Nickel and Cadmium-related Changes in Growth, Plasma Membrane Lipid Composition, ATPase Hydrolytic Activity and Proton-pumping of Rice (Oryza sativa L. cv. Bahia) Shoots

Six-day-old rice plants (Oryza sativa L. cv. Bahia) were grownin 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 amedium containing no heavy metal for 5 or 10 d. Plasmalemmavesicles from shoots of treated, transferred (recovery experiments)and control plants were isolated, ATPase activity and proton-pumpingwere 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% in5 and 10 d Ni-treated plants. However, neither the initial rateof H⁺ transport nor the proton-pumping rate at steady-statewere significantly affected by the treatments. The relativeproportion (%) of the plasmalemma sterols campesterol and ⁵-avenasteroldecreased while sitosterol increased during heavy metal treatment.The overall plasmalemma phospholipid fatty acyl chain lengthand degree of unsaturation were also reduced. In experimentswhere plants recovered from Cd and Ni treatment, differencesbetween treated and control plants were reverted, particularlyin 10 d Ni-recovered plants. The possible involvement of lipidsin the regulation of the plasmalemma ATPase as well as the relationshipbetween growth, ATPase and adaptations to stress conditionsare discussed. Key words: Cadmium, nickel, sterols, phospholipids, ATPase     

Comparison Between the Effect of the Fruit and of Exogenous GA3-Applications on Source-Sink Relationships in Citrus Sprouts

Inflorescence leaves of citrus (Citrus sinensis L. Osbeck) accumulatecarbohydrate reserves at the beginning of the fruit set period.This effect is mimicked by exogenous GA₃ applications in deflorateinflorescences. The effect of the hormone on two processes thatcould result in carbohydrate accumulation, i.e. increased ribulosebisphosphate carboxylase (RuBPCase) activity and changes inthe import/export balance of assimilates in the sprouts, wasstudied. Neither RuBPCase activity nor respiration rates were affectedby the hormonal treatment. On the other hand, blocking of thephloem connections with the rest of the plant induced an increasein carbohydrate contents in the leaves that was proportionallylower in GA₃-treated sprouts than in control deflorate inflorescences.This increase was minimal in leaves from inflorescences at laterstages of fruit development. This was in spite of a lower fruitgrowth rate that, in turn, brought about a decrease in totaldry weight of the sprout. In contrast, total dry weight washigher in girdled deflorate inflorescences, whether or not theywere treated with the hormone. The presence of the fruit induceda thickening of the stems of intact inflorescences that wasalso seen in ungirdled GA₂-treated sprouts. This increase indry weight per unit length, however, had a different chemicalbasis depending upon whether it was caused by the fruit or thehormone. From these data, the possible causes for the enhancement ofcarbohydrate accumulation in inflorescence leaves, and the involvementof gibberellin in the effect of fruit on the sprouts is discussed. Carbohydrates, Citrus sinensis L. Osbeck, gibberellic acid, girdling, orange, ribulose bisphosphate carboxylase, source-sink