Exogenous Brassinosteroid Facilitates Xylem Development in Pinus massoniana Seedlings

Abstract

Brassinosteroids (BRs) are known to be essential regulators for wood formation in herbaceous plants and poplar, but their roles in secondary growth and xylem development are still not well-defined, especially in pines. Here, we treated Pinus massoniana seedlings with different concentrations of exogenous BRs, and assayed the effects on plant growth, xylem development, endogenous phytohormone contents and gene expression within stems. Application of exogenous BR resulted in improving development of xylem more than phloem, and promoting xylem development in a dosage-dependent manner in a certain concentration rage. Endogenous hormone determination showed that BR may interact with other phytohormones in regulating xylem development. RNA-seq analysis revealed that some conventional phenylpropanoid biosynthesis- or lignin synthesis-related genes were downregulated, but the lignin content was elevated, suggesting that new lignin synthesis pathways or other cell wall components should be activated by BR treatment in P. massoniana. The results presented here reveal the foundational role of BRs in regulating plant secondary growth, and provide the basis for understanding molecular mechanisms of xylem development in P. massoniana.

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“…Finally, the cellulose content of stems was determined using the kit (G0715W, Suzhou Grace Bio-technology Co. LTD, Suzhou, China) based on hydrolysis and dehydration of cellulose into furfural compounds, which can react with anthrone ( Fan et al., 2021 ). Briefly, 0.1 g of fresh sample was weighed, and 1.5 mL of 80% ethanol was added to grind the homogenate.…”

“…Thirdly, the lignin content of stems was determined using a kit (G0708W, Suzhou Grace Bio-technology Co. LTD, Suzhou, China) according to the manufacturer’s instructions, based on acetylation of lignin phenolic hydroxyl group ( Fan et al., 2021 ). Briefly, an appropriate amount of the tissue sample was taken for drying and grinding, and passed it through 40 mesh sieves.…”

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“…After centrifugation at 12,000 rpm for 10 min, the precipitate was collected and dried at 95 °C for quantifying lignin. Finally, based on the acetylation of the lignin phenolic hydroxyl group, the content of lignin was further determined using spectrophotometry at 280 nm following the manufacturer's instructions (Suzhou Grace Bio-technology Co. Ltd., China) or performed as described by Fan et al 41…”

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“…In view of the low content of plant-synthesized brassinolide, cheap and efficient synthetic EBR is applied to agricultural production. Fan et al found that application of EBR can regulate the xylem development of masson pine and accelerate its timber formation [ 138 ]. Zhang et al found that application of EBR is good for the leaf size and expansion of tobacco [ 139 ].…”