Changes in growth, chlorophyll content and peroxidase and alpha-amylase activities in sunflower calli after UV-C irradiation

Sunflower (Helianthus annuus L. cv. Girapac SH222) calli were induced and g rown on modified MURASHIGE & SKOOG (1962) medium. Two-month-old calli were exposed for 15 minutes to four UV-C radiation treatments : one irradiance o f 3.170 mW.cm(-2) for one day (treatment T1); one irradiance of 3.170 mW.cm -2 every day for seven days (treatment T2); one irradiance of 5.350 mW.cm(- 2) for one day (treatment T3) and one irradiance of 5.350 mW.cm(-2) for sev en days (treatment T4). Control calli were maintained under white light con ditions (treatment T0). Eight-day-old sunflower plants, grown under greenho use conditions, were also exposed to UV-C radiation (T1 and T2). Irradiated calli soon became dark and with necrotic areas, but they were more toleran t to UV irradiation than plants, since they could sustain growth. Ca2+ and K+ contents were not significantly affected in irradiated calli cells. On a calli fresh weight basis, T1 and T2 treatments resulted in a significant i ncrease of soluble protein levels. Calli cells from UV treatments suffered a significant reduction in guaiacol peroxidase activity and an increase in alpha-amylase activity. In control calli alpha-amylase activity decreased w ith time. The present study shows that sunflower calli are more tolerant to UV rays than plants, and demonstrates interactions between UV-C radiation and peroxidase and alpha-amylase activities.