A COMPARISON OF CLEISTOGAMOUS AND CHASMOGAMOUS FLORAL DEVELOPMENT IN COLLOMIA GRANDIFLORA DOUGL. EX LINDL. (POLEMONIACEAE)

An individual of Collomia grandiflora typically produces both closed or cleistogamous (CL) and open or chasmogamous (CH) flowers. The developmental origin of these dimorphic floral types within a plant was investigated using histological techniques, allometric relationships, and scanning electron microscopy. Prior to archesporal cell stage in the anthers, CL and CH meristems are indistinguishable. In the CL anther, an absence of ventral locule cell differentiation together with a shorter period of time between archesporial cell differentiation and meiosis in the two dorsal locules results in accelerated anther dehiscence and a smaller mature anther size and pollen grain number. Divergence between the CL and CH patterns of corolla development is coincident with microspore mitosis in the CH anther. At this point, there is an increase in growth in corolla length relative to growth in calyx length in the CH flower which does not occur in the CL flower. Calyx and ovary development are similar in the two floral forms; however, ovary expansion due to fertilization occurs earlier in the CL flower as a result of precocious anther development and stigma receptivity. The hypothesis that anther differentiation may trigger organ growth rate changes and differentiation events in the flower and hypothetical roles for abscisic acid and gibberellin in modifying floral development in C. grandiflora are discussed.     

COMPARATIVE FLOWER DEVELOPMENT IN THE CLEISTOGAMOUS SPECIES VIOLA ODORATA. I. A GROWTH RATE STUDY

In Viola odorata, chasmogamous (CH) or open flowers and small, short-petioled leaves are produced under 11 hr or less of daylight, cleistogamous (CL) or closed flowers and large, long-petioled leaves under 14 hr or more of daylight, and intermediate floral and leaf forms under transitional photoperiods. CL flowers are approximately four times smaller than CH flowers and differ morphologically in repressed growth of the anterior petal spur and staminal nectaries, and recurving of the style which remains enclosed within the cone formed by anther appendages. Both CH and CL shoot systems conform to a (2 + 3) phyllotaxis with minor differences in leaf divergence angles and phyllotactic indices. The larger CL leaf grows significantly faster than the CH leaf, and an increased rate of leaf initiation occurs in the CL apex represented by a plastochron of 3.4 days compared to 4.3 days in the CH apex. The plastochron index was used to indirectly age young floral primordia nondestructively until prophase of meiosis I within the anthers. This event occurs 8 days earlier in the CL than the CH flower. Time from meiosis until flower maturity, determined by direct observation, is about 14 days for the CL flower, versus 21 days for the CH flower.     

AN ANATOMICAL BASIS FOR THE DIVERGENT FLORAL FORMS IN THE CLEISTOGAMOUS SPECIES,LAMIUM AMPLEXICAULE L. (LABIATAE)

The pattern of variation in mature corolla form has been documented throughout the main shoot inflorescence of the cleistogamous species Lamium amplexicaule L. A heteroblastic development occurs within the cymose inflorescence at a single node as well as between different nodes. Variation involves an increase in cell number and expansion in the upper corolla and also an increase in cell number in the anther sacs, expressed as pollen count increases, in progressively produced flowers in the inflorescence. The corolla base region in all flowers shows an increased cell expansion from the first produced cleistogamous (CL) flowers to the later produced chasmogamous (CH) flowers which expand at anthesis. Cell numbers are equivalent in the corolla base region of all flowers. It appears that in successively produced flowers in the inflorescence, prolonged cell division and expansion occurs in both the upper corolla region and the anthers until a threshold is reached, at which point flowers may undergo anthesis and become CH. The CL corolla form in Lamium amplexicaule is not caused by a lack of cell expansion alone; rather, both cell division and expansion are arrested in the upper corolla region.     

The mac1 mutation alters the developmental fate of the hypodermal cells and their cellular progeny in the maize anther.

