As senescence progresses, the sensitivity of wheat organs to plant hormones during the grain-filling stages cannot be ignored. Especially under water deficit situation, non-leaf organs (spikes) have better photosynthesis and drought-tolerance traits than flag leaves. However, the mechanism of ethylene synthesis in wheat organs under water deficit remains unclear. We have studied the influence of water deficit in wheat flag leaves and spike bracts on photosynthetic parameters and on the expression of key enzymes involved in the ethylene biosynthesis pathway during the late grain-filling stages. More stable chlorophyll content (Chl), maximum PSII quantum yield (Fv/Fm), nonphotochemical quenching (NPQ) and maximal efficiency of PSII photochemistry under light adaptation (Fv'/Fm') were observed in the spike bracts than that in the flag leaves during the late grain-filling stages. In addition, the activity of glutathione reductase (GR), γ-glutamylcysteine synthetase (γ-ECS), 1-aminocyclopropane-1-carboxylic (ACC) acid synthase (ACS), and ACC oxidase (ACO) induced ethylene synthesis and influenced plant growth. Further analysis of genes encoding cysteine-ethylene related proteins (γ-ECS, GR, ACO, ACS1, and ASC2) demonstrated that ear organs and flag leaves exhibited different expression patterns. These findings will facilitate future investigations of the regulatory senescence response mechanisms of cysteine interaction with ethylene in wheat under conditions of drought stress.
