Abstract
Drought is one of the most important abiotic stress factors limiting maize production worldwide. The objective of this study was to investigate whether photoprotection of PSII was associated with the degree of drought tolerance and yield in three maize hybrids (30Y87, 31R88, P3939). To do this, three maize hybrids were subjected to three cycles of drought, and we measured the activities of photosystem II (PSII) and photosystem I (PSI). In a second field experiment, three maize hybrids were subjected to drought by withholding irrigation, and plant water status, yield and yield attributes were measured. Drought stress decreased leaf water potential (ΨL) in three maize hybrids, and this reduction was more pronounced in hybrid P3939 (−40%) compared to that of 30Y87 (−30%). Yield and yield attributes of three maize hybrids were adversely affected by drought. The number of kernels and 100-kernel weight was the highest in maize hybrid 30Y87 (−56%, −6%), whereas these were lowest in hybrid P3939 (−88%, −23%). Drought stress reduced the quantum yield of PSII [Y(II)], photochemical quenching (qP), electron transport rate through PSII [ETR(II)] and NPQ, except in P3939. Among the components of NPQ, drought increased the Y(NPQ) with concomitant decrease in Y(NO) only in P3939, whereas Y(NO) increased in drought-stressed plants of hybrid 30Y87 and 31R88. However, an increase in cyclic electron flow (CEF) around PSI and Y(NPQ) in P3939 might have protected the photosynthetic machinery but it did not translate in yield. However, drought-stressed plants of 30Y87 might have sufficiently downregulated PSII to match the energy consumption in downstream biochemical processes. Thus, changes in PSII and PSI activity and development of NPQ through CEF are physiological mechanisms to protect the photosynthetic apparatus, but an appropriate balance between these physiological processes is required, without which plant productivity may decline.
Highlights
Increasing sustainable crop productivity under water-limited conditions by developing drought-tolerant cultivars is one of the most challenging issues for the plant scientist [1,2,3]
These results indicate that drought-tolerant maize hybrid 30Y87 had some drought tolerance mechanism, such as greater uptake of water through roots or lower loss of water through transpiration, or more retention of water through osmotic adjustment [19,30]
Our results showed that drought stress did not significantly affect Y(NPQ) as a function of actinic light intensity in all the three maize hybrids
Summary
Increasing sustainable crop productivity under water-limited conditions by developing drought-tolerant cultivars is one of the most challenging issues for the plant scientist [1,2,3]. Since plant growth and yield mainly depend on plant photosynthetic activity, several researchers are of the view that selection of cultivars/varieties based on photosynthetic traits may help in developing high-yielding and stress-tolerant crop cultivars [5,6,7,8,9,10]. Some are of view that counteracting drought stress induces ROS production, and improving solar energy capture by photosystems may enhance the crop yield [11,12,13]. Most of the studies have focused on improving the activity of rubisco with enhanced CO2 fixation, or lowering carbon loss through photorespiration [7,8,9,10].
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