Further evidence of incraased carbon dioxide production accompanying photosynthesis

Abstract.Using an open and a closed system of gas analysis, it was found that CO., evolution in light and in darkness from plant leaves (sunflower, soybean, watermelon, eggplant, and jackbean) have a different response to temperature. While the rate of CO, evolution in light increased with incre-asing temperature from 17 to 350 and then declined, the rate of CO, evolution in darkness increased continuously up to 400. The rate of CO, evolution in light was affected by light intensity. At 1800 ft-c and below 350 the rate of CO2 evolution in light was greater than in darkness, but above 350 it beoame lower than in darkness. The Q10 for CO2 evolution in light was consistently lower than that in darkness.Apparent photosynthesis decreased with increasing temperature, from 20 to 400 and its rate was affected 'by both light intensity and oxygen concentration. In leaves of dicotyledonous plants studied 'the decrease in apparent photosynthesis between 20 to 300 at 21 % 02 was shown to be due primarily to an increase in CO. evolution in light with relatively little effect on photosynthesis.In corn which does not evolve CO2 during illumination there was little effect of increasing temperature on the rate of apparent photosynthesis.The different response to temperature of CO., evolution in light and in darkness support the earlier conclusion that these are 2 different processes.It has been reported that the rates of CO2 evolution by green leaves in light are affected by both O, concentration (6, 9, 11, 14, 29) and light intensity (3,6,15, 17,18,27). Decker (3) has shown that the post-illumination CO., outburst from tobacco at 33.5' was 3 times as large as that at 17.50 and Zelitch (34) has also shown that CO., evolution in light increases with a temperature increase from 250 to 350. Further data on the effect of temperature on CO. evolutioni in light is scanity although the response of CO.2 evolution in darkness has been well documented (19). Additional knowledge would be of interest since there is increasing evidence to in.dicate that in green 'leaves the processes leading to the evolution of CO., in light and in darkness mav be different (6,9,11, 17,23 35-day old watermelon and eggplants were used. The closed and the open systems of gas analysis were the same as described previously ( 15, 16). The closed system was used to study the magnitude of the post-illumination CO. outburst, the CO., compen'sation point, and the effect of CO) concen,tration on -the rate of apparent photosynthesis at various temperattures. The open system. was used to studv the effect of temperature on the steadv rates of apparent photosynthesis at 0.03 % CO2 in air anid CO., evolution into CO-free air in light and in darkness.The various leaf temperatures were obtained by circulating water (Hakke temperature controller) of the desired temperature around the leaf chamber.

Section: Discussionsupporting

confidence: 60%

Effects of Temperature on Photosynthesis and CO₂ Evolution in Light and Darkness by Green Leaves

Hew¹,

Krotkov²,

Canvin³

1969

“…Surveys of assimilatory capacity have generally indicated a substantially greater rate of net assimilation in plants with the latter pathway. Since plants carboxylating ribulose-1 , 5-diP also possess an active photorespiratory pathway coupled to glycolate oxidase (8,9,15,17,28), the CO2 loss associated with these reactions may generate the lower assimilatory efficiency.…”

mentioning

confidence: 99%

Photosynthesis and Photorespiration in Typha latifolia

McNaughton

Fullem

1970

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

“…is -an effect of CO. concen,tration above the compensation point on photorespiration. When utsing thi,s method, it 'is generally assume,d ithalt ithere is no 'such effect (2,3). However, if photorespiration increases with increasing photosynthesis above the CO., compensation point, resuilt's obtiained from extrapolation will uindereistimaite pho,tores!piration occurring at normal atmosspheric CO2 concentration.…”

Section: Discussionmentioning

confidence: 99%

“…Thie rate of CO, uptake by the jllants in light was plotted against the ekterniall CO., concentration, and the restlting gra,phs were extrapolated to zero CO., concentration to obtain the CO, eviolution in l'ight. Thiis method was followed by Decker (3) wiho interpreted the rate at zero CO. concentration as photorespiraition. Tregulnna et al (14) used essentially the same priniciple to calculate photorespiration at the CO., comipen,saltion point.…”

Section: Methodsmentioning

confidence: 99%

Influence of Light Intensity at Different Temperatures on Rate of Respiration of Douglas-Fir Seedlings

Brix¹

1968

Abstract. The rate of photorespiration of Douglas-fir seedlings was measured under different light intensities by: (1) extrapolating the curve for CO., uptake in reilation to atmospheric CO, content to zero CO2, content, and (2) The laboratory air was eliched w-ith CO2, to a concenitration of about 600 ppm in the closed system, and the rate of CO,, utpitake in light was measutred with decrea.sing concentration down to the CO, compensation point. The system was then le,ft for about 15 minutes to ensure a steady state. This procedure was repeated for differen't light in,tenisities and tem!peratures. After isitudying CO. uptake in the light, t;he chamber was darkened and the raite of CO., evoluition measuired afiter a 5-minute interval. Thie rate of CO, uptake by the jllants in light was plotted against the ekterniall CO., concentration, and the restlting gra,phs were extrapolated to zero CO., concentration to obtain the CO, eviolution in l'ight. Thiis method was followed by Decker (3) wiho interpreted the rate at zero CO. concentration as photorespiraition. Tregulnna et al. (14) used essentially the same priniciple to calculate photorespiration at the CO., comipen,saltion point.They mul'tipilied the CO., concenltration ait the compens'ation point by the .sliope of the cuirve for rate of CO., tu,ptake ploltted against CO., concentration.Moss (10)