GH3 :: GUS reflects cell-specific developmental patterns and stress-induced changes in wood anatomy in the poplar stem

GH3 genes related tot he auxin-inducible glycine max (L.) Merr. GrnGH3 gene encode enzymes that conjugate amino acids to auxin. To investigate the role of GH3 enzymes in stress responses and normal wood development. Populus x canescens (Ait.) was transformed with the promoter-reporter construct GH3::GUS containing a GH3 promoter and the 5' UTR from soybean. beta-Glucuronidase (GUS) activity was present in the vascular tissues of leaves and in developing lateral roots and was inducible in silent tissues by external auxin application. A decrease in GUS activity front the stern apex to the bottom corresponded to decreases ill auxin concentrations in these tissues. High auxin concentration and high GH3::GUS activity were present ill the pith tissue, which may provide storage for auxin compounds. GH3 reporter was active in ray cells, paratracheal parenchyma cells, maturing vessels and ill cells Surrounding maturing phloem fibers but not ill the cambium and immature phloem, despite high auxin concentrations in the latter tissues. However, the GH3 promoter in these tissues became active when the plants were exposed to abiotic stresses, like bending or salinity, causing changes in wood anatomy. We suggest that adjustment of the internal auxin balance in wood in response to environmental cues involves GH3 auxin conjugate synthases.