Phenylalanine ammonia lyase activity and anthocyanin accumulation in the aleurone tissue

The phenylalanine ammonia lyase activity in the developing aleurone tissue of C C kernels was investigated in order to see whether there is any correlation between anthocyanin accumulation and phenylalanine ammonia lyase levels. Phenylalanine ammonia lyase was assayed (Zuker, 1965 and Saunders et al., 1975 with certain modifications) in acetone powder extracts of fresh aleurone tissue (25mM sodium borate buffer pH 8.8 with polyvinylpolypyrrolidone, mg/mg). The 3 ml reaction mixture consists of 1 ml of enzyme extract, 1 ml of sodium borate buffer and 1 ml of 10 mM L-phenylalanine. The reaction mixture was incubated at 40 C and O.D. at 290 nm was recorded at 30 and 60 minutes. One unit of enzyme activity is defined as that quantity of enzyme which catalyzes the formation of 1 µg of cinnamic acid per hour at 40 C. Protein content was estimated as per Lowry's method. The results are given in the figure.

These preliminary studies indicate that the phenylalanine ammonia Iyase activity is at a maximum in 19 DAP aleurone and gradually decreases thereafter. Aleurones from 30 DAP kernels show significantly reduced levels of phenylalanine ammonia lyase activity. Anthocyanin accumulation reaches a peak around 30 DAP and continues to remain the same or increase slightly thereafter. Further, it was found that C-I C-I aleurone extracts also show phenylalanine ammonia lyase activity, though in greatly reduced amounts during development (data not shown). It was also observed that phenylalanine ammonia lyase activity was localized primarily in aleurone (84%) compared to the endosperm (5%) and the embryo (11%) tissue. Further studies using both radioactive and non-radioactive procedures including high performance liquid chromatography are in progress (We thank Prof. E.H. Coe Jr., University of Missouri for providing us the C C and C-I C-I stocks).

Figure.

Ch. Jarayam and A. R. Reddy


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