Effects of Gibberellic Acid on Floral Development in vivo and in vitro in the Cleistogamous Species, Lamium amplexicaule L.

Using established developmental markers in the corolla and androeciumof Lamium amplexicaule L., we investigated the apparent inductionof open (chasmogamous — CH) from closed (cleistogamous— CL) flowers after application of GA₃ (0.1 mM). In vivotreatment of potentially CL flower primordia caused cell expansionbut not the increased cell division in anthers and corolla necessaryto convert a CL into a CH flower. Floral primordia that appearedto be of undetermined floral type were grown in vitro on a basalmedium supplemented with kinetin (0.1 p.p.m.) and grew to maturityas CL flowers. On media additionally supplemented with GA₃,flowers underwent anthesis, but no true CH flower was produced.Gibberellins appear to be directly responsible for anthesisin the CH flower; but additional, as yet unknown growth factorsare involved in the switch from CL to CH floral form in a developinginflorescence. floral morphogenesis, Lamium amplexicaule L, henbit, cleistogamy, gibberellin, kinetin, anthesis     

INTRA-INFLORESCENCE VARIABILITY IN POLLEN/OVULE RATIOS IN THE CLEISTOGAMOUS SPECIES LAMIUM AMPLEXICAULE (LABIATAE)

A comparative study was made of the various floral forms in the main shoot inflorescence of the cleistogamous species Lamium amplexicaule L. (Labiatae). This study revealed significant differences in pollen/ovule (P/O) ratios between successively produced flowers. The variation in P/O ratio is due to a change in pollen count/flower and not in ovule number. The study included two plant populations, one grown in November when only closed flowers are produced, and the other grown in April when open flower production occurs at the upper nodes. The intra-inflorescence variation in P/O ratio among the spring population showed a correlation between P/O ratio and breeding system. The cleistogamous flowers had low P/O ratios of about 200 while the chasmogamous flowers had higher P/O ratios of about 600.     

EFFECTS OF WATER STRESS,ABSCISIC ACID,AND GIBBERELLIC ACID ON FLOWER PRODUCTION AND DIFFERENTIATION IN THE CLEISTOGAMOUS SPECIES COLLOMIA GRANDIFLORA DOUGL. EX LINDL. (POLEMONIACEAE)

The effects of water stress, abscisic acid (ABA), and gibberellic acid (GA₃) on flower production and differentiation by Collomia grandiflora were investigated. An untreated plant typically produced both small, closed cleistogamous (CL) and large, open chasmogamous (CH) flowers. The larger corolla of CH flowers was due to a greater cell number and size. When plants were water-stressed or sprayed with ABA, both the percentage of CH flowers and the total number of flowers were reduced significantly. The corolla dimensions and epidermal cell numbers and sizes of CL flowers produced by water-stressed and ABA-sprayed plants did not differ from those of CL flowers produced by control plants. Application of GA₃ to both well-watered and water-stressed plants significantly increased the percentage of CH flowers formed compared to well-watered controls. In the absence of GA₃, water-stressed plants produced almost entirely CL flowers. GA₃-sprayed plants produced CH flowers whose corolla dimensions were intermediate between those of CL and CH flowers formed by control plants. Epidermal cells of these intermediate corollas were reduced only in number and not in size when compared to control CH flowers. Endogenous levels of ABA and gibberellins may control the type of flower produced by C. grandiflora and may mediate some of the observable effects of water stress on flowering.     

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.     

Is plasticity across seasons adaptive in the annual cleistogamous plant Lamium amplexicaule?

Background and aims Many angiosperms exhibit cleistogamy, the production of both cleistogamous flowers (CL), which remain closed and obligately self-pollinated, and chasmogamous flowers (CH), which are potentially open-pollinated. The CH proportion can be plastic. Plasticity is adaptive if environmental changes can be reliably assessed and responded to with an appropriate phenotype and if plastic genotypes have higher fitness in variable environments than non-plastic ones.Methods We studied the plastic response of four natural populations from northern and southern France of an annual cleistogamous plant, Lamium amplexicaule, to predictable seasonal variation. Plants were grown in a semi-controlled environment in spring and in autumn. We assessed the variation in flower number, phenology and cleistogamy-related traits, which were all plastic with respect to season. The CH proportion was higher in spring than in autumn in all four populations.Key Results We showed significant stabilizing selection for cleistogamy traits, with higher optimal CH proportions and more pronounced stabilizing selection in spring than in autumn. Observed CH proportions were close to the predicted optimal CH proportions in each season except in autumn for southern populations, which do not experience the autumnal growing season in nature.Conclusions These results are consistent with adaptive plasticity across seasons of cleistogamy in L. amplexicaule. We propose that adaptive plasticity of cleistogamy could be driven by pollination environment variation, with CL flowers providing reproductive assurance when pollinators are scarce and CH flowers reducing the inbreeding depression in offspring when pollinators are abundant.     

