RESPIRATORY PATHWAYS IN GERMINATING MAIZE RADICLES CORRELATED WITH DESICCATION TOLERANCE AND SOLUBLE SUGARS

We have assessed the activities of the cytochrome and alternative pathways in total respiration and their role in each stage of germination of Zea mays L. radicles. Throughout imbibition, the salicylhydroxamic acid (SHAM) concentration needed to inhibit the cyanide-resistant pathway, without any side effects, decreased from 15 mM in quiescent embryos to 5 mM at 72 h after imbibition. Electrons predominantly flowed through the cytochrome pathway although the alternative pathway was already present at early imbibition. The capacity of the alternative path was about 70% of the control rate of respiration. Its engagement progressively increased from 18% after 10 min of imbibition to 70% at the radicle emergence and then decreased to 50% at 96 h after imbibition, concomitant with the onset of radicle growth. The alternative pathway was, however, not essential for germination. The observed activity of the alternative path correlated with the monosaccharide (glucose + fructose) content, suggesting that the alterative pathway could be acting according to the 'energy overflow model'. On the other hand, up to 24 h after imbibition at 16-degrees-C, maize radicles tolerate a severe desiccation, becoming intolerant at 72 h. On reimbibition of tolerant radicles, respiration increased immediately and the alternative pathway was rapidly engaged. At 72 h, no respiration was measured, indicating a total loss of the respiratory systems. The possible correlation between carbohydrate content, loss of desiccation tolerance and activity of the two respiratory pathways is discussed.