Effect of exogenous IAA on tension wood formation by facilitating polar auxin transport and cellulose biosynthesis in hybrid poplar (Populus deltoids × Populus nigra) wood

Abstract

Auxins as phytohormons, responsible for coordination of growing processes, also contribute to the formation of tension wood (TW) in trees, but the mechanism of this process is still unclear. In this study, it has been tried to induce TW formation in erect hybrid poplar trees (in opposite to inclined or bended trees) by treatment with exogenous indole-3-acetic acid (IAA, as one of the auxins) or N-1-naphthylphthalamic acid (NPA) as an auxin transport inhibitor. The treatment with IAA resulted in TW formation and, as expected, NPA treatment did not. The gelatinous fiber formation and higher cellulose content in the cell wall were unambiguous indicators for TW formation. Real-time polymerase chain reaction (PCR) analysis revealed that genes of PIN1, ABCB1, and AUX2 involved in polar auxin transport were highly expressed in trees treated with exogenous IAA. Moreover, expressions of cellulose biosynthesis related genes of UGP1, UGP2 and CesA13 were strongly up-regulated. These observations indicate that the accelerated intercellular polar auxin transport caused by exogenous IAA is accounted for TW formation, i.e. the signal transduction of auxin is affected, which then facilitates cellulose biosynthesis. In contrast, the transcript abundances of PIN1 and all selected cellulose synthases (CesAs) were decreased after NPA treatment via inhibiting the cellular auxin efflux with negative effects on plant's primary growth. These results are interpreted that TW formation is closely associated with the acceleration of intercellular polar auxin transport.

Genome-wide analysis of lncRNA and mRNA expression and endogenous hormone regulation during tension wood formation in Catalpa bungei

“…Four ARFs were downregulated in TW compared with NW. As shown in the study by Yu et al (2017), exogenous IAA increased the expression of the IAA transport-related genes PIN1 , ABCB1 , and AUX2 , accelerating the polar transport of auxin and inducing TW formation [ 22 ]. Hellgren et al (2004) did not observe significant differences int the endogenous IAA concentration in the cambium between TW and NW; thus, IAA was considered to have no correlation with TW formation [ 23 ].…”

“…In addition, exogenous indoleacetic acid (IAA) exerts a significant regulatory effect on xylem formation. After IAA treatment, the secondary xylem of hybrid poplar forms TW, with a concomitant increase in the expression of the genes related to auxin transport and cellulose biosynthesis [ 22 ]. As shown in the study by Hellgren et al (2004), the endogenous IAA content in TW is not significantly different from that in NW but was higher than in OW [ 23 ].…”

Auxin regulation and MdPIN expression during adventitious root initiation in apple cuttings

“…4 and S4). Although the physiological basis of how these two processes relate to AR formation is known, the fact that grain depletion and new membrane system formation were promoted by IAA and inhibited by NPA suggests that PAT is the initial driving force for these processes 35 .…”

Exogenous Brassinosteroid Facilitates Xylem Development in Pinus massoniana Seedlings

“…Numerous experiments using exogenous hormones have demonstrated the potential effects of triggering xylem differentiation and stem growth. Auxin is proven to be a preliminary regulator in regulating wood formation by facilitating polar auxin transport and biosynthesis [ 7 , 8 ]. GA treatment induces the tension wood formation, accompanied with enhancing auxin response and upregulating key genes involved in BR response [ 9 , 10 ].…”