Plant sterility under drought stress is caused by antioxidant inefficiency?

In a paper entitled `Drought-induced spikelet sterility is associated with an inefficient antioxidant defence in rice panicles` published in Physiologia Plantarum 121:462-471 (2004) (abstract below) the authors (Selote and Khanna-Chopra) report on a test of two rice varieties under drought stress. The susceptible variety had greater panicle sterility than the resistant one under stress. The susceptible variety also had less antioxidant activity than the resistant variety. The authors therefore concluded that "inefficient antioxidant defense" was the likely cause of rice panicle sterility under drought stress.

This far reaching conclusion was made while in the same paper the authors also report that the susceptible variety had relatively lower panicle relative water content (RWC) and turgor under stress. Neither the authors nor the peer reviewers or the editor of this specific paper (A. Marion-Poll) considered the possibility that this lower panicle RWC and turgor in the dehydrated susceptible cultivar could be the real cause of sterility, irrespective of the found antioxidant status.

Abstract

Water stress-induced spikelet sterility limits rice production under upland conditions. The causes of spikelet sterility under drought stress are poorly understood. In this study the role of antioxidant defence management in drought-induced spikelet sterility was investigated in two rice (Oryza sativa) genotypes differing in drought resistance. Drought-resistant N22 genotype showed less water stress-induced spikelet sterility when compared to the susceptible N118 genotype under upland conditions. The N22 panicles maintained higher RWC and turgor potential and lower H2O2 levels across the developmental stages under water stress than that of N118 panicles. Drought-induced enhancement in superoxide dismutase (SOD, EC 1.15.1.1) activity coupled with higher ascorbate (AsA), glutathione (GSH) content and enhanced ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) activities resulted in lower H2O2 levels in N22 panicles. In contrast, insufficient enhancement in SOD, APX and GR activities resulted in relatively higher H2O2 levels under water stress in N118 panicles. The N22 panicles exhibited a higher number of SOD and APX isozymes in comparison with N118 panicles that might provide better reactive oxygen species scavenging. Hence it is concluded that well-equipped antioxidant defence plays an important role in minimizing water stress-induced spikelet sterility in upland rice.