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Yifang Tsay - One of the best experts on this subject based on the ideXlab platform.

  • disruption of the rice Nitrate Transporter osnpf2 2 hinders root to shoot Nitrate transport and vascular development
    Scientific Reports, 2015
    Co-Authors: Jie Ouyang, Yifang Tsay, Ya-yun Wang, Kuaifei Xia, Jun Duan, Yaqin Wang, Mingyong Zhang
    Abstract:

    Plants have evolved to express some members of the Nitrate Transporter 1/peptide Transporter family (NPF) to uptake and transport Nitrate. However, little is known of the physiological and functional roles of this family in rice (Oryza sativa L.). Here, we characterized the vascular specific Transporter OsNPF2.2. Functional analysis using cDNA-injected Xenopus laevis oocytes revealed that OsNPF2.2 is a low-affinity, pH-dependent Nitrate Transporter. Use of a green fluorescent protein tagged OsNPF2.2 showed that the Transporter is located in the plasma membrane in the rice protoplast. Expression analysis showed that OsNPF2.2 is Nitrate inducible and is mainly expressed in parenchyma cells around the xylem. Disruption of OsNPF2.2 increased Nitrate concentration in the shoot xylem exudate when Nitrate was supplied after a deprivation period; this result suggests that OsNPF2.2 may participate in unloading Nitrate from the xylem. Under steady-state Nitrate supply, the osnpf2.2 mutants maintained high levels of Nitrate in the roots and low shoot:root Nitrate ratios; this observation suggests that OsNPF2.2 is involved in root-to-shoot Nitrate transport. Mutation of OsNPF2.2 also caused abnormal vasculature and retarded plant growth and development. Our findings demonstrate that OsNPF2.2 can unload Nitrate from the xylem to affect the root-to-shoot Nitrate transport and plant development.

  • uptake allocation and signaling of Nitrate
    Trends in Plant Science, 2012
    Co-Authors: Ya-yun Wang, Yifang Tsay
    Abstract:

    Plants need to acquire nitrogen (N) efficiently from the soil for growth. Nitrate is one of the major N sources for higher plants. Therefore, Nitrate uptake and allocation are key factors in efficient N utilization. Membrane-bound Transporters are required for Nitrate uptake from the soil and for the inter- and intracellular movement of Nitrate inside the plants. Four gene families, Nitrate Transporter 1/peptide Transporter (NRT1/PTR), NRT2, chloride channel (CLC), and slow anion channel-associated 1 homolog 3 (SLAC1/SLAH), are involved in Nitrate uptake, allocation, and storage in higher plants. Recent studies of these Transporters or channels have provided new insights into the molecular mechanisms of Nitrate uptake and allocation. Interestingly, several of these Transporters also play versatile roles in Nitrate sensing, plant development, pathogen defense, and/or stress response.

  • Arabidopsis Nitrate Transporter NRT1.9 Is Important in Phloem Nitrate Transport
    The Plant cell, 2011
    Co-Authors: Ya-yun Wang, Yifang Tsay
    Abstract:

    This study of the Arabidopsis thaliana Nitrate Transporter NRT1.9 reveals an important function for a NRT1 family member in phloem Nitrate transport. Functional analysis in Xenopus laevis oocytes showed that NRT1.9 is a low-affinity Nitrate Transporter. Green fluorescent protein and β-glucuronidase reporter analyses indicated that NRT1.9 is a plasma membrane Transporter expressed in the companion cells of root phloem. In nrt1.9 mutants, Nitrate content in root phloem exudates was decreased, and downward Nitrate transport was reduced, suggesting that NRT1.9 may facilitate loading of Nitrate into the root phloem and enhance downward Nitrate transport in roots. Under high Nitrate conditions, the nrt1.9 mutant showed enhanced root-to-shoot Nitrate transport and plant growth. We conclude that phloem Nitrate transport is facilitated by expression of NRT1.9 in root companion cells. In addition, enhanced root-to-shoot xylem transport of Nitrate in nrt1.9 mutants points to a negative correlation between xylem and phloem Nitrate transport.

