EFFECT OF HEAT-STRESS ON ENZYMES THAT AFFECT SUCROSE LEVELS IN POTATOSHOOTS

Potato (Solanum tuberosum L,) responds to heat stress with a shift in partitioning from tubers to shoots. Enzymes responsible for sucrolysis previously have been used as Indicators of sink strength and are like ly involved in controlling flow of carbon into developing organs, Chan ges in activity of enzymes involved in sucrose metabolism were investi gated in shoots of two potato cultivars that previously were character ized as susceptible and tolerant to heat stress, Enzyme activity of su crose synthase (SS) and invertases was determined for mature leaves, y oung leaves, and stems of plants adapted to 21/19 degrees C, or after transferring plants to 29/27 degrees C for 3 days. High temperatures r esulted in a nonsignificant increase in activities of SS, acid, and ne utral invertase in young growing leaves but not in stems or; mature le aves. The combined activity of the two invertases was approximate to 4 0 times higher than SS activity in young leaves, There was no temperat ure x genotype interaction with regard to these enzymes in tile tissue s investigated, A previously reported increase in activity of sucrose- phosphate synthase in mature leaves of plants subjected to high temper ature was reversed after these plants: were returned to a normal growi ng temperature.