Petal Primordia Research Articles

Morphogenesis, megagametogenesis, and microgametogenesis in Actinidia arguta flower buds

In dioecious plants, understanding sexual differentiation is important for improving cultivation techniques. Flower bud morphogenesis and gametophyte formation underlie the mechanism of sexual differentiation. Actinidia arguta (hardy kiwi) is a unisexual plant, and there have been few studies on its flower bud differentiation or gametophyte formation. We studied flower bud morphogenesis and gametophyte formation in A. arguta using paraffin sections and found that the morphogenesis of male and female flower buds was divided into six stages: the undifferentiated stage, inflorescence initials differentiation stage, calyx primordium differentiation stage, petal primordium differentiation stage, stamen primordium differentiation stage, and pistil primordium differentiation stage. Morphogenesis in the male inflorescence can reach quaternary flower primordia, and morphogenesis in the female inflorescence can reach the tertiary flower primordia, however, no Stage 4 lateral flowers in the male inflorescence or Stage 3 lateral flowers in the female inflorescence were found in natural situation. The embryo sac in female plants was a monocellular Polygonum type, and the embryo sac development in male plants was incomplete; abortion occurred before the archesporial cells developed. The male gametophyte differentiation process in the male plant was normal, with pollen grains similar in shape to a rugby ball and arranged neatly in the anther. The pollen grain differentiation in female plants was abnormal; abortion occurred at the uninucleate microspore stage, and mature pollen grains were irregularly spherical.

Screening of flower bud differentiation conditions and changes in metabolite content of Phalaenopsis pulcherrima

Using the Phalaenopsis pulcherrima (P. pulcherrima) as the test material, the optimal conditions for flower bud differentiation were selected by setting different photoperiods and temperatures. The process of flower bud differentiation was observed, and changes in the content of carbohydrates, hormones, and other metabolites during flower bud differentiation were studied. The results showed that the optimum time of illumination was 16 h. d−1 and the temperature was 30 ℃ / 25 ℃. According to the characteristics of the flower bud development of P. pulcherrima, the differentiation process can be divided into six periods: the initial differentiation phase, inflorescence primordium differentiation phase, flower primordium differentiation phase, sepal primordium differentiation phase, petal primordium differentiation phase, and column and pollinia differentiation phase. The soluble sugar content in the leaves showed a trend of first increasing and then decreasing. The soluble sugar content was highest 30 days after the treatment, when the differentiation of the inflorescence primordium was completed. The starch content first decreased, then increased, and finally decreased. The starch content was lowest at 30 days of treatment and highest at 35 days. The soluble protein content in the leaves reached a maximum after 30 days of treatment. With the continuous differentiation of flower buds, the soluble protein content showed an overall decreasing trend. The zeatin (ZT) content reached a maximum at day 35, showing an overall decreasing trend from days 35 to 50 and reaching a minimum at day 50. The gibberellin (GA3) and auxin (IAA) content first decreased and then increased during the process of flower bud differentiation. The changes in soluble sugar and soluble protein content during flower bud differentiation are consistent, while the changes in GA3 and IAA are consistent.

Investigation of endogenous phytohormones and critical flowering genes during flower development in Iris germanica

With showy display and multi-color, Iris germanica (Bearded iris) is one of the most popular ornamental perennials, of which molecular mechanisms in regulation of flowering are poorly understood. The objectives of this study were to reveal profiles of endogenous phytohormones and identify critical genes in floral regulation during flower development. The development process of flowering from initiation of inflorescence to flower stem elongation was observed. Based on the observation results, plant materials at four critical development stages were collected to identify the endogenous phytochromes and genes regulating flowering by using high performance liquid chromatography (HPLC) and high-throughput RNA sequencing. The concentration of different endogenous phytohormones showed various trends at four stages. Among identified phytohormones, the concentrations of Indole-3-acetic acid (IAA) and abscisic acid (ABA) were relatively high when compared with the active forms of other phytohormones. Besides, the concentration of IAA was low at pistil and petal primordium stage under winter low temperature conditions and increased at petal and stem elongation stages, while the concentration changes of ABA showed opposite trend. With comprehensive analysis of the DEGs annotated with the GO, KEGG and NR databases, homologs of critical genes in flowering regulatory pathway, such as IgAP2, IgFRI, IgSVP, IgVIN3-1, IgVIN3-2, IgGI et al. were identified. Correlation analysis between DEGs and phytohormones showed that IgFLC, IgFRI, IgVIN3-1 had closely negative relations with IAA and positive relations with ABA. The result indicates that IgFLC, IgFRI and IgVIN3-1 might be key genes in regulation of the flowering process during the flower bud development. The profiles of endogenous phytohormones and critical flowering genes identified in this study could provide references for further research on regulation of flower time in I. germanica or other species in this genus.

