Iron-catalysed oxygen radical formation and its possible contribution to drought damage in nine native grasses and three cereals

The origin, sequence and location of molecular damage arising during sub-lethal drought is described in 4-week-old wheat (Triticum aestivum L.). Short episodes of water deprivation increased the uptake of iron within 6 h of drought. Superoxide, precursor of the highly reactive hydroxyl radical in the presence of iron, was formed in the thylakoid membranes. Further droughting promoted destruction of chlorophylls (but not carotenoids), which was detectable after 14 h and preceded significant losses in relative water content. Peroxidation of lipids and a decreased protein content occurred after 26 h of cumulative water deprivation but was confined to the shoots. In contrast, there was no significant loss of protein nor peroxidation of lipids in the root tissue, despite quantitatively larger, more rapid, losses in water content. These results indicate that damage arising in the early phases of drought appears to be initiated within the chloroplast and to be largely confined to the photosynthetic tissue. The pattern of drought-induced damage in 11 other non-xerophytes of the north temperate region was qualitatively similar to wheat, although the response to drought of the three cereals was more extreme than in the indigenous grasses and less extreme in ecologically stress-tolerant species. A method for the simultaneous quantification of carotenoids in the presence of chlorophylls is provided.