Professor University of Vermont Burlington, Vermont
Body of Abstract: As plant roots grow through a heterogeneous soil environment, the hormone Abscisic Acid (ABA) integrates information about the environment to modulate growth of the root system. One of the most important aspects of the environment that ABA mediates is availability of nutrients, particularly nitrate. Nitrogen is one of the most important nutrients for plants and the presence of nitrate in the root environment alters root growth, shaping the architecture of the root system. Recently, we found that nitrate stimulates ABA accumulation in the endodermis of Arabidopsis root tips. We adapted this immunofluorescence protocol for use in legumes and found that ABA accumulation in the endodermis is conserved in both Medicago truncatula and Lotus japonicus roots. We also found that nitrate stimulates ABA accumulation in 4-day old roots of M. truncatula, as it does in Arabidopsis and wheat, but inhibits ABA accumulation in the young portion of 18-day old roots. This regulation of ABA accumulation requires the nitrate transporter MtLATD/NIP (MtNPF1.7). Plants lacking a functional LATD/NIP transporter accumulated higher levels of ABA in the root endodermis than wild-type, and that accumulation was insensitive to regulation by nitrate in 18-day old plants, a time at which the mutant phenotype is the strongest. Together, these observations identify LATD/NIP as the transporter that functions in nitrate signaling to regulate root endodermal ABA accumulation in M. truncatula.