In angiosperm ovules and anthers, the hypodermal cell layer provides the progenitors of meiocytes. We have previously reported that the multiple archesporial cells1 (mac1) mutation identifies a gene that plays an important role in the switch of the hypodermal cells from the vegetative pathway to the meiotic (sporogenous) pathway in maize ovules. Here we report that the mac1 mutation alters the developmental fate of the hypodermal cells of the maize anther. In a normal anther a hypodermal cell divides periclinally with the inner cell giving rise to the sporogenous archesporial cells while the outer cell, together with adjacent cells, forms the primary parietal layer. The cells of the parietal layer then undergo two cycles of periclinal divisions to give rise to three wall layers. In mac1 anthers the primary parietal layer usually fails to divide periclinally so that the three wall layers do not form, while the archesporial cells divide excessively and most fail to form microsporocytes. The centrally located mutant microsporocytes are abnormal in appearance and in callose distribution and they fail to proceed through meiosis. These failures in development and function appear to reflect the failure of mac1 gene function in the hypodermal cells and their cellular progeny.     

西瓜小孢子囊发育及雄配子体发生的观察

西瓜(Citrullus lanatus)小孢子囊的孢原细胞出现在雄花原基出现后4—6天,孢原细胞数目推测只有一列;初生造孢细胞经过2—3次分裂,形成次生造孢细胞。开花前7—8天,小孢子囊发育健全,小孢子母细胞进入减数分裂期。同一花药不同花粉囊相同一药室,花粉母细胞减数分裂和小孢子的发育,并不是高度同步的。绒毡层为异型细胞,腺质绒毡层。雄配子体的发育开始于开花前6—7天,充分成熟的西瓜花粉已分裂为三细胞花粉。     

The Mechanics of the Grass Flower: Anther Dehiscence and Pollen Shedding in Maize

In this paper on the flower mechanics of the grasses, the openingmechanism of the maize anther is studied. Both the septum betweeneach two locules and the stomium of these porate-dehiscing anthersappear to be opened due to lysis of the middle lamellae of theircells. Additional mechanical force of the expanding pollen mightbe necessary to completely dissociate the parenchyma cells ofthe septum. A number of hours before anthesis the anther isstructurally able to dehisce. At anthesis the dehydrating endotheciumcells bend the locule walls bordering the pore in outward direction.Presumably evaporation is not the only cause for this dehydration. Poaceae; Zea mays ; flower; anther; dehiscence; endothecium; pollen     

Cleistogamy as a bet‐hedging strategy in Oxalis acetosella, a perennial herb

1 Phenology and reproduction were studied in three populations of the cleistogamous herb Oxalis acetosella during three growing seasons, in order to see how the balance between chasmogamous (CH) and cleistogamous (CL) reproduction varies with temporal and spatial environmental variation and with plant size. The numbers of CH and CL flower buds, flowers, immature capsules and mature capsules were counted per ramet, ramet sizes were estimated, and mature capsules were collected for seed counts.
2 Both CH and CL flower numbers were positively correlated with ramet size expressed as leaf number, but the correlation was much stronger in the CL phase. CL flower production also varied significantly between years and sites. Thus, CL production in O. acetosella was not independent of resources and climatic variation.
3 When the effects of year and site were taken into account, the probability of an individual flower developing into a mature fruit was not higher in the CL phase than in the CH phase.
4 CL production was affected by fertilization success in the CH phase. Ramets with one or more CH flowers left unfertilized generally produced more CL buds than ramets with all their CH flowers fertilized. The former group also tended to have more seeds per CL capsule.
5 Since reproductive success in the two phases varies in different temporal and spatial patterns, cleistogamy in O. acetosella is considered to be a bet‐hedging strategy optimizing reproductive output in fluctuating environments.
6 The findings of this study are in conflict with the general view on cleistogamy as a fail‐safe mechanism for back‐up seed production, unaffected by variations in resource supply and environmental conditions.     

