Root characteristics and hormone activity of wheat in response to hypoxia and ethylene

Understanding the physiological mechanisms of hypoxia tolerance is important for developing hypoxia-tolerant genotypes. This experiment investigated whether differential responses to hypoxia and ethylene exist in root characteristics, hormonal activity, and shoot growth for two wheat (Triticum aestivum L.) cultivars, Bayles and Jackson, differing in waterlogging tolerance. Rooting characteristics, ethylene production, cellulase activity, and shoot growth were determined after application of hypoxia and various concentrations of ethylene to the rooting medium in a growth chamber. Hypoxia limited root elongation for both cultivars but enhanced production of crown roots for tolerant Jackson. Hypoxia induced root aerenchyma formation and enhanced root ethylene production for both cultivars, but the response was greater for Jackson than Bayles. Ethylene effects on root growth and aerenchyma formation were similar to those observed for hypoxia treatment. All concentrations of ethylene (0.1, 1.0, and 5.0 microliters L-1) hastened the production of crown roots for Jackson but inhibited root elongation at the highest ethylene concentration (5 microliters L-1). For sensitive Bayles, crown root production was promoted by the lowest concentration of ethylene, whereas root elongation was restricted at all levels of ethylene. Ethylene also promoted formation of aerenchyma in crown roots by increasing cellulase 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 results showed that the effects of ethylene on roots varied with cultivar and ethylene concentration