The Role of Glycolic Acid Oxidase in the Respiration of Leaves

Flavin mononucleotide control of glycolic Acid oxidase and photorespiration in corn leaves

Enzyme preparations from young corn shoots lacked the coenzyme, flavin mononucleotide, that is required for glycolic acid oxidation. When the coenzyme was added to the shoots, the rate of carbon dioxide production during photosynthesis increased. Shoots of wheat or oats did not lack the coenzyme.

Evolution of C4 photosynthesis in response to changes in carbon and oxygen concentrations in the atmosphere through time

The hypothesis is presented that C4 photosynthesis has evolved at lease in part in response to reduced efficiency of C3 photosynthesis due to increased oxygen partial pressures in our recent atmosphere. Oxygen competition with carbon dioxide for the active site on ribulose diphosphate carboxylase was of little consequence when atmospheric levels of CO2 were high and those of O2 were low. However at the present low CO2 and high O2 partial pressures, adaptations for protecting the enzyme from oxygen have been selected.

On the formation of glycolate in photosynthesizing Chlorella using a new gas-liquid chromatography method

Suspensions of Chlorella vulgaris were allowed to photosynthesise with two concentrations of (14)CO2 (101 and 543 ppm) in 80% oxygen, and the incorporation of (14)C into glycolate and 3-phosphoglyceric acid (3-PGA) was followed. The relative specific activity (RSA) of the glycolate formed at both CO2 concentrations decreased initially and then increased slowly. The RSA of glycolate was much lower when the suspension photosynthesised in 101 ppm (14)CO2 compared to 543 ppm. The RSA of 3-PGA was nearly always lower than that of glycolate and the results suggest that refixed dark respiratory CO2 or respiratory 3-PGA, or both, substantially contribute to the total 3-PGA in the algae. It is concluded that glycolate is formed from recent photosynthate as well as from storage material, but the relative contribution of these substrates depends on the conditions under which the algae are grown, as well as those obtaining at the time of glycolate excretion.

An investigation of glycolate excretion in two species of blue-green algae

The amount of (14)C-glycolate excreted by Oscillatoria sp. and Anabaena flos-aquae is less than 1% of the (14)C fixed by the algae during photosynthesis. Transfer of cells grown on 5% CO2 in air to a medium of low bicarbonate concentration or treatment of the cells with isonicotinyl hydrazide (INH) during photosynthesis, caused little increase in glycolate excretion. α-Hydroxysulfonates failed to stimulate massive excretion of glycolate. Although these blue-green algae excreted little glycolate, a significant proportion of the photosynthetically fixed carbon was excreted in the form of basic, neutral and acidic compounds, and such excretion was greater in 5% CO2-grown cells than in air-grown cells.

[Blue-light-enhanced acid production of chlorella under anaerobiosis]

Under anaerobiosis the pH-value of the medium (0.002 M phosphate buffer) of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris (211-11h/20) drops slowly due to the excretion of acid fermentation end products. Blue light enhances this acidification of the medium (Figs. 1 and 2). Preliminary determinations of glycolic acid (color reaction with 2,7-dihydroxynaphthalene) indicate that there is about twice as much of this compound in the medium of an anaerobic culture kept in blue light as there is in the medium of one kept in the dark.Addition of oxygen after a period of anaerobiosis in darkness or in blue light results in a greater O2-uptake by the previously illuminated cells (Fig. 3), indicating aerobic consumption of the acids released under nitrogen. The latter is proven by the experiment shown in Fig. 4, in which parallel cell samples develop a greater O2-consumption when suspended in the isolated media (phosphate buffer) of anaerobic cultures of the same organism instead of in fresh phosphate buffer, and a greater O2-consumption when suspended in the medium of an illuminated rather than in that of a dark anaerobic culture.In experiments in which acid production is determined by measurement of the amount of 0.01 N NaOH required to keep the pH constant (Fig. 5), it can be shown that even traces of blue light can be effective in increasing the acidification of the medium of anaerobically kept cells; application of about 250 ergs cm(-2) sec(-1) of λ455 nm yields half-saturation (Fig. 6). Wavelengths around 470 and 370 nm are most effective in increasing this acid excretion; there is a minimum of activity around λ400 nm and no effect at all with yellow, red and far-red light (Fig. 7).From the similarity between these intensity and spectral dependences and those for a light stimulation in respiration of the same organism found earlier (KOWALLIK, 1967), and from the fact that the acids released into the medium under anaerobiosis can be respired by the algae, we feel that both these increases are based on the same light reaction. The action of blue light in bringing about an enhancement in respiration might then consist in furnishing additional substrate.

GLYCOLIC ACID OXIDASE AND FUSARIOSE WILT OF TOMATOES

When roots of tomato plants are infected with Fusarium, systemic changes are induced in the activities of glycolic acid oxidase and glyoxylic reductase of the leaves. A marked decrease in glycolic acid oxidase activity is apparent 8–16 days after inoculation when the leaves show chlorotic symptoms. The depressed activity of this enzyme is due to a general decrease in the concentration of its flavin coenzyme, FMN. Both FMN and FAD begin to decrease after 8 days. On the other hand glyoxylic acid reductase shows an increased activity 20 days after infection. These alterations in enzymic activity result in a twofold accumulation of glycolic acid 20 days after infection even though the fungus is never present in the leaves.