Important progress has been made in the study of the regulation of flowering period in China

Double-flowered calloused purpurea. Courtesy of Zeng Songjun’s team

Recently, Zeng Songjun, a researcher at the South China Botanical Garden of the Chinese Academy of Sciences, and the Institute of Environmental Horticulture of the Guangdong Academy of Agricultural Sciences have made important progress in the study of the regulation of the flowering period of the Orchid. The study was published online in Horticulture Research. Yin Yuying, a doctoral student at the South China Botanical Garden, is the first author of the paper, and Fang Lin, an associate researcher, and Zeng Songjun, a researcher, are co-corresponding authors.

The flower type of the plant of the genus Lycaena is unique and has high ornamental value, and flowering time and flowering abundance are important agronomic traits that determine the ornamental value of Lycopoda. The popular Hoodlando on the market is a cultivated single-flower hybrid, due to its diverse flowering habits, mostly adopt the production mode of natural flowering, and there is no stable flowering regulation technology, which seriously affects its industrialization development. All single-flowered orchids can differentiate multiple flower buds, but often only one can open normally, and the rest of the flower buds are often sterilized. There is currently less research on the flowering mechanism of the orchid. Exogenous gibberellin (GA) treatment is an important means to regulate flowering, and it has important scientific significance and application prospects to unlock the mechanism behind the regulation of flowering abundance and flowering period by exploring the effect of exogenous GA on flowering.

Using the single-flowered species Paphiopedilum callosum as the research material, the researchers identified its 8 main stages from vegetative growth to flowering through cytological morphological observation. Among them, the flower organ differentiation stage (stage 5) is the key stage that determines the flowering abundance. At this time, the main flower has completed the differentiation of flower organs, the secondary flower is in the initial stage of differentiation, if there is no exogenous GA treatment, the secondary flower often stops developing and fails to breed, so the top of the callosocarpus orchid often produces single flowers.

The appropriate concentration of exogenous GA treatment can advance flowering by 35 days and promote the development of corpus callosan subflower buds. Paraffin section results showed that gibberellin had no effect on the early development of corpus callosum orchid, but in the stage of flower organ differentiation, by promoting the elongation of the inflorescence axis and the development of secondary flowers, the corpus callosum orchid flowering stage was advanced and a double flower phenomenon appeared. In the stage of flower organ differentiation, exogenous GA treatment significantly reduced the content of cytokinin (CTK) in flower buds, promoted the accumulation of endogenous IAA, GA1 and GA3, and made the flower buds show high GA and low proportion of CTK/IAA levels. At the same time, exogenous GA promoted the expression of PcAP3, PcPI, and PcSEP genes in flower buds, further promoting the formation of secondary flowers.

In addition, high levels of endogenous GA promote the expression of PcXTH9 and PcTCP15, promoting esoterics. The results show that exogenous GA treatment can effectively advance flowering and promote the development of secondary flower buds, forming a double flower, and the double flower rate increased from 8.9% to 86.9%. A combined analysis based on morphology, physiology and transcriptomics found that exogenous GA treatment was achieved by promoting convulsion rather than influencing flower induction, and exogenous GA affected the development of para-flower buds by regulating the level of endogenous hormones and the expression of flower development genes.

This study is the first to elaborate the influence mechanism of exogenous GA on the flowering of Purpurea, which can provide technical support for the flowering regulation of Purpurea and can also provide a reference for further study of the flowering mechanism of Purana and other perennial non-model plants. (Source: China Science Daily Zhu Hanbin)

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