Timing of morphological and histological development in premeiotic anthers of Nicotiana tabacum cv. Xanthi (Solanaceae)

The tobacco stamen has been the object of many developmental studies, and the organ has more recently become a model for molecular genetic studies of anther differentiation. However, the spatial and temporal details of cellular differentiation of early anther development have never been thoroughly characterized. In the present study, the age of 15 tobacco flowers from plants grown under constant light and temperature was estimated using growth analysis. Prior to tissue fixation for light microscopy, moulds of stamen and anther primordia were made with a dental impression polymer so morphological and histological observations could be made on each tissue sample. Flower ages spanned an 8-d interval during which petal and stamen initiation occurred, and sporogenous cells reached the leptonema stage of meiosis. The initial development of the tetrasporangiate anther shape largely preceded periclinal division of archesporial initials. Anatomically, periclinal divisions in the hypodermal ∗∗∗(l₂) layer were observed before archesporial initials began to divide. These data indicate differences in the cellular basis of tobacco anther development compared to earlier clonal analyses of Datura. The pattern of mitotic cell division associated with microsporangial development suggested modal peaks in division over time. The ability to estimate developmental time in the tobacco anther has implications for future studies directed at understanding mechanisms of anther evolution via heterochrony.     

DEVELOPMENT OF THE STAMINATE FLOWER IN THE DWARF MISTLETOE,ARCEUTHOBIUM

A study of the staminate flower of Arceuthobium provided information on the development of the central cushion and the archesporial cells of the anther. From this study it was not possible to substantiate claims that the central cushion of the flower represents a rudimentary pistil. The archesporium of the anther was found to be unilocular from the very beginning and not derived by a breakdown of partitions and subsequent fusion of several locules as previously reported.     

Anther ontogeny in Campsis radicans (L.) Seem. (Bignoniaceae)

In this study anther ontogeny of Campsis radicans (L.) Seem. was investigated by transmission electron microscopy and light microscopy with special reference to the development of the anther wall. The anther wall formation follows the dicotyledonous type. The differentiation in anther starts with the appearance of archesporial cells which undergo periclinal divisions to give primary parietal layer to the epidermal site and the primary sporogenous cells to the inside. The primary parietal layer also divides to form two secondary parietal layers. Later, the outer secondary parietal layer (spl1) forms the endothecium and the middle layer by periclinal division whereas the inner one (spl2) directly develops into the outer tapetum forming the inner most layer of the anther wall. The sporogenous tissue is generally organized in two rows of cells with a horseshoe-shaped outline. The remainder of the tapetum lining the sporogenous mass is derived from the connective tissue. The tapetum thus has dual origin and dimorphic. Anthers are tetrasporangiate. The wall of the anther consists of an epidermis, endothecium, middle layer, and the secretory type tapetum. Tapetal cells are usually binucleated. Epidermis and Endothecium layers of anther wall remain intact until the end of anther and pollen development; however, middle layer and tapetum disappear during development.     

Rice (Oryza sativa L.) cultivars tolerant to high temperature at flowering: anther characteristics

We examined the relationship between morphological characteristics of anthers and fertility in japonica rice cultivars subjected to high temperature (37.5(26 degrees C day/night) at flowering. Percentage fertility was negatively correlated with the number of cell layers that separated the anther locule from the lacuna that formed between the septum and the stomium. The cell layers consisted of the remaining septum and degraded tapetum, and serve to keep the adjacent two locules closed. Anther dehiscence therefore requires the rupture of the cell layers. We conclude that the tight closure of the locules by the cell layers delayed locule opening, and decreased fertility at high temperatures.     

Divergent pollination systems in the cleistogamous species,Collomia grandiflora (Polemoniaceae)

Summary A structural study of pollination in the dimorphic flowers ofCollomia grandiflora, a cleistogamous species, reveals significant differences in stigma behavior during pollination, stylar structure, the timing of generative cell division, and pollen tube growth rate patterns. The cleistogamous flower shows a loss of protandry and the stigma is receptive only after reflexing and closing of its lobes. In contrast, the chasmogamous stigma is receptive when reflexed and closes when pollen has been deposited on the lobes. Pollen tube penetration of the dry stigma papillae and entry into the style is similar in the two morphs. The chasmogamous style is solid and the cleistogamous style partly hollow. The matrix of secretion produced by the transmitting tract cells is mainly carbohydrate with a trace of lipids. It is fibrillar in nature and appears to be partly comprised of wall material from the transmitting tract cells. In the chasmogamous pollen, the generative cell enters the tube before division, which occurs between 30 and 60 min after pollination. This division correlates with an increased growth rate for the pollen tube. In the cleistogamous pollen, contact with the stigma triggers generative cell division inside the hydrated pollen grain before germination. The two resulting sperm cells exit the grain 15–30 min after pollination when the pollen tube is in the stigma lobes. The cleistogamous pollen tube shows only one phase of growth which occurs at a rate similar to that of the slow, first phase of the chasmogamous pollen.Abbreviations CH chasmogamous - CL cleistogamous - DAPI 4, 6-diamidino-2-phenylindole     

