Metabolic Changes Associated with the Sink-Source Transition During Sprouting of the Axillary Buds on the Sugarcane Culm

Abstract

Sucrose, glucose and fructose concentrations, and sucrolytic enzyme activities were measured in the developing shoots and internodes of sprouting sugarcane setts (Saccharum spp, variety N19). The most striking change during the sink-source transition of the internode and germination of the axillary bud is a more than five-fold induction of cell wall invertase in the germinating bud. In contrast, soluble acid invertase is the main sucrose hydrolytic activity induced in the internodal tissue. A cycle of breakdown and synthesis of sucrose was evident in both the internodes and the shoots. During shoot establishment, the sucrose content decreased and the hexose content increased in the internodal tissues while both sucrose and hexoses continuously accumulated in the shoots. Over the sprouting period internode, dry mass was reduced by 25 and 30 % in plants incubated in a dark/light cycle or total darkness, respectively. Sucrose accounted for 90 % of the dry mass loss. The most significant changes in SuSy activity are in the synthesis direction in the shoots resulting in a decrease in the breakdown/synthesis ratio. In contrast the SuSy activity in the internodal tissue decrease and more so in the synthesis activity resulting in an increase in the breakdown to synthesis ratio.