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.