Roles of the APETALA3-3 ortholog in the petal identity specification and morphological differentiation in Delphinium anthriscifolium flowers.

The genus Delphinium (Ranunculaceae) with its unique and highly complex floral structure is an ideal system to address some key questions in terms of morphological and evolutionary studies in flowers. In D. anthriscifolium, for example, the original eight petal primordia differentiate into three types at maturity (i.e., two dorsal spurred, two lateral flat, and four ventral reduced petals). The mechanisms underlying their identity determination and morphological differentiation remain unclear. Here, through a comprehensive approach combining digital gene expression (DGE) profiles, in situ hybridization, and virus-induced gene silencing (VIGS), we explore the role of the APETALLATA3-3 (AP3-3) ortholog in D. anthriscifolium. Our findings reveal that the DeanAP3-3 not only functions as a traditionally known petal identity gene but also plays a critical role in petal morphological differentiation. The DeanAP3-3 gene is expressed in all the petal primordia before their morphological differentiation at earlier stages, but shows a gradient expression level difference along the dorsventral floral axis, with higher expression level in the dorsal spurred petals, intermediate level in the lateral flat petals and lower level in the ventral reduced petals. VIGS experiments revealed that flowers with strong phenotypic changes showed a complete transformation of all the three types of petals into non-spurred sepals. However, in the flowers with moderate phenotypic changes, the transformation of spurred petals into flat petals is associated with moderate silencing of the DeanAP3-3 gene, suggesting a significant impact of expression level on petal morphological differentiation. This research also shed some insights into the role of changes in gene expression levels on morphological differentiation in plants.

An epigenetic timer regulates the transition from cell division to cell expansion during Arabidopsis petal organogenesis.

A number of studies have demonstrated that epigenetic factors regulate plant developmental timing in response to environmental changes. However, we still have an incomplete view of how epigenetic factors can regulate developmental events such as organogenesis, and the transition from cell division to cell expansion, in plants. The small number of cell types and the relatively simple developmental progression required to form the Arabidopsis petal makes it a good model to investigate the molecular mechanisms driving plant organogenesis. In this study, we investigated how the RABBIT EARS (RBE) transcriptional repressor maintains the downregulation of its downstream direct target, TCP5, long after RBE expression dissipates. We showed that RBE recruits the Groucho/Tup1-like corepressor TOPLESS (TPL) to repress TCP5 transcription in petal primordia. This process involves multiple layers of changes such as remodeling of chromatin accessibility, alteration of RNA polymerase activity, and histone modifications, resulting in an epigenetic memory that is maintained through multiple cell divisions. This memory functions to maintain cell divisions during the early phase of petal development, and its attenuation in a cell division-dependent fashion later in development enables the transition from cell division to cell expansion. Overall, this study unveils a novel mechanism by which the memory of an epigenetic state, and its cell-cycle regulated decay, acts as a timer to precisely control organogenesis.

Comparative floral development in Mimosa (Fabaceae: Caesalpinioideae) brings new insights into merism lability in the mimosoid clade.

