Influence of IAA and ABA on maize stem vessel diameter and stress resistance in variable environments

The plasticity of the xylem and its associated hydraulic properties play crucial roles in plant acclimation to environmental changes, with vessel diameter (D_v) being the most functionally prominent trait. While the effects of external environmental factors on xylem formation and D_v are not fully understood, the endogenous hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) are known to play significant signalling roles under stress conditions. This study investigates how these hormones impact D_v under various environmental changes. Experiments were conducted in maize plants subjected to drought, soil salinity, and high CO₂ concentration treatments. We found that drought and soil salinity significantly reduced D_v at the same stem internode, while an elevated CO₂ concentration can mitigate this decrease in D_v. Remarkably, significant negative correlations were observed between D_v and the contents of IAA and ABA when considering the different treatments. Moreover, appropriate foliar application of either IAA or ABA on well-watered and stressed plants led to a decrease in D_v, while the application of corresponding inhibitors resulted in an increase in D_v. This finding underscores the causal relationship between D_v and the levels of both IAA and ABA, offering a promising approach to manipulating xylem vessel size.