Ripening grape berries remain hydraulically connected to the shoot

Area of Science:

• Plant Physiology
• Viticulture
• Plant Water Relations

Background:

• Grape berry development and ripening involve complex physiological processes.
• Understanding water transport dynamics in grapevines is crucial for optimizing fruit quality and yield.
• Xylem functionality changes throughout the plant's life cycle, particularly during reproductive stages.

Purpose of the Study:

• To investigate the changes in xylem functionality in grape berries during ripening.
• To determine the impact of water availability and root zone pressure on berry size and xylem transport.
• To elucidate the mechanisms governing water movement into and out of ripening grape berries.

Main Methods:

• Monitoring berry diameter during controlled drought and rewatering cycles in Vitis vinifera and Vitis labruscana.
• Applying root system pressurization to assess plant hydraulic responses.
• Using xylem-mobile dye (basic fuchsin) to trace water and solute movement within the berry vasculature before and after veraison.
• Infusing dye via shoot base and stylar end to differentiate transport pathways.

Main Results:

• Berry size was maintained under water stress before veraison but declined irreversibly post-veraison.
• Root pressurization affected berry diameter only before veraison; some berries cracked post-veraison.
• Xylem-mobile dye movement into berries decreased during ripening, becoming confined to the brush area.
• Dye infused stylar end moved readily back to the plant, indicating retained transport capacity.

Conclusions:

• Grape berry xylem conduits maintain water and solute transport capacity throughout ripening.
• A decline in xylem water influx post-veraison may be due to apoplastic phloem unloading and solute accumulation.
• The grapevine xylem may play a role in recycling excess phloem water back to the shoot during berry ripening.