The genus Mimosa L. (Leguminosae; Caesalpinioideae; mimosoid clade), comprising more than 500 species, is an intriguing genus because, like other members of the mimosoid clade, it presents an enormous variation in floral characteristics and high merism lability. Thus, this study aimed to elucidate the floral development and identify which ontogenetic pathways give rise to merism variation and andromonoecy in Mimosa caesalpiniifolia, M. pudica, M. bimucronata, and M. candollei. Floral buds at various stages of development and flowers were collected, fixed, and processed for surface analysis (SEM). The development of the buds is synchronous in the inflorescences. Sepals appear simultaneously as individualized primordia in M. caesalpiniifolia and in reversed unidirectional order in M. bimucronata, with union and formation of an early ring-like calyx. Petal primordia appear in unidirectional order, with a noticeably elliptical shape in M. caesalpiniifolia. The wide merism variation in Mimosa results from the absence of organs from inception in the perianth and androecium whorls: in dimerous, trimerous, or tetramerous flowers, the additional organs primordia to compose the expected pentamerous flowers are not initiated. The haplostemonous androecium of M. pudica results from the absence of antepetalous stamens from inception. In the case of intraspecific variations (instabilities), there is no initiation and subsequent abortion of organs in the events of reduction in merosity. In addition, extra primordia are initiated in supernumerary cases. On the other hand, staminate flowers originate from the abortion of the carpel. Mimosa proved to be an excellent model for studying merism variation. The lability is associated with actinomorphic and rather congested flowers in the inflorescences. Our data, in association with others of previous studies, suggest that the high lability in merism appeared in clades that diverged later in the mimosoid clade. Thus, phylogenetic reconstruction studies are needed for more robust evolutionary inferences. The present investigation of ontogenetic processes was relevant to expand our understanding of floral evolution in the genus Mimosa and shed light on the unstable merism in the mimosoid clade.

Development of Flowers Buds and Mixed Buds in the Dichasial Inflorescence of Geranium koreanum Kom. (Geraniaceae).

Flower bud differentiation is of great significance for understanding plant evolution and ecological adaptability. The development of flower buds and mixed buds in the dichasial inflorescence of Geranium koreanum was described in this paper. The morphogenesis, surface structure, and organ morphology at different growth stages of G. koreanum buds were examined in detail using scanning electron microscope and stereo microscope. The development of mixed buds started from the flattened apical meristem. The stipule and leaf primordia arose first. Subsequently, the hemispherical meristem was divided into two hemispheres, forming a terminal bud and floral bud primordia, followed by lateral bud differentiation. The formation of the terminal and lateral buds of G. koreanum was sequential and their differentiation positions were also different. The floral bud primordia would develop into two flower units and four bracts. The primordia of a flower bud first formed the sepal primordia, then the stamen and petal primordia, and finally the pistil primordia. Compared to the stamen primordia, the growth of the petal primordia was slower. Finally, all organs, especially the petals and pistil, grew rapidly. When the pistil and petals exceeded the stamens and the petals changed color, the flower bud was ready to bloom.

Sympetaly in the mimosoid clade (Leguminosae, Caesalpinioideae): An unusual trait in the rosid group

Sympetaly is a notable feature within the mimosoid clade (Leguminosae: Caesalpinioideae), specially as it is uncommon in rosids. The way the petals are organized, forming a tubular corolla by the union of the petals directly affects the perception of pollinators. This study examines whether the petal union leading to a sympetalous corolla in the mimosoid clade is widespread and whether there is variation in type and extent. For this purpose, floral buds and flowers of 16 species from 13 genera were collected, fixed, and processed for analysis by light and scanning electron microscopy. Most species studied display a pentamerous sympetalous corolla with free lobes. The petal primordia are individualized and emerge simultaneously on the floral apex, alternating with the sepal primordia. Petals remain free at the beginning of the intermediate stages of development, and subsequently, the petals curve and approach each other, and their margins touch. Epidermal papillae are found on the petals’ apical margin interconnecting the lobes, which enclose the inner organs of the floral bud. The structure of the sympetalous corolla is variable regarding the type and extent of the union. Four different types of sympetaly were found and classified as follows: 1. full connation - petals fully united along their length; 2. connation-coherence - petals genuinely united in the basal portion and coherent in the median and apical portion; 3. full coherence - petals intertwined with papillae throughout; and 4. partial coherence - free petals at the base and intertwined with papillae in the middle and apical portion. Thus, sympetaly of mimosoid legumes results from postgenital union of the petals at the apical, median, and basal regions during their development by tissue union (connation), intertwining of epidermal papillae (coherence), or both processes. The mucilage cells found along the petals guarantee the stabilization and flexibility of the tubes, in addition to contributing to the protection of the internal organs of the flower. Although more studies on floral development are needed to understand the evolution of this unusual trait, connation appears to be a derived trait within mimosoids.