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.     

Does cleistogamy variation translate into outcrossing variation in the annual species Lamium amplexicaule (Lamiaceae)?

The maintenance of cleistogamy, the ability to produce closed, obligately selfing flowers (CL), and open, potentially outcrossed flowers (CH), in different proportions, is classically explained through different morphological/physiological properties of the two floral types, but rarely as a mechanism of adjusting the outcrossing rate. We explore the link between CH proportion and overall outcrossing rate in natural populations of Lamium amplexicaule. We assessed number of calices, CH proportion, CH and overall outcrossing rate in four natural populations in two distant areas in France. In each region, we had one favorable and one unfavorable habitat population. Unfavorable habitats produce smaller plants (with fewer calices) with higher CH proportions compared to favorable habitats, regardless of the geographic origin of the populations. CH outcrossing rate did not change significantly among populations. Thus, the overall outcrossing rate in L. amplexicaule is mainly determined by the CH proportion. Contrary to the classical view, unfavorable environments in our study are associated with higher rate of chasmogamous flowers, supposedly more costly to produce. We propose that cleistogamy variation can be considered as a variation of the outcrossing rate and could be explained by classic forces driving the evolution of mating systems (inbreeding depression, pollinators’ abundance).     

Why is there variation in mean seed size among plants within single populations? test of the fertilization efficiency hypothesis

We tested the fertilization efficiency hypothesis, which attempts to explain mean seed size variation among plants within single populations, by comparing the patterns of seed size variation between chasmogamous (CH) flowers and cleistogamous (CL) flowers in Impatiens noli-tangere and Viola grypoceras, respectively. The fertilization efficiency hypothesis predicts that larger plants produce larger seeds if the number of pollen grains captured by a plant increases with increased allocation of resources to its attractive structures (e.g., corolla and nectar), but with diminishing gains. Thus, seed size should depend on plant size in seeds from CH flowers because of the diminishing gains of capturing pollen in these flowers, whereas seed size should not depend on plant size in seeds from CL flowers because CL flowers need not capture outcross pollen. We found significant positive correlations between mean seed size per plant and plant size for seeds from CH flowers in both species. However, there was no significant positive correlation between these two factors for seeds from CL flowers of both species. The results of the present investigations were thus consistent with the fertilization efficiency hypothesis.     

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     

Physiological Controls on the Production of Cleistogamous and Chasmogamous Flowers in Lamium amplexicaule L

Plants of Lamium amplexicaule, grown under short-day field conditionsin Northern California produce predominantly closed flowers.Under long-day field conditions, plants may produce up to 50per cent open flowers, the same total number of flowers beingproduced under each daylength regime. A 20 ml drop of GA₃ or GA₇ (100µM) was applied to themain shoot apex of plants growing under short-day conditions,and all subsequently produced flowers opened. CCC, an inhibitorof gibberellin synthesis, was applied (0.06 per cent) to thesoil of seedlings grown under long-day conditions. The CCC-treatedplants were dwarfed and bore only closed flowers. With GA₇ appliedexogenously to the CCC-treated shoots, inhibition was released,resulting in elongated internodes and open flower production.The timing of flower production and internodal extension inLamium amplexicaule are positively correlated. When floral primordiawere removed from main shoots, the average internode lengthsdecreased. The number of nodes produced in treated plants wasincreased as a result of flower removal. Exogenous GA₇ (10 µM)applied to the nodes from which flowers were removed resultedin internodal extension but had no effect on node number. Twoprocesses that may contribute to the control of the productionof open and closed flowers in Lamium amplexicaule are: (1) anincreasing anther sac size from lower to upper node flowersthat may exert control locally, via GN production, on corollaexpansion, and (2) a photoperiodic control. Lamium amplexicaule L, henbit, cleistogamy, chasmogamy, gibberellins, gibberellic acid (GA₃), (2 chloroethyl) trimethylammonium chloride (cycocel)     

Development of the dimorphic anthers in Collomia grandiflora; evidence for heterochrony in the evolution of the cleistogamous anther

