Root Glutamate Dehydrogenase Research Articles

Phytotoxic Effects of Residual Glufosinate on the Nitrogen Assimilation of Transplanted Rapeseed Seedlings

ABSTRACTHerbicide application is an efficient method to control weed growth in modern agriculture production, but there is concern about the ecological impact of unwanted herbicide residues in the soil. Rapeseed varieties ZS11 and D148 were used to evaluate the phytotoxic effects of residual glufosinate on the assimilation of nitrogen (N) in rapeseed seedlings transplanted to untreated [0 g hm−2 glufosinate] or treated [450 g hm−2 and 900 g hm−2 glufosinate] soils. Glutamine synthetase (GS) and glutamate dehydrogenase (GDH) activities, the contents of ammonium (NH4+), free amino acids (FAA), and soluble protein (SP), and seedling dry weight (DW) were determined at 5, 8, 11, 20, 40, and 70 d post-transplant. Both concentrations of glufosinate induced physiological phytotoxicity on the N assimilation of transplanted seedlings of both varieties, as their leaves and roots presented reduced GS activities and SP contents, and increased GDH activities, and NH4+ and FAA content. Glufosinate phytotoxicity on the N assimilation of transplanted seedlings reached a plateau at 11 to 20 d. further, GDH in roots and GS in leaves were still significantly different at 70 d. Meanwhile, ZS11 might be more sensitive to glufosinate than D148 since ZS11 had more variation than D148 at the same treatment, and the overdose of glufosinate more strongly inhibited N assimilation than the recommended dose. Therefore, it is essential to apply a suitable glufosinate dose to the transplanted variety, to minimize adverse effects on crops and the environment.Abbreviations: N, Nitrogen; GS, Glutamine synthetase; GDH, glutamate dehydrogenase; NH4+, ammonium; FAA, free amino acids; SP, soluble proteins; DW, Dry weight; ANOVA, one-way analysis of variance; NO3−, nitrate; OECD, Organisation for Economic Co-operation and Development; PPT, phosphinothricin; USEPA, United States Environmental Protection Agency

Effect of ammonium or nitrate nutrition on photosynthesis, growth, and nitrogen assimilation in tomato plants

AbstractNitrogen (N) is taken up by most plant species in the form of nitrate (NO$ _3^- $) or ammonium (NH$ _4^+ $). Plant response to continuous NH$ _4^+ $ nutrition is species‐dependent. In this study, we compare the responses of tomato (Solanum lycopersicum L. cv. Rio Grande) plants to N source (NO$ _3^- $ or NH$ _4^+ $). To this end, early plant growth, photosynthesis, chlorophyll, carbohydrate, and N‐compound concentrations as well as the activities of main enzymes involved in N metabolism (nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate dehydrogenase) were analyzed. Early plant growth was remarkably ameliorated under NH$ _4^+ $‐ in comparison to NO$ _3^- $‐based nutrition. Concomitantly, photosynthetic activity, total chlorophyll, and carbohydrate concentrations were significantly increased. With increasing external NH$ _4^+ $ concentration, NH$ _4^+ $ accumulated mainly in roots. In addition, root protein concentration was significantly increased, reflecting high NH$ _4^+ $ incorporation into organic nitrogen. Root glutamine synthetase (GS) activity was enhanced by NH$ _4^+ $ for concentrations below 5 mM, whereas root glutamate dehydrogenase (GDH) activity increased in parallel to NH$ _4^+ $ availability. Together with the positive effect of NH$ _4^+ $ on tomato plant cv. Rio Grande growth, these results reveal that GDH could have, in addition to GS, a possible role in NH$ _4^+ $ detoxification and tolerance of NH$ _4^+ $‐based nutrition.

Symbiotic Nitrogen Fixation and Ammonium Nitrogen Assimilation in rrrbrb-, rrRbRb-, and RRrbrb-Pea Mutants

Wrinkled-seeded pea mutants (Pisum sativum L., genotypes rrrbrb-, rrRbRb-, and RRrbrb-) have seeds with reduced, but different, starch content and modified starch properties. Analysis of these mutants revealed an enhanced capacity of root nodules for symbiotic nitrogen fixation and of host plant organs for assimilation of ammonium nitrogen. This observation was confirmed by morphological data on organization of symbiotic system, by elevated nitrogenase activity, high protein accumulation in plants due to nitrogen fixation, and by enhanced activity of glutamine synthase in leaves and glutamate dehydrogenase in roots of mutants, as compared with the organs of wild-type pea. It is supposed that the aforementioned advantages of mutants are related to accumulation in seeds of elevated protein reserves that satisfy their demand for nitrogen during formation of symbiotic systems.

NITRATE REDUCTASE AND GLUTAMATE DEHYDROGENASE ACTIVITIES OF RESISTANT AND SENSITIVE CULTIVARS OF WHEAT AND BARLEY UNDER BORON TOXICITY

ABSTRACT In this study, changes in activity of key enzymes of nitrogen assimilation, namely nitrate reductase and glutamate dehydrogenase upon boron (B) toxicity in wheat (Triticum aestivum) and barley (Hordeum vulgare) cultivars were investigated. Ten-day-old seedlings were exposed to 10 mM boric acid for a duration of five days. Plants growing on the nutrient solutions and receiving no excess B, were maintained as controls. All experiments were conducted on leaf and root tissues of control and B-treated seedlings of B-tolerant and B-sensitive cultivars. For estimation of activity of nitrate reductase, an in vivo assay was used. Compared to controls (no B treatment) activity of nitrate reductase tended to decrease (15–17%) following B toxicity in root and leaf tissues of all cultivars, however, no significant difference was observed between resistant and sensitive cultivars. Boron stress increased activity of glutamate dehydrogenase in roots and leaves of all cultivars by an average of 81% and 30%, respectively. Compared to sensitive variety, the boron tolerant wheat variety exhibited a significantly higher increase in shoot tissue GDH activity, whereas no significant difference was observed in root tissues. It was concluded that, the increase in activity of glutamate dehydrogenase could be an adaptive mechanism in these species and possibly plays a protective role under boron-stress conditions.