Morphological Development and Nutritional Metabolism during Floral Bud Differentiation in Acca Sellowiana (Feijoa)

ABSTRACT To provide scientific and technological support for the smooth development of flowers, regulation of florescence, and cultural management, among others, this study analyzes the corresponding relationship between bioclimatology and the characteristics of growth, development, and reproductive biology of A. sellowiana. Berg (Feijoa). Therefore, through optimized paraffin sections, this study examined the floral bud differentiation in five-year-old A. sellowiana trees and analyzed the dynamic changes in carbohydrate and nitrogenous compound metabolism during floral bud differentiation and flower development under natural growth conditions. The results showed that there were six stages in the differentiation process of A. sellowiana floral buds: the initiation of differentiation, inflorescence primordium differentiation, sepal primordium differentiation, petal primordium differentiation, stamen primordium differentiation and pistil primordium differentiation. Differentiation of floral buds began in late March in the Mianyang region, China, and lasted approximately 30 days. Following bud differentiation, the growth enters a period of bud development lasting approximately five months. Throughout the entire differentiation process, the flower buds contained significantly higher levels of total sugar, starch, soluble sugar, and nucleic acid than those in the leaves, and a peak of total nitrogen, nitrate nitrogen, and sucrose during the physiological transition period. Total nucleic acid and RNA content both increased, with RNA content increasing more significantly.

TARGET OF EAT3 (TOE3) specifically regulates fruit spine initiation in cucumber (Cucumis sativus L.).

The presence or absence of spines is an important economic trait of cucumber fruit. Spines are believed to be a type of specialized trichome on the fruit surface and all the identified cucumber trichome-less mutants lack fruit spines. However, genes that specifically regulate fruit spine initiation remain to be identified. Here, we found that knocking out cucumber TARGET OF EAT3 homolog (CsTOE3), belonging to the APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) family, affected flower development, and more interestingly, inhibited cucumber fruit spine initiation. On analyzing expression patterns by qRT-PCR and in situ hybridization assay, CsTOE3 was found to be highly expressed in male and female flowers, and its mRNA accumulated in the tips of sepal and petal primordia and in the cells of fruit spines and peels. Biochemical analyses indicated that CsTOE3 directly interacts with GLABRA1 (CsGL1) and TRANSPARENT TESTA GLABRA1 (CsTTG1), which are positive regulators of trichome formation. In addition, RNA-seq showed that the transcription levels of eight ERFs were significantly upregulated in CsTOE3 knockout lines. Phytohormone content analysis also revealed a significant increase in the amount of ethylene released by CsTOE3 knockout lines; treatment with the ethylene synthesis inhibitor aminoethoxyvinyl-glycine (AVG) partly restored the spineless phenotype. Our results suggest that CsTOE3 specifically regulates fruit spine initiation but does not affect the formation of trichomes on other organs in cucumber. Our findings may have a far-reaching significance for cucumber germplasm improvement and quality breeding using fruit spines as the target trait.

RhAGL24 Regulating Auxin-Related Gene RhARF18 Affects Stamen Petaloidy in Rose

AGAMOUS-LIKE 24 (AGL24) is a key gene regulating floral transition, but its involvement in flower organ identity remains largely unknown. In this study, we found that RhAGL24 is strongly related to petal and stamen development in rose. Its expression increases rapidly at the petal primordium development stage and maintains a high level until the complete differentiation stage. RhAGL24 silencing increases the number of malformed petals and decreases the number of stamens, indicating that this gene affects stamen petaloidy. RhAG (AGAMOUS), a class C gene associated with petal and stamen development, is downregulated in RhAGL24-silenced plants. Moreover, we found that RhAGL24 could directly bind to the promoter region of RhARF18 (AUXIN RESPONSE FACTORS 18), a regulator of RhAG. Our results suggested that RhAGL24-RhARF18 module regulates stamen petaloidy in rose and provide new insights into the function of AGL24 for plants.

Is seasonal flowering time of Paphiopedilum species caused by differences in initial time of floral bud differentiation?

