Organ-distinctive changes in respiration rates of rice plants under nickel stress

Abstract

Nickel (Ni) is an essential mineral element that may accumulate to toxic levels in soils due to anthropogenic activities. The growth of rice plants cultured hydroponically was severely impaired when Ni concentration was raised from 0.1 to 0.5 mM. However, the decrease in plant growth was not accompanied by any significant effect on respiration rates at the whole plant level. Short-term treatments of excised roots with 0.1–1.0 mM Ni did not result in any significant changes in respiration. However, long-term treatments of whole plants induced clear distinctive effects on shoots and roots. There was a significant decline in growth of these organs when the plants were cultured for 10 days at 0.5 mM Ni. Although no significant changes in respiration occurred in shoots, it was drastically reduced in roots. Ni withdrawal after 5 days’ treatment caused an increase in respiration in roots, but a decrease in shoots, despite the fact that stress alleviation induced a similar and significant increase in fresh weight of both organs. Our results point to organ-related differences in the distribution of the energy resulting from respiration under Ni stress.