Reproductive investment in a cleistogamous morph of <Emphasis Type="Italic">Polygonum jucundum</Emphasis> (Polygonaceae)

Cleistogamy, a breeding system with permanently closed and self-pollinated flowers, is expected to assure reproductive success at a lower cost. Previous studies have inferred the occurrence of cleistogamous flowers in Polygonum, but there are no detailed studies on their reproductive investment compared with that of the chasmogamous flowers in this genus. Here, we studied a cleistogamous morph of P. jucundum to investigate the investment in pollen number, tepal and nectary size. The number of pollen grains per flower was counted with a light microscope. Nectaries and perianths were observed via scanning electron microscope and light microscopy, photographed and measured via ImageJ. The perianths of the cleistogamous flowers, as well as the pollen numbers and nectary sizes, were significantly smaller than those of the chasmogamous flowers. The pollen numbers of the CL flowers were seven times lower than those in the CH flowers. The tepal areas of the CL flowers were, on average, approximately 38% those of the CH flowers. The nectary areas of the CH flowers were almost twice those of the CL flowers. In addition, the nectaries of the cleistogamous flowers were degenerated and inconspicuous, in distinct contrast with the well-developed and conspicuous nectaries of the chasmogamous flowers. Self-fertilization was completed and produced seeds. The cleistogamous P. jucundum, compared with chasmogamous individuals, exhibited lower costs in male function, pollinator attraction and reward structure investment. This cleistogamy appears to be favourable for the plant reproduction under suboptimal conditions.     

Abnormal anther development and high sporopollenin synthesis in benzotriazole treated male sterile Helianthus annuus L

Foliar application of 1.5% benzotriazole induced 100% pollen sterility in H. annuus. Pollen abortion in treated plants was mainly associated with abnormal behaviour of tapetum. A limited number of anther locule showed early degeneration of tapetum followed by disintegration of sporogenous tissues. On the other hand, some locules showed normal development of tapetum at initial stages. However, this tapetum exhibited degenerated and non-functional cell organelles. In both these situations tapetum failed to provide proper nourishment to developing microspores. The ultrastructure of both tapetum and microspores is different from that of control material with irregularities of exine deposition, endopolyploidy of tapetal nuclei and an alteration of organelle composition being correlated with sterility. Pollen grains thus developed were devoid of nucleus and cell organelles and were complete sterile.     

A novel extinction screen in Arabidopsis thaliana identifies mutant plants defective in early microsporangial development

Few Arabidopsis mutants defective in early male or female germline development have been reported. A novel extinction screen has been devised which permits the identification of mutants deficient in the earliest stages of anther development. Using mutagenized plants carrying GUS reporter constructs driven by tapetal-specific promoters originally derived from Brassica genes, a wide spectrum of mutants have been identified in Arabidopsis, ranging from those defective in archesporial cell differentiation to others expressed later in development. Crosses between these lines and known anther development mutants have enabled the identification of lines carrying mutations in genes expressed during very early anther formation. Initial characterization reveals these early mutants fall into two classes, gne (GUS-negative) 1-like, and gne2-like. Members of the gne1 mutant class initiate all four layers of the anther wall and an appropriate number of sporogenous cells; however, as development proceeds the tapetal and middle-layer cells enlarge, eventually crushing the sporogenous cells. The gne2 class anthers are disrupted at an earlier stage, with the middle and tapetal layers failing to form, and an excess of sporogenous cells developing until the germline aborts late in meiosis II. Analysis of these mutants has already raised questions about the accuracy of current models of angiosperm anther development.     

