Effect of nickel toxicity on the alteration of phosphate pool and the suppressing activity of phosphorolytic enzymes in germinating seeds and growing seedlings of rice

Abstract

To determine the effects of nickel on the phosphate pool and the activity of phosphorolytic enzymes in rice germinating seeds and growing seedlings, rice cvs. Malviya-36 and Pant-12 were germinated for 120 h, submitted to 200 and 400 μM NiSO4 and the level of phosphate pool and the activities of key phosphorolytic enzymes acid phosphatase, alkaline phosphatase and inorganic pyrophosphatase were observed in germinating seeds and growing seedlings. The result showed that in germinating rice seeds, 400 μM NiSO4treatment caused a decline in phosphate pool at 24 h of germination but during the later period of 72 to 120 h, an increase in phosphate level was observed in both endosperms and embryoaxes, while in seedlings raised for 10 to 20 days, a decline in total phosphate pool was noticed. With a nickel treatment level of 400 µM in situ, about 19 to 38% decline in acid phosphatase activity was observed in endosperms and embryoaxes at 96 h of germination and 23 to 52% decline in activity in roots and shoots in 15 day grown seedlings. Similarly the seeds germinating in presence of 400 µM Ni2+ showed about 17 to 41% decline in alkaline phosphatase activity in endosperms and about 51 to 59% in embryoaxes at 72 h of germination while about 21 to 60% inhibition of alkaline phosphatase activity was noticed in roots and shoots of 15 day grown seedlings under 400 µM Ni2+ treatment. The activity of inorganic pyrophosphatase was also inhibited substantially in germinating rice seeds and growing rice seedlings in presence of 200 µM or 400 µM Ni2+. The results suggested that alteration in the level of phosphate pool and inhibition in the activities of phosphorolytic enzymes might contribute to reduced metabolic activities, delayed germination of rice seeds and decreased vigour of seedlings in Ni2+ polluted environment. Key words: Germination, nickel, phosphate, phosphatase, rice, seedling.