SUMMARYOn germination, maize seeds rapidly become intolerant of desiccation. Germinating seeds exposed to dehydrating conditions for 24 h show a significant rise in lipid peroxidation and the accumulation of an electron paramagnetic resonance-detectable organic radical, in parallel with the development of desiccation intolerance. Throughout the 5-d-long germination phase and the period of loss of desiccation tolerance, the radical scavengers a-and ytocopherol and glutathione accumulate in response to episodes of dehydration. However dehydration suppresses, or delays, increases in activity of superoxide dismutase, peroxidase and glutathione reductase, major components in the protection against activated forms of oxygen. We present evidence of a sequence of events in which activated oxygen plays an early and probably causative role in loss of tolerance of desiccation in these seeds.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 129.180.Summary 1. Ortho-dihydroxyphenol and cyanoglycoside concentrations were determined in seeds of over 80 species, drawn largely from the native British flora but including a number of weeds and other species of agricultural significance. 2. All seeds examined contained at least trace amounts of hydroxyphenols and threequarters released hydrogen cyanide on hydrolysis. A highly significant correlation was found between (a) seed persistence in the soil and ortho-dihydroxyphenol concentration and (b) between protein content, as a measure of the nutritional value of the seed, and ortho-dihydroxyphenol content. No such relation was found with cyanoglycosides. 3. Particularly high concentrations of ortho-dihydroxyphenols were found throughout species within the order Myrtales (Onagraceae and relatives), all with little or no seed endosperm. 4. From this broad survey we conclude that ortho-dihydroxyphenols, as a class, play an important role in maintaining seed persistence in the soil, probably by deferring or decreasing the rate of decomposition by microbes as well as by defending against herbivory, and that this is one important mechanism, along with morphological adaptations, which confers longevity and persistence on seeds buried in cool temperate and relatively moist soil conditions.

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