The final split: the regulation of anther dehiscence

Controlling male fertility is an important goal for plant reproduction and selective breeding. Hybrid vigour results in superior growth rates and increased yields of hybrids compared with inbred lines; however, hybrid generation is costly and time consuming. A better understanding of anther development and pollen release will provide effective mechanisms for the control of male fertility and for hybrid generation. Male sterility is associated not only with the lack of viable pollen, but also with the failure of pollen release. In such instances a failure of anther dehiscence has the advantage that viable pollen is produced, which can be used for subsequent rescue of fertility. Anther dehiscence is a multistage process involving localized cellular differentiation and degeneration, combined with changes to the structure and water status of the anther to facilitate complete opening and pollen release. After microspore release the anther endothecium undergoes expansion and deposition of ligno-cellulosic secondary thickening. The septum separating the two locules is then enzymatically lysed and undergoes a programmed cell death-like breakdown. The stomium subsequently splits as a consequence of the stresses associated with pollen swelling and anther dehydration. The physical constraints imposed by the thickening in the endothecium limit expansion, placing additional stress on the anther, so as it dehydrates it opens and the pollen is released. Jasmonic acid has been shown to be a critical signal for dehiscence, although other hormones, particularly auxin, are also involved. The key regulators and physical constraints of anther dehiscence are discussed.     

Rapid Swelling of Pollen Grains in the Dehiscing Anther of Two-rowed Barley (Hordeum distichum L. emend. LAM .)

The role of rapid swelling of pollen grains in anther dehiscencein Hordeum distichum L. emend. L AM. and the mechanism of thisswelling were examined. Artificial opening of the floret inducedrapid swelling of pollen grains and thecae dehiscence. The thecadehisced as pollen grains became swollen and dehisced anthershad larger pollen grains than indehisced anthers. Septa in theanther segments dehisced as a result of water-induced pollenpressure. These results strongly support the theory that therapid swelling of pollen grains is a driving force for antherdehiscence. On the other hand, potassium was detected in pollengrains from dehisced anthers, but not in pollen grains in indehiscedanthers. This suggests that potassium ions function as a turgorregulator in the rapid swelling of pollen grains. The mechanismof anther dehiscence is discussed in relation to the swellingof pollen grains, as is the possible mechanism of this swelling.Copyright 2000 Annals of Botany Company Anther dehiscence, Hordeum distichum L. emend. L AM., pollen swelling, potassium ion, two-rowed barley     

高州普通野生稻主要生殖性状的数理统计分析

高州野生稻各采样点的生殖特性表现出明显的多样性。对141份野生稻的花粉育性、裂药指数、胚囊育性和结实率进行通径分析。结果表明,花粉育性、裂药指数和胚囊育性决定了结实率变异的61．17％,其中裂药指数对结实率的直接作用最大,通径系数为0．6495;花粉育性和胚囊育性对结实率的直接作用较小,通径系数分别为0．2356和0．2137,花粉育性通过裂药指数还有较大的间接通径系数（0．2960）。通过系统聚类,将高州普通野生稻分为4群,并时各群进行方差分析和邓肯氏多重比较,可归纳为：Ⅰ群的花粉育性、胚囊育性和裂药指数对结实率影响小;Ⅱ群主要由胚囊育性影响结实率;Ⅲ群主要由裂药指数影响结实率;Ⅳ群主要由花粉育性和裂药指数共同影响结实率。     

京白梨花药开裂异常的解剖学研究

比较研究了京白梨(Pyrus ussuriensis Maxim.)、鸭梨、雪花梨花药开裂特性、环境条件对花药开裂的影响以及花药开裂异常的解剖学结构,结果表明:(1)京白梨花药开裂率明显低于鸭梨和雪花梨,使其产生花粉的量较少,从而导致传粉能力较弱.(2)京白梨、鸭梨、雪花梨在环境温度为25℃,相对湿度在 60%～80%时最适宜花药开裂,但京白梨花药开裂率始终低于鸭梨和雪花梨.(3)在京白梨花药发育后期不能形成开裂腔是引起花药不开裂的主要原因,而导致开裂腔不能形成的原因可能与单核期的绒毡层细胞不退化和药室内壁细胞不进行'U'字型加厚有关.     

