Proline accumulation induced by excess nickel in detached rice leaves

The regulation of proline accumulation in detached rice leaves exposed to excess NiSO4 was investigated. NiSO4 treatment increased proline and Ni contents but had no effect on relative water content, indicating that proline accumulation in Ni-exposed detached rice leaves was due to Ni uptake per se, rather than to water stress. Proline accumulation caused by NiSO4 was related to protein hydrolysis, a decrease in proline dehydrogenase activity, and a decrease in proline utilization. It seems that an increase in the content of ammonia and an increase in the activities of Δ1-pyrroline-5-carboxylate reductase and ornithine-δ-aminotransferase play minor if any role in Ni-induced proline accumulation in detached rice leaves.