Abstract
Six-day-old rice plants (Oryza sativa L. cv. Bahia) were grown in the presence of 0-5 mol m-3 Ni or Cd for 5 or 10 d. Five days after treatment, some plants were transferred to a medium containing no heavy metal for 5 or 10 d. Plasmalemma vesicles from shoots of treated, transferred (recovery experiments) and control plants were isolated, ATPase activity and proton-pumping were assessed, and free sterols and phospholipids determined. The ATPase hydrolytic activity was increased by 37% and 34% in 5 and 10 d Cd-treated plants, respectively; and by 66% in 5 and 10 d Ni-treated plants. However, neither the initial rate of H + transport nor the proton-pumping rate at steady-state were significantly affected by the treatments. The relative proportion (%) of the plasmalemma sterols campesterol and d5-avenasterol decreased while sitosterol increased during heavy metal treatment. The overall plasmalemma phospholipid fatty acyl chain length and degree of unsaturation were also reduced. In experiments where plants recovered from Cd and Ni treatment, differences between treated and control plants were reverted, particularly in 10 d Ni recovered plants. The possible involvement of lipids in the regulation of the plasmalemma ATPase as well as the relationship between growth, ATPase and adaptations to stress conditions are discussed.
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