植物花药开裂的细胞学和分子生物学机制

植物花药开裂具有重要的生物学意义,花药开裂异常所导致的最直接后果为花粉粒不能正常散粉,影响到植物受精过程。现从细胞和分子生物学角度综述了植物花药开裂过程中花药组织的细胞结构和生理变化及调控花药开裂相关基因的分离和克隆。     

Expression of rolB in tobacco flowers affects the coordinated processes of anther dehiscence and style elongation

The effect of auxin on stamen and pistil development in tobacco flowers was investigated by means of the localized expression of rolB (root loci B), an Agrobacterium oncogene that increases auxin sensitivity in a cell-autonomous fashion. When rolB is driven by the promoter of the meiosis-specific Arabidopsis gene DMC1 (disrupted meiotic cDNA 1), expression occurs earlier in male than in female developing organs, resulting in a delay in anther dehiscence with respect to normal timing of pistil development. As a consequence of this developmental uncoupling, self-pollination is prevented in pDMC1:rolB plants. Histological analysis of pDMC1:GFP plants indicates that in tobacco, this promoter is active not only in meiocytes but also in somatic tissues of the anther. In contrast, simultaneous expression of rolB in anther and pistil somatic tissues, achieved by expressing a construct containing rolB under the control of the promoter of the petunia gene FBP7 (floral binding protein 7), results in a concomitant delay of both anther dehiscence and pistil development without affecting self-pollination of the plants. Analysis of plants harboring the pFBP7:GUS construct shows that in tobacco, this promoter is active not only in the ovules, as described for petunia, but also in pistil and anther somatic tissues involved in the dehiscence program. The delay in anther dehiscence and pistil development could be phenocopied by exogenous application of auxin. Jasmonic acid (JA) could not rescue the delay in anther dehiscence. These results suggest that auxin plays a key role in the timing of anther dehiscence, the dehiscence program is controlled by the somatic tissues of the anther, and auxin also regulates pistil development.     

The diversity of anther structures and dehiscence patterns among Hamamelididae

HUFFORD, L. D. & ENDRKSS, P. K., 1989. The diversity of anther structures and dehiscence patterns among Hamamelididae. This survey of anther structures and dehiscence patterns focuses on the range of diversity among extant Hamamelididae. The definition and structure of the anther stomium are considered in detail to provide a basis for characterizing dehiscence patterns. We are concerned particularly with the structural basis and distribution of so-called valvate dehiscence, which we define here as occurring only in those anthers that possess stomial bifurcations or markedly eccentric stomia. Valvate dehiscence is restricted to Trochodendrales and Hamamelidales among Hamamelididae, although some Hamamelidaceae possess only linear, not markedly eccentric stomia that lead to longitudinal dehiscence patterns. Anther forms are somewhat variable and do not appear to be highly correlated with stomial patterns, although stomial bifurcations occur most frequently in anthers with broad, thick connectives that extend for the full length (or nearly so) of the thecae. Valvate dehiscence usually occurs in anthers in which the pollen sacs are embedded in bulky superficial tissues. An evolutionarily secondary extension of the stomium around the thecal shoulders seems to have occurred in taxa with a nonextensive connective and may facilitate a broader anther opening in cases of longitudinal dehiscence. An endothecial-like connective hypodermis is a notable characteristic among examined 'Lower Hamamelididae' (except Disanthus) and is also present in Daphnipfiyllum and Eucommia. We hypothesize that this specialized connective hypodermis facilitates a broader opening of the anther.     

生态因子对滇重楼花药开裂的影响

滇重楼为延龄草科重楼属植物,具有极高的药用价值,由于重楼传统药用部位生长缓慢、繁殖力低下,以及人们对野生重楼资源的过度采挖使其资源日趋枯竭。滇重楼的花药在整个花期中存在开裂－关闭的现象,花药的有效闭合应是保护花粉、延长花粉寿命、增强雄性适合度的一种适应机制。该研究以滇重楼为对象,通过设计正交实验和对比实验,观测其花药开裂过程中的光照强度、温度、湿度的变化,探究光照强度、温度、湿度等生态因子对滇重楼花药开裂的影响以及滇重楼花药开裂与生态因子变化的关系。结果表明：(1)在滇重楼花药开裂的过程中,光照强度增强、温度升高、相对湿度下降;(2)温度是影响滇重楼花药开裂时间的主导因子,升温促进花药开裂,降温促进花药关闭;(3)高湿度及黑暗推迟花药开裂,但并不能阻止花药开裂;(4)低温可使滇重楼花药持续关闭,而光照强度越高,花药持续关闭所需的温度越低。该研究有利于解释滇重楼花药白天开裂夜晚关闭的现象与环境因子的关系,对滇重楼的栽培育种提供理论指导。     

