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Nitrate reductase and glutamine synthetase activities in relation to growth and nitrogen assimilation in red oak and red ash seedlings: effects of N-forms, N concentration and light intensity

The effects of growing seedlings of red oak (Quercus rubra) and red ash (Fraxinus pennsylvanica) with Hoagland solutions containing five N-regimes, differing in the N-forms (NH4, NO3) and concentrations (High and Low), in relation to light intensity were investigated by the utilization of enzymatic markers of the N assimilation pathway, nitrate reductase (NR) and glutamine synthetase (GS). Red oak and red ash showed different patterns of N-assimilation. Red oak seedlings assimilated NO3 in low amounts in their roots and leaves, whereas red ash seedlings assimilated high amounts of NO3, mostly in the leaves. A significant amount of constitutive NR activity was found in red oak seedlings supplied with NH4 N-regime. This could be characteristic of a species adapted to soils that are poor in nitrogen. Root GS activity was lower in red oak seedlings than in red ash seedlings, indicating that the rate of NH4 assimilation differed in these two hardwood species. Low irradiance reduced growth of both hardwood species, but greatly affected the specific leaf area of red ash and reduced NO3 assimilation (when data are expressed per leaf area). Both species reacted similarly to N-regimes in terms of relative growth rate.

Elevated C02 Does not Provide Protection against Ozone Considering the Activity of Several Antioxidant Enzymes in the Leaves of Sugar Maple

Summary Seedlings of sugar maple ( Acer saccharum Marsch.) were exposed for 46 days to 700 ppm of C0 2 , 200 ppb of ozone, and 700 ppm of C0 2 + 200 ppb of ozone. A significant increase in the activity of H 2 0 2 scavenging enzymes, i.e. ascorbate peroxidase [EC 1.11.1.11] and catalase [EC 1.11.1.6], was measured due to the action of 0 3 . This increase was rather negatively affected by elevated C0 2 . A tendency of decreased activity of glutathione reductase [EC 1.6.4.2] and superoxide dismutase [EC 1.15.1.1] due to the action of 0 3 was detected. Elevated C0 2 does not provide enhanced tolerance to oxidative stress in the seedlings of sugar maple. Changes in the activity of antioxidant enzymes were more pronounced in the young leaves (developed during the experiment) than in the old leaves (developed before starting the experiment). Stimulation of chloroplastic FeSOD by elevated C0 2 was observed, indicating oxidative stress in chloroplasts evoked by elevated C0 2 level. This effect did not result in enhanced protection against the detrimental effect of ozone, most probably due to compartmentation of C0 2 and 0 3 effects within the cell.

Nitrate reductase activity in relation to growth and soil N forms in red oak and red ash planted in three different environments: forest, clear-cut and field

Abstract Experimental hardwood plantations were established in three different environments (forest with partial openings, clear-cut and abandoned agricultural field) with different soil nitrogen status (N form and nitrification rates), in order to verify if NO 3 − assimilation of planted red oak and red ash seedlings could be linked to the performance of both species in the different plantation sites (where half of the plots were sprayed with herbicide). Nitrate reductase activity (NRA) in leaves and roots as an index of NO 3 − assimilation was chosen, as this enzyme is inducible and is also the first key enzyme involved in the assimilation of NO 3 − . Results show that NRA varied in relation to time, plantation environment, herbicide application and species of tree. Red ash always had higher values (18.43 μmol NO 2 g −1 dry weight (DW) h −1 ) than red oak (2.06 μmol NO 2 g −1 DW h −1 ) in herbicide plots in open environments, especially in the field plantation in July 1990. Herbicide spraying increased NO 3 − availability in soils and acted as a test for the presence of inducible nitrate reductase in both species. An increase in NRA is found in relation to herbicide application. Red ash shows greater differences than red oak between herbicide and control treatments. Both species show different values of height and diameter increment, and relative growth rate (RGR) in relation to the plantation sites. Red oak seedlings show greater growth gains in clear-cut with herbicide treatment (RGR = 0.79 g g −1 month −1 ), whereas the field plantation site produced the largest red ash seedlings (RGR = 0.56 g g −1 month −1 ) in herbicide plots. In limited light conditions (clear-cut control plots and forest environment), red oak had higher RGR than red ash. These results suggest that NRA in the leaves of hardwood trees can provide a useful index to evaluate the physiological status of tree seedlings, which reflects their response to environmental conditions. The use of such an index could facilitate the matching of hardwood species, according to their N requirements, to plantation sites, evaluated in terms of soil N status and light conditions.

