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 (A_N) due to decreased stomatal and mesophyll conductances (g_s and g_m, 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 A_N and g_m in a species-dependent manner, they were linked with g_m/g_s 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, A_N. 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.