Poster: Photosynthesis

Abs # 310: Regulation of sucrose as an osmotic signal on starch biosynthesis of rice (O. Sativa, L) grains

Presenter:	Liang, Jiansheng , jsliang@mail.yzu.edu.cn
Authors	Liang, Jiansheng  (A)   Chen, Yun  (A)   Gao, Hongming  (A)
Affiliations:	(A): College of Bioscience & Biotechnology, Yangzhou University

Sucrose is the major end product of photosynthetic CO₂ fixation and the translocated form of sugars of plants. Sucrose is also known as a metabolic regulator at different functional levels and plays important roles in plant growth and development. During grain filling of rice, sucrose is translocated and unloaded to endosperm cells, where sucrose is metabolized into hexoses catalysized by either sucrose synthase (SuS) or invertase (IT) or both and transformed into starch. Therefore, instant sucrose level in the endosperm cells represented the balance between source and sink, as well as the major roles in source-sink signaling. Our prvious results showed that SuS activity could be a good indicator of grain sink strength. In this experiment, we used detached grain culture and isotopic labelling technique to study the roles of sucrose in regulating rice grain filling. At initial stage of grain filling(about 3 to 6 days after anthesis), sucrose content of endosperm cells increased continually and then decreased sharply and the SuS activity and starch accumulation increased significantly at the same time. The dry matter accumulation of detached grains was significantly enhanced by sucrose and glucose plus mannitol, but not glucose alone (same osmotic potential). When rice plants were fed with sucrose and labeled with ¹⁴C-CO₂, starch biosynthesis in the endosperm cells was also stimulated in comparing with that fed with glucose. Western blotting result indicated that expression of SuS protein was stimulated by high sucrose concentration. These results suggested that sucrose is as an important osmotic signaling molecule and plays a key role in regulating grain filling process of rice.