Leaf age-dependent elastic adjustment and photosynthetic performance under drought stress in Arbutus unedo seedlings

Abstract

[eng] The relationship between photosynthesis performance under drought stress and osmotic and elastic adjustments has yielded contrasting results so far, despite the potential role of water relations in turgor maintenance and stomatal functioning. Photosynthesis and pressure-volume derived parameters were investigated in Arbutus unedo old and young leaves after two months of limited water availability. Young and old leaves were clearly differentiated in CO2 assimilation rate and its underlying mechanisms, modulus of elasticity and leaf structure under well-watered conditions. Additionally, their response to drought stress differed: old leaves were able to sustain similar assimilation values, whereas photosynthesis and stomatal conductance were significantly reduced in young leaves. Elastic adjustment and other elasticity-related parameters were also different depending on leaf age, with no apparent relationship with basic cell wall composition. Although the mechanisms of elastic adjustment are not clear from the presented results, such adjustment apparently contributes to regulate the photosynthetic response under drought stress by maintenance of turgor and hence stomatal aperture.