  • chl1 functions as a Nitrate sensor in plants
    Cell, 2009
    Co-Authors: Yifang Tsay, Chenghsun Ho, Hengcheng Hu
    Abstract:

    Ions serve as essential nutrients in higher plants and can also act as signaling molecules. Little is known about how plants sense changes in soil nutrient concentrations. Previous studies showed that T101-phosphorylated CHL1 is a high-affinity Nitrate Transporter, whereas T101-dephosphorylated CHL1 is a low-affinity Transporter. In this study, analysis of an uptake- and sensing-decoupled mutant showed that the Nitrate Transporter CHL1 functions as a Nitrate sensor. Primary Nitrate responses in CHL1T101D and CHLT101A transgenic plants showed that phosphorylated and dephosphorylated CHL1 lead to a low- and high-level response, respectively. In vitro and in vivo studies showed that, in response to low Nitrate concentrations, protein kinase CIPK23 can phosphorylate T101 of CHL1 to maintain a low-level primary response. Thus, CHL1 uses dual-affinity binding and a phosphorylation switch to sense a wide range of Nitrate concentrations in the soil, thereby functioning as an ion sensor in higher plants. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

  • the arabidopsis Nitrate Transporter nrt1 7 expressed in phloem is responsible for source to sink remobilization of Nitrate
    The Plant Cell, 2009
    Co-Authors: Shuchun Fan, Chounsea Lin, Pokai Hsu, Shanhua Lin, Yifang Tsay
    Abstract:

    Several quantitative trait locus analyses have suggested that grain yield and nitrogen use efficiency are well correlated with Nitrate storage capacity and efficient remobilization. This study of the Arabidopsis thaliana Nitrate Transporter NRT1.7 provides new insights into Nitrate remobilization. Immunoblots, quantitative RT-PCR, b-glucuronidase reporter analysis, and immunolocalization indicated that NRT1.7 is expressed in the phloem of the leaf minor vein and that its expression levels increase coincidentally with the source strength of the leaf. In nrt1.7 mutants, more Nitrate was present in the older leaves, less 15 NO3 2 spotted on old leaves was remobilized into N-demanding tissues, and less Nitrate was detected in the phloem exudates of old leaves. These data indicate that NRT1.7 is responsible for phloem loading of Nitrate in the source leaf to allow Nitrate transport out of older leaves and into younger leaves. Interestingly, nrt1.7 mutants showed growth retardation when external nitrogen was depleted. We conclude that (1) Nitrate itself, in addition to organic forms of nitrogen, is remobilized, (2) Nitrate remobilization is important to sustain vigorous growth during nitrogen deficiency, and (3) sourceto-sink remobilization of Nitrate is mediated by phloem.

Nigel M Crawford - One of the best experts on this subject based on the ideXlab platform.

  • a genetic screen for Nitrate regulatory mutants captures the Nitrate Transporter gene nrt1 1
    Plant Physiology, 2009
    Co-Authors: Rongchen Wang, Xiujuan Xing, Yong Wang, Amy Tran, Nigel M Crawford
    Abstract:

    Nitrate regulatory mutants (nrg) of Arabidopsis (Arabidopsis thaliana) were sought using a genetic screen that employed a Nitrate-inducible promoter fused to the yellow fluorescent protein marker gene YFP. A mutation was identified that impaired Nitrate induction, and it was localized to the Nitrate regulatory gene NLP7, demonstrating the validity of this screen. A second, independent mutation (nrg1) mapped to a region containing the NRT1.1 (CHL1) Nitrate Transporter gene on chromosome 1. Sequence analysis of NRT1.1 in the mutant revealed a nonsense mutation that truncated the NRT1.1 protein at amino acid 301. The nrg1 mutation disrupted Nitrate regulation of several endogenous genes as induction of three Nitrate-responsive genes (NIA1, NiR, and NRT2.1) was dramatically reduced in roots of the mutant after 2-h treatment using Nitrate concentrations from 0.25 to 20 mm. Another nrt1.1 mutant (deletion mutant chl1-5) showed a similar phenotype. The loss of Nitrate induction in the two nrt1.1 mutants (nrg1 and chl1-5) was not explained by reduced Nitrate uptake and was reversed by nitrogen deprivation. Microarray analysis showed that Nitrate induction of 111 genes was reduced and of three genes increased 2-fold or more in the nrg1 mutant. Genes involved in Nitrate assimilation, energy metabolism, and pentose-phosphate pathway were most affected. These results strongly support the model that NRT1.1 acts as a Nitrate regulator or sensor in Arabidopsis.

