Carbohydrate accumulation in inferior grains in rice panicles subjected to moderate post-anthesis water stress is regulated by NAC transcription factors that activate the expression of WAXY.
Nitrogen deficiency induces leaf senescence. However, whether or how nitrate might affect this process remains to be investigated. Here, we report an interesting finding that nitrate-instead of nitrogen-starvation induced early leaf senescence in nrt1.5 mutant, and present genetic and physiological data demonstrating that nitrate starvation-induced leaf senescence is suppressed by NRT1.5. NRT1.5 suppresses the senescence process dependent on its function from roots, but not the nitrate transport function. Further analyses using nrt1.5 single and nia1 nia2 nrt1.5-4 triple mutant showed a negative correlation between nitrate concentration and senescence rate in leaves. Moreover, when exposed to nitrate starvation, foliar potassium level decreased in nrt1.5, but adding potassium could essentially restore the early leaf senescence phenotype of nrt1.5 plants. Nitrate starvation also downregulated the expression of HAK5, RAP2.11, and ANN1 in nrt1.5 roots, and appeared to alter potassium level in xylem sap from nrt1.5. These data suggest that NRT1.5 likely perceives nitrate starvation-derived signals to prevent leaf senescence by facilitating foliar potassium accumulation.
Nitrate transporters are primarily responsible for absorption of nitrate from soil and nitrate translocation among different parts of plants. They deliver nitrate to where it is needed. However, recent studies have revealed that nitrate transporters are extensively involved in coping with adverse environmental conditions besides limited nitrate/nitrogen availability. In this review, we describe the functions of the nitrate transporters related to abiotic stresses and their regulation. The expected and unexpected roles of nitrate transporters in plant abiotic stress resistance will also be discussed.
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