Abstract: 【Objective】The objective of the experiment was to investigate the effect of drought stress on photosynthetic characteristics and contents of endogenous hormones and to provide a scientific basis for exploring and utilizing the stay-green sorghum. 【Method】 A pot-grown experiment was conducted with green-stayed sorghum (B35) and non-green-stayed sorghum (Sanchisan) as materials with two water treatments including non-drought stress (75%-80% of the field moisture capacity) and drought stress (45%-50% of the field moisture capacity) at anthesis stage or grain filling stage, respectively. Photosynthesis, chlorophyll fluorescence and endogenous hormone contents including abscisic acid (ABA) and cytokinin (CTK) both in leaves and roots were examined under drought stress. In addition, the dynamic balance of endogenous hormone contents in leaves and roots and the relationship between photosynthetic characteristics and endogenous hormone contents in leaves under drought stress were analyzed. 【Result】 Photosynthesis of the two different stay-green sorghum materials were restrained by drought stress at both anthesis stage or grain filling stage, however, the chlorophyll contents (Chl), photosynthetic rate (Pn), stomatal conductance (Gs), PSⅡ original fluorescence (Fo), maximal photochemical efficiency (Fv/Fm), photochemical quenching (qL) and electron transport rate (ETR) of B35 decreased significantly less than those of Sanchisan under drought stress. At filling stage, in Sanchisan, the decrease of Chl under drought stress was more obvious, and Pn decreased markedly, which might be resulted from damage or inactivity of the structure of PSⅡreaction centre. Drought increased ABA contents in leaves and roots of the two different stay-green sorghum cultivars. ABA contents in leaves and roots of B35 increased significantly greater than those in Sanchisan especially at grain filling stage. While drought decreased CTK contents in leaves and roots of the two different stay-green sorghum cultivars. CTK contents in leaves and roots decreased significantly greater than those in B35 especially at grain filling stage. ABA contents of B35 and Sanchisan were higher in leaves than in roots, while CTK contents were the opposite. CTK/ABA both in leaves and roots decreased under drought stress, and the reduction extents in B35 were greater than those in Sanchisan at both anthesis stage and grain filling stage. Moreover, ABA contents were negatively related with Pn at 0.05 level and with ETR at 0.01 level, and CTK contents were positively related with Gs at 0.05 level and with Chl, Pn, Fv/Fm, qL and ETR at 0.01 level.【Conclusion】 Stay-green sorghum has higher chlorophyll contents and photosynthetic capacity than non green-stayed sorghum under drought stress. Interaction between ABA and CTK influences the movement of stomata and other related physiological process regarding photosynthesis such as Pn and ETR.

Key words: sorghum , stay green , drought stress , photosynthetic characteristics , endogenous hormone