Abstract
High temperature is recognized to be a major abiotic stress involved in di verse 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 Na2HAsO4 and exposed to 45oC for the above mentioned periods. Na2HAsO4 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 en hance 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 45oC. 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 .
Highlights
Diverse environmental stresses differentially affect plant processes that lead to loss of cellular homeostasis accompanied by the formation of reactive oxygen species (ROS), which causes oxidative damage to membrane, lipids, proteins and nucleic acids (Srivalli et al, 2003)
Leaves of B. alba were exposed to high temperature for 48 h period and the average Polyphenol oxidase (PPO) activity was 13697.78 ±408.90 Unit while for the respective control plant, the enzyme activity was recorded as 11244.44 ± 540.92 Unit g–1 of leaf
The results showed that the PPO level in leaf had been enhanced (7.64%) when the plants were exposed to high temperature for 72 h when compared to control (Figure 4)
Summary
Diverse environmental stresses differentially affect plant processes that lead to loss of cellular homeostasis accompanied by the formation of reactive oxygen species (ROS), which causes oxidative damage to membrane, lipids, proteins and nucleic acids (Srivalli et al, 2003). The enzymatic destruction of phenolics is typically an oxidative process with molecular oxygen (O2) serving as the oxidant for oxidases and hydrogen peroxide (H2O2) as the oxidant for peroxidases (Mayer, 2006). Polyphenol oxidases are enzymes with molecular weight of 60 kDa located in the chloroplast bound to thylakoid membranes, belonging to a group of copper containing metalloproteins and are members of oxido-reductases that catalyze the oxidation of a wide range of phenolic compounds by utilizing molecular oxygen (Queiroz et al, 2008). In presence of atmospheric oxygen and PPO, monophenol is hydroylated to o-diphenol and diphenol can be oxidized to o-quinones which undergo polymerization to yield dark brown polymers
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
