Abstract: Isolated spinach (spinacia oleracea L.) mesophyll cells, after being preilluminated for 40 min for storage photosynthates loading (14C), were shifted into CO2-free mixture for investigation of storage photosynthates degradation and its regulatory factors. The loss of fixed carbon (14C) after 30 min incubation in CO2-free mixture in light was about 20%, which was much higher than that in dark (about 4.5%). The loss of fixed carbon was apparently stimulated by the increase of light intensity or O2 concentration and depressed by DCMU or NH4C1. Moreover, the loss of fixed carbon, especially the soluble fraction, was reduced by the addition of glycolate in light but not in dark. The obvious degradation of starch in spinach mesophyll cells in CO2-free system was monitored both in light and in dark. Unlike in dark, starch degradation in light was not associated with a detectable accumulation of the soluble products (PGA, Ribulose5-phosphate, sucrose etc.). Based on the above results, the different metabolic patterns for the products of starch degradation in light and in dark were discussed and the possible physiological roles were also proposed.

Key words: Spinacia oleracea, Mesophyll cells, CO2-free mixture, Photosynthetic energy stress, Degradation of storage photosynthates