Growth and N nutrition, monitored by enzyme assays, in a hardwood plantation: effects of mulching materials and glyphosate application

Abstract The effects of mulching materials (black plastic and straw) and herbicide application (glyphosate) on growth and nitrogen nutrition of butternut ( Juglans cinerea ), white ash ( Fraxinus americana ) and bur oak ( Quercus macrocarpa ) were studied in a plantation established in an abandoned field in southern Quebec (Canada) since 1987. To ascertain the efficiency of mulching materials on the performance of tree seedlings, a herbicide (glyphosate, 6 l ha −1 ) was applied in half of the experimental plots in June 1990 and 1991. Soil parameters (temperature, moisture) and soil nitrate and ammonium concentrations were measured during the growing season in 1991. In summer 1991, nitrogen nutrition of the seedlings was monitored using enzyme assays (nitrate reductase activity (NRA), glutamine synthetase activity (GSA)) of the leaves of the three deciduous tree species. Mulching affected soil parameters, with black plastic producing the highest soil temperature (23.4°C) and straw the highest soil moisture (183.6 g kg −1 ) in June. NRA varied in relation to tree species, herbicide application, mulching material and time. GSA was poorly correlated to silvicultural treatments. Butternut showed the highest NRA, especially in herbicide plots irrespective of mulching material. Bur oak NRA showed less variation between herbicide and non-herbicide plots and reacted more to the mulching treatments. White ash NRA only showed an herbicide effect in June. All species reacted positively to the addition of an herbicide around the mulching material, but not to the same degree. Height and diameter increment ratios (with/without glyphosate application) indicate that butternut growth was the most improved by herbicide applications, followed by white ash and bur oak. This indicates that the effectiveness of mulching alone decreases in the following order: bur oak > white ash > butternut. The utilization of mulching material in abandoned fields as an alternative to herbicide application is closely linked to the species chosen. Enzyme assays (NRA) were shown to be a valuable tool for monitoring physiological status of planted trees subjected to environmental changes brought on by silvicultural practices.

Endogenous ascorbate level modulates ozone tolerance in Euglena gracilis cells

Abstract A wild type (WT) and a colourless mutant (CM) of Euglena gracilis were used to study the biochemical effects of ozone (O3) stress on the components of the ascorbate-glutathione cycle (AA-GSH cycle). The WT cells had higher initial ascorbate (AA) and ascorbate peroxidase (APX, EC 1.11.1.11) activity but lower glutathione (GSH), glutathione reductase (GR, EC 1.1.1.49) and glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) activities than the CM cells. Ozone exposure (1.0 μmol O3·min−1) of both cell types resulted in a viability loss of 9 % and 15 % for the WT and CM cells, respectively. After O3 exposure, a similar reduction in GSH content was observed in both cell types, whereas the other components of the AA-GSH cycle showed no change. Our results indicate that the higher tolerance of the WT cells to O3 is associated with a higher initial AA content. To confirm this, the endogenous AA content in both cell types was modified by adding L-galactono-γ-lactone (L-GAL) or D-galactono-γ-lactone (D-GAL) to the growth medium. L-GAL treatment resulted in a 5.2-fold increase in the initial AA content and an increase of O3 tolerance in the CM cells. On the other hand, D-GAL treatment decreased the AA content as well as O3 tolerance of WT cells. Together, these results suggest that O3 tolerance is closely correlated with the AA content in Euglena cells.

Clone-Specific Response in Leaf Nitrate Reductase Activity among Unrelated Hybrid Poplars in relation to Soil Nitrate Availability

In this field study, we used in vivo NRA activity in hybrid poplar leaves as an indicator of assimilation for five unrelated hybrid poplar clones. We also examined if leaf NRA of these clones is influenced to the same extent by different levels of soil availability in two riparian agroforestry systems located in pastures. Leaf NRA differences of more than one order of magnitude were observed between the clones, clearly showing their different abilities to reduce in leaves. Clone DxN-3570, a P. deltoides x P. nigra hybrid (Aigeiros intrasectional hybrid), always had the highest leaf NRA during the field assays. This clone was also the only one to increase its leaf NRA with increasing soil availability, which resulted in a significant Site x Clone interaction and a positive relationship between soil concentration and NRA. All of the four other clones studied had one or both parental species from the Tacamahaca section. They had relatively low leaf NRA and they did not increase their leaf NRA when grown on the rich site. These results provide evidence that assimilation in leaves varies widely among hybrid poplars of different parentages, suggesting potential preferences for N forms.