AUTHOR=Liang Guihong , Zhang Zhenhua TITLE=Reducing the Nitrate Content in Vegetables Through Joint Regulation of Short-Distance Distribution and Long-Distance Transport JOURNAL=Frontiers in Plant Science VOLUME=11 YEAR=2020 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01079 DOI=10.3389/fpls.2020.01079 ISSN=1664-462X ABSTRACT=

As an important nitrogen source, nitrate (NO3) absorbed by plants is carried throughout the plant via short-distance distribution (cytoplasm to vacuole) and long-distance transportation (root to shoot), the two pathways that jointly regulate the content of NO3 in plants. NO3 accumulation within the vacuole depends on the activities of both tonoplast proton pumps and chloride channel (CLC) proteins, and less NO3 is stored in vacuoles when the activities of these proteins are reduced. The ratio of the distribution of NO3 in the cytoplasm and vacuole affects the long-distance transport of NO3, which is regulated by the proteins NPF7.3 and NPF7.2 that play opposite but complementary roles. NPF7.3 is responsible for loading NO3 from the root cytoplasm into the xylem, whereas NPF7.2 regulates the unloading of NO3 from the xylem, thereby facilitating the long-distance transport of NO3 through the roots to the shoots. Vegetables, valued for their nutrient content, are consumed in large quantities; however, a high content of NO3 can detrimentally affect the quality of these plants. NO3 that is not assimilated and utilized in plant tissues is converted via enzyme-catalyzed reactions to nitrite (NO2), which is toxic to plants and harmful to human health. In this review, we describe the mechanisms underlying NO3 distribution and transport in plants, a knowledge of which will contribute to breeding leafy vegetables with lower NO3 contents and thus be of considerable significance from the perspectives of environmental protection and food safety.