Effects of shoot orientation on growth, net photosynthesis, and hydraulic conductivity of Vitis vinifera cv. Cortese.

Grapevine (Vitis vinifera cv. Cortese) plants were grown in containers, and their single shoot was trained either upwards or it was bent to a horizontal or downward position. Clusters and lateral shoots were removed. Downward shoots had less leaf area and a lower stem diameter than did horizontal and upward shoots. In downward shoots, net photosynthesis and stomatal conductance, measured at maximum irradiance, were lower than in horizontal and upward shoots; these differences were more evident at the middle nodes of the shoot. The substomatal CO 2 concentration was not affected by shoot orientation, suggesting a non-stomatal limitation of photosynthesis. This hypothesis was supported by a reduced protein content and a lower activity of ribulose 1,5-bisphosphate carboxylase/oxygenase in leaves of downward shoots. Downward shoots also had less xylem transectional area and a lower hydraulic conductance than did horizontal and upward shoots. Conductance was more reduced at the point of bending than at other internodes.