Gibberellin and spermidine synergistically regulate polyamine metabolism during the development of Rhododendron flowers

Abstract

Polyamines (PAs) are involved in various plants developmental processes, especially in owering. Their signi cant in uence has been established, but the exact mechanisms by which PAs modulate oweringare not yet understood. To understand the PA metabolism during owering/senescence in Rhododendron simsii 'Zichendian' plants, exogenous gibberellin (GA 3 , 0-2400 mg L − 1 ) and spermidine (Spd, 0-1 mM) were applied separately or in combination during the early stage of ower bud formation. The application of GA 3 alone advanced the initial owering by promoting the free Put (F) fraction and decreasing the Spd/Put ratio at the squaring stage, whereas Spd alone delayed the initial owering by increasing the soluble conjugated (C) form, insoluble bound Put (B) fraction and Spd/Put ratio. When GA 3 plus Spd was applied, the initial owering advanced by 2 days. Furthermore, endogenous PA levels as well as the C and B fractions of PAs and key enzymes (diamine oxidase, PA oxidase, arginine decarboxylase, ornithine decarboxylase and S-adenosylmethionine decarboxylase) of PA metabolism increased, while the Spd/Spm ratio decreased by GA 3 and Spd applications during owering, resulting in delayed ower senescence. In addition, the structural equation model (SEM) showed that Spd directly participated in PA metabolism, while GA 3 regulated owering by modulating PA metabolism via Spd (c.f. 0.27). Taken together, our study provides comprehensive evidence regarding the clear relationships between GA 3 , Spd and owering time, supporting the positive effect of PA metabolism on delaying ower senescence, and helps to provide a thorough understanding of the PA interconversions, biosynthesis and catabolism during owering and senescence.

Chinese cherry CpMYB44‐CpSPDS2 module regulates spermidine content and florescence in tobacco

“…It was reported that PA metabolism was involved in floral organ development and acceleration of flowering (Liu et al, 2009; Merelo et al, 2022; Xu et al, 2022). SPDS encodes a spermidine synthase that converts Put to Spd (Tiburcio et al, 2014).…”

“…Nevertheless, flowering could be restored upon transferring plants to an inhibitor‐free medium (Applewhite et al, 2000). In addition, the administration of Spd was found to significantly advance flowering in Gentian trillium and Rhododendron (Imamura et al, 2015; Xu et al, 2022). These results collectively suggested that Spd shortens the flowering time.…”