Members of the genus Paphiopedilum are world-famous for their large, colourful flowers, unique floral morphology and long floral lifespan. Most Paphiopedilum species bloom in spring or autumn. The control of flowering time is of great significance to the commercial production of floral crops, because it affects the sales and prices of flowers. However, the mechanism that regulates when Paphiopedilum species bloom is unclear. In the present study, floral bud initiation and development of P. micranthum (spring-flowering species with one flower per stalk), P. dianthum (autumn-flowering species with multiple flowers per stalk) and P. henryanum (autumn-flowering species with one flower per stalk) were investigated by morphological and anatomical methods. We divided Paphiopedilum floral bud differentiation into six phases: the initiation of differentiation, inflorescence primordium differentiation, flower primordium differentiation, sepal primordium differentiation, petal primordium differentiation and column primordium differentiation. We found that the timing of floral bud differentiation for the three species was synchronized when experiencing the same environment, while the period from initiation to flowering largely differed. In addition, initiation of floral bud differentiation in P. dianthum was earlier at a warmer environment. The difference in flowering time of three species was mainly caused by the duration of floral bud development, rather than the initiation time. The findings were of great significance for the cultivation and flowering regulation of Paphiopedilum species.

Flower development in Fedia graciliflora and Valerianella locusta (Valerianaceae)

Valerianaceae provides a model clade for examining diversification in floral shape, especially involving size, bilateral symmetry, asymmetry, and handedness. Fedia species have pink, strongly bilaterally symmetrical corollas while Valerianella species generally have white, near-radially symmetrical corollas. In this study we examine the early floral ontogeny of Valerianella locusta and Fedia graciliflora to compare early growth and developmental traits that may lead to the difference in their mature flowers. Fedia graciliflora and V. locusta inflorescences at varying stages of development were collected and dissected to remove subtending bracts and bracteoles. Images of floral development were taken using a stereomicroscope and a Scanning Electron Microscope. The inflorescence primordium appears to continuously bifurcate as it grows, resulting in an inflorescence with densely packed flowers of varying ages. Flowers of both F. graciliflora and V. locusta initiate petals and stamens simultaneously on a ring-like common primordium. We demonstrate that stamen primordia arise in a spiral pattern, grow faster than other organs, and dominate growth until they are nearly mature. Five petal primordia and two stamens arise in F. graciliflora. In contrast, in V. locusta which has three stamens, four petal primordia initiate, which appear as an open ring-like or U-shaped primordium with a furrow on one side. This likely provides the space for the additional large stamen. Sepal development is not evident and lobes are lacking. The gynoecium does not begin to develop until the flower bud is nearing maturity. These data provide a framework for future developmental genetic work in these species.

Comprehensive transcriptomic analysis provides new insights into the mechanism of ray floret morphogenesis in chrysanthemum

BackgroundThe ray floret shapes referred to as petal types on the chrysanthemum (Chrysanthemum × morifolium Ramat.) capitulum is extremely abundant, which is one of the most important ornamental traits of chrysanthemum. However, the regulatory mechanisms of different ray floret shapes are still unknown. C. vestitum is a major origin species of cultivated chrysanthemum and has flat, spoon, and tubular type of ray florets which are the three basic petal types of chrysanthemum. Therefore, it is an ideal model material for studying ray floret morphogenesis in chrysanthemum. Here, using morphological, gene expression and transcriptomic analyses of different ray floret types of C. vestitum, we explored the developmental processes and underlying regulatory networks of ray florets.ResultsThe formation of the flat type was due to stagnation of its dorsal petal primordium, while the petal primordium of the tubular type had an intact ring shape. Morphological differences between the two ray floret types occurred during the initial stage with vigorous cell division. Analysis of genes related to flower development showed that CYCLOIDEA genes, including CYC2b, CYC2d, CYC2e, and CYC2f, were differentially expressed in different ray floret types, while the transcriptional levels of others, such as MADS-box genes, were not significantly different. Hormone-related genes, including SMALL AUXIN UPREGULATED RNA (SAUR), GRETCHEN HAGEN3 (GH3), GIBBERELLIN 2-BETA-DIOXYGENASE 1 (GA2OX1) and APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF), were identified from 1532 differentially expressed genes (DEGs) in pairwise comparisons among the flat, spoon, and tubular types, with significantly higher expression in the tubular type than that in the flat type and potential involvement in the morphogenesis of different ray floret types.ConclusionsOur findings, together with the gene interactional relationships reported for Arabidopsis thaliana, suggest that hormone-related genes are highly expressed in the tubular type, promoting petal cell division and leading to the formation of a complete ring of the petal primordium. These results provide novel insights into the morphological variation of ray floret of chrysanthemum.

