Nickel toxicity inhibits ribonuclease and protease activities in rice seedlings: protective effects of proline
2007
Maheshwari, Ruchi | Dubey, R. S
Seedlings of two rice cvs Malviya-36 and Pant-12, when grown under increasing levels of nickel (Ni²⁺: 200 and 400 μM) in the nutrient medium, showed increased levels of RNA, soluble proteins and free amino acids, especially proline over a total growth period of 5-20 days. Ribonuclease (RNase) and protease activities decreased in both roots and shoots due to Ni treatment in situ. Under in vitro conditions, a gradual inhibition of RNase activity was observed with increasing concentrations of Ni²⁺ (0-2500 μM) in the assay medium. Artificial desiccation simulated by 40% PEG or the presence of 2.5 mM Ni²⁺ in the reaction medium resulted in about 52-53% loss of RNase activity. Such a loss could be partially restored by 1 M proline in the assay medium. The activity staining of RNase revealed seven and four isoforms of RNase in roots and shoots, respectively. The intensity of most of the bands decreased with increasing levels of Ni²⁺ treatment in situ. The results suggest that Ni toxicity in rice seedlings suppresses the hydrolysis of RNA and proteins by inhibiting the activity of RNase and protease, respectively. Proline appears to act as a protectant of the enzyme RNase against metal- and PEG-induced damages.
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