Cell wall metabolism during development of rambutan fruit

Abstract

SummaryCell wall metabolism during fruit development in ‘Rongrien’ rambutans (Nephelium lappaceum L.) was investigated. Around 80% of the cell wall composition in the skin and around 60% in the pulp was cellulose. The firmness of skin increased towards harvest. In the skin, water-soluble pectic substances (WSP), hemicellulose and cellulose decreased with days after full bloom (DAFB), but hexametaphosphate-soluble pectic substances (HMP) increased. Cellulose concentrations were high throughout fruit development, that is, they never fell below 27 g kg–1 FW. The inconsistency of the skin firmness with cellulose and hemicellulose suggests that if they remained at a certain minimum level, their concentrations might not be reflected in the firmness. In the skin, HMP concentrations may influence firmness. Pectin esterase (PE) activity in the skin decreased towards harvest, but endo-polygalacturonase (PG) activity increased. Thus their activities may not be associated with the cell wall polyuronide degradation in the skin. The firmness of pulp decreased towards harvest, and coincided with the changes of HMP, hemicellulose and cellulose, but WSP increased. From 56 DAFB to 98 DAFB (harvest), cellulose decreased 70% from 10 g kg–1 FW and hemicellulose decreased 60% from 5 g kg–1 FW. Although PE activity in the pulp did not change during fruit development, endo-PG increased towards harvest. This result suggests that endo-PG may relate to cell wall polyuronide degradation in the pulp. However, the WSP concentration was very low compared with other components. In contrast to the skin, the decreases of cellulose and hemicellulose may be related to the softening of pulp.