The estimation of phenylalanine ammonia-lyase (PAL)-activity in intact cells of higher plant tissue : II. Correlations and discrepancies between activities measured in intact cells and cell-free extracts.

Fluctuations in the activity of phenylalanine ammonia-lyase (PAL) in tissues of buckwheat seedlings were monitored by an intact cell assay and compared with results obtained with the conventional in vitro assay. Good correlation between measurements with the different assays was found for PAL activity changes during 1) growth of seedlings in the dark, 2) illumination of seedlings, and 3) incubation of hypocotyl segments. When leaf disks of buckwheat, strawberry, or sunflower were allowed to float on either water or a sugar solution, PAL activities determined with the intact cell assay increased irrespective of the presence of sugar, while PAL activities determined in cell homogenates increased only in disks floating on a sugar solution. Possible explanations for these discrepancies are discussed.