Prolonged root hypoxia effects on enzymes involved in nitrogen assimilation pathway in tomato plants

Abstract

IntroductionPlants grow in a dynamic environment, which frequently imposes constraints on growth and development. Among the adverse environmental factors commonly encountered by land plants, flooding is one of the most significant abiotic stresses. 1 Flooding of the soil can have a tremendous impact on the growth and survival of plants, and thereby on agricultural as well as natural ecosystems. In the last decades considerable progress has been made in our understanding of the mechanisms that enable certain plant species and cultivars to withstand periods with excess soil water or even complete submergence. Much of the research has been carried out with crop plant species, such as Oryza sativa, Zea mays, Trifolium subterraneum and Medicago sativa, 2-5 but wild species originating from wetland habitats have been also used, mostly for comparative studies. 6,7 With transient flooding or irrigation followed by slow drainage, or in natural wetlands, plant roots can become oxygen deficient because of slow transfer of dissolved oxygen in the waterfilled pore space of the soil. The decrease in ambient oxygen may not be, itself or alone, the perceived signal but could trigger metabolic responses, which then initiate the signalling cascade. 8 The immediate consequence of oxygen depletion is the reduction in respiration, thus diminishing ATP generation, and leading to a decrease in the ATP/ADP ratio and the adenylate energy charge. 9 In order to investigate the effects of root hypoxia (1-2% oxygen) on the nitrogen (N) metabolism of tomato plants (Solanum lycopersicum L. cv. Micro-Tom), a range of N compounds and N-assimilating enzymes were performed on roots and leaves of plants submitted to root hypoxia at the second leaf stage for three weeks. Obtained results showed that root hypoxia led to a significant decrease in dry weight (DW) production and nitrate content in roots and leaves. conversely, shoot to root DW ratio and nitrite content were significantly increased. contrary to that in leaves, glutamine synthetase activity was significantly enhanced in roots. The activities of nitrate and nitrite reductase were enhanced in roots as well as leaves. The higher increase in the Nh 4 + content and in the protease activities in roots and leaves of hypoxically treated plants coincide with a greater decrease in soluble protein contents. Taken together, these results suggest that root hypoxia leaded to higher protein degradation. The hypoxia-induced increase in the aminating glutamate dehydrogenase activity may be considered as an alternative N assimilation pathway involved in detoxifying the Nh 4 + , accumulated under hypoxic conditions. With respect to hypoxic stress, the distinct sensitivity of the enzymes involved in N assimilation is discussed. and 0.13 ± 0.03 g, respectively. The changes in the root and shoot dry weights (DW) and in shoot/root ratio were investigated after a three week period of hypoxic treatment. Root hypoxia decreased root and leaf DW production by 34 and 18%, respectively. Shoot to root DW ratio increas...

RNA-Seq reveals novel genes and pathways associated with hypoxia duration and tolerance in tomato root

“…− to NO 2 − (50 to 100 fold) and NR preference for NO 3 − rather than NO 2 − . However, hypoxia results in a higher accumulation of NO 2 − and therefore a higher level of NO can be produced via the NR pathway and mitochondrial cytochrome c oxidase [31][32][33] .…”

Biochemical metabolism of two cultivars of cowpea treated with 24-Epibrassinolide and subjected to saline stress

“…Oliveira (2010) pointed out another characteristic of the enzyme to use of energy from photosynthesis, which regulates the supply of carbon skeletons for incorporation of nitrogen into amino acids. The free ammonium accumulation in plant tissue in high concentrations of NaCl may be attributed to their direct uptake, nitrate reduction, deamination of nitrogenous compounds by photorespiratory cycle or by biological fixation (Horchani and Ashi-Smiti, 2010). Several authors have shown that plants under salt stress conditions promote an increase in the activity of the enzymes glutamine synthetase (GS) and glutamate synthase (GOGAT) involved in ammonium assimilation, which are assimilated on the alternative route glutamate dehydrogenase (GDH) (Carvalho, 2012;Taiz and Zeiger, 2013).…”

Keep Calm and Survive: Adaptation Strategies to Energy Crisis in Fruit Trees under Root Hypoxia

“…The GS/GOGAT cycle is the principal route of ammonium assimilation in plants [ 125 ]. In tomato ( Solanum lycopersicum L.), the activity of the ATP-consuming GS was significantly enhanced in roots during prolonged root hypoxia [ 126 ]. Here, a striking contrast in the GS transcriptional pattern was evidenced between ‘Mariana 2624’ and ‘Mazzard F12/1’ roots under hypoxic conditions, as GS transcripts were strongly accumulated in the hypoxia-tolerant genotype after 24 h of waterlogging, but consistently downregulated as stress progressed in the hypoxia-sensitive one ( Figure 1 ).…”