Dynamics of Pectins and Photosynthetic Traits in Sunflower and Tomato Subjected to Gradual Recoveries Preceded by Water Deprivation.

Drought affects plant traits and cell wall composition. Here, sunflower and tomato plants were subjected to six treatments differing in water availability: control (CL, full irrigation), short-term water deficit stress (ST) and gradual recoveries addressed after 3, 6, 12 and 24 h of rewatering plants previously subjected to ST (ST-Rec 3, 6, 12 and 24 h, respectively). Under ST, both species reduced net CO2 assimilation (AN) due to decreased stomatal and mesophyll conductances (gs and gm, respectively), enhancing water use efficiency (WUE). Nonetheless, these traits were gradually restored upon ST-Rec, reaching control values under ST-Rec at 24 h. Similarly, modifications in the cell wall main composition (i.e., cellulose, hemicelluloses, pectins and lignin) were found. While changes in pectins concentration across treatments could have influenced AN and gm in a species-dependent manner, they were linked with gm/gs variations when pooling data for both crops together. However, a significant relationship between pectins and WUE was only detected in sunflowers. We suggest that these modifications in pectins content could have remodelled the cell wall assembly, influencing CO2 diffusion through the leaf and, ultimately, AN. Although further experiments should be performed to reinforce our findings, we propose that variations in cell wall composition-especially pectins-may have affected the gradual photosynthetic recovery in plants previously subjected to water deprivation.