  • the Nitrate Transporter atnrt1 1 chl1 functions in stomatal opening and contributes to drought susceptibility in arabidopsis
    The Plant Cell, 2003
    Co-Authors: Fangqing Guo, Jared W Young, Nigel M Crawford
    Abstract:

    The movement of guard cells in stomatal complexes controls water loss and CO(2) uptake in plants. Examination of the dual-affinity Nitrate Transporter gene AtNRT1.1 (CHL1) revealed that it is expressed and functions in Arabidopsis guard cells. CHL1 promoter-beta-glucuronidase and CHL1 promoter-green fluorescent protein constructs showed strong expression in guard cells, and immunolocalization experiments with anti-CHL1 antibody confirmed these results. To assess CHL1 function, chl1 mutant plants grown in the presence of Nitrate were examined. Compared with wild-type plants, chl1 mutants had reduced stomatal opening and reduced transpiration rates in the light or when deprived of CO(2) in the dark. These effects result in enhanced drought tolerance in chl1 mutants. At the cellular level, chl1 mutants showed reduced Nitrate accumulation in guard cells during stomatal opening and failed to show Nitrate-induced depolarization of guard cells. In wild-type guard cells, Nitrate induced depolarization, and Nitrate concentrations increased threefold during stomatal opening. These results identify an anion Transporter that functions in stomatal opening and demonstrate that CHL1 supports stomatal function in the presence of Nitrate.

  • the arabidopsis dual affinity Nitrate Transporter gene atnrt1 1 chl1 is regulated by auxin in both shoots and roots
    Journal of Experimental Botany, 2002
    Co-Authors: Fangqing Guo, Rongchen Wang, Nigel M Crawford
    Abstract:

    The AtNRT1.1 (CHL1) gene of Arabidopsis encodes a dual-affinity Nitrate Transporter and contributes to both low and high affinity Nitrate uptake. Localization studies have shown that CHL1 expression is preferentially targeted to nascent organs and growing regions of roots and shoots in Arabidopsis. In roots, CHL1 expression is concentrated in the tips of primary and lateral roots and is activated during lateral root initiation. In shoots, strong CHL1 expression is found in young leaves and developing flower buds. These findings suggest that CHL1 expression might be regulated by a growth signal such as the phytohormone auxin. To test this, auxin regulation of CHL1 was examined. Using transgenic Arabidopsis plants containing CHL1::GUS/GFP DNA constructs, it was found that treatment with exogenous auxin or introduction of the auxin overproducing mutations (yucca and rooty) resulted in a strong increase in CHL1::GUS/GFP signals in roots and leaves. When mature roots were treated with auxin to induce lateral root formation, CHL1::GFP signals were dramatically enhanced in dividing pericycle cells and throughout primordia development. RNA blot analysis showed that CHL1 mRNA levels in whole seedlings increase within 30 min of auxin treatment. The distribution of CHL1 expression in Arabidopsis roots and shoots was found to be similar to that of DR5::GUS, a synthetic, auxin-responsive gene. These results indicate that auxin acts as an important signal regulating CHL1 expression and contributes to the targeting of CHL1 expression to nascent organs and root tips in Arabidopsis.

  • the arabidopsis chl1 protein plays a major role in high affinity Nitrate uptake
    Proceedings of the National Academy of Sciences of the United States of America, 1998
    Co-Authors: Rongchen Wang, Dong Liu, Nigel M Crawford
    Abstract:

    The CHL1 (NRT1) gene of Arabidopsis encodes a Nitrate-inducible Nitrate Transporter that is thought to be a component of the low-affinity (mechanism II) Nitrate-uptake system in plants. A search was performed to find high-affinity (mechanism I) uptake mutants by using chlorate selections on plants containing Tag1 transposable elements. Chlorate-resistant mutants defective in high-affinity Nitrate uptake were identified, and one had a Tag1 insertion in chl1, which was responsible for the phenotype. Further analysis showed that chl1 mutants have reduced high-affinity uptake in induced plants and are missing a saturable component of the constitutive, high-affinity uptake system in addition to reduced low-affinity uptake. The contribution of CHL1 to constitutive high-affinity uptake is higher when plants are grown at more acidic pH, conditions that increase the level of CHL1 mRNA. chl1 mutants show reduced membrane depolarization in root epidermal cells in response to low (250 μM) and high (10 mM) concentrations of Nitrate. Low levels of Nitrate (100 μM) induce a rapid increase in CHL1 mRNA. These results show that CHL1 is an important component of both the high-affinity and the low-affinity Nitrate-uptake systems and indicate that CHL1 may be a dual-affinity Nitrate Transporter.