外源茉莉酸甲酯通过调节相关基因表达诱导光温敏雄性不育小麦BS366离体花药开裂

植物育性与花药开裂性状相关. 茉莉酮酸甲酯(methyl jasmonic acid, MeJA)是一种植物激素,广泛参与植物的胁迫应答和生长发育过程. 植物体内存在6类基因所编码的酶共同维持茉莉酮酸(JA)代谢途径的畅通,并与植物花药开裂有关. 本研究以小麦光温敏不育系BS366为材料,于抽穗期—开花期进行穗部离体48 h的 MeJA外源处理. 分别于0、1、3、6、12、24和48 h时间点收集花药并进行RNA提取. 通过半定量RT-PCR分析发现,在内参基因甘油醛-3-磷酸脱氢酶(glyceraldehyde-3- phosphate dehydrogenase, GAPDH)表达基本一致的情况下,BS366的JA代谢途径中参与调控的6种基因均存在不同程度的诱导表达. 经MeJA 的48 h处理后的离体花药开裂程度明显增大. 本研究获得了BS366离体环境下JA代谢途径基因经MeJA诱导后表达水平的概况,并为诱导BS366花药开裂及人工调控育性,达到高效制种及繁种的目的提供了初步的理论依据.     

Mechanism of Anther Dehiscence in Rice (Oryza sativa L.)

This paper presents a new explanation of the mechanism of antherdehiscence in rice during the period from floret opening topollen dispersal. The theca dehisced on the stomium in the apicalpart and the anther wall in the basal part of the large locule.Comparison of the anther dehiscence process under various airhumidity conditions showed that the process, until the splittingat the apical and basal parts, was a moisture-requiring processwhereas the widening of the splits in both parts was a desiccatoryprocess. Observation of the anther transverse section, revealedthe marked development of the U-shaped thick cell wall in theendothecium adjacent to these two splits. From these observations,the anther dehiscence mechanism may be explained as follows.At the time of anthesis, pollen grains swell rapidly in responseto the floret opening and cause the theca to bulge, rupturingthe septum. The pollen pressure combined with the inward bendingof the locule walls adjacent to the stomium causes splittingof the stomium in the apical part of the theca. At the sametime, the septum rupture extends to the bottom of the largelocule supported by the pollen pressure. After these processes,the locule walls adjacent to both splits straighten probablydue to their water loss. This straightening widens the splitsand the swollen pollen grains overflow from the widened splits.Copyright1999 Annals of Botany Company Anther dehiscence, Oryza sativa L., pollen grain swelling, rice, septum, stomium, theca.     

THE PROCESSES OF ANTHER DEHISCENCE AND POLLEN DISPERSAL III. THE DEHYDRATION OF THE FILAMENT TIP AND THE ANTHER IN THREE MONOCOTYLEDONOUS SPECIES

The relationship between anther dehiscence and dehydration of the filament tip and the connective tissue were followed in Gasteria verrucosa (Mill.) H. Duval, Allium cepa L. and Lilium hybrida cv.'Enchantment'using various microscopical techniques, including direct observations of living tissues in the SEM.
In G. verrucosa anther dehiscence immediately follows anthesis, with concomitant dehydration and shrivelling of the filament tip. In L. hybrida the filament tip dehydrates and shrivels before anthesis. The anthers start to dehisce immediately after anthesis. In A. cepa the filament tip dehydrates and shrivels slowly after anthesis and dehiscence, which may take up to several days, correlates with the rate of extension of the filament.
The attenuated period of dehiscence in A. cepa may be related to the absence of stomata on the anther. Experiments on xylem conductivity and transpiration reveal that the presence of continuously open stomata on the anthers sets the time of dehiscence after anthesis in G. verrucosa and L. hybrida.
The shrinking filament tip in all three species functions as a hinge which suspends the dangling anther after dehiscence. The uniformly thickened epidermal cell walls on the anthers opposite the filament prevent the outwardly bending locule walls from embracing the filament.     

