In Vitro Regeneration of Style-stigma-like Structure from Stamens of Crocus sativus

Style-stigma-like structures were regenerated from stamens of Crocus sativus L. The age of the stamen explant has an obvious effect on the induction rate. Auxin NAA. has larger effect on the induction of filament style-stigma-like structure. Auxin NAA of higher concentration can lead to higher induction rate. Temperature and light have different effects on the induction of style-stigma-like structure from anther's filament of C. sativus with exogenous hormones at different levels. Ultraviolet tests show that style-stigma-like structure from anther's filament of C. sativus contains crocin, safranal and picrocrocin, contents of which are obviously more than those contained in the style-stigma-like from style. Floral reversion was observed in the induction of style-stigma-like structure from petals, ovaries and styles.

Intrafloral differentiation of stamens in heterantherous flowers

Flowers that have heteromorphic stamens （heterantherous flowers） have intrigued many researchers ever since the phenomenon was discovered in the 19th century. The morphological differentiation in androecia has been suggested as a reflection of ＂labor division＂ in pollination in which one type of stamens attracts pollinators and satisfies their demand for pollen as food and the other satisfies the plant＇s need for safe gamete dispersal. The extent and patterns of stamen differentiation differ notably among taxa with heterantherous flowers. Seven species with heteromorphic stamens in three genera were sampled from Leguminosae and Melastomataceae, and the morphological difference of androecia, pollen content, pollen histochemistry and viability, pollen micro- morphology, as well as the main pollinators were examined and compared. Pollen number differs significantly between stamen sets of the same flower in most species investigated, and a correlation of pollen number and anther size was substantiated. Higher pollen viabilities were found in the long （pollinating） stamens of Senna alata （L.） Roxb. and S. bicapsularis （L.） Roxb. Dimorphic pollen exine ornamentation is reported here for the first time in Fordiophytonfaberi Stapf. The height of stigma and anther tips of the long stamens in natural conditions was proved to be highly correlated, supporting the hypothesis that they contact similar areas of the pollinator＇s body.

Morpho-anatomical characterization of Rhododendron subsessile Rendle,an endangered species of the Cordillera Central Range,Philippines

Conservation of endangered plant species requires a prerequisite basic knowledge of their taxonomy and ecology.Unfortunately in the Cordillera Central Range,several species have not been studied,even though this area harbors a unique type of vegetation not found in other parts of the Philippines.This study documents the morpho-anatomical characteristics of Rhododendron subsessile Rendle,one of the unique and endangered fl ora in the area.The species exhibits a morphology typical of plants in high elevations,being a hardy shrub with small tough leaves,and showy pink fl owers that rival those of commercial rhododendron species.New fi ndings on the species morphology include a variable number of corolla lobes,stamens and a description of its fruits and seeds.The anatomical features of the species are reported here for the fi rst time.The plant exhibits a typical dicot anatomy with dorsiventral leaves,woody stem and root system with the usual arrangement of periderm followed by secondary phloem,vascular cambium,secondary xylem with vessel elements and pith(in the case of the stem).A unique characteristic was identifi ed as the biseriate upper epidermis of the leaf.Documenting themorphological and anatomical features of the species should prove valuable as input baseline information in formulating measures for its conservation.

Floral Organogenesis and Ring Meristem in <i>Phytolacca</i>

To further study the floral organogenesis and discussing the floral origin of Phytolacca, the procedures of floral organogenesis were observed in Phytolacca esculenta and Phytolacca zhejiangensis. The results showed that the floral organogenesis was consistent in Phytolacca. Their sepals were 2/5 helix, and with counter-clockwise and clockwise, usually the first sepal located at non-median of abaxial side. The first sepal of Phytolacca esculenta was initiated at non-median of adaxial side. There was no evident relationship between sepal and stamen initiating position, and the stamens initiated on ring meristem, they initiated approximately at the same time, and when the androecium member was numerous, they initiated centrifugally, the outer stamen initiated irregularly. Carpel initiated alternately with inner stamens. And the carpels connected by septum, if the septum grew more, the carpel was syncarpous at morphology, otherwise the carpel was apocarpous at morphology. So the syncarpous and the apocarpous have no successively relationship on evolution. Ovule initiated inside the carpel and opposite to carpel. Androecium, carpel and ovule initiated at ring meristem.

AGAMOUS AND TERMINAL FLOWER controls floral organ identity and inflorescence development in Medicago truncatula

Angiosperms integrate a multitude of endogenous and environmental signals to control floral development,thereby ensuring reproductive success.Here,we report the identification of AGAMOUS AND TERMINAL FLOWER(AGTFL),a novel regulator of floral development in Medicago truncatula.Mutation of AGTFL led to the transformation of carpels and stamens into numerous sepals and petals and altered primary inflorescence identity.AGTFL encodes a nucleus-localized proteincontaining a putative Myb/SANT-like DNA-binding domain and a PKc kinase domain.Molecular and genetic analyses revealed that AGTFL regulates the transcription of MtAGs and MtTFL1 to control floral organ identity and inflorescence development.

Regulation of Stamen Development by Coordinated Actions of Jasmonate, Auxin, and Gibberellin in Arabidopsis

Proper stamen development is essential for plants to achieve their life cycles. Defects in stamen development will cause male sterility. A vast array of research efforts have been made to understand stamen developmental processes and reg- ulatory mechanisms over the past decades. It is so far reported that phytohormones, including jasmonate, auxin, gibberellin, brassinosteroid, and cytokinin, play essential roles in regulation of stamen development. This review will briefly summarize the molecular basis for coordinated regulation of stamen development by jasmonate, auxin, and gibberellin in Arabidopsis.