  • chl1 encodes a component of the low affinity Nitrate uptake system in arabidopsis and shows cell type specific expression in roots
    The Plant Cell, 1996
    Co-Authors: Nienchen Huang, Nigel M Crawford, Chiensung Chiang, Yifang Tsay
    Abstract:

    The Arabidopsis CHL1 (AtNRT1) gene confers sensitivity to the herbicide chlorate and encodes a Nitrate-regulated Nitrate Transporter. However, how CHL1 participates in Nitrate uptake in plants is not yet clear. In this study, we examined the in vivo function of CHL1 with in vivo uptake measurements and in situ hybridization experiments. Under most conditions tested, the amount of Nitrate uptake by a chl1 deletion mutant was found to be significantly less than that of the wild type. This uptake deficiency was reversed when a CHL1 cDNA clone driven by the cauliflower mosaic virus 35S promoter was expressed in transgenic chl1 plants. Furthermore, tissue-specific expression patterns showed that near the root tip, CHL1 mRNA is found primarily in the epidermis, but further from the root tip, the mRNA is found in the cortex or endodermis. These results are consistent with the involvement of CHL1 in Nitrate uptake at different stages of root cell development. A functional analysis in Xenopus oocytes indicated that CHL1 is a low-affinity Nitrate Transporter with a K(m) value of approximately 8.5 mM for Nitrate. This finding is consistent with the chlorate resistance phenotype of chl1 mutants. However, these results do not fit the current model of a single, constitutive component for the low-affinity uptake system. To reconcile this discrepancy and the complex uptake behavior observed, we propose a "two-gene" model for the low-affinity Nitrate uptake system of Arabidopsis.

Kunhsiang Liu - One of the best experts on this subject based on the ideXlab platform.

  • switching between the two action modes of the dual affinity Nitrate Transporter chl1 by phosphorylation
    The EMBO Journal, 2003
    Co-Authors: Kunhsiang Liu, Yifang Tsay
    Abstract:

    To counteract fluctuating nutrient environments, plants have evolved high- and low-affinity uptake systems. These two systems were traditionally thought to be genetically distinct, but, recently, two Arabidopsis Transporters, AtKUP1 and CHL1, were shown to have dual affinities. However, little is known about how a dual-affinity Transporter works and the advantages of having a dual-affinity Transporter. This study demonstrates that, in the case of CHL1, switching between the two modes of action is regulated by phosphorylation at threonine residue 101; when phosphorylated, CHL1 functions as a high-affinity Nitrate Transporter, whereas, when dephosphorylated, it functions as a low-affinity Nitrate Transporter. This regulatory mechanism allows plants to change rapidly between high- and low-affinity Nitrate uptake, which may be critical when competing for limited nitrogen. These results demonstrate yet another regulatory role of phosphorylation in plant physiology.

  • cloning and functional characterization of an arabidopsis Nitrate Transporter gene that encodes a constitutive component of low affinity uptake
    The Plant Cell, 1999
    Co-Authors: Nienchen Huang, Kunhsiang Liu, Yifang Tsay
    Abstract:

