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Mixed‐linkage glucan:xyloglucan endotransglucosylase ( MXE ) re‐models hemicelluloses in E quisetum shoots but not in barley shoots or E quisetum callus
Author(s) -
Mohler Kyle E.,
Simmons Thomas J.,
Fry Stephen C.
Publication year - 2013
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.2012.04371.x
Subject(s) - xyloglucan , shoot , callus , botany , coleoptile , biology , chemistry , cell wall
Summary Among land‐plant hemicelluloses, xyloglucan is ubiquitous, whereas mixed‐linkage (1→3),(1→4)‐β‐ d ‐glucan ( MLG ) is confined to the Poales (e.g. cereals) and E quisetales (horsetails). The enzyme MLG :xyloglucan endotransglucosylase ( MXE ) grafts MLG to xyloglucan. In E quisetum , MXE often exceeds extractable xyloglucan endotransglucosylase ( XET ) activity; curiously, cereals lack extractable MXE . We investigated whether barley possesses inextractable MXE . Grafting of endogenous MLG or xyloglucan onto exogenous [ 3 H ]xyloglucan oligosaccharides in vivo indicated MXE and XET action, respectively. Extractable MXE and XET activities were assayed in vitro . MXE and XET actions were both detectable in living E quisetum fluviatile shoots, the MXE : XET ratio increasing with age. However, only XET action was observed in barley coleoptiles, leaves and roots (which all contained MLG ) and in E . fluviatile intercalary meristems and callus (which lacked MLG ). In E . fluviatile , extractable MXE activity was high in mature shoots, but extremely low in callus and young shoots; in E . arvense strobili, it was undetectable. Barley possesses neither extractable nor inextractable MXE , despite containing both of its substrates and high XET activity. As the P oales are xyloglucan‐poor, the role of their abundant endotransglucosylases remains enigmatic. The distribution of MXE action and activity within E quisetum suggests a strengthening role in ageing tissues.