Development of water stress in kale leaves of different insertion levels

The mutual relationship between the water potential (γ w ), its components, namely the osmotic potential (γ s ) and the pressure potential (γ p ), and the water saturation deficit (ΔW sat ) were determined in the leaves of different insertion levels. During the water stress development in kale plants induced by decreasing soil moisture theγ w decreased, parallely in all the leaves but the same decrease ofγ q was accompanied by the highest decrease of theγ p , probably due to the accumulation of osmotically active solutes, and the lowest decrease ofγ p in the upper leaves and with the lowest decrease ofγ s and the highest decrease ofγ p in the lower leaves. Also the corresponding values of the ΔW sat were always lower in the upper than in the middle and lower leaves. Thus the upper leaves wilted at more negative values ofγ w than the other leaves. On the contrary, during the wilting of the cut off leaves the relationship betweenγ w and ΔW sat in the upper, middle and lower leaves was practically the same. The very slightly higher decrease ofγ s in the upper leaves in comparison with the other leaves was compensated by a lower deerease of theirγ p . These changes in the ratios ofγ w ,γ s ,γ p and ΔW sat with the leaf insertion levels enabled the preference of the upper leaves in retaining the necessary water supply during the wilting of plantsin situ.