Ethylene production of two wheat cultivars exposed to desiccation, heat, and paraquat-induced oxidation

Drought and heat are the major limitations to wheat (Triticum aestivum L.) production worldwide. Insufficient water supply, often accompanied by high temperature, reduces plant growth, hastens senescence, and produces considerable yield losses. Ethylene production has been often associated with reduced growth and premature senescence, and may therefore be an indicator of plant susceptibility to stress such as drought and heat. A system of rapid and sensitive measurement of plant ethylene production could have potential to identify cultivar-dependent response to environmental constraint. There have been no studies regarding genetic differences in ethylene production rate (EPR) in wheat. The purpose of this study was to compare EPR of two wheat cultivars previously characterized for field performance under drought with a new system of ethylene measurement. Seedlings of the winter wheat cultivars Dropia (stress resistant) and Delia (stress susceptible) were exposed to optimum and stress conditions and measured for EPR. Stress conditions included desiccation, high temperature, and paraquat (Pq; 1,1'-dimethyl-4,4'-bipyridinium) induced oxidation. Ethylene was measured with a CO2 laser-driven intracavity photoacoustic (PA) detector which could detect ethylene concentrations as low as 10 pL L-1 and a time response of 40 s. Additional physiological parameters related to stress resistance were measured in eight wheat cultivars including Delia and Dropia. Under desiccation, EPR decreased in both cultivars, and then increased by 2 to 5 fold upon rewatering. Ethylene evolution decreased more in Delia than in Dropia under desiccation. However, Delia produced consistently and significantly more ethylene than Dropia under optimum and all other stress conditions. Enhanced EPR by Delia was consistent with all other physiological measurements, indicating that Delia was more stress-sensitive than Dropia.