Sectoriality in xylem connections between the bunch and leaves of the grapevine (Vitis vinifera) shoot

• Xylem connections to the grapevine bunch stem are sectorial.
• Grapevine shoot xylem sectoriality parallels phloem transport patterns.
• Isotope accumulation patterns identify potential tissue nutrient sampling sites.

It is not clear how the xylem of a plant organ with a low transpiration rate, such as the grapevine (Vitis vinifera L.) bunch, is anatomically linked to surrounding leaves. The aim was to test the hypothesis that xylem connections to the grapevine bunch are sectorial using an apoplastic dye and a radioactive membrane-permeable nutrient analogue. The transport of eosin and pertechnetate (99mTcO4−) revealed that bunches bearing unripe berries have xylem connections with primary leaves located on the same side of the shoot (common orthostichy) as the bunch. These connections also exist with secondary shoots arising from axillary buds in the same orthostichy as the bunch. These connections can include leaves in both orthostichies of the secondary shoot. Connections between the bunch and primary leaves in the opposite orthostichy are relatively uncommon. The challenge for future research is to determine the degree to which these connections are functional under normal physiological conditions.