Morphological and physiological analysis of cleistogamy in barley (Hordeum vulgare)

We previously reported that cleistogamy/chasmogamy (CL/CH) of barley ( Hordeum vulgare L.) is controlled by either two tightly linked genes or one gene with multiple alleles. To clarify the morphological and physiological mechanisms of barley CL, we analysed the lodicule size and auxin response of two cultivars whose CL/CH was controlled by two different genes, cly1 and Cly2 . In both cases, lodicules of the CL parent were smaller than those of the CH parent. Analyses of lodicule size and flowering phenotype of f ₁ plants and segregation analyses of the mapping population indicated that lodicule size co-segregated with the flowering phenotype. Indole-3-acetic acid (IAA) and other synthetic auxins, such as 2,4-dichlorophenoxyacetic acid, induced abnormal flowering in CH ears, in which florets remained open for a few days instead of the normal hour or so, but not in CL ears. This auxin effect also co-segregated with the flowering phenotype. Analyses of auxin-related compounds in the floret organs revealed that the anther contained high levels of IAA, whereas indole-3-carboxylic acid, a putative decarboxylated metabolite of IAA, accumulated only in lodicules of CH plants just at flowering. These results indicate that lodicule size and auxin response are pleiotropic effects of the CL gene, which may play a role in auxin response or metabolism.     

Components of resistance to the sorghum midge, Contarinia sorghicola

Studies were conducted on components of resistance to sorghum midge on four resistant (DJ 6514, AF 28, TAM 2566 and IS 15107) and two susceptible cultivars (CSH 1 and Swarna). Data were recorded on the numbers of eggs, larvae, emerged adults and grain damage in panicles of different genotypes infested with 60 midge females/panicle under no-choice conditions. The size of floral parts (glume, lemma, palea, lodicule, stigma, style, ovary and anther), rate of grain development and tannin content of grain were measured. The lengths of glume gl and 82, lemma L1 and L2, palea, lodicule, anther, style and stigma were positively associated with susceptibility to sorghum midge. Rate of grain development (between 3rd and 7th day after anthesis) was negatively associated with susceptibility to sorghum. Tannin content of grain was also negatively correlated with midge susceptibility, although there were distinct exceptions (e.g. DJ 6514 is highly resistant bur has a low tannin content).     

Pollen semi-sterility1 encodes a kinesin-1-like protein important for male meiosis, anther dehiscence, and fertility in rice

In flowering plants, male meiosis produces four microspores, which develop into pollen grains and are released by anther dehiscence to pollinate female gametophytes. The molecular and cellular mechanisms regulating male meiosis in rice (Oryza sativa) remain poorly understood. Here, we describe a rice pollen semi-sterility1 (pss1) mutant, which displays reduced spikelet fertility (~40%) primarily caused by reduced pollen viability (~50% viable), and defective anther dehiscence. Map-based molecular cloning revealed that PSS1 encodes a kinesin-1-like protein. PSS1 is broadly expressed in various organs, with highest expression in panicles. Furthermore, PSS1 expression is significantly upregulated during anther development and peaks during male meiosis. The PSS1-green fluorescent protein fusion is predominantly localized in the cytoplasm of rice protoplasts. Substitution of a conserved Arg (Arg-289) to His in the PSS1 motor domain nearly abolishes its microtubule-stimulated ATPase activity. Consistent with this, lagging chromosomes and chromosomal bridges were found at anaphase I and anaphase II of male meiosis in the pss1 mutant. Together, our results suggest that PSS1 defines a novel member of the kinesin-1 family essential for male meiotic chromosomal dynamics, male gametogenesis, and anther dehiscence in rice.     

Epidermal jasmonate perception is sufficient for all aspects of jasmonate‐mediated male fertility in Arabidopsis

Jasmonate (JA) signaling is essential for several environmental responses and reproductive development in many plant species. In Arabidopsis thaliana, the most obvious phenotype of JA biosynthetic and perception mutants is profound sporophytic male sterility characterized by failure of stamen filament elongation, severe delay of anther dehiscence and pollen inviability. The site of action of JA in the context of reproductive development has been discussed, but the ideas have not been tested experimentally. To this end we used targeted expression of a COI1‐YFP transgene in the coi1‐1 mutant background. As COI1 is an essential component of the JA co‐receptor complex, the null coi1‐1 mutant is male sterile due to lack of JA perception. We show that expression of COI1‐YFP in the epidermis of the stamen filament and anther in coi1 mutant plants is sufficient to rescue filament elongation, anther dehiscence and pollen viability. In contrast, filament expression alone or expression in the tapetum do not restore dehiscence and pollen viability. These results demonstrate that epidermal JA perception is sufficient for anther function and pollen viability, and suggest the presence of a JA‐dependent non‐autonomous signal produced in the anther epidermis to synchronize both anther dehiscence and pollen maturation.     

