The large nitrate transporter 1/peptide transporter family (NPF) has been shown to transport diverse substrates, including nitrate, amino acids, peptides, phytohormones, and glucosinolates. However, the rice (Oryza sativa) root-specific expressed member OsNPF7.2 has not been characterized. Here, our data show that OsNPF7.2 is a tonoplast localized low-affinity nitrate transporter, and affects rice growth under high nitrate supply. The expression analysis showed that OsNPF7.2 was mainly expressed in the elongation and maturation zones of roots, especially in the root sclerenchyma, cortex and stele. It was also induced by high concentrations of nitrate. Subcellular localization analysis showed that OsNPF7.2 was localized on the tonoplast of large and small vacuoles. Heterogenous expression in Xenopus laevis oocytes suggested that OsNPF7.2 was a low-affinity nitrate transporter. Knock-down of OsNPF7.2 retarded rice growth under high concentrations of nitrate. Therefore, we deduce that OsNPF7.2 plays a role in intracellular allocation of nitrate in roots, and thus influences rice growth under high nitrate supply.

The total phenolic, flavonoid, coumarin, and volatile contents and antioxidant activities in three tissues of six Citrus grandis ‘Tomentosa’ (CGT) fruit varieties were investigated. Two flavones, 3 coumarins and 147 volatiles were identified. The exocarp contained 3 coumarins, however, no coumarins were identified in the mesocarp, and only isoimperatorin was found in the pulp. In the exocarp, mesocarp and pulp, 104, 79 and 71 volatiles were identified, respectively. FuMao (FM) contained the highest total phenolic, naringin and rhoifolin amounts; HouYeZhengMao (HY-ZM) contained the highest meranzin hydrate and bergapten amounts; and XiYangZhengMao (XY-ZM) contained the highest isoimperatorin amount. The ABTS radical scavenging power of HuangLongZhengMao (HL-ZM) was the strongest, and FM had the strongest DPPH radical scavenging effect and ferric ion reducing antioxidant power. According to overall performance, FM and HY-ZM are the top two varieties with the highest total phenolic, flavonoid, and coumarin contents and antioxidant capacities.

Citrus grandis ‘Tomentosa’, commonly known as ‘Huajuhong’ pummelo (HJH), is used in traditional Chinese medicine and can moisten the lungs, resolve phlegm, and relieve coughs. A spontaneous bud mutant, named R-HJH, had a visually attractive phenotype with red albedo tissue and red juice sacs. In this study, the content and composition of carotenoids were investigated and compared between R-HJH and wild-type HJH using HPLC–MS analysis. The total carotenoids in the albedo tissue and juice sacs of R-HJH were 4.03- and 2.89-fold greater than those in HJH, respectively. The massive accumulation of carotenoids, including lycopene, β-carotene and phytoene, led to the attractive red color of R-HJH. However, the contents of flavones, coumarins and most volatile components (mainly D-limonene and γ-terpinene) were clearly reduced in R-HJH compared with wild-type HJH. To identify the molecular basis of carotenoid accumulation in R-HJH, RNA-Seq transcriptome sequencing was performed. Among 3948 differentially expressed genes (DEGs), the increased upstream synthesis genes (phytoene synthase gene, PSY) and decreased downstream genes (β-carotene hydroxylase gene, CHYB and carotenoid cleavage dioxygenase gene, CCD7) might be the key factors that account for the high level of carotenoids in R-HJH. These results will be beneficial for determining the molecular mechanism of carotenoid accumulation and metabolism in pummelo.