Regulatory mechanism of enhancing polyphenol oxidase activity in leaf of Basella alba induced by high temperature stress

High temperature is recognized to be a major abiotic stress involved in diverse metabolic regulation in plants. However, the regulatory mechanism of high temperature induced polyphenol oxidase (PPO) activity in Basella alba is not clarified. B. alba plants grown in pots were exposed to 45°C for 24, 48 and 72 h periods and the control plants were kept at 30°C. The PPO activity in leaves of plants was up regulated and the effects were more pronounced at 24h of treatment. To clarify the regulatory mechanism of enhancing the effect, plants were treated with 10 mM [Na.sub.2]HAs[O.sub.4] and exposed to 45°C for the above mentioned periods. [Na.sub.2]HAs[O.sub.4] along with high temperature causes similar stimulatory effects of PPO activity when compared to respective control. Therefore, both high temperature and arsenic treatment may cause additive stresses and enhance the PPO activity. To further clarify the mechanism of high temperature induced PPO activity, plants were treated with 1 mM Nifedipine, a recognized calcium channel blocker and exposed to 45°C. Treatment with blocker effectively prevented the activity induced by high temperature almost to the control level which shows clearly that high temperature-induced activity is mediated through calcium channel and may affect cellular concentration of calcium. The results suggests that increased PPO activity might be due to oxidative stress and that arsenic and calcium play a critical role in this phenomenon, thereby the plants survive in adverse environment.