The arabidopsis DELAYED DEHISCENCE1 gene encodes an enzyme in the jasmonic acid synthesis pathway

delayed dehiscence1 is an Arabidopsis T-DNA mutant in which anthers release pollen grains too late for pollination to occur. The delayed dehiscence1 defect is caused by a delay in the stomium degeneration program. The gene disrupted in delayed dehiscence1 encodes 12-oxophytodienoate reductase, an enzyme in the jasmonic acid biosynthesis pathway. We rescued the mutant phenotype by exogenous application of jasmonic acid and obtained seed set from previously male-sterile plants. In situ hybridization studies showed that during the early stages of floral development, DELAYED DEHISCENCE1 mRNA accumulated within all floral organs. Later, DELAYED DEHISCENCE1 mRNA accumulated specifically within the pistil, petals, and stamen filaments. DELAYED DEHISCENCE1 mRNA was not detected in the stomium and septum cells of the anther that are involved in pollen release. The T-DNA insertion in delayed dehiscence1 eliminated both DELAYED DEHISCENCE1 mRNA accumulation and 12-oxophytodienoate reductase activity. These experiments suggest that jasmonic acid signaling plays a role in controlling the time of anther dehiscence within the flower.     

Characterization and mapping of a new male sterility mutant of anther advanced dehiscence （t） in rice

Anther dehiscence is very important for pollen maturation and release.The mutants of anther dehiscence in rice (Oryza sativa L.) arefew,and related research remains poor.A male sterility mutant of anther dehiscence in advance,add(t),has been found in Minghui 63 and its sterility is not sensitive to thermo-photo.To learn the character of sterilization and the function of the add(t) gene,the morphological and cytological studies on the anther and pollen,the ability of the pistil being fertilized,inheritance of the mutant,and mapping of add(t)gene have been conducted.The anther size is normal but the color is white in the mutant against the natural yellow in the wild-type.The pollen is malformed,unstained,and small in the KI-I2 solution.The anther dehiscence is in advance at the bicellular pollen stage.A crossing test indicated that the grain setting ratio of the add(t) is significantly lower than that of the CMS line 2085A.The ability of the pistil being fertilized is most probably decreased by the add(t) gene.The male sterility is controlled by a single recessive gene of add(t).This gene is mapped between the markers of R02004 (InDel) and RM300 (SSR) on chromosome 2,and the genetic distance from the add(t) gene to these markers is 0.78 cM and 4.66 cM,respectively.     

Elucidating the mechanism of poricidal anther dehiscence in Miconia species (Melastomataceae)

Melastomataceae have porate anthers. However, unlike Solanaceae and many monocots, in which the poricidal dehiscence depends on the presence of a mechanical layer (often the endothecium), most members of Melastomataceae have no evident specialized layer related to the poricidal opening. The goal of this study was to characterize the tissues that form the apical pore of the anther in 10 Miconia species, which may help to understand the nearly unknown mechanism of anther dehiscence in this genus, considered to be one of the largest and most diverse New World genera. Before anthesis, the apical pores of all of the species are closed by a uniseriate epidermis, the cells of which lack a cuticle. In contrast, the epidermis of the remainder of the anther is covered by a thick, ornamented cuticle. Among Myrtales, the Melastomataceae form a clade with Alzateaceae, Crypteroniaceae and Penaeaceae, almost all of which have anthers with endothecium lacking wall thickenings. In these families, the endothecium may or may not be present in the mature anther, with degenerating cells in the latter case. Anther dehiscence does not depend on the endothecium as the mechanical layer, and this process is still not well understood. However, in the Miconia species studied here, the cuticle may prevent tissue dehydration, and the pore opening seems to be due to the passive process of dehydration taking place only in the pore region due to the absence of the cuticle.