Research On Dynamic Of Starch In Hevea Brasiliensis Bark And Xylem

Starch is an important non-structural carbohydrate in higher plants. It is also the richest and most important reserve polysaccharide in plants. As the most important final product of photosynthesis, starch is widely distributed in various organs of the plant.The Starch content in the plant would change with the seasons, phenology, climate, and other physiological stress. Dynamic of starch in plants can reveal the growth and development of plants to some extent. The factors affecting the dynamic of starch in Hevea brasiliensis are more than others plants. Tapping, stimulation tapping, seasons, phenology changes and other factors affect the starch synthesis and accumulation in Hevea brasiliensi. Research on the dynamic of starch in Hevea brasiliensis can guide us arrange time and intensity of tapping legitimately.In this study, dynamic of starch in Hevea brasiliensis was researched by measuring the content of starch and soluble sugar in bark and xylem; The expression of starch synthesis key enzyme genes was analyzed to explore the relationship between starch synthesis and tapping intensity.The results indicated the level of soluble sugar in bark was much higher than that in xylem; the level of starch in xylem was much higher than that in bark. Tapping under different intensity indicated tapping under ethylene stimulation, the level of soluble sugar in bark increased, but the level of starch in xylem decreased. Sampling at different trunk height indicated the bark close to the site the secant has higher soluble sugar and starch content.while, the xylem close to the site the secant has lower soluble sugar and starch content. Soluble sugar and starch content changed with the phenological phases,that is the content of soluble sugar and starch increased with the end of tapping and reduced with the germination of the branch.One cDNA sequence of AGPase large subunit and One cDNA sequence of AGPase small subunit were isolated from Hevea brasiliensi xylem by RACE (rapid amplification of cDNA ends) technique. Named HbLSUI (GenBank accession No. KJ020930) and HbSSUl (GenBank accession No. KJ629572). Quantitative PCR indicated:tapping and ethylene stimulate tapping reduced the transcript levels of HbLSUI and HbSSUl significantly.Obviously, Soluble sugar of bark participated in the rubber synthesis metabolic directly. While, Starch distributed in the xylem as a storage material. Tapping promoted the synthesis and transformation of soluble sugar in bark. Ethylene stimulation tapping led to the decomposition of starch in the xylem. From the perspective of gene expression, The damage caused by tapping and tapping under ethylene stimulate has a negative impact on starch synthesis.The content of soluble sugar and starch in bark and xylem changes with the phenology, The content of soluble sugar in bark and starch in the xylem increased after stop tapping.while,decreased in period of budding and germination. Finally, The content of soluble sugar and starch keep stable. During this period tapping can be carried out.