Vascular function in berries of Vitis vinifera (L) cv. Shiraz

Anatomical studies on the movement of a xylem tracer dye were combined with functional studies on changes in grape berry volume during final stages of berry ripening to gauge xylem effectiveness. Movement of a xylem tracer dy e into pre-veraison fruit was compared with movement into post-veraison fru it by feeding a solution of acid fuchsin to excised shoots with bunches sti ll attached, and then sectioning fruit for photo-microscopy. Those comparis ons confirmed published studies showing an apparent blockage to dye movemen t along major vessels within the brush tissue of post-veraison fruit. Howev er, our functional approach yielded a different impression of vascular acti vity. A continuation of xylem transport in ripening fruit was inferred from comparisons of berry volume where pedicels were either girdled (phloem int errupted, but xylem intact) or excised (both phloem and xylem interrupted). Volume changes in manipulated berries were compared with immediately adjac ent intact control berries within the same bunch. Control fruit lost volume subsequent to 78 days after flowering (DAF) while manipulated fruit lost v olume from the first day of treatment at 67 DAR By harvest time at 95 DAF, both control fruit and girdled fruit had fallen to 91% and excised fruit to 46% of maximum volumes recorded around 78 DAR Berry volume loss in girdled fruit was further enhanced by deficit irrigation. We conclude that xylem f low into those Shiraz berries must have continued beyond veraison despite d ye evidence of a vessel blockage within the brush region of analogous post- veraison fruit.