EFFECT OF HEAT-STRESS DURING SEED DEVELOPMENT AND MATURATION ON WHEAT(TRITICUM-DURUM) SEED QUALITY .2. MITOCHONDRIAL RESPIRATION AND NUCLEOTIDE POOLS DURING EARLY GERMINATION

Marzak and Oum-rabia wheat seeds were produced under three temperature regimes (20:15, 28:21, 36:29 degrees C) starting 10 d after anthesis through harvest. Nucleotide levels and respiratory activity of mitocho ndria isolated from imbibing embryos were determined. Mitochondrial st ructure from the radicle meristem region of imbibed embryos was examin ed under electron microscopy. Embryos from low-temperature treatments showed rapid accumulation of adenosine triphosphate (ATP) and higher e nergy levels and rates of oxygen uptake than embryos from high-tempera ture treatments. Embryos from medium-temperature treatments exhibited intermediate values. Parallel to these metabolic changes during early seed germination, results from electron microscopy revealed visible di fferences in mitochondrial structure. Mitochondria from the low-temper ature regime were well developed with visible membranes and cristae; t hose from the high-temperature regime were degenerating. These results provide clear evidence of the influence of parent temperature conditi ons on the seed metabolism during early stages of germination.