Development of cold hardiness in Solanum tuberosum by abscisic acid and mefluidide

Solanum tuberosum, the worldwide cultivated potato, is sensitive to frosts compared to other tuber-bearing Solanum species. Its killing temperature is about -2à to -2.5°C. I It is one of the potato species that cannot be cold acclimated. Although no symptom of injury is evident after long periods of exposure to low temperatures such as 2°C. During cold acclimation, an increase in free ABA content and an increase in soluble proteins are believed to be involved in the development of cold hardiness in potato. These two events, however, were not bserved in S. tuberosum under the cold acclimation condition. Thus, the inability of S. tuberosum for cold acclimation may attribute to either the unchanged ABA content or incapable of synthesis of proteins or both in a low temperature regime. Experiments were designed with the aid of ABA, mefluidide, and cycloheximide to answer the following questions. From the mefluidide experiments that were carried out with pot-grown plants of S. tuberosum (cv. Red Pontiac), we observed that mefluidide is capable of inducing 1° to 2°C of cold hardiness in leaf tissues. The increase was observed 4 to 5 days after a foliar spray of mefluidide (15 mg/l), and the increase occurred only in warrn temperature-grown plants. The increased cold hardiness is transient. An increase in free ABA content was initiated 1 day after mefluidide treatment and peaked on day 4. Plants grown at the 5°C regime showed no increase in cold hardiness and remained unchanged in free ABA content when treated with mefluidide. These results suggest that the development of cold hardiness in S. tuberosum is correlated with an increase in endogenous ABA content. Increases in both ABA content and cold hardiness after mefluidide treatment also were observed in other plants. From the ABA and cycloheximide experiments that were carried out with plantlets of S. tuberosum stem culture, we observed that ABA induces cold hardiness in both warrn and cold temperature-grown plants. An increase of 2°C in cold hardiness was achieved. ABA-induced cold hardiness has been reported in many plants. Cycloheximide, a protein synthesis inhibitor, inhibits the development of cold hardiness induced by ABA in S. tuberosum, and the inhibition occurred in both warm and cold temperature-grown plants. Cycloheximide also inhibits the development of cold hardiness in S. commersoni, a potato that can be cold acclimated, and in wheat. These results suggest that the development of cold hardiness in S. tuberosum is related to the synthesis of proteins, and that the synthesis can occur in a low temperature regime if an increase in ABA content was present in the system. In conclusion, S. tuberosum that is unable to be cold acclimated is not due to its inability to synthesize proteins in a cold regime, but rather due to a lack of ability to increase endogenous free ABA content. The increased cold hardiness is only a couple of degrees. It is rather small compared to the ABA-induced hardiness in other species. This may be due to the limitation of the genetic potential of S. tuberosum.