Exogenously applied ABA alleviates dysplasia of maize ( <i>Zea mays</i> L.) ear under drought stress by altering photosynthesis and sucrose transport

Drought stress inhibits the development of maize ears. Abscisic acid (ABA) is a plant hormone that can regulate the physicology metabolism under abiotic stress. In this study, maize varieties Zhengdan 958 (ZD958) and Xianyu 335 (XY335) with different filling stages were used as materials. Three treatments were set in the filling period: normal irrigation (CK), drought stress (stress); exogenous ABA + drought stress (ABA+stress). They were used to study the physiological regulation of exogenous ABA on maize ears development during drought stress. Exogenous ABA inhibited bald tip and the decline of maize plant biomass, and increased the number and weight of grains per ear at harvest under drought stress by regulating photosynthetic pigment content (Chla, Chlb, Car), gas exchange parameters (Pn, Tr, gs, Ci, Ls), Chla fluorescence parameters (Fv/Fm, ФPSII, ETR, qP, NPQ), chloroplast structure and function, photosynthetic enzyme activity, and the transcription level of genes coding SUTs (ZmSUT1, ZmSUT2, ZmSUT4, ZmSUT6). There was a significant correlation between physiological indexes of sucrose loading in maize and yield factors. This study discussed the mechanism of exogenous ABA alleviating maize ear dysplasia at grain filling stage under drought stress from the perspective of photosynthesis and sucrose transport.