The Arabidopsis PIP1;1 Aquaporin Represses Lateral Root Development and Nitrate Uptake Under Low Nitrate Availability.

Nitrate (NO₃ ^-) deficiency decreases root water uptake and root hydraulic conductance. This adaptive response is correlated with reduced abundance and activity of plasma membrane intrinsic protein (PIP) aquaporins. We therefore screened changes in the root architecture of a complete set of Arabidopsis pip loss-of-function mutants grown under NO₃ ^- deficiency to systematically approach the impact of PIPs under these conditions. NO₃ ^- deprivation led to attenuated responses of specific pip single mutants compared to the strongly altered LR parameters of wild-type plants. In particular, pip1;1 exhibited a lower relative reduction in LR length and LR density, revealing that PIP1;1 represses LR development when NO₃ ^- is scarce. Indeed, PIP1;1 compromises root and shoot NO₃ ^- accumulation during early developmental stages. A fluorescent VENUS-PIP1;1 fusion revealed that PIP1;1 is specifically repressed in the pericycle, endodermis and at the flanks of emerging LRs upon NO₃ ^- deficiency. Thus, LR plasticity and NO₃ ^- uptake are affected by an interactive mechanism involving aquaporins (PIP1;1) and nitrate accumulation during seedling development under NO₃ ^--deficient conditions.