    The Arabidopsis CHL1 ( AtNRT1 ) gene encodes an inducible component of low-affinity Nitrate uptake, which necessitates a “two-component” model to account for the constitutive low-affinity uptake observed in physiological studies. Here, we report the cloning and characterization of a CHL1 homolog, AtNRT1:2 (originally named NTL1 ), with data to indicate that this gene encodes a constitutive component of low-affinity Nitrate uptake. Transgenic plants expressing antisense AtNRT1:2 exhibited reduced Nitrate-induced membrane depolarization and Nitrate uptake activities in assays with 10 mM Nitrate. Furthermore, transgenic plants expressing antisense AtNRT1:2 in the chl1-5 background exhibited an enhanced resistance to chlorate (7 mM as opposed to 2 mM for the chl1-5 mutant). Kinetic analysis of AtNRT1:2 -injected Xenopus oocytes yielded a K m for Nitrate of ∼5.9 mM. In contrast to CHL1 , AtNRT1:2 was constitutively expressed before and after Nitrate exposure (it was repressed transiently only when the level of CHL1 mRNA started to increase significantly), and its mRNA was found primarily in root hairs and the epidermis in both young (root tips) and mature regions of roots. We conclude that low-affinity systems of Nitrate uptake, like high-affinity systems, are composed of inducible and constitutive components and that with their distinct functions, they are part of an elaborate Nitrate uptake network in Arabidopsis.

  • chl1 is a dual affinity Nitrate Transporter of arabidopsis involved in multiple phases of Nitrate uptake
    The Plant Cell, 1999
    Co-Authors: Chiying Huang, Kunhsiang Liu, Yifang Tsay
    Abstract:

    Higher plants have both high- and low-affinity Nitrate uptake systems. These systems are generally thought to be genetically distinct. Here, we demonstrate that a well-known low-affinity Nitrate uptake mutant of Arabidopsis, chl1 , is also defective in high-affinity Nitrate uptake. Two to 3 hr after Nitrate induction, uptake activities of various chl1 mutants at 250 μM Nitrate (a high-affinity concentration) were only 18 to 30% of those of wild-type plants. In these mutants, both the inducible phase and the constitutive phase of high-affinity Nitrate uptake activities were reduced, with the inducible phase being severely reduced. Expressing a CHL1 cDNA driven by the cauliflower mosaic virus 35S promoter in a transgenic chl1 plant effectively recovered the defect in high-affinity uptake for the constitutive phase but not for the induced phase, which is consistent with the constitutive level of CHL1 expression in the transgenic plant. Kinetic analysis of Nitrate uptake by CHL1 -injected Xenopus oocytes displayed a biphasic pattern with a Michaelis–Menten K m value of ~50 μM for the high-affinity phase and ~4 mM for the low-affinity phase. These results indicate that in addition to being a low-affinity Nitrate Transporter, as previously recognized, CHL1 is also involved in both the inducible and constitutive phases of high-affinity Nitrate uptake in Arabidopsis.

Mingyong Zhang - One of the best experts on this subject based on the ideXlab platform.

  • knock down of a tonoplast localized low affinity Nitrate Transporter osnpf7 2 affects rice growth under high Nitrate supply
    Frontiers in Plant Science, 2016
    Co-Authors: Diyang Qiu, Xiaorong Fan, Anthony J Miller, Yi Chen, Xiaoping Pan, Mingyong Zhang
    Abstract:

    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.

  • disruption of the rice Nitrate Transporter osnpf2 2 hinders root to shoot Nitrate transport and vascular development
    Scientific Reports, 2015
    Co-Authors: Jie Ouyang, Yifang Tsay, Ya-yun Wang, Kuaifei Xia, Jun Duan, Yaqin Wang, Mingyong Zhang
    Abstract:

    Plants have evolved to express some members of the Nitrate Transporter 1/peptide Transporter family (NPF) to uptake and transport Nitrate. However, little is known of the physiological and functional roles of this family in rice (Oryza sativa L.). Here, we characterized the vascular specific Transporter OsNPF2.2. Functional analysis using cDNA-injected Xenopus laevis oocytes revealed that OsNPF2.2 is a low-affinity, pH-dependent Nitrate Transporter. Use of a green fluorescent protein tagged OsNPF2.2 showed that the Transporter is located in the plasma membrane in the rice protoplast. Expression analysis showed that OsNPF2.2 is Nitrate inducible and is mainly expressed in parenchyma cells around the xylem. Disruption of OsNPF2.2 increased Nitrate concentration in the shoot xylem exudate when Nitrate was supplied after a deprivation period; this result suggests that OsNPF2.2 may participate in unloading Nitrate from the xylem. Under steady-state Nitrate supply, the osnpf2.2 mutants maintained high levels of Nitrate in the roots and low shoot:root Nitrate ratios; this observation suggests that OsNPF2.2 is involved in root-to-shoot Nitrate transport. Mutation of OsNPF2.2 also caused abnormal vasculature and retarded plant growth and development. Our findings demonstrate that OsNPF2.2 can unload Nitrate from the xylem to affect the root-to-shoot Nitrate transport and plant development.