Developmental Genetics of Corolla Tube Formation: Role of the tasiRNA-ARF Pathway and a Conceptual Model.

Over 80,000 angiosperm species produce flowers with petals fused into a corolla tube. The corolla tube contributes to the tremendous diversity of flower morphology and plays a critical role in plant reproduction, yet it remains one of the least understood plant structures from a developmental genetics perspective. Through mutant analyses and transgenic experiments, we show that the tasiRNA-ARF pathway is required for corolla tube formation in the monkeyflower species Mimulus lewisii Loss-of-function mutations in the M. lewisii orthologs of ARGONAUTE7 and SUPPRESSOR OF GENE SILENCING3 cause a dramatic decrease in abundance of TAS3-derived small RNAs and a moderate upregulation of AUXIN RESPONSE FACTOR3 (ARF3) and ARF4, which lead to inhibition of lateral expansion of the bases of petal primordia and complete arrest of the upward growth of the interprimordial regions, resulting in unfused corollas. Using the DR5 auxin-responsive promoter, we discovered that auxin signaling is continuous along the petal primordium base and the interprimordial region during the critical stage of corolla tube formation in the wild type, similar to the spatial pattern of MlARF4 expression. Auxin response is much weaker and more restricted in the mutant. Furthermore, exogenous application of a polar auxin transport inhibitor to wild-type floral apices disrupted petal fusion. Together, these results suggest a new conceptual model highlighting the central role of auxin-directed synchronized growth of the petal primordium base and the interprimordial region in corolla tube formation.

Floral morphology and morphogenesis in Sanguisorba (Rosaceae): flower diversification despite petal reduction and spatial constraints

Abstract Most Rosaceae flowers are pentamerous and have petals, but subtribe Sanguisorbinae have small tetramerous (or trimerous) flowers without petals, and their floral morphology and morphogenesis remain poorly known. We investigated the floral development of three Sanguisorba spp. using scanning electron microscopy to clarify the relationship between floral development and mature flowers, with emphasis on floral constraints affecting reduction of petals, diversity of androecial patterns and the development of the gynoecium and ovule, and to clarify the pollination mechanisms in the absence of petals. All species have botryoids, with numerous flowers initiated acropetally, and the maturation of flowers follows different directions. All flowers are tetramerous and sepals emerge pairwise. No petal primordia appear. Antesepalous stamens are initiated in a pairwise manner; only S. hakusanensis has a second whorl. The ovary appears inferior by development of a cystiform hypanthium. There is only one ovule with a single integument by reduction of the inner. The space occupied by the larger sepals forces the stamens to develop sequentially. Our data demonstrate that petals are basically absent and that there is a possible shift of pollination mechanisms in Sanguisorba among the mainly wind-pollinated Sanguisorbinae, as both anemophilous and entomophilous characters are found in this genus.

A design principle for floral organ number and arrangement in flowers with bilateral symmetry.

The bilateral symmetry of flowers is a striking morphological achievement during floral evolution, providing high adaptation potential for pollinators. The symmetry can appear when floral organ primordia developmentally initiate. Primordia initiation at the ventral and dorsal sides of the floral bud is differentially regulated by several factors, including external organs of the flower and CYCLOIDEA (CYC) gene homologues, which are expressed asymmetrically on the dorso-ventral axis. It remains unclear how these factors control the diversity in the number and bilateral arrangement of floral organs. Here, we propose a mathematical model demonstrating that the relative strength of the dorsal-to-ventral inhibitions and the size of the floral stem cell region (meristem) determines the number and positions of the sepal and petal primordia. The simulations reproduced the diversity of monocots and eudicots, including snapdragon Antirrhinum majus and its cyc mutant, with respect to organ number, arrangement and initiation patterns, which were dependent on the inhibition strength. These theoretical results suggest that diversity in floral symmetry is primarily regulated by the dorso-ventral inhibitory field and meristem size during developmental evolution.

