Adaptation of cucumber seedlings to low temperature stress by reducing nitrate to ammonium during it’s transportation

Abstract

Background Low temperature severely depresses the uptake, translocation from the root to the shoot, and metabolism of nitrate and ammonium in thermophilic plants such as cucumber (Cucumis sativus). Plant growth is inhibited accordingly. However, the availability of information on the effects of low temperature on nitrogen transport remains limited. Results Using non-invasive micro-test technology, the net nitrate (NO3−) and ammonium (NH4+) fluxes in the root hair zone and vascular bundles of the primary root, stem, petiole, midrib, lateral vein, and shoot tip of cucumber seedlings under normal temperature (NT; 26 °C) and low temperature (LT; 8 °C) treatment were analyzed. Under LT treatment, the net NO3− flux rate in the root hair zone and vascular bundles of cucumber seedlings decreased, whereas the net NH4+ flux rate in vascular bundles of the midrib, lateral vein, and shoot tip increased. Accordingly, the relative expression of CsNRT1.4a in the petiole and midrib was down-regulated, whereas the expression of CsAMT1.2a–1.2c in the midrib was up-regulated. The results of 15N isotope tracing showed that NO3−-N and NH4+-N uptake of the seedlings under LT treatment decreased significantly compared with that under NT treatment, and the concentration and proportion of both NO3−-N and NH4+-N distributed in the shoot decreased. Under LT treatment, the actual nitrate reductase activity (NRAact) in the root did not change significantly, whereas NRAact in the stem and petiole increased by 113.2 and 96.2%, respectively. Conclusions The higher net NH4+ flux rate in leaves and young tissues may reflect the higher NRAact in the stem and petiole, which may result in a higher proportion of NO3− being reduced to NH4+ during the upward transportation of NO3−. The results contribute to an improved understanding of the mechanism of changes in nitrate transportation in plants in response to low-temperature stress.

Ammonium Phytotoxicity and Tolerance: An Insight into Ammonium Nutrition to Improve Crop Productivity

“…An appropriate ratio of NH 4 + : NO 3 -(10:90) has effectively mitigated the low light intensity stress in Brassica pekinensis by modulating the expression of ammonium assimilatory enzymes, such as GS and NR [105]. In cucumber, the greater flux rate of NH 4 + into vascular bundles of the lateral vein, midrib, and shoot tip, due to the increased conversion of NO 3 to NH 4 + , has substantially aided in overcoming low-temperature stress, as an energy conservatory mechanism [130]. An equal ratio of ammonium and nitrate (50:50) was found to improve the biomass, photosynthetic efficiency, protein content, and decrease lipid peroxidation in baby lettuce under heat stress conditions [131].…”

Genome-Wide Identification and Expression Analysis of NPF Genes in Cucumber (Cucumis sativus L.)

“…Two homologous genes in cucumber, CsNPF6.2 and CsNPF6.3 , are highly expressed in the petioles of young leaves and may be responsible for the storage of nitrate in the petioles of young leaves. Liu et al showed that low temperature treatment significantly inhibited the expression of CsNPF6.3 ( CsNRT1.4a ) in petiole and midrib, which may be closely related to nitrate transport in petiole and midrib, which further verified the function of CsNPF6.3 in petiole [ 55 ]. In addition, CsNPF6.2 was significantly expressed in cucumber tendrils, indicating that it may differentiate into other functions, in addition to mediating nitrate storage.…”

Enhancing iron content and growth of cucumber seedlings with MgFe-LDHs under low-temperature stress

“…N is the most essential mineral nutrient for plants [ 48 ] and plays a critical role in the synthesis of amino acids, proteins, and nucleic acids [ 49 ]. Plant roots primarily take up nitrogen in the form of nitrate anions (NO 3 − ) and ammonium cations (NH 4 + ), with terrestrial plants favouring NO 3 − [ 50 ].…”