Cytokinins and Abscisic Acid Act Antagonistically in the Regulation of the Bud Outgrowth Pattern by Light Intensity.

Adrien Corot,Nathalie Leduc,Sylvie Citerne,Odile Douillet,Jessica Bertheloot,Maria-Dolores Perez-Garcia,Soulaiman Sakr,Hanaé Roman,Hervé Autret,Sabine Demotes-Mainard

doi:10.3389/fpls.2017.01724

Abstract

Bud outgrowth is a key process in the elaboration of yield and visual quality in rose crops. Although light intensity is well known to affect bud outgrowth, little is known on the mechanisms involved in this regulation. The objective of this work was to test if the control of bud outgrowth pattern along the stem by photosynthetic photon flux density (PPFD) is mediated by sugars, cytokinins and/or abscisic acid in intact rose plants. Rooted cuttings of Rosa hybrida ‘Radrazz’ were grown in growth chambers under high PPFD (530 μmol m-2 s-1) until the floral bud visible stage. Plants were then either placed under low PPFD (90 μmol m-2 s-1) or maintained under high PPFD. Bud outgrowth inhibition by low PPFD was associated with lower cytokinin and sugar contents and a higher abscisic acid content in the stem. Interestingly, cytokinin supply to the stem restored bud outgrowth under low PPFD. On the other hand, abscisic acid supply inhibited outgrowth under high PPFD and antagonized bud outgrowth stimulation by cytokinins under low PPFD. In contrast, application of sugars did not restore bud outgrowth under low PPFD. These results suggest that PPFD regulation of bud outgrowth in rose involves a signaling pathway in which cytokinins and abscisic acid play antagonistic roles. Sugars can act as nutritional and signaling compounds and may be involved too, but do not appear as the main regulator of the response to PPFD.

Highlights

Branching – or tillering for monocots – is a key process in the elaboration of crop yield and quality
Changes in photosynthetic photon flux density (PPFD) led to variations in endogenous CK, abscisic acid (ABA), and sugar contents in internode 4, consistent with bud outgrowth response to PPFD: CKs and sugars, which promote bud outgrowth, had their levels decreased under low PPFD, while ABA, an outgrowth inhibitor, had its content increased
The variations in endogenous CK, ABA, and sugar contents in internode 4 preceded the outgrowth of the adjacent bud under high PPFD by at least 4 days; this supports the hypothesis that these chemicals could contribute to the regulation of bud outgrowth

Summary

Introduction

Branching – or tillering for monocots – is a key process in the elaboration of crop yield and quality. Branching can affect yield directly – through the number of fertile branches (Bredmose, 1993; Valério et al, 2009) – or indirectly by increasing the competitive ability of crops against weeds (Lemerle et al, 1996; Zhao et al, 2006) or by constraining pest infestation (Simon et al, 2012). In ornamental plants such as rose bush, plant architecture is derived from branching, and influences plant visual quality and consumers’ preferences (Boumaza et al, 2010; Garbez et al, 2015). Under optimal growth conditions, the bud outgrowth pattern of a stem of the rose bush Rosa hybrida ‘Radrazz’ is acrotonic, meaning that apical buds grow out more frequently than median or basal buds (Demotes-Mainard et al, 2013b)

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