THE OCCURRENCE OF A STABLE QUINONE RADICAL ACCUMULATING IN-VIVO DURING NATURAL AND INDUCED SENESCENCE IN A RANGE OF PLANTS

A correlation has been firmly established, in a wide range of plants, between environmental stress, the onset of senescence, loss of viabili ty in seeds and the development and accumulation of a stable organic f ree radical. On the basis of the EPR response obtained at 95 GHz (W-ba nd) and ENDOR spectra, and comparisons with quinone radical anions, we present evidence from contrasted plant species, plant tissues and sub -cellular fractions that this stable radical originates from one or mo re quinones possibly, though perhaps not exclusively, associated with stressed or age-impaired photosynthetic and respiratory electron trans port chains. The radical appears to be ubiquitously associated with su b-lethal stress-induced damage and with senescence and arises during t he sub-cellular structural and biochemical processes associated with t he final phases of metabolism prior to death. As the free radical pers ists for some considerable time after death, it may have value in long -term studies of seed viability and in broader areas of plant patholog y and stress physiology.