Sucrose and starch metabolism during Fargesia yunnanensis shoot growth

Bamboo is one of the fastest growing plants in the world, but their shoot buds develop very slowly. Information about the sugar storage and metabolism during the shoot growth is lacking. In the present study, we determined the activity of sucrose and starch metabolizing enzymes during the developmental period of Fargesia yunnanensis from shoot buds to the young culms that have achieved their full height. The soluble sugars and starch contents were also determined and analyzed in shoot buds and shoots at different developmental stages. The results showed that there were higher sucrose contents in shoot buds than shoots, which coincides with the sweeter taste of shoot buds. As the shoot buds sprouted out of the ground, the starch and sucrose were depleted sharply. Coupled with this, the activity of soluble acid invertase (SAI), cell wall-bound invertase (CWI), sucrose synthase at cleavage direction (SUSYC) and starch phosphorylase (STP) increased significantly in the rapidly elongating internodes. These enzymes dominated the rapid elongation of internodes. The activities of SAI, CWI, SUSYC and STP and adenosine diphosphate-glucose pyrophosphorylase were higher as compared to other enzymes in the shoot buds, but were far lower than those in the developing shoots. The slow growth of shoot buds was correlated with the low activity of these enzymes. These results complement our understanding of the physiological differences between shoot buds and elongating shoots and ascertain the physiological mechanism for the rapid growth of bamboo shoots.