ROOT CHARACTERISTICS AND HORMONE-ACTIVITY OF WHEAT IN RESPONSE TO HYPOXIA AND ETHYLENE

Understanding the physiological mechanisms of hypoxia tolerance is imp ortant for developing hypoxia-tolerant genotypes. This experiment inve stigated whether differential responses to hypoxia and ethylene exist in root characteristics, hormonal activity, and shoot growth for two w heat (Triticum aestivum L.) cultivars, Bayles and Jackson, differing i n waterlogging tolerance. Rooting characteristics, ethylene production , cellulase activity, and shoot growth were determined after applicati on of hypoxia and various concentrations of ethylene to the rooting me dium in a growth chamber. Hypoxia limited root elongation for both cul tivars but enhanced production of crown roots for tolerant Jackson. Hy poxia induced root aerenchyma formation and enhanced root ethylene pro duction for both cultivars, but the response was greater for Jackson t han Bayles. Ethylene effects on root growth and aerenchyma formation w ere similar to those observed for hypoxia treatment. All concentration s of ethylene (0.1, 1.0, and 5.0 mu L L-1) hastened the production of crown roots for Jackson but inhibited root elongation at the highest e thylene concentration (5 mu L L-1). For sensitive Bayles, crown root p roduction was promoted by the lowest concentration of ethylene, wherea s root elongation was restricted at all levels of ethylene. Ethylene a lso promoted formation of aerenchyma in crown roots by increasing cell ulase activity. This effect occurred earlier and was more dramatic for Jackson. The promoting effect of ethylene on aerenchyma formation was also more pronounced for newly formed than pre-existing roots. The re sults showed that the effects of ethylene on roots varied with cultiva r and ethylene concentration.