The effects of daily exposure to UV-A light on phenylalanine ammonia-lyase activity during the growth of barley plants.

The activity of phenylalanine ammonia-lyase (PAL) during the life cycle of barley plants (Hordeum distichon L.) exposed to UV-A radiation (355 nm) during 15, 30 and 60 min day-1 was studied. In comparison with the control plants, a stimulatory effect on PAL activity was observed. This effect was directly related to the exposure time to UV-A radiation. It was also noted that the amount of protein extracted, decreased significantly with age increase in all treatments. The studied enzyme showed its highest activity during early stages of growth. A sharp and progressive decline in PAL activity was observed in older plants. This decrease was more evident during the development of the ear.