Bio-Molecular Characterization of Hibiscus rosa-sinensis L. Floral Senescence

Flower life is a rapid and highly regulated programmed process that is tightly correlated with pollination process. The signals of degenerative processes may be derived from different flower tissue. Plant hormones such as ethylene and abscisic acid (ABA) undergo strong changes and their interaction may affect flower senescence. The current study was performed on Hibiscus rosa-sinesis flowers; we suggest this species as model system to study floral senescence for various reasons: its large flowers with floral tissues are very well developed and easily separable; the flower is ephemeral, thus the entire process of flowering is short and predictable; the plant is characterized by a continuous flowering, with a turn-over of flower mid-high. To elucidate the mechanisms regulating the senescence process of ephemeral flower, it was investigated the physiological changes in ABA content and ethylene production, macro and micronutrient alteration and the content of total soluble sugars (TSS) which normally occur during flower development and senescence. The senescence of Hibiscus flower was found to be regulated by both, ethylene and ABA. To delve deeper into the transcriptional regulation of Hibiscus rosa-sinensis L. flower development and senescence, two cDNAs encoding ethylene biosynthetic genes (HrsACS and HrsACO), as well as two cDNAs encoding ethylene receptor genes HrsETR and HrsERS), were isolated and characterized upon promoters of flower senescence, such as ABA and 1-aminocyclopropane 1-carboxylic acid (ACC), or ethylene perception inhibitor, like 1-methylcyclopropene (1-MCP). It was observed that 1-MCP effectively impeded petal in-rolling in opened flower and at latter stage decreased ABA content rather than suppress ethylene evolution. ACC treatment markedly accelerated flower senescence and increased the ethylene production mainly in style-stigma plus stamens and was positively correlated with the induction of ethylene biosynthetic and receptor genes in this tissue. ABA shows a dynamic role, in fact, enhanced flower senescence, reduced the ethylene production and determined changes in the transcriptional regulation of HrsACS, HrsACO, HrsETR and HrsERS by reducing their expression levels. Moreover, this study investigated the differential hormonal profiles for both ethylene and ABA, in petals of various Hibiscus cultivars displaying different flower longevity. The ethylene production and ABA content were inversely proportional to flower longevity. In fact the longest flower life was observed in Hibiscus plants that had the lowest ethylene production and ABA content. Finally we developed a transformation and regeneration procedure that is the first to successfully produce transformed H. rosa-sinensis plants. In conclusion, these findings suggest that both ABA and ethylene are spatially and temporally involved in the differential coordination of Hibiscus flower tissue senescence and pave the way for antisense RNA interference (RNAi) and sense technologies to further characterize senescence-related genes using transgenic Hibiscus