Are xylem radial development and hydraulic conductivity in downwardly-growing grapevine shoots influenced by perturbed auxin metabolism?
Downwardly-growing grapevine shoots have smaller and more frequent vessels than upwardly-growing ones and, as a consequence, a lower hydraulic conductivity. Here, grapevine (Vitis vinifera L.) shoot growth orientation was manipulated to test whether downward shoot orientation negatively affects vessel growth in the apex via a shortage of water and nutrients. The orientation of the central vine shoot portion was inverted by two consecutive 135 degrees bends, resulting in double-bent N-shaped vines; the central downward shoot portion was of different lengths in the experimental treatments to induce increasing reductions of shoot conductivity. These treatments reduced shoot conductivity and water flow, but had no effects on vessel development and frequency in the apex. In a second experiment, auxin concentration was assessed in shoots of upwardly- and downwardly-growing plants. IAA concentration at the apical internodes was higher in downwardly-oriented shoots than in shoots growing upwar