  • altered expression of the ptr nrt1 homologue osptr9 affects nitrogen utilization efficiency growth and grain yield in rice
    Plant Biotechnology Journal, 2013
    Co-Authors: Zhongming Fang, Stefan Meier, Marianne Suter Grotemeyer, Doris Rentsch, Xin Yang, Xinlan Xu, Mingyong Zhang
    Abstract:

    The plant PTR/NRT1 (peptide Transporter/Nitrate Transporter 1) gene family comprises di/tripeptide and low-affinity Nitrate Transporters; some members also recognize other substrates such as carboxylates, phytohormones (auxin and abscisic acid), or defence compounds (glucosinolates). Little is known about the members of this gene family in rice (Oryza sativa L.). Here, we report the influence of altered OsPTR9 expression on nitrogen utilization efficiency, growth, and grain yield. OsPTR9 expression is regulated by exogenous nitrogen and by the day-night cycle. Elevated expression of OsPTR9 in transgenic rice plants resulted in enhanced ammonium uptake, promotion of lateral root formation and increased grain yield. On the other hand, down-regulation of OsPTR9 in a T-DNA insertion line (osptr9) and in OsPTR9-RNAi rice plants had the opposite effect. These results suggest that OsPTR9 might hold potential for improving nitrogen utilization efficiency and grain yield in rice breeding.

Chenghsun Ho - One of the best experts on this subject based on the ideXlab platform.

  • chl1 functions as a Nitrate sensor in plants
    Cell, 2009
    Co-Authors: Yifang Tsay, Chenghsun Ho, Hengcheng Hu
    Abstract:

    Ions serve as essential nutrients in higher plants and can also act as signaling molecules. Little is known about how plants sense changes in soil nutrient concentrations. Previous studies showed that T101-phosphorylated CHL1 is a high-affinity Nitrate Transporter, whereas T101-dephosphorylated CHL1 is a low-affinity Transporter. In this study, analysis of an uptake- and sensing-decoupled mutant showed that the Nitrate Transporter CHL1 functions as a Nitrate sensor. Primary Nitrate responses in CHL1T101D and CHLT101A transgenic plants showed that phosphorylated and dephosphorylated CHL1 lead to a low- and high-level response, respectively. In vitro and in vivo studies showed that, in response to low Nitrate concentrations, protein kinase CIPK23 can phosphorylate T101 of CHL1 to maintain a low-level primary response. Thus, CHL1 uses dual-affinity binding and a phosphorylation switch to sense a wide range of Nitrate concentrations in the soil, thereby functioning as an ion sensor in higher plants. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

  • Nitrate Transporters and peptide Transporters
    FEBS Letters, 2007
    Co-Authors: Yifang Tsay, Chi Chou Chiu, Chyn Bey Tsai, Chenghsun Ho
    Abstract:

    In higher plants, two types of Nitrate Transporters, NRT1 and NRT2, have been identified. In Arabidopsis, there are 53 NRT1 genes and 7 NRT2 genes. NRT2 are high-affinity Nitrate Transporters, while most members of the NRT1 family are low-affinity Nitrate Transporters. The exception is CHL1 (AtNRT1.1), which is a dual-affinity Nitrate Transporter, its mode of action being switched by phosphorylation and dephosphorylation of threonine 101. Two of the NRT1 genes, CHL1 and AtNRT1.2, and two of the NRT2 genes, AtNRT2.1 and AtNRT2.2, are known to be involved in Nitrate uptake. In addition, AtNRT1.4 is required for petiole Nitrate storage. On the other hand, some members of the NRT1 family are dipeptide Transporters, called PTRs, which transport a broad spectrum of di/tripeptides. In barley, HvPTR1, expressed in the plasma membrane of scutellar epithelial cells, is involved in mobilizing peptides, produced by hydrolysis of endosperm storage protein, to the developing embryo. In higher plants, there is another family of peptide Transporters, called oligopeptide Transporters (OPTs), which transport tetra/pentapeptides. In addition, some OPTs transport GSH, GSSH, GSH conjugates, phytochelatins, and metals.