Glycerol-3-Phosphate Acyltransferase 6 （GPAT6） Is Important for Tapetum Development in Arabidopsis and Plays Multiple Roles in Plant Fertility

Glycerol-3-phosphate acyltransferase （GPAT） mediates the initial synthetic step for the formation of glycer- olipids, which act as the major components of biological membranes and the principal stored forms of energy. GPAT6 is a member of the Arabidopsis GPAT family, which is crucial for cutin biosynthesis in sepals and petals. In this work, a func- tional analysis of GPAT6 in anther development and plant fertility was performed. GPAT6 was highly expressed in the tapetum and microspores during anther development. The knockout mutant, gpat6, caused a massive reduction in seed production. This report shows that the ablation of GPAT6 caused defective tapetum development with reduced endoplas- mic reticulum （ER） profiles in the tapetum, which largely led to the abortion of pollen grains and defective pollen wall formation. In addition, pollen germination and pollen tube elongation were affected in the mutant plants. Furthermore, the double mutant analysis showed that GPAT6 and GPAT1 make joint effects on the release of microspores from tetrads and stamen filament elongation. This work shows that GPAT6 plays multiple roles in stamen development and fertility in Arabidopsis.

OsMADS16 Genetically Interacts with OsMADS3 and OsMADS58 in Specifying Floral Patterning ~in Rice

Rice （Oryza sativa） has unique floral patterns that contribute to grain yield. However, the molecular mechanism underlying the specification of floral organ identities in rice, particularly the interaction among floral homeotic genes, remains poorly understood. Here, we show that the floral homeotic gene OsMADS16 （also called SUPERWOMAN1, SPWl, a B-class gene） acts together with the rice C-class genes OsMADS3 and OsMADS58 in specifying floral organ patterning. OsMADS16 and the two C-class genes have an overlapping expression pattern in the third whorl founder cells. Compared with the single mutants, both spwl-1 osmads3-4 and spwl-1 osmads58 double mutants exhibit additional whorls of glume-like organs within the flower, particularly an extra whorl of six glume-like structures formed at the position of the wild-type stamens. These ectopic glume-like structures were shown to have palea identity through cellular observation and in situ hybridization analysis using marker genes. Our results suggest that B- and C-class genes play a key role in suppressing indeterminate growth within the floral meristem, particularly whorl-3 primordia. We also hypothesize that, in contrast to previous assumptions, the specialized spikelet organ in rice, the palea, is the counterpart of the sepal in eudicots, and the lemma is homologous to the bract.

The chromatin remodeling complex imitation of switch controls stamen filament elongation by promoting jasmonic acid biosynthesis in Arabidopsis

Plant reproduction requires the coordinated development of both male and female reproductive organs.Jasmonic acid(JA)plays an essential role in stamen filament elongation.However,the mechanism by which the JA biosynthesis genes are regulated to promote stamen elongation remains unclear.Here,we show that the chromatin remodeling complex Imitation of Switch(ISWI)promotes stamen filament elongation by regulating JA biosynthesis.We show that AT-Rich Interacting Domain 5(ARID5)interacts with CHR11,CHR17,and RLT1,several known subunits of ISWI.Mutations in ARID5 and RLTs caused a reduced seed set due to greatly shortened stamen filaments.RNA-seq analyses reveal that the expression of key genes responsible for JA biosynthesis is significantly down-regulated in the arid5 and rlt mutants.Consistently,the JA levels are drastically decreased in both arid5 and rlt mutants.Chromatin immunoprecipitationquantitative PCR analyses further show that ARID5 is recruited to the chromatin of JA biosynthesis genes.Importantly,exogenous JA treatments can fully rescue the defects of stamen filament elongation in both arid5 and rlt mutants,leading to the partial recovery of fertility.Our results provide a clue how JA biosynthesisis positively regulated by the chromatin remodeling complex ISWI,thereby promoting stamen filament elongation in Arabidopsis.

Gibberellin and Jasmonate Crosstalk during Stamen Development

Gibberellin （GA） and jasmonate （JA） are two types of phytohormones that play important roles during stamen development. For example, Arabidopsis plants deficient in either of GA or JA develop short stamens. An apparent question to ask is whether GA action and JA action during stamen filament development are independent of each other or are in a hierarchy. Recent studies showed that GA modulates the expression of genes essential for JA biosynthesis to promote JA production and high levels of JA will induce the expression of three MYB genes MYB21, MYB24 and MYB57. These three MYB genes are crucial factors for the normal development of stamen filament in Arabidopsis.

A Gene Expression Profiling of Early Rice Stamen Development that Reveals Inhibition of Photosynthetic Genes by OsMADS58

Stamen is a unique plant organ wherein germ cells or microsporocytes that commit to meiosis are initiated from somatic cells during its early developmental process. While genes determining stamen identity are known according to the ABC model of floral development, little information is available on how these genes affect germ cell initiation. By using the Affymetrix GeneChip Rice Genome Array to assess 51 279 tran- scripts, we established a dynamic gene expression profile （GEP） of the early developmental process of rice （Oryza sativa） stamen. Systematic analysis of the GEP data revealed novel expression patterns of some developmentally important genes including meiosis-, tapetum-, and phytohormone-related genes. Following the finding that a substantial amount of nuclear genes encoding photosynthetic proteins are ex- pressed at the low levels in early rice stamen, through the ChlP-seq analysis we found that a C-class MADS box protein, OsMADS58, binds many nuclear-encoded genes participated in photosystem and light reac- tions and the expression levels of most of them are increased when expression of OsMADS58 is downre- gulated in the osmads58 mutant. Furthermore, more pro-chloroplasts are observed and increased signals of reactive oxygen species are detected in the osmads58 mutant anthers. These findings implicate a novel link between stamen identity determination and hypoxia status establishment.