Effect of nitrite and nitrate on chlorophyll fluorescence in green algae

A New Trophic State Index for Lagoons

This paper proposes a new nitrogen-based trophic state index (TSI) for the estimation of status of eutrophication in a lagoon system. Nitrite-nitrogen (NO2-N) is preferable because of its greater abundance in Chilika lagoon and its relation to other criteria of trophic state, for example, chlorophyll-a (Chl-a) and Secchi disk depth (SDD). Nitrite is preferable over nitrate because the former decreases the fluorescence and affects photosynthesis, thereby controlling primary production. This paper also computes TSI using Chl-a and SDD. The three parameters account for the biological, chemical, and physical characteristics of the lagoon. It will be possible to estimate the TSI of freshwater and brackish water lagoons and other water bodies using the new expressions taking into consideration the spatial and temporal variability in the dataset. Depending on the data availability, alternative TSI (Chl-a) and TSI (SDD) can account for the biological and physical contributions to eutrophication. The estimated TSI can account for Chl-a and NO2-N up to 322.18 mg m−3 and 61.99 μg L−1, respectively. The TSI based on these three parameters can serve as a complimentary and predictive tool for lagoon management and field programs to monitor the health of a lagoon.

Tansley Review No. 24 Why are atmospheric oxides of nitrogen usually phytotoxic and not alternative fertilizers?

Atmospheric pollution by the oxides of nitrogen, NO and NO₂ , can cause reductions in growth but rarely visible injury. This review considers their uptake into foliage, as well as their subsequent metabolism and physiology, and attempts to explain why these gases are often phytotoxic. The combined stresses of resisting cellular acidification, enhanced levels of nitrite (and ammonia), and the direct interference of the free radical ('N=O) with critical enzymes, reaction centres and regulatory mechanisms are thought to be the main reasons why oxides of nitrogen, especially NO, inhibit growth. If other air pollutants such as SO₂ are also present with NO or NO₂ then free radical-induced injury, similar to that caused by O₃ alone, also occurs. CONTENTS Summary 395 I. Introduction 396 II. Uptake and cycling of oxides of nitrogen 396 III. Biochemical responses to NO and NO₂ 405 IV. Physiological responses to NO and NO₂ 410 V. Combinations of NO and NO₂ with other pollutants 416 VI. Recapitulation and beyond 418 Acknowledgements 420 References 420.

Nitrate and nitrite as 'in vivo' quenchers of chlorophyll fluorescence in blue-green algae

The effect of nitrate and nitrite on long-term chlorophyll fluorescence has been studied in filamentous blue-green algae. Cells grown autotrophically with nitrate as nitrogen source show, under argon atmosphere, a high level of fluorescence. The addition of either nitrete or nitrite induces a significant fluorescence quenching, but, whereas in the case of nitrite no previous treatment is required, in the case of nitrate the cells have to be sonicated or treated with Triton X-100 in advance without destroying their cellular integrity. DCMU Abbreviations: BQ, p-benzoquinone; DCMU, 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea; FCCP, carbonylcyanide 4-trifluoromethoxyphenylhydrazone; FeCy, potassium ferricyanide. strongly inhibits the quenching of fluorescence caused by nitrate or nitrite. Using cells grown with ammonia, a nutritional repressor of the two enzymes of the nitrate-reducing system, the fluorescence quenching observed in either case becomes negligible. These results clearly indicate that both nitrate and nitrite can physiologically act as primary Hill reagents in photosynthesis in blue-green algae.

The interaction of nitrogen assimilation with photosynthesis in nitrogen deficient cells of Chlorella

Nitrogen-limited chemostat cultures of Chlorella fusca var. vacuolata, when given nitrogen in the inorganic forms of nitrate, nitrite and ammonium divert photo-generated electrons, from CO2 fixation to nitrogen assimilation. Addition of nitrate or nitrite, but not ammonium, stimulates rate of oxygen evolution. All but the most severely nitrogen-deficient culture have increased dark respiration rates after addition of inorganic nitrogen. The nitrite reduction step of nitrogen assimilation is the most light-dependent reaction.

