Involvement of endogenous abscisic acid and cytokinin in photosynthetic performance of different stay green inbred lines of maize under drought

Abstract

Stay green, a characteristic of delaying leaf senescence, is desirable for maintaining photosynthetic activities, particularly under drought conditions. This study investigated the endogenous abscisic acid (ABA) and cytokinin (CTK) in maize plants and their potential relations with photosynthetic activities during late growth stage under drought stress. Two maize inbred lines, including stay green inbred line (Dan598) and non-stay green inbred line (Huangzao4), were planted in pots. Plants were treated with non-drought stress (75-80% of the field moisture capacity) and drought stress (45-50% of the field moisture capacity), which were maintained by using soil moisture sensor at anthesis or grain filling stage, respectively. The green leaf area per plant, chlorophyll contents (Chl), photosynthetic rate (Pn), and stomatal conductance (Gs) of Huangzao4 decreased more considerably compared to those of Dan598 under drought stress. Maize plants with stay green had greater photosynthetic performance than non-stay green under drought conditions. In addition, chlorophyll fluorescence parameters including maximal photochemical efficiency (Fv/Fm), photochemical quenching (qL), and electron transport rate (ETR) of both maize inbred lines had the same decreasing trend as compared to their respective Pn. Drought reduced photosystem II (PS II) original fluorescence (Fo) in Dan598 but increased Fo in Huangzao4. Drought stress had substantially increased ABA but reduced zeatin riboside (ZR) contents in the leaves and roots. Moreover, ABA content was negatively correlated with Pn, while ZR and ZR/ABA were positively correlated with Chl, Pn, Gs, Fv/Fm, qL, and ETR. Overall, the results suggested that both ABA and CTK were involved in controlling photosynthetic performance, and greater photosynthetic activity of stay green maize could be attributed to higher ZR and ZR/ABA when subjected to drought.