Metabolic Activity of Isolated Leaf Cells of Phaseolus vulgaris in Relation to Leaf Development

Mesophyll cells were isolated from primary leaves of 5- to 21-day Phaseolus vulgaris plants. The rate of photosynthesis and respiration, and RNA, protein, and lipid synthesis was determined for these cells. Appropriate (14)C substrates and product purification procedures were used for each process prior to liquid scintillation counting. The size of the leaves increased about 5-fold between days 5 and 11, and then remained relatively constant. The greatest increase in size occurred between days 5 and 6. The age of the leaf from which the cells were isolated had a pronounced effect on the rate of all of these processes. The largest changes occurred during the period of leaf expansion (days 5-11). Initially the rate of RNA, protein, and lipid synthesis increased rapidly, maintained a maximum rate for only 1 day (day 6 or day 7), and then declined. The rate of photosynthesis increased more slowly reaching a maximum at day 9, remained relatively constant until day 15, and then declined. The rate of respiration decreased during the first 4 days to low level which was maintained throughout the experiment. The time course patterns of these biochemical processes in isolated cells were similar to those which have been reported for intact leaves. It seems that isolation of leaf cells does not modify their metabolic activity.