SPATIAL AND TEMPORAL VARIATION IN CHASMOGAMY AND CLEISTOGAMY IN OXALIS MONTANA (OXALIDACEAE)

Chasmogamous (CH) and cleistogamous (CL) flower production was investigated in natural populations of the perennial herb Oxalis montana in southern Quebec, Canada. Every 10–12 days during two flowering seasons, we recorded the reproductive output of approximately 2,000 plants distributed among five forest sites. The percentage of plants flowering, proportion of flowering plants producing CH and CL flowers, CH and CL flower number per flowering plant, and the proportion of flowers that are CL differed significantly among sites and corresponded to site differences in forest type and habitat quality. Unlike patterns in most CL species, however, reproduction by cleistogamy increased in sites with habitat conditions favorable to plant growth and sexual reproduction, and decreased in less productive sites. Chasmogamous and CL flower production increased with increasing plant size but plant size explained a significantly greater proportion of the variation in CL flower numbers. The percentage of flowering plants producing CH flowers decreased between years while the proportion of CL flowers increased at all sites during the second flowering season. The somewhat unusual aspects of reproduction in Oxalis may stem from its perennial habit which allows use of stored resources in adjusting the balance of cleistogamy versus chasmogamy in different environmental regimes.     

柽柳大、小孢子发生和雌、雄配子体发育的观察

利用常规石蜡制片技术,对柽柳(Tamarix chinensis Lour.)的大、小孢子发生及雌、雄配子体发育过程进行了观察。主要结果如下:(1)花药壁由五层细胞组成,从外向内分别为表皮、药室内壁,两层中层和绒毡层。药壁的发育属于基本型。绒毡层为分泌型。(2)孢原细胞为多孢原起源。小孢子母细胞减数分裂过程中的胞质分裂为连续型,形成的四分孢子为四面体型;同一药室的小孢子母细胞减数分裂几乎完全同步。(3)成熟花粉粒为2细胞型,具3个萌发孔。(4)柽柳为三心皮构成的单室复子房,每子房具有10~20个胚珠,基底胎座,胚珠为双珠被、厚珠心、倒生型。大孢子母细胞减数分裂形成1+3排列的4个大孢子, 4个大孢子全部参与胚囊的形成。(5)胚囊发育为贝母型,反足细胞在胚囊成熟时充分发育。(6)同一朵花中,前期雄蕊的发育早于雌蕊的发育,后期当花粉成熟时,雌配子体也达到成熟,雌雄蕊发育趋于同步。     

Cleistogamy in Scutellaria indica (Labiatae): effective mating system and population genetic structure

Scutellaria indica is a perennial herb with both chasmogamous (CH) and cleistogamous (CL) flowers on the same plant in some populations, and only CL flowers in other populations. Actual seed production by CH and CL flowers was investigated in populations of S. indica. The average seed set of CL flowers was 19 times higher than CH flowers, indicating much greater fertilization success. The CL seeds were also significantly heavier than the CH seeds. However, the resource cost of producing a CH flower was much higher than that of producing a CL flower. The CH flower was approximately seven times larger, and its pollen/ovule ratio was approximately five times higher than flowers. The level and pattern of genetic diversity at both allozyme and random amplified polymorphic DNA (RAPD) levels were consistent with a predominantly selfing system in the species. The average amount of within-population genetic variation was extremely low (A = 1.025, P = 2.36%, HO = 0.001 and HE = 0.008 based on allozyme data, and P = 8.94% and HE = 0.03 based on RAPD data). At the species level, the estimates of total gene diversity (HT) were 0. 101 based on allozyme data and 0.139 based on RAPD data. A very high level of genetic differentiation occurred between populations (allozyme GST = 0.92 and RAPD GST = 0.81). Genetic drift coupled with predominant cleistogamous selfing apparently played the major role in determining the population genetic structure in S. indica. Although the features associated with CH and CL flower and seed production seem to be sufficient for the evolution of complete cleistogamy in S. indica, random fixation of alternative alleles for dimorphic or complete cleistogamy in small populations could maintain the multiple strategy of chasmogamous and cleistogamous reproduction in the species.