RESPIRATION AND MITOCHONDRIAL CHARACTERISTICS OF IMBIBING MAIZE EMBRYOS DAMAGED BY HIGH-TEMPERATURES DURING DESICCATION

Hybrid maize (Zen mays L.) seed artificially dried to 120 g H2O kg(-1) moisture in air temperatures of either 35 (LT) or 45 degrees C (HT) w as used to study the effect of desiccation temperature on mitochondria l function during early imbibition. In embryo culture experiments, emb ryo growth was delayed for embryos excised from HT treated seed compar ed with LT samples. After 1 h of imbibition, the rate of O-2 uptake by LT axis tissue was greater than for HT dried samples. Uptake rates co ntinued to increase for LT samples through the first 6 h of imbibition while rates for HT axes remained constant. Mitochondria isolated from LT axis tissue that had undergone imbibition for 4 h exhibited respir atory control with oxidative phosphorylation efficiency values of 0.79 and 0.77 for NADH and succinate assays, respectively. Mitochondria fr om imbibing HT axis tissue exhibited no respiratory control. Electron micrographs of cells from the radicle meristem region of both treatmen ts showed that mitochondrial development during the initial 24 h of im bibition was impaired in HT samples. These results suggest that mitoch ondrial function and development, during the initial stages of embryon ic tissue hydration, is impaired when maize seed are artificially drie d with high air temperatures. We conclude that the development of mito chondrial function during this period is a key element in determining the rate of germination and subsequent seedling growth.