Abstract:

Objective: The aim of this paper is to explore the changes of cell structure and photosynthetic pigments during the formation of colorful leaves of Sasaella glabra ‘Albostriata’, as well as the relationship among leaf color, photosynthetic pigment and cell structure in different areas, so as to provide reference for clarifying the formation mechanism of striped leaves. Method: At different development stages of S. glabra ‘Albostriata’, the changes of the internal microstructure of the leaves were observed through scanning electron microscopy. The leaves were divided into yellow and green areas according to their colors, free hand sections were made, and the internal structures of the yellow and green areas of the leaves were compared under an optical microscope. Simultaneously, the contents of photosynthetic pigments and chlorophyll synthesis precursors of the leaves at each stage were determined. Result: There were significant differences in microstructure, ultrastructure, photosynthetic pigment content and chlorophyll synthesis precursor content in the leaves of S. glabra ‘Albostriata’ at different development stages, and there were also significant differences in the leaf structure and photosynthetic pigment in different zones of mature functional leaves. 1) During the development process of leaves, epidermal cells and mesophyll cells gradually increased, and the leaf vein area increased. 2）During the developmental process, chloroplasts in mesophyll cells in green stripe area developed normally and their internal structures were intact. The number of chloroplasts and grana lamellae in chloroplasts increased gradually, and their inner arrangement tended to be tight; While the differentiation degree of mesophyll cells in yellow district was relatively low. The layers of arm cells was fewer, and the mesophyll cells had large cavities and abnormal chloroplasts. 3) The leaf epidermis structure was similar in the yellow and green stripes, but the distribution position of chloroplasts in the mesophyll cells was obviously different between yellow and green stripes. Chloroplasts were distributed in all mesophyll cells of the green stripe, while they were only distributed in the mesophyll cells near the lower epidermis in the yellow stripe. 4) The content of photosynthetic pigment gradually accumulated during the development process of leaves, and the pigment content in green stripes was significantly higher than that in yellow stripes. 5) Urogen III and Coprogen III are key substances in the chlorophyll synthesis pathway during the development of bamboo leaves. With the appearance of stripes, the transformation from Urogen III to Coprogen III increased, while the conversion from Coprogen III to Proto IX was reduced. Conclusion: During the development process of bamboo leaves, the leaf thickness gradually increases, the number of epidermal cells, mesophyll cells and veins increase, and the photosynthetic pigment content accumulates. For the green stripe, the number of chloroplasts increases gradually and chlorophyll content accumulates normally with the leaf development. While the mesophyll cells in yellow stripe have large cavities and abnormal chloroplasts, with fewer layers of finger like arm cells. In general, the formation of striped leaf of S. glabra ‘Albostriata’ is related to low differentiation of arm cells, abnormal chloroplast development and obstruction of chlorophyll synthesis.

Key words: Sasaella glabra ‘Albostriata’, coloured leaf, chloroplast, photosynthetic pigment, microstructure, ultrastructure