Stoichiometry between photosynthetic nitrate reduction and alkalinisation by Ankistrodesmus braunii in vivo

The uptake of nitrate or nitrite in the light, the release of nitrite and ammonia, and the corresponding alkalinisation of the medium were measured in synchronous Ankistrodesmus braunii (Naeg.) Brunnth. The increase in the OH(-) concentration in the medium reflects a stoichiometric ratio between OH(-) and NO3 (-) of 1.3-1.8 in air, reaching almost 2.0 in CO2-free air or nitrogen. At low CO2 concentrations a large proportion of the nitrogen taken up as nitrate is released as ammonia, much less as nitrite. The stoichiometry of alkalinisation and NO3 (-) or NO2 (-) uptake can be quantitatively explained by assuming: 1) a counter-transport, at a ratio of 1:1, of OH(-) against NO3 (-) at the plasmalemma and of OH(-) against NO2 (-) at the chloroplast envelope, and 2) a co-transport of 1:1 of OH(-) and NH4 (+) to the medium through both membranes. The first OH(-) required is formed by proton consumption in nitrite reduction, the second OH(-) by proton consumption in the formation of NH4 (+) ions. Transport of K(+), Na(+) and Ca(2+) is not or only scarcely involved. This proposed transport system could provide charge equilibrium between inside and outside the cells and could enable the cells to avoid nternal pH changes in nitrate and nitrite reduction.

Nitrate, nitrite and ammonia assimilation by leaves: Effect of light, carbon dioxide and oxygen

The assimilation of nitrate, nitrite and ammonia in barley, wheat, corn and bean leaves was studied using (15)N-labelled molecules and either leaf chamber experiments with the uptake of the nitrogen species in the transpiration stream, or vacuum-infiltration experiments. The assimilation of (15)NO3 (-) into amino nitrogen was strictly dependent on light and ceased abruptly when the light was extinguished. If the leaves were exposed to air, CO2-free air or N2 there was no effect on the rate of NO3 (-) assimilation over 0.5 h. After 1.25 h of CO2-free air, NO3 (-) assimilation into amino acids was sharply reduced. Resupply of air at this time stimulated NO3 (-) assimilation and restored it to the rate observed in leaves exposed to air only. There was no recovery by tissue pretreated for 1.25 h in N2 and subsequently resupplied with air. Incorporation of (15)NO2 (-) was also markedly dependent on light with little reduction occurring in the dark. Incorporation of (15)NH4 (+) into amino acids was stimulated 5 fold by light but considerable incorporation occurred in the dark. The presence of 100 mM NO3 (-) had no effect on the rate of incorporation of (15)NO2 (-) or (15)NH4 (+). Nitrite at 1 mM had no effect on (15)NO3 (-) incorporation but at 10 mM inhibited it completely after 0.5 h. Ammonia at 1 mM had no effect on (15)NO3 (-) or (15)NO2 (-) incorporation and while 10 mM inhibited incorporation for 0.5 h this inhibition did not persist.

Nitrite reduction in leaves; Studies on isolated chloroplasts

Chloroplast preparations from spinach leaves containing a high percentage of intact chloroplasts were capable of light dependent nitrite reduction at rates around 9 μmol/mg chlorophyll/h for at least 50 min. This reduction was inhibited by DCMU but unaffected by uncouplers of photosynthetic phosphorylation. Nitrite reduction was not accompanied by a stoichiometric evolution of oxygen evolution. The disappearance of nitrite was accompanied by an approximately stoichiometric formation of reduced nitrogen.

[The nitrate- and nitrite-dependent O2-evolution in N 2 by Ankistrodesmus braunii]

O2-evolution in N2 by young cells of synchronous Ankistrodesmus braunii was measured manometrically in the presence and in the absence of nitrate or nitrite. Nitrate-starved cells produce O2 as a function of nitrate concentration with an optimum at 10 mM nitrate. The optimum rates are strongly dependent upon the pH of the medium culminating at pH 8.0.Nitrite excretion is initially slow and has its optimum at the same nitrate concentration as O2-evolution. It is slower under anaerobic conditions than in the presence of CO2 and slower at pH 5.6 than at pH 8.0. At pH 8.0 in N2 an accumulation of nitrite starts 40 to 100 min after the addition of nitrate to the algae.O2-evolution is faster with nitrite than with nitrate. No optimum curve is observed at pH 8.0 with various concentrations of nitrite in the medium; however, at pH 5.6 a distinct peak is found at 3 mM nitrite. This peak is found for a fast short-time reaction as well as for the following low rates of O2-evolution.The uncoupler carbonylcyanide-m-chlorophenylhydrazone (CCCP) equally inhibits nitrate- and nitrite-dependent O2-evolution and the incorporation of (32)P into cellular phosphate compounds. There is no indication of uncoupling in vivo of nitrite reduction which is completely independent of ATP in vitro. The inhibition of the nitrate-dependent O2-evolution by high concentrations of nitrate cannot be explained by an accumulation of products such as ammonia or nitrite.