Catalyzes xyloglucan endohydrolysis (XEH) and/or endotransglycosylation (XET). Cleaves and religates xyloglucan polymers, an essential constituent of the primary cell wall, and thereby participates in cell wall construction of growing tissues. Has a high XET activity, but little or no XEH activity in vitro. Acceptor preferences are XXXGol > XLLGol = XLFGol > XXLGol > XXFGol. breaks a beta-(1->4) bond in the backbone of a xyloglucan and transfers the xyloglucanyl segment on to O-4 of the non-reducing terminal glucose residue of an acceptor, which can be a xyloglucan or an oligosaccharide of xyloglucan. xyloglucan + H2O = xyloglucan oligosaccharides. KM for xyloglucan as donor substrate is 2.87 mg/ml. KM is quoted in mg/ml, not uM, because XTHs are able to utilise any segment of the polysaccharide chain equally well, not just one site per molecule as with the acceptor. Optimum pH is 6 for the XET activity. Strongly expressed in roots, hypocotyls and cotyledons. Aslo detected in inflorescence stems and in the carpels and styles in flowers. Down-regulated by auxin (PubMed:11673616). Down-regulated by aluminum (PubMed:21285327). Repressed by far-red light (FRc) (PubMed:14645728). Contains at least one intrachain disulfide bond essential for its enzymatic activity. No visible growth defects, but increased aluminum resistance. Belongs to the glycosyl hydrolase 16 family. XTH group 2 subfamily.