NPF4.6-mediated ABA transport modulates stomatal responses to fluctuating light

Stomatal responses to fluctuating light (FL) strongly influence photosynthetic efficiency and biomass accumulation in seed plants. The abscisic acid (ABA) transporter NPF4.6 (also known as NRT1.2 or AIT1) mediates hormone import into guard cells, but its physiological roles in leaves remain unclear. Here, we examined the functions of NPF4.6 in Arabidopsis thaliana by characterizing two independent loss-of-function mutants (npf4.6) under both steady and FL conditions. Compared with wild type, npf4.6 showed a 21-43% reduction in the half-time of stomatal opening and a 26-32% increase in the mean net CO2 assimilation rate under simulated field light conditions, resulting in a 41-48% increase in shoot biomass. In contrast, no marked differences in photosynthetic efficiency were observed between the wild type and npf4.6 under drought stress, suggesting that the role of NPF4.6 is more pronounced under well-watered, dynamic-light conditions. Overall, these findings demonstrate that NPF4.6 contributes to the fine-tuning of stomatal kinetics under variable light environments, and highlight hormone transport as a promising target for improving photosynthesis and growth in the field.