Persistence of photosynthetic components and photochemical efficiency in ears of water‐stressed wheat (Triticum aestivum)

Abstract

Ear photosynthesis may be an important source of C for grain growth in water‐stressed plants of cereals. The main objectives of this work were to determine the stability of the photosynthetic apparatus and the photochemical efficiency of ears in plants subjected to post‐anthesis drought. Plants of wheat (Triticum aestivum L. cv. Granero INTA) were grown in pots under a rain shelter and subjected to water stress (soil water potential around −0.6 to −0.8 MPa) starting 4 days after anthesis. Post‐anthesis drought substantially accelerated the loss of chlorophyll, Rubisco and the light‐harvesting complex of photosystem II (LHCII) in the flag leaf, but the degradation of these photosynthetic components was much less affected by water deficit in awns and ear bracts. Quantum yield of PSII (ΦPSII) decreased in leaves of water‐stressed plants. In contrast, ear bracts had a higher ΦPSII than leaves, and ΦPSII of ear bracts did not decrease at all in response to drought. Removing the grains immediately before fluorescence measurements (less than 30 min) slightly reduced ΦPSII, indicating that CO2 supplied by grain respiration may contribute to the high photochemical efficiency of ears in droughted plants. However, other factors may be involved in maintaining high ΦPSII, since even in the absence of grains ΦPSII remained much higher in ear bracts than in the flag leaf. The relative stability of ear photosynthetic components and their relatively high photochemical efficiency may help to maintain ear photosynthesis during the grain filling period in droughted plants.