Physiological regulation of bud burst in grapevine

Abstract

Supplementary Movies: 1. 34 2 Word count: 7794 35 36 Highlights 37• The apoplastic pore size between the grapevine bud and the mother vine is 38 dynamically regulated in the transition to bud burst. 39• The molecular exclusion size of the apoplastic connection between the bud and cane 40 is calculated 2.1 nm prior to the initiation of bud burst. 41• The structural heterogeneity of the bud explains the spatial variance in tissue oxygen 42 status, and the meristematic core is oxygenated during the initiation of bud burst. 43• Long distance maternal signals are not a requirement for bud burst. 44 45Abstract 46 The physiological constraints on bud burst in woody perennials, including the prerequisite for 47 vascular development remain unresolved. Both light and tissue oxygen status have emerged 48 as important cues for vascular development in other systems, however, light requirement 49 appears to be facultative in grapevine, and the information related to the spatial variability of 50 oxygen in buds is unclear. Here, we analysed apoplastic development at early stages of 51 grapevine bud burst and combined molecular modelling with histochemical techniques to 52 determine the pore size of cell walls in grapevine buds. The data demonstrate that quiescent 53 grapevine buds were impermeable to apoplastic dyes (acid fuchsin and eosin Y) until after 54 bud burst was established. The molecular exclusion size was calculated to be 2.1 nm, which 55 would exclude most macromolecules except simple sugars and phytohormones. In vivo 56 experiments show that grapevine buds were able to resume growth even following excision 57 from the cane, and that the outer scales of grapevine buds may participate in the biochemical 58 repression of bud burst. Furthermore, we demonstrate that the tissue oxygen partial pressure 59 data correlated well with structural heterogeneity within the bud and differences in tissue 60 density. These data consolidate evidence that the meristematic core becomes rapidly 61 oxygenated during bud burst. Taken together, and when put in the context of earlier studies, 62 these data provide solid evidence that the physiological and biochemical events that initiate 63 bud burst reside within the bud, and question the role of long distance signalling in this 64 developmental transition. 65 66