A modification characterizing all cleistogamous species is reduction in anther size of the CL (cleistogamous or closed) flower. In Collomia grandiflora the CL anther, in addition to being smaller, has only two locules; the CH (chasmogamous or open) flower anther has four locules. As a consequence, there is a modification in CL anther shape. From initially similar primordia, a divergence in histology between the two anther forms appears at archesporial cell differentiation when only two locules are established in the CL anther. The process of form divergence in the two anther types is examined in this study using histological, allometric, and 3-D computer graphic techniques. Allometric data from SEM images demonstrates the equivalence of primordial shapes at anther inception and divergence just prior to archesporial cell division, which signals the onset of sporogenous cell proliferation. Reconstructions of the anthers at archesporial cell division stage revealed differences in external and internal form and size, features unrelated to locule number. Fewer initial archesporial cells and a shorter duration of sporogenous cell proliferation in the CL anther correlates with a smaller anther with 1/10th the number of pollen grains at maturity. The CL anther shows less cell division activity from the time of archesporial cell division and no trace of the intercalary growth which appears during meiosis in the CH anther. The divergent CL anther size and form may be attributed to an earlier onset of abaxial locule differentiation in a smaller primordium which may itself preclude adaxial locule initiation. Heterochrony, or alteration in developmental timing, is proposed as the mode of evolution of the CL from the ancestral CH form.     

The Life History of Euryale ferox Salisb. in Southwestern Japan with Special Reference to Reproductive Ecology

Abstract The life history of Euryale ferox Salisb, observed in Akashi, Southwestern Japan, is described. Cleistogamous (CL) flowers appear from early July and precocious pollination occurs. Chasmogamous (CH) flowers are seen during a limited period between mid-August and mid-September. The abundance of CH flowers varies among populations and/or from year to year. Few insects visit CH flowers and self-pollination occurs prior to anthesis. The number of seeds produced by CL flowers significantly exceeds that of CH flowers. Considering the shorter period of CH flower production and the lesser quantity of seed produced, the significance of CL flowers in the maintenance of E. ferox populations must be considered greater than that of CH flowers.     

CLEISTOGAMY IN MICROLAENA POLYNODA (GRAMINEAE): AN EXAMINATION OF SOME MODEL PREDICTIONS

A population of the cleistogamous grass, Microlaena polynoda, was investigated to determine some of the factors responsible for adjusting the balance between reproduction by chasmogamous (CH) and cleistogamous (CL) flowers, the tissue costs associated with the two reproductive modes, the fate of progeny produced by each mode, and the genetic diversity of the progeny. Cleistogamous flower production begins earlier in the season than CH flower production. There is a distinct threshold of low light intensity below which mostly CL flowers are produced. Paternal expenditure per plant is an order of magnitude larger for the CH than the CL component. The opposite relation holds for maternal expenditure. Increased maternal expenditure in the CL component may be due to greater fertilization success and retrieval of paternal costs. Cleistogamous seeds are dispersed later than CH seeds. Following dispersal, the spikelet encloses the CL seed but not the CH seed, and is responsible for inducing dormancy. The ratio of seedlings arising from CH seeds to that from CL seeds in a natural habitat is significantly lower than the ratio of estimated numbers of CH to CL seeds produced. There were no detectable polymorphisms among ten presumptive enzyme loci assayed. Many of the features associated with CH and CL reproduction in M. polynoda are in accord with the theoretical requirements for the evolution of closed flower self-pollination and the maintenance of two distinct methods of reproduction.     

THE BALANCE BETWEEN CHASMOGAMY AND CLEISTOGAMY IN COLLOMIA GRANDIFLORA (POLEMONIACEAE)

The extent of cleistogamy (CL) and chasmogamy (CH) was investigated in natural populations of Collomia grandiflora Dougl. ex Lindl. The ubiquitous occurrence of CL flowers was documented in 18 populations from throughout the geographic range of the species. The interrelationship of environmental perturbation, vegetative weight, and the balance between CH and CL flowers was investigated by means of a factorial experiment which varied plant density, incident light and soil mix. An ANOVA revealed that total plant weight increased significantly under conditions of low density, low light and low sand content, with density accounting for most of the variance in plant weight. Interactions involving density were not significant. The number of CH and CL flowers and estimated percent outcrossing increased significantly with increased plant weight, low density, low light, and low sand content, although an analysis of covariance showed that plant weight and density accounted for most of the variance in these traits. Among large, multibranched plants, the proportion of CL flowers increased in a basipetal pattern, whereas most of the CH flowers were restricted to the terminal and upper inflorescences. The smallest plants produced only a single terminal inflorescence comprising entirely CL flowers. The proportion of reproductive effort allocated to outcrossing was dependent upon plant size as estimated from total weight, whereas the proportion allocated to ***selfing was relatively independent. Studies of outcrossed vs. inbred progenies of five populations revealed little evidence for immediate inbreeding depression with respect to plant weight and the number of CH or CL flowers, but indicated that significant quantitative genetic differences exist for these traits among populations of diverse ecological or geographical origin.     

