Responses of Photosynthetic Electron Transport to Drought and Re-watering in Two Maize Genotypes

Effects of drought stress on photosynthesis have been well-documented. However, photosynthetic electron transport process in response to combined drought stress and recovery in maize is relatively scant. In this study, the photosynthetic electron flow, the energy quenching in PSII and PSI, and cyclic electron flow (CEF) activity in two maize (Zea mays L.) genotypes were measured. In both genotypes, chlorophyll a fluorescence transient (OJIP) showed progressive drought caused increases of J and I step, the positive of K-band and L-band; and decreases in TR0/ABS, ET0/TR0, ET0/ABS, RE0/ET0 and PIABS. Analysis of the modulated 820 nm reflection (MR) showed progressive drought decreased the values of VPSI and VPSII-PSI. Decreases in quantum yields of Y(I) and Y(II) were accompanied by increase of Y(NPQ) and CEF. Compare to Shaanke9 (SK9), the drought-induced changes in Dafeng30 (DF30) were stronger, and SK9 kept higher CEF under drought stress. After re-watering, SK9 recovered more completely in all parameters than DF30, suggesting that the reversible down-regulation of PSII and PSI in SK9 maintained the functional integrity of photosystems. The photosynthetic apparatus of SK9 cultivar is more resistant to drought than that of DF30. These results indicate that more efficient regulation of photosynthetic electron transport between two photosystems and higher CEF in the SK9 jointly play crucial role in recovery from drought damages, which could contribute to a better adaptation under varying drought environment.