Vascular occlusion in xylem conduits is a common response to environmental stresses, and plant species are recognized as primarily
tylose-forming or gel-forming. These stresses occur throughout the year, but there is little information on the
wound responses throughout the year and in growing and dormant tissues.
Wound-induced vascular occlusions were evaluated by type (
tylose or gel), temporal progress, and spatial distribution for grape stems pruned in four seasons through an entire year.
Tyloses were formed predominantly in summer and
gels in winter. Cytohistological analyses indicated that
wound-induced
gels were
pectin-rich. Both gel formation and
tylose development were complete within 7 d and 10 mm from the cut regardless of the season of the wounding. Most vessels were affected by wounding, but a higher fraction of vessels developed occlusions in summer and autumn (over 80%) than in winter and spring (about 60%). The study is the first to show a single species is capable of producing primarily either
tyloses or
gels and that the type of
wound-induced occlusion is dependent upon the season in which wounding occurs. Winter conditions limit the
wound response to reversible gel formation that may contribute to refilling of embolized vessels in the spring.