THE BEHAVIOR OF FREE RADICALS DURING MATURATION AND AGING OF WHEAT (TRITICUM SPP.) AND BARLEY (HORDEUM VULGARE L.) SEED

This study was conducted to evaluate, by electron paramagnetic resonance (EPR) techniques, the behavior of free radical concentrations in naturally and artificially aged barley seed and in wheat seed during maturation and storage. A second objective was to determine if changes in the fatty composition occurred in naturally and artificially aged barley seed.;Seed of three cultivars of wheat, representing three maket classes, were harvested at regular intervals during maturation from a period approximating the hard-dough stage to three weeks after physiological maturity. Whole seed (WS) and nonembryo portions (NE) of the seed from each harvest date were frozen in liquid nitrogen, lyophilized, and the free radical concentration analyzed by EPR techniques. In addition, seed from two points in the maturation period were placed into a storage at 10, 20, and 30 C and the free radical concentration, percent germination, and speed of germination index characterized after 7, 14, and 21 days of storage.;The free radical concentration of all three cultivars increased during the maturation period. The increases appeared to be most dramatic as the seed moisture content approached 20 percent. When the free radical concentration was highest, the EPR signal was higher in the WS than in the NE for two of the three cultivars. Precipitation during the latter part of the sampling period may have been responsible for a dramatic decline in the free radical concentration. The free radical concentration of seed placed into storage when the EPR signal was high decayed more rapidly at 30 than at 10 or 20 C. Storage temperature did not cause significant decay of the free radicals of wheat seed placed into storage when the EPR signal was low. The free radical concentration may have reached a stable background level in this case.;Fatty acid analysis of the neutral and polar lipid fraction from the E and NE portions of the seed indicated that changes in the fatty acid composition of naturally and artificially aged barley were similar. Decreases in the percent linoleic and increases in the percent palmitic and stearic acids with increasing age were most common. These changes were most pronounced in the polar lipid fraction from the E portion of the seed. The fatty acid composition appeared to be less stable in Vantage than in Hannchen barley seed during aging. The mechanism(s) responsible for the changes in fatty acid composition could not be determined.;Seed of two barley cultivars, 'Hannchen' and 'Vantage,' were obtained, ranging in age from freshly harvested to 32 years old. The free radical concentration, as defined by the peak-to-peak amplitude of the first order derivative of the EPR signal, was highest in freshly harvested seed and decayed with increasing length of storage. There appeared to be significant year-to-year variation in the free radical concentration. The EPR signal was located in the nonembryo portion of the seed, and regression analysis indicated that changes in the free radical concentration were probably not directly related to changes in percent germination or speed of germination index at 10 or 20 C.