Kiradjiev, K. B. | Search bioRxiv

bioRxiv2026

Water stress adaptive responses in plants require movement of ABA and AB-aldehyde from vascular to target tissues

Vascular plants rapidly coordinate root and shoot responses to water stress. Abscisic acid (ABA) mediates these adaptations; however, it remains unclear which cells produce ABA, whether ABA synthesis shifts during stress, and whether ABA movement is required for its adaptive functions. Here, we map ABA biosynthesis at cellular resolution in Arabidopsis and report that water-stress adaptive responses in roots and shoots require movement of ABA and its precursor AB-aldehyde from vascular tissues to target cells. We suggest that ABA accumulation arises from two parallel routes: (i) ABA synthesized in the vasculature via ABA2 and AAO3, then moving to guard cells, and (ii) phloem-derived AB-aldehyde being converted to ABA in the epidermis or bundle sheath by AAO1 and AAO2. Finally, we predict that tightly packed cells beneath leaf veins facilitate efficient ABA delivery to guard cells, an anatomical arrangement that has enabled angiosperms to evolve the use of ABA to rapidly close stomata.

plant biology↗

bioRxiv2025

A balance of metabolism and diffusion articulates a gibberellin hormone gradient in the Arabidopsis root

The plant hormone gibberellin (GA4) regulates numerous developmental processes. Within the root, GA4 controls growth, in part, by controlling the extent of cell elongation. The nlsGPS1 FRET biosensor revealed a GA4 gradient within the Arabidopsis root growth zones, with GA4 levels correlating with cell length. We developed a multiscale mathematical model to understand how biosynthesis, catabolism and transport create the GA4 distribution within the root growth zones. The model showed that phloem delivery of the biosynthetic intermediate GA12 contributes to higher levels of bioactive GA4 in the elongation zone, with the GA4 synthesis pattern being further modified by local GA12 synthesis in the quiescent centre region and the spatial distribution of biosynthesis enzymes (GA20ox and GA3ox). Model predictions revealed that whilst GA20ox and GA3ox transcript is present throughout the growth zones, these enzymes are inactive in the dividing cells, which explains steep GA4 gradients observed in GA20ox and GA3ox over-expression lines, and improves agreement between model predictions and data in wildtype, ga20ox and ga3ox lines. The model revealed that the GA4 gradient also depends a balance of diffusion through plasmodesmata and catabolism. Both model predictions and biosensor data demonstrated that plasmodesmatal diffusion enables a more gradual GA4 gradient, with higher diffusion antagonizing the GA4 gradient. Model predictions suggested that catabolism limits GA4 levels, which we validated via biosensor imaging in the ga2oxhept mutant. We concluded that GA4 distribution mediates root growth programming via local GA4 synthesis combining with diffusion and catabolism to create a spatial gradient that provides positional information and patterns cell elongation.

plant biology↗