Suppression in mitochondrial electron transport is the prime cause behind stress induced proline accumulation

Exposure of six day old rice (Oryza sativa) seedlings to salt or cadmium stress lead to an increase in the level of proline with a simultaneous decline in the mitochondrial electron transport activity. Mitochondrial electron transport inhibitors - rotenone, antimycin A or potassium cyanide also stimulated proline accumulation in rice seedlings with a concurrent decline in the mitochondrial electron transport activity. Four to five fold enhancement in proline level was noted in seedlings after 48 h exposure to electron transport inhibitors. A significant rise in the level of NADH was also noted in seedlings exposed to salt stress, cadmium stress or any of the electron transport inhibitors. These results show for the first time that the suppression in the mitochondrial electron transport activity lead to proline accumulation. Our results also suggest that the increase in the ratio of NADH to NAD+ due to the suppression in mitochondrial electron transport might be the prime reason behind proline accumulation in plants exposed to environmental stresses.