Intraspecific variation in life history traits of Viola brevistipulata (Violaceae) in Hokkaido

Intraspecific life‐history variations of Viola brevistipulata var. brevistipulata were examined with special reference to reproductive features based on quantitative and qualitative monitoring of chasmogamous (CH) and cleistogamous (CL) flowers. We selected 10 populations in southwestern Hokkaido in common deciduous forests, and marked 40–70 individual plants at each population. Marked individuals were monitored every 1–2 weeks. The expression of CH and CL flowers was distinct among the populations. That is, there were populations consisting of plants with only CH flowers, while other populations produced CL flowers after CH flowers with greater shoot longevity This phenomenon was observed even in populations located at the same site. The results suggest that V. brevistipulata var. brevistipulata shows distinct life‐history variations among the populations.     

THE HETEROCHRONIC ORIGIN OF THE CLEISTOGAMOUS FLOWER IN ASTRAGALUS CYMBICARPOS (FABACEAE)

Members of the species Astragalus cymbicarpos form chasmogamous and cleistogamous flowers, as well as a large variety of intermediate floral types. Bivariate allometry and Gould's clock models were used to investigate the possible heterochronic evolution of the cleistogamous flower from the chasmogamous flower. In three of the whorls analyzed (pistil, stamens, and corolla) comparison of chasmogamous, pseudocleistogamous, and cleistogamous flowers revealed a progressive “juvenilization” of the adult form. This paedomorphic morphology proved to be partly the result of a process of progenesis, also evident in acceleration of sexual maturity. The retardation of shape with respect to size in these three whorls suggests, however, the existence of a heterochronic process other than progenesis.     

CLEISTOGAMY IN SALPIGLOSSIS SINUATA

Cleistogamy in Salpiglossis sinuata L. (Solanaceae) involves a series of developmental events that includes germination of pollen tetrads en masse inside the anther, penetration of pollen tubes through the anther wall toward the stigma which is in contact with the anther, growth of pollen tubes down the style, and, finally, fertilization. This occurs within 6 days from the first appearance of the flower as compared to 10–12 days for normal anthesis of chasmogamous flowers. Coincident with these events in cleistogamous flowers are lack of corolla development and reduced size of androecium and gynoecium.     

CHASMOGAMY/CLEISTOGAMY IN TRIODANIS PERFOLIATA (CAMPANULACEAE): SOME CH/CL COMPARISONS IN FITNESS PARAMETERS

The chasmogamous/cleistogamous (CH/CL) breeding system has evolved independently many times, but its ecological role has been studied in few species. In Triodanis perfoliata, we studied the natural phenology of flowering and seed set, how successful CH flowers were at setting seed, whether seed from CH and CL flowers differed in germination behavior, and whether plants derived from these two seed types differed in vigor. Most notably, we found that the later the CH flowers were produced, the fewer seed they successfully matured. In general the two seed types did not show differences in germination behavior, but for some maternal parents the two seed types differed. For these, the CL seed germinated less readily. Finally, there was some indication that plants from CL seed were not as vigorous as those from CH seed.     

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.     

Cleistogamy: A tool for the study of floral morphogenesis,function and evolution

Cleistogamy—the production of open (chasmogamous—CH) and closed (cleistogamous—CL) floral forms by a species—is widespread among the angiosperms. While the CL flower is autogamous, the CH flower may provide a means for outcrossing. The term “cleistogamy” has also been used to describe other phenomena. A classification of types of cleistogamy is proposed. In this review, a restricted definition of cleistogamy is used to refer to species which show real floral dimorphisms, with divergent developmental pathways leading to CL and CH as well as intermediate floral forms. Reductions in the androecium and corolla are the most common feature of the CL flowers. The structural, developmental, and functional aspects of cleistogamy are reviewed. Evidence is presented to show that the CL flowers have modifications in their development which ensure self pollination. A proposal is made for using this phenomenon of dimorphic flower production as a system for the study of floral morphogenesis, function and evolution.