Abstract
Gibberellin (GA) is a key signal molecule inducing differentiation of tracheary elements, fibers, and xylogenesis. However the molecular mechanisms underlying the effect of GA on xylem elongation and secondary wall development in tree species remain to be determined. In this study, Betula platyphylla (birch) seeds were treated with 300 ppm GA3 and/or 300 ppm paclobutrazol (PAC), seed germination was recorded, and transverse sections of hypocotyls were stained with toluidine blue; the two-month-old seedlings were treated with 50 μM GA3 and/or 50 μM PAC, transverse sections of seedling stems were stained using phloroglucinol–HCl, and secondary wall biosynthesis related genes expression was analyzed by real-time quantitative PCR. Results indicated that germination percentage, energy and time of seeds, hypocotyl height and seedling fresh weight were enhanced by GA3, and reduced by PAC; the xylem development was wider in GA3-treated plants than in the control; the expression of NAC and MYB transcription factors, CESA, PAL, and GA oxidase was up-regulated during GA3 treatment, suggesting their role in GA3-induced xylem development in the birch. Our results suggest that GA3 induces the expression of secondary wall biosynthesis related genes to trigger xylogenesis in the birch plants.
Highlights
The expansion of xylem tissue is crucial for plant growth, the growth of woody plants.this process is of particular interest to commercial forestry
Our results showed that GA3 promoted germination of birch seeds and ameliorated the impact of PAC on germination
In a previous study [25], differential gene expression (DGE) indicated that 4 NAC, 5 MYB, 2 cellulose synthase (CESA), and 2 phenylalanine ammonialyase (PAL) genes were altered with higher RPKM values among tension wood (TW), opposite wood (OW) and normal wood (NW), suggesting that these genes may play a role in regulating xylem development in the birch
Summary
The expansion of xylem tissue is crucial for plant growth, the growth of woody plants. Gibberellins (GAs) are tetracyclic diterpenoid plant growth hormones that regulate diverse physiological processes including seed germination, stem elongation, leaf expansion, root growth, and the development of reproductive organs [3,4,5]. We hypothesized that the NAC, MYB, CESA, and PAL genes of birch plants controlled the xylem development process regulated by GA. In order to investigate the effect of GA3 on the germination of seeds and development of xylem in the birch we monitored the germination, hypocotyl height, and fresh weight of seedlings, measured transverse sections of hypocotyls and seedling stems and analyzed the expression of NAC and MYB transcription factors, CESA, PAL and GA oxidase genes by real-time quantitative PCR (RT-PCR). This work further characterizes the mechanisms of xylem development in birch
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