     

Phytohormone Levels in the Florets of a Single Wheat Spikelet during Pre-Anthesis Development and Relationships to Grain Set

Lee, B. T., Martin, P. and Bangerth, F. 1988. Phytohormone levelsin the florets of a single wheat spikelet during pre-anthesisdevelopment and relationships to grain set.—J. exp. Bot.39: 927–933. The gradient in grain number found within a single spikeletof wheat (higher grain numbers in proximal positions than indistal positions) was investigated with respect to endogenouslevels of hormones in anthers and carpels. Auxins, abscisicacid and cytokinins were measured using radioimmunoassay. Measurementswere made on both whole ears and floral organs (anthers andcarpels) of a single spikelet during pre-anthesis development.Similar hormonal trends in whole ears compared to those of anthersand carpels were only found for anther abscisic acid and indoleacetic acid levels and carpel zeatin/zeatin riboside levels.In the distal floret positions of the spikelet where fewer orno grains were set, anther abscisic acid levels were higherthan in those of the proximal positions. Key words: Hormones, grain, wheat.     

A new scale for the assessment of wheat spike morphogenesis

The period prior to anthesis determines to a great extent the yield in wheat by modifying the number of fertile florets and hence the number of grains per spike. For an easy and accurate identification of this period to researchers and cereal growers a simple numerical scale of wheat spike development is proposed. It includes 20 distinct stages, starting from the apex transition stage and ending just prior to heading, with the stages being separated by similar‐sized steps in thermal time to produce a continuous scale. The scale describes the whole process of wheat apical development and is convenient (e.g. uses easily detectable characters without great magnification, such as the development of awns, lemmas and glumes) and precise (e.g. uses combination of more stable characters, such as pistil and stamen development as well as the sequence of floret initiation, in order to accurately assess the development of the spike). The proposed scale was used to describe the development of the durum wheat cultivar “Mexicali 81” during two seasons. The meteorological conditions during the different cultivation seasons affected the onset and the duration of the spike developmental phases. Additionally, a variation was observed concerning the synchronisation between spike morphogenesis and plant external developmental phases (e.g. tillering, jointing and boot). The advantages of the new scale with respect to the already existing ones are discussed.     

Transcriptomes of Fruit Cavity Revealed by De Novo Sequence Analysis in Nai Plum (<Emphasis Type="Italic">Prunus salicina</Emphasis>)

Nai plum (Prunus salicina) is an important fruit crop in China having good taste and flavour. Cavity formation occurring during fruit development affects fruit quality. However, the molecular mechanism underlying cavity formation is unclear. To obtain differential expression profiles of cavity fruit (CF) and non-cavity fruit (nCF) in P. salicina, we sequenced the fruits at different time intervals of 7 days after anthesis (DAA), 21 and 28 DAA, respectively, and 83,869 unigenes, 3811 differentially expressed genes, 22,971 simple sequence repeats and over 14,000 single nucleotide polymorphisms were obtained. Twenty-three differentially expressed genes were selected for verification by qRT-PCR. The contents of phytohormones during fruit development showed that there was a positive relevance between phytohormone contents (IAA, ZR and GA), fruit size and ABA contents in the fruits, whereas there was a negative correlation with ZR, GA and IAA. Lower GA content in fruit before 14 DAA and higher IAA and ZR levels during later developmental stages resulted in cavity appearance. Further studies showed that differential expression of phytohormone-related genes IPT, CKX, YUCCA, GA20ox, GID1, CCS1 was determined at key fruit development stages, which is consistent with content changes of IAA, GA, ABA and ZR. Our results suggest that ABA might inhibit the synthesis of IAA, ZR and GA and cause fruit cavity formation in Nai plum.     

藤本月季“安吉拉”花芽分化形态结构及内源激素变化研究

以藤本月季“安吉拉”为试验材料,通过石蜡切片、体视显微镜观察及内源激素的测定,研究花芽分化过程的形态结构及内源激素的变化,为花期调控、景观品质的提升及相关育种工作提供基础数据。藤本月季“安吉拉”花芽各部分分化顺序由外向内进行,分为5个时期,共历时30 d,首先是生长锥呈圆锥状突起的形态分化期;扁平生长锥周围出现5个突起,即为萼片原基分化期;萼片原基的内方分化出成轮状的多个花瓣原基,即为花瓣原基分化期;花瓣原基基部从上向下分化出多轮雄蕊原基,即为雄蕊原基分化期;扁平的生长锥顶端突起形成多个雌蕊原基,为雌蕊原基分化期。随花芽分化进程脱落酸(ABA)、细胞分裂素(CTK)浓度变化规律相似,均呈先升高再下降趋势,萼片原基分化期其浓度均显著高于其他时期;生长素(IAA)浓度呈逐渐上升的趋势;赤霉素(GA)浓度呈逐渐下降趋势。随花芽分化进程IAA/GA和IAA/ABA比值呈逐渐上升趋势,CTK/GA和(ABA+CTK)/GA比值在萼片原基分化期显著高于形态分化期。内源激素测定结果表明:ABA、CTK浓度在萼片原基分化期显著升高与花芽分化诱导有关,较低的IAA浓度以及GA浓度的降低有利于藤本月季“安吉拉”的花芽分化;萼片原基分化期CTK/GA和(ABA+CTK)/GA比值升高可能与花芽分化诱导有关,高水平的IAA/ABA和IAA/GA比值可能与花器官原基的进一步发育相关。     

Possible correlation between high temperature-induced floret sterility and endogenous levels of IAA,GAs and ABA in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

In order to explore the possible physiological mechanism of high temperature induced sterility in rice, we examined the floret sterility and endogenous plant growth regulator contents in pollens of two hybrid rice cultivars Shanyou63 and Teyou559 that are tolerant and susceptible to high temperature, respectively. Indexes of floret sterility, pollen activity, and variation of endogenous indole-3-acetic acid (IAA), gibberellic acids (GAs), abscisic acid (ABA), free proline and soluble proteins in anthers were measured. We found that during the course of high temperature treatment, both cultivars exhibited a marked decrease in pollen activity, pollen germination and floret fertility; however, the high temperature tolerant Shanyou63 showed a much slower rate of decrease than the high temperature susceptible Teyou559. In addition, anthers of both cultivars displayed a decrease in the contents of IAA, GAs, free proline and soluble proteins but an increase in the ABA content. Yet compared to Teyou559, Shanyou63 retained significantly higher levels of free praline and GAs and a lower level of ABA, along with higher pollen vigour and pollen germination rate even after prolonged high temperature treatment. Our study suggests a possible correlation between pollen viability/floret sterility and high temperature-caused changes in IAA, GAs, ABA, free proline and soluble protein contents. The severity in these changes may reflect the variation of rice cultivars in their heat stress sensitivities for floret development.