Callus Growth and Proline Accumulation in Response to Polyethylene Glycol-induced Osmotic Stress in Rice, Oryza sativa L.

Abstract

The responses of Hassawi rice (Oryza sativa L.) callus was studied to varying degrees of polyethylene glycol (PEG)-induced water stress including callus growth, water content and proline accumulation. To characterize callus growth in response to PEG, 2.5 g embryogenic callus was grown in 125 ml flasks containing 50 ml each of liquid MS medium supplemented with PEG (MW 8000) at 0, 50, 100, 150, 200, 250 and 300 g l-1. Results revealed that increasing water stress induced by increasing concentration of PEG caused a progressive reduction in callus fresh weight. Significant reduction in callus weight was observed in response to 50 g l-1 PEG, but the inhibitory concentration was identified to be 200 g l-1. Increasing PEG concentration was also associated with a progressive reduction in callus water content, which caused increase in proline accumulation reaching significant increase over the control at 100 g l-1 PEG. This study serves as a precursor for genetic improvement efforts to enhance the tolerance of Hassawi rice to water stress.