Short-term ammonium supply stimulates glutamate dehydrogenase activity and alternative pathway respiration in roots of pea plants

The changes of C and N metabolism after switching Pisum sativum L. plants from nitrate to ammonium were studied. Pea plants were grown for three weeks in nutrient solution containing 0.5 mmol/L nitrate, and then randomly divided into five sets for five different nitrogen treatments: control (0.5 mmol/L nitrate) and four ammonium concentrations (0.5, 1, 2.5 and 5 mmol/L). After 72 hours, activities of enzymes related to C and N metabolism were measured. Ammonium content in roots increased with ammonium concentration showing saturation from a concentration of 2.5 mmol/L. Increasing external ammonium concentration also increased free amino acid content (mainly glutamine and asparagine), whereas starch content decreased and neither organic acid or soluble carbohydrates changed. Glutamine synthetase (GS; EC 6.3.1.2) activity decreased and root glutamate dehydrogenase (GDH; EC 1.4.1.2) activity increased with ammonium regardless of the concentration used. Root respiration rate increased with ammonium, due mainly to an increase of the alternative pathway. These results could be consistent with the assumption of a possible role for GDH in ammonium detoxification. Our results show a close relationship between GDH activity and respiration rate through alternate pathways in order to ensure the supply of C skeletons for ammonium assimilation, whereas surplus NADH is oxidised directly via the non-phosphorylating route.

Effects of copper exposure upon nitrogen metabolism in tissue cultured Vitis vinifera

The present study analyses the effects of copper treatment on nitrogen metabolism in a closed system. Sauvignon grapevines were cultured in agar and exposed to copper levels ranging from 0.07 (control) to 5 μg Cu g −1 medium. Ammonium, nitrate, nitrite, individual and total amino acids and protein contents were determined in root, and leaves. Enzyme activities of nitrate and nitrite reductases, glutamine synthetase, glutamate synthase and glutamate dehydrogenase were also determined. Copper exposure produces a dramatic change in nitrogen metabolism, with a reduction of total nitrogen, which reflects the reduction on nitrate and free amino acid contents in both root and leaves. The assimilation of nitrate the main nitrogen source in the medium, requires nitrate reductase, which is reduced to negligible activity as response to copper exposure. Primary nitrogen metabolism is also reduced in leaves, although to a lesser extent than in roots, which may explain the differences between the two organs in response to copper exposure. An alternative system for assimilation of nitrogen through glutamate dehydrogenase in roots is proposed, while higher levels of ammonium and glutamine may fullfil the needs of organic nitrogen in the leaves.

Nitrogen nutrition in the estuarine zone: the case of Suaeda maritima var. macrocarpa

Suaeda maritima L. var. macrocarpa is a halophytic species distributed in the lower parts of salt marshes of the French coasts. The influence of salinity on nitrogen nutrition and on levels of the key enzymes involved in nitrogen assimilation is analyzed by growing Suaeda under experimental conditions. Use of 15N-labelled NO 3 − and NH 4 + shows that both ions are effective sources of inorganic nitrogen for Suaeda. The plant is found to use NH 4 + ions with a good yield, chiefly at high salinities (up to 130 mM). Nitrate reduction and ammonium assimilation by the glutamine synthetase/ glutamate synthase pathway occurs mainly in leaves when Suaeda is grown at optimal saline conditions (130 mM NaCl). Absence of NaCl creates less favourable conditions and lowers the activity of nitrate reductase and glutamine synthetase but leads to an important activity of glutamate dehydrogenase in roots. This enzyme could play a major role under suboptimal environmental conditions (i.e., absence of NaCl for Suaeda maritima).

Different Effects of Cadmium in vitro and in vivo on Enzyme Activities in Bean Plants (Phaseolus vulgaris L.c.v. Sankt Andreas)

The effect of cadmium in vitro and in vivo on the activities of the enzymes glutamate dehydrogenase (GDH) and malate dehydrogenase (MDH) from roots and shoots of bean plants has been investigated. In vitro cadmium inhibited the activities of GDH and MDH in a concentration dependent manner, GDH being more susceptible to high cadmium concentrations (10−2 M CdSO4) than MDH. In vitro cadmium was bound more tightly to GDH than to MDH. The nature of the cadmium inhibition was non-competitive for both enzymes. Application of cadmium in vivo significantly stimulated GDH in roots and shoots. High root cadmium concentrations inhibited the activity of MDH in vivo, too. The different effects of cadmium in vitro and in vivo are discussed in terms of possible mechanisms of cadmium toxicity.

Localization of Glutamate Dehydrogenase and Glutamate Synthase in Roots and Nodules of Lupinus Seedlings

Activities of glutamate dehydrogenase (EC 1.4.1.2. GDH) and glutamate synthase (EC 1.6.1.53. GOGAT) in bacteroids, mitochondria, and cytosol of root nodules, as well as in mitochondria and cytosol of roots of yellow lupine were studied. A high NADH-dependent GDH activity was proved in the nodules, localized mainly in the mitochondrial fraction. In bacteroids and cytosol of the nodules, the NADH-dependent GOGAT activity exceeded the GDH activity. Both GDH and GOGAT revealed a significantly higher activity with NADH than in the presence of NADPH. Histochemical studies demonstrated the highest activity of glutamate dehydrogenase in the roots of lupine in the cells surrounding the nodule. Preliminary electron-microscopic investigations showed that in these cells two morphological types, at least, of mitochondria are apparent.