ABSCISIC-ACID AND MEFLUIDIDE IN THE REGULATION OF COLD-HARDINESS DEVELOPMENT IN SOLANUM-TUBEROSUM L POTATO

Plants of Solanum tuberosum L. potato do not cold acclimate when expos ed to low temperature such as 5-degrees-C, day/night.When ABA (45 muM) was added to the culture medium, stem-cultured plantlets of S. tubero sum, cv. Red Pontiac, either grown at 20-degrees-C/15-degrees-C, day/n ight, or at 5-degrees-C, increased in cold hardiness from -2-degrees-C (killing temperature) to -4.5-degrees-C. The increase in cold hardine ss could be inhibited in both temperature regimes if cycloheximide (70 muM) was added to the culture medium at the inception of ABA treatmen t. Cycloheximide did not inhibit cold hardiness development, however, when it was added to the culture medium 3 days after ABA treatment. Wh en pot-grown plants were foliar sprayed with mefluidide (50 muM), ABA content increased from 10 nmol to 30 nmol g-1 dry weight and plants in creased in cold hardiness from -2-degrees-C to about -3.5-degrees-C. T he increases in free ABA and cold hardiness occurred only in plants gr own at 20-degrees-C/15-degrees-C; neither ABA nor cold hardiness incre ased in plants grown at 5-degrees-C. The results suggest that an incre ase in ABA and a subsequent de novo synthesis of proteins are required for the development of cold hardiness in S. tuberosum regardless of t emperature regime, and that the inability to synthesize ABA at low tem perature, rather than protein synthesis, appears to be the reason why S. tuberosum does not cold acclimate.