Floral ontogeny and molecular evaluation of anthocyanin biosynthesis pathway in pinwheel phenotype of Saintpaulia inontha Wendl. periclinal chimera

The color of African violet flowers (Saintpaulia ionantha Wendl.) is derived from anthocyanin pigments. A mutation in the L1 layer of the SAM suppresses the anthocyanin biosynthesis pathway and eventually generates a pinwheel phenotype of periclinal chimera (cells of different genotypes). The aim of the present research was to understand the coloration pathway of petals and how color changes with phenotype. Flower development was investigated by light and scanning electron microscopy (SEM). Expression of nine genes involved in anthocyanin biosynthesis pathway in monochromatic and pinwheel phenotypes were evaluated by Real-Time PCR. Anthocyanin present in pinwheel petals was analyzed by HPLC. Microscopic studies revealed that the ventral petals were formed before the dorsal petals and that the petal primordia separated in the early stages of floral development. Saintpaulia flower is protandry and the tapetum layer is of the secretory type. The ovules are anatropous and are within the superior ovary with lateral placentation. Gene expression analysis showed that CHS and CHI genes were expressed at all stages of floral development, but hydroxylase genes increased during intermediate stages. Biosynthetic genes were highly expressed in the purple sections of the pinwheel petals, whereas the expression of F3H gene was significantly lower in the white section. The WDR transcription factor appears to have no association with the anthocyanin biosynthesis pathway genes in the white section. HPLC analysis showed that when F3H gene expression was reduced in the white part of the petals, the product of this gene (dihydrokaempferol component) did not accumulate. Color change is one of the most effective methods to create new cultivars. Details of floral pigment biosynthesis pathway and the production of new cultivars can respond to consumer demand and market preservation.

Changes in the morphology of the bud meristem and the levels of endogenous hormones after low temperature treatment of different Phalaenopsis cultivars

Phalaenopsis (Orchidaceae) is one of the most popular and trendy potted plants in the world. In order to achieve a better understanding of the influence of cold treatment to flowering, the morphological and hormonal changes were determined in three Phalaenopsis cultivars during flower bud differentiation and development. It was found that the three cultivars were all coordinated by the cold-induced release of reproductive bud dormancy, which was vernalisation pathway. The morphological development of flower bud differentiation was similar in Phalaenopsis cultivars: flower organ differentiation began with the formation of the outer petal primordia, followed by the inner petal primordia and finally, by the lip and column (stamen and carpel) primordia. The earlier the flower bud started differentiation, the earlier the flower bloomed. The timing of inflorescence primordium differentiation and flower bud development was controlled by plant hormones. It was found that ABA and GA3 levels of apical meristems of stalk before flower bud differentiation was high. High levels of IAA and ZR controlled the vegetative growth phase and the floral inductive phase, like the elongation of stalk.

Low Overnight Temperature-Induced Gibberellin Accumulation Increases Locule Number in Tomato.

The number of locules in tomato affects fruit size, shape, and the incidence of malformation. Low temperature increases locule number and the incidences of malformation in tomato plants. In this study, three flower bud developmental stages (pre-flower bud differentiation, sepal and petal primordium formation, and carpel primordium formation) under different night temperatures (10, 15, and 20 °C) were used to analyze the reason behind locule number change using an RNA sequencing (RNA-seq) approach, Quantitative real-time PCR (qRT-PCR), and ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS). The results showed that the “plant hormone signal transduction”, “starch and sucrose metabolism”, and “diterpenoid biosynthesis” categories were remarkably activated during flower bud differentiation. Transcripts of gibberellin (GA)-related genes and endogenous levels of GAs were analyzed, and it was discovered that SlGA2ox genes were significantly downregulated and bioactive GA1 and GA4 accumulated at lower overnight temperature. Exogenous application of bioactive GA1, GA4, and PAC (paclobutrazol) showed that GA1 and GA4 increased the locule number, while PAC decreased the locule number. Taken together, our results suggest that lower overnight temperature reduced the expression of SlGA2ox genes, leading to GA1 and GA4 accumulation, thereby increasing locule number in tomato.