Low-temperature effects on phenylalnine ammonia-lyase activity in gherkin seedlings.

Treatment at temperatures below 10° causes in both dark-grown and pre-irradiated gherkin seedlings a rise in the activity of the enzyme phenyl-alanine ammonia-lyase (PAL). This increase takes place both in the course of the cold treatment or after transfer to higher temperature; in the latter case, however, it is followed by a decline. The results can be explained, on the basis of evidence obtained previously, that at temperatures above 10° a PAL-inactivating system compensates for PAL synthesis and that the end products (hydroxycinnamic acids) of the reaction catalysed by PAL are involved in the induction and/or functioning of the inactivating system. It is inferred that as a consequence of the low rate of synthesis of these products at lower temperatures newly synthesized PAL is not inactivated and previously synthesized PAL is released from an enzyme-inactivator complex.