Manganese superoxide dismutase can reduce cellular damage mediated by oxygen radicals in transgenic plants.

In plants, environmental adversity often leads to the formation of highly reactive oxygen radicals. Since resistance to such conditions may be correlated with the activity of enzymes involved in oxygen detoxification, we have generated transgenic tobacco plants which express elevated levels of manganese superoxide dismutase (MnSOD) within their chloroplasts or mitochondria. Leaf discs of these plants have been analyzed in conditions in which oxidative stress was generated preferentially within one or the other organelle. It was found that high level overproduction of MnSOD in the corresponding subcellular location could significantly reduce the amount of cellular damage which would normally occur. In contrast, small increases in MnSOD activity were deleterious under some conditions. A generally applicable model correlating the consequences of SOD with the magnitude of its expression is presented.

ATP-synthesis by proteoliposomes incorporating Rhodospirillum rubrum F0F1 as measured with firefly luciferase: dependence on delta psi and delta pH.

ATP-synthesis catalyzed by proteoliposomes incorporating Rhodospirillum rubrum F0F1 was driven by artificially applied electrochemical proton gradients. The time-course of ATP-synthesis was followed continuously by means of firefly luciferase. Correction methods were developed which allow one to calculate the initial rate of ATP-synthesis from the observed luminescence kinetics. The following results were obtained: (1) ATP-synthesis occurred above a threshold delta mu H+ of 90 mV; this threshold is not imposed by the activation requirement of the enzyme; (2) delta psi and delta pH appear to be equivalent as driving forces for ATP-synthesis if allowance is made for the effect of the electrical capacitance of the liposome membrane on the distribution of K+ at equilibrium; and (3) the highest rate observed so far is 200 mol ATP per mol F0F1 per s.