POTATO COLD-HARDINESS DEVELOPMENT AND ABSCISIC-ACID .2. DE-NOVO SYNTHESIS OF PROTEINS IS REQUIRED FOR THE INCREASE IN FREE ABSCISIC-ACID DURING POTATO (SOLANUM-COMMERSONII) COLD-ACCLIMATION

During cold acclimation of potato plantlets (Solanum commersonii Dun, PI 458317), there are two transitory increases in free ABA content cor responding to a three-fold increase on the 2nd day and a five-fold inc rease on the 6th day (Ryu and Li 1993). During this period, plantlets increased in cold hardiness from -5-degrees-C (killing temperature, co ntrol grown at 22/18-degrees-C, day/night) to -10-degrees-C by the 7th day of exposure to 4/2-degrees-C (day/night). This increase in free A BA was not found when cycloheximide (CHI), an inhibitor of cytoplasmic protein synthesis, was added to the culture medium 6 h before exposur e to low temperatures. Plantlets treated with CHI did not acclimate to cold, maintaining a hardiness level (-5-degrees-C) similar to that of the 22/18-degrees-C-grown plantlets. When the CHI-treated plantlets w ere exposed to low temperatures for 3 days, transferred to CHI-free cu lture medium and grown at low temperatures, the plantlets showed a tra nsitory increase in free ABA 2 days later. This increase was followed by the development of cold hardiness (-8-degrees-C). Application of CH I to the culture medium after 3 days of cold acclimation, when the fir st ABA peak and a partial development of cold hardiness (-8-degrees-C) had occurred, blocked the second transitory increase in free ABA and resulted in no further development of cold hardiness. These results su ggest that de novo synthesis of proteins is required for these transit ory increases in free ABA during cold acclimation of potato plantlets.