Photosynthesis and Photorespiration in Typha latifolia

Abstract

NaH'4CO3 (105 Cpm) to 1.3 ml of the enzyme preparation. At intervals, 0.4-ml samples were removed and acidified with 0.1 ml of 6 N acetic acid. Controls consisted of a zero time sample that was acidified immediately upon mixing the reaction components, and a reaction mixture lacking ribulose-1, 5-diP which was acidified at the end of the experimental period. The same enzyme preparation procedure was used for phosphopyruvate carboxylase except that dithioerythritol was sometimes substituted for reduced glutathione to provide an alternative test for sulfhydryl protection. The assay system for this enzyme, after Slack and Hatch (25), contained 1.55 ,umoles of phosphopyruvate and 15 ,umoles of sodium glutamate in substitution for the ribulose-1,5-diP used above. Controls were the same. For the assay of glycolate oxidase activity, leaves were homogenized in 0.067 M phosphate buffer (pH 7.8) and filtered through four layers of 60 mesh cheesecloth. This homogenate was used directly in a polarographic assay (10) with the Clark electrode. The reaction was initiated by adding 10 .moles of sodium glycolate in 0.2 ml of the phosphate buffer to 2.8 ml of the enzyme preparation. Controls were samples to which no glycolate was added. Addition of the enzyme cofactor, flavin mononucleotide, was not found to be stimulatory, and this was omitted from the assay system. Reagents were from Sigma.For "4CO0 assimilation experiments, leaves were preilluminated in 2 X 106 ergs cm-2 sec-l of light with their base in distilled water or a glycolate oxidase inhibitor, 0.01 M a-hydroxypyridinemethanesulfonic acid (Aldrich), for 30 min prior to release of "4CO2 by the acidification of a bicarbonate solution. Carbon dioxide concentration was 370 ,ul liter-' after addition of bicarbonate, to eliminate artifacts arising from high CO2 concentrations. Following 10 min of photosynthesis with water or 20 min with the inhibitor, the leaves were killed with boiling 80%-ethanol. In the controls, 1.8 AC of "CO, were used. In the experiments with inhibitor, 2.02 ,C of "CO2 were used. The different time periods and specific radioactivities of "CO2 were used to assure that approximately the same amount of radioactivity would be recovered from chromatograms of both treatments without overloading with plant extracts. Total cpm recovered from chromatograms per g of leaf extracted were 43,200 + 21,600 (0.95 confidence interval) for the water controls and 53,600 + 8,300 for experiments in inhibitor. For

Why is marsh productivity so high? New insights from eddy covariance and biomass measurements in a Typha marsh

“…Scirpus lacustris, Cyperus papyrus, Allium cepa) have shown that little (i.e. 0.25-2.2%) of the CO 2 in the aerenchyma is recycled and used for photosynthesis (McNaughton and Fullem, 1970;Singer et al, 1994;Byrd et al, 1995). The isotopic signature of leaf d 13 C at the SJFM confirmed that CO 2 recycling does not play a major role in increasing GPP.…”

Photosynthetic characteristics of mesophyll eells isolated from sunflower (helianthus annuus L.) leaves

“…Panicum milioMes possesses a higher PEP carboxylase activity than C3 species [21]. In Typha latifolia, McNaughton and Fullem reported that malate was not a photosynthetic product but might be derived from glycolate metabolism [16]. Our own results suggest that PEP carboxylase may be involved in CO2 fixation by sunflower leaves.…”

The effect of ammonium and nitrate on carbondioxide compensation point and enzymes associated with carbondioxide exchange in wheat

“…Nitrate reductase (EC (1.6.6.4) was assayed using the in vivo method of Klepper et al (1971). Glycolate oxidase (EC 1.1.3.1) was assayed according to McNaughton and Fullen (1970).…”