The maintenance of photosynthetic electron transport in relation to osmotic adjustment in durum wheat cultivars differing in drought resistance

Abstract

The relationships between photosynthesis and osmotic adjustment (OA) under water stress are not yet well understood. Therefore, a possible association between the quantum yield of photosynthetic electron transport at the Photosystem II level ( Φ PSII) and OA was evaluated in drought-stressed durum wheat plants in this paper. Four cultivars (cvs) differing in the degree of drought resistance as estimated by the Φ PSII maintenance, were grown in a growth chamber under two different water stress cycles; in both cases two stress intensities (moderate and severe) were used. Leaf water potential ( Ψ W), osmotic potential at full turgor ( Ψ π100 ), Φ PSII and the efficiency of excitation capture by open Photosystem II reaction centres (EC PSII) were determined in the different experimental conditions, both in control and stressed plants. Φ PSII and EC PSII were evaluated by in vivo chlorophyll fluorescence analysis. Φ PSII showed a significant decrease only under severe water stress and for the drought susceptible cvs; on the other hand, EC PSII showed no change under the different water stress conditions. The percent decrease of Φ PSII under water deficit was confirmed to be a good indicator of drought resistance in durum wheat. OA was estimated as the difference in the Ψ π100 between leaves from water-stressed and well-watered plants. No relationship between the maintenance of the Φ PSII and OA under water deficit was observed in the adopted experimental conditions; this result is discussed in the light of the contrasting evidence in the literature.