Auxin-independent effects of apical dominance induce changes in phytohormones correlated with bud outgrowth

Abstract

The inhibition of shoot branching by the growing shoot tip of plants, termed apical dominance, was originally thought to be mediated by auxin. Recently the importance of the shoot tip sink strength during apical dominance has re-emerged with recent studies highlighting roles for sugars in promoting branching. This raises many unanswered questions on the relative roles of auxin and sugars in apical dominance. Here we show that auxin depletion after decapitation is not always the initial trigger of rapid cytokinin increases in buds that are instead correlated with enhanced sugars. Auxin may also act through strigolactones which have been shown to suppress branching after decapitation, but here we show that strigolactones do not have a significant effect on initial bud outgrowth after decapitation. We report here that when sucrose or cytokinin is abundant, strigolactones are less inhibitory during the bud release stage compared to during later stages and that strigolactone treatment rapidly inhibits cytokinin accumulation in pea (Pisum sativum) axillary buds of intact plants. After initial bud release, we find an important role of gibberellin in promoting sustained bud growth downstream of auxin. We are therefore able to suggest a model of apical dominance that integrates auxin, sucrose, strigolactones, cytokinins and gibberellins and describes differences in signalling across stages of bud release to sustained growth.

Regulation of Energy Supply and Redox State in Bermudagrass: Role of H2O2 in Trimming-induced Tillering

“…In our study, both CTK content and its biosynthetic genes were found to increase after trimming, especially at the 1st node. This is consistent with ndings in pea, where CTK levels were signi cantly enhanced at the upper nodes after decapitation (Cao et al 2023). Therefore, the accumulation of CTK induced by trimming may depend on the distance from the site of trimming.…”

The activation of Arabidopsis axillary buds involves a switch from slow to rapid committed outgrowth regulated by auxin and strigolactone

“…Further evidence for this link comes from analysis of the role of gibberellin (GA) in shoot branching. Bud growth rate is promoted by GA in vegetative pea buds (Cao et al ., 2023). GA modulates PIN2 abundance and trafficking in Arabidopsis roots, and GA biosynthetic and signalling mutants have lower auxin transport (Willige et al ., 2011; Löfke et al ., 2013).…”

“…Previous efforts to characterise different stages of bud regulation have led to a two‐phase model of bud outgrowth based primarily on data from pea and rose (reviewed in Beveridge et al ., 2023). The first stage of ‘bud release’ occurs immediately post‐decapitation, regulated in an auxin‐independent manner, followed by a second phase of ‘sustained growth’, during which auxin transport out of the bud would be established (Barbier et al ., 2015; Chabikwa et al ., 2019; Bertheloot et al ., 2020; Cao et al ., 2023).…”

Climate‐resilient crops: Lessons from xerophytes

“…Plant genomes encode very large families of membrane‐localised receptor‐like kinases (RLK) (Monshausen & Haswell, 2013), so it is plausible to suggest that the difference in stomata operation between xerophytes and mesophytes may be related to their functional expression/sensitivity. More recent evidence also suggests that sucrose may operate as a long‐distance signalling molecule, which activates the trehalose‐6‐phosphate signal when transferred from the phloem into the buds, triggering axillary bud outgrowth (Cao et al., 2023).…”