Regulation of Phenylalanine Ammonia-lyase in Germinating Lettuce Seeds (Lactuca sativa L. cv. Grand Rapids): Effects of Abscisic Acid and Water Stress

Abstract

Summary Abscisic acid (ABA) and polyethylene glycol (PEG, 35%) completely inhibited germination of Grand Rapids lettuce seeds in light. A parallel inhibition of the activity of L-phenylalanine ammonia-lyase (PAL) was also observed under these conditions. Effects of ABA were not reversed by GA 3 and only slightly reversed by benzyladenine. Seeds germinated in water showed a steady increase in PAL activity during a 20 h period. If seeds germinated in water were transferred to 0.02 mM ABA, the activity of PAL in these seeds significantly declined during the next 24 h. Transfer of germinated seeds to PEG resulted in a much faster loss of PAL activity during this period. The disappearance of PAL activity on transfer to ABA and PEG occurred with calculated half-lives of 11 and 3 h, respectively. The loss of PAL caused by PEG was readily reversible on removal of the osmoticum.