It’s branching that means plants don’t live their lives as stems, but how do branches start? Botanists have identified H2O2 as part of the process that initiates growth in axillary buds, but haven’t been sure how. Research by Alexis Porcher and colleagues shows that H2O2 may keep buds dormant, with ascorbate-glutathione pathway scavenging reducing the in H2O2 buds, allowing growth to start.
The growth of buds is driven by cellular division. Quiescent axillary bud cells are paused at the G1 phase of the cell cycle. Once bud outgrowth starts, the cell moves into S phase, and starts duplicating its DNA. Porcher and colleagues aimed to characterize H2O2 abundances and metabolism in quiescent bud and during the outgrowth process. “The evolution of bud H2O2 content in wild type plants as well as its metabolism have, to our knowledge, never been investigated during a natural bud outgrowth process,” write the authors in their article.
“We determined that the quantity of H2O2 was high in the quiescent buds compared to that measured in the stem and continuously decreased in buds after the beheading that initiated the outgrowth process. Additionally, the stability of low levels in the neighboring stem, strongly suggesting that this response actually concerns the outgrowth process and not a wounding systemic response to the beheading. Furthermore, H2O2 level remained similar to that found in quiescent bud in the presence of the synthetic auxin NAA that mimicked apical dominance. This result is in line with the observations made by Wang and Faust (1988) which showed a strong presence of radical compounds in dormant apple tree buds.”
When buds started growing there was an increase ascorbate and glutathione metabolism. This is involved in H2O2 scavenging, and the scientists found an increase in gene expressions and activity levels of cytoplasmic forms of both APX and GR in bud during the outgrowing process.
“Taken together, our results on H2O2 metabolism suggest that the passage of redox status of bud from oxidized to reduced state during bud outgrowth confirming its role in branching process, as proposed by Considine and Foyer (2014),” write Porcher and colleagues. “Our data suggest that H2O2 scavenging, through the AsA-GSH cycle, appears as an important component of bud outgrowth mechanism confirming a major role for H2O2 in bud outgrowth control, as previously suggested.”