ENZYME-ACTIVITIES IN DEVELOPING COTTON FIBERS

The activity of various enzymes in cotton (Gossypium hirsutum L. var. Stoneville glandless) fibres was measured during fibre development wit h the aim of characterizing their physiological state during the trans ition phase between cell elongation and secondary wall formation. Buff er-soluble ATP-dependent phosphofructokinase (ATP-PFK, EC 2.7.1.11), p yrophosphate:fructose 6-P 1-phosphotransferase (PPi-PFK, EC 2.7.1.90), invertase (EC 3.2.1.26), glucose 6-P dehydrogenase (G6PDH, EC 1.1.1.4 9), UDP-glucose pyrophosphorylase (UDPG-PP, EC 2.7.7.9), acid phosphat ase (ACP, EC 3.1.2.3), isocitrate dehydrogenase (LDH, EC 1.1.1.42), as partate aminotransferase (ASAT, EC 2.6.1.1), malate dehydrogenase (MDH , EC 1.1.1.37), peroxidase (POD, EC 1.11.1.7), glutathione reductase ( GSR, EC 1.6.4.2) as well as cell-wall-bound malate dehydrogenase (cw-M DH), peroxidase (cw-POD) and acid phosphatase (cw-ACP) activities were assayed. Whereas the activities of most of the enzymes implicated in sucrose metabolism decreased, the activity of UDPG-PP was found to inc rease with fibre development. Older fibres showed increased MDH and PO D activities while GSR activity was higher in young fibres. The activi ties of ACP, IDH and ASAT remained more or less constant throughout fi bre development. The cell-wall bound enzymes cw-MDH, cw-ACP and cw-POD showed maximum activities at 16, 28 and 24 days post anthesis respect ively. Since no marked differences were observed in the proteins prese nt at the stages of cell elongation and secondary cell-wall formation the transition could be related to a shift in enzyme equilibrium.