Therapong, Chacharee¹, Rupali Datta¹, Dibyendu Sarkar¹ 
(1) University of Texas at San Antonio, San Antonio, TX

ABSTRACT: Comparative Arsenic Stress Response in Monocot Seedlings

Bioavailability, uptake and phytotoxicity of arsenic in plants depend upon factors such as arsenic concentration, arsenic species, plant species etc. Phytotoxicity of arsenic results in growth inhibition, chlorosis, defoliation and water-deficiency stress. Plants respond to stress in several ways, including the activation of enzymatic antioxidative systems such as superoxide dismutase (SOD) and peroxidase (POD). We investigated the effect of sodium arsenate (0.5, 1, 2 and 3 mM) on rice and maize seedlings. Accumulation of arsenic in root and shoot tissues was measured using graphite furnace atomic absorption spectrometry. Growth inhibition was studied by monitoring root and shoot lengths as well as seedling biomass. Biochemical stress response was studied by monitoring activities of SOD and POD enzymes by native polyacrylamide gel electrophoresis followed by activity staining. We observed a progressive decrease in root/shoot lengths and biomass with increasing arsenate concentration. Significantly, rice seedlings were able to accumulate twice as much arsenic in their shoots compared to maize seedlings. While rice seedlings accumulated higher arsenic concentration in shoots, most of the arsenic in maize remained in the roots. Arsenic also induced SOD and POD enzymes, predominantly in the shoot tissues. Interestingly, at the highest arsenate concentration, a diminution in the stress response was observed in the form of decrease in enzyme activity and a decline in growth inhibition, particularly in rice seedlings. These results indicate that growth inhibition in monocot seedlings by arsenate is an outcome of strong oxidative stress, and rice seedlings are more tolerant to arsenic toxicity compared to maize.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.