Effect of Oxygen on Photosynthesis, Photorespiration and Respiration in Detached Leaves. I. Soybean

Abstract

Summinuarv. The effect of O., onl the CO., exchange of (letaclhe(I soybean leaxves was miieasured with a Clark oxygen electrode and infrare(d carlbon (lioxide alnalvsers in both open and closed systems.The rate of apparent photosynthesis was inhibited 1y O. while the steady rate of respiration after a few nminutes in the dark was not affected. Part of the inhibition of apparent photosynthesis was shown to be a result of increased photorespiration. This stimulation of photorespirationi by O. was manifested by an increase in the CO, compensation poiInt.The differential effects of 0., Oli dark respiration (n1o effect) anid( photorespiration (stimulatioln) indicated that these were 2 different processes.Moreover the extrapolation of the CO., compensationi poilnt to zero at zero O. indicated that dark respiration was suippressed in the light at least at zero 0. concelntrationi.The rate of apparent photosynthesis has been showlv to be inhibited 1)v 02 in a -ivide range of plant species (13). Until recently, however. 110 satisfactory explanationi of this phenomiienioni has been proposed. The possibility that part of this inhibitioll miiight be due to a stimiiulation of respiration was not considere(d because A) the respiratory-process wlhiclh operates in the dark was thought to continiue during photosynthesis (3, 13), and B) O. has no effect on the clark respirationi of green leaves (7. 9, 13).Recent evidence stiggests that (lark respiration is inhibited in the light in green leaves andaIlgae and is replaced by a different respiratory process photorespirationi (4, 6, 12).The questionl now to he answered is whether O. has anl effect on photorespiration i.e. onl the evolution of CO., ill light. Il the experimiienits reported below these effects of O3 were iilvestigated miore fully, Using a (liffereilt planit species, a wider range of O3 anid CO., conicenltratioris aild steadv staite conditions. Materials and MethodsSoybean plailts, Glxcinic nma.mlMerr. v-ar. Coimiet, were growvn in pots of v-ermiiicuilite in a growtlh cllanllber. Thle ligllt intensitv was 1,500 ft-c, and(I the dav lengtll 16 hoturs. The teiimperature was 22.50 dturing tile da ( and 190

Regulation of Soybean Net Photosynthetic CO2 Fixation by the Interaction of CO2, O2, and Ribulose 1,5-Diphosphate Carboxylase

“…In the absence of 02, the scheme indicates that net photosynthesis will increase by about 43(>. This expected increase is consistent with experimental observations (12,19 rate of change of P-glycolate concentration was zero, and the rates of glycolate accumulation and P-glycolate hydrolysis were determined from the solution of two simultaneous equations (3). In these calculations, it was assumed that the rate of P-glycolate hydrolysis was proportional to the P-glycolate concentration (i.e.…”

“…The total oxygen inhibition of soybean photosynthesis in air equals 40 to 45% of net photosynthesis (12,19). The stoichiometry presented in Figure 8 is consistent with this observation, and predicts that, in the absence of 02, net photosynthesis will increase from 3.5 to 5.0 units, an increase of 43%.…”

“…The P-glycolate formed in this reaction can be hydrolyzed to glycolate by P-glycolate phosphatase (22), and glycolate can then be oxidized to CO2, glycine, and serine by the photorespiratory pathway (25). If Figure 2 and by previous observation (5,12,16 (Fig. 4).…”

Influence of Temperature on the Ratio of Ribulose Bisphosphate Carboxylase to Oxygenase Activities and on the Ratio of Photosynthesis to Photorespiration of Leaves

“…Disagreement between gas exchange and RuBPCO kinetics cannot be explained by effects of dark respiration. (1) If dark respiration, which is saturated at 20 kPa p(O 2 ) (Forrester, Krotkov, and Nelson, 1966), affected the data in Fig. 2A, then the lines would not pass through the origin.…”

Physiological responses of an aspen-poplar hybrid to temperature and soil moisture treatments

“…This is the net photorespiratory rate since the gross rate must be corrected What portion of net photorespiration is due to dark respiration processes is not known. There is evidence that weak illumination curtails the dark respiration process and simultaneously initiates light-dependent photorespiration (Fock and Egle 1966;Forrester, et al 1966;Poskuta 1968a;1968b;Poskuta, et al 1967;Tregunna, et al 1966). Carbon dioxide (Hew, et al 1969;Holmgren and Jarvis 1967) and oxy gen (Govindjee, et al 1963;Hoch, et al, 1963) measurements indicate that dark respiration exceeds photorespiration at low light intensities but that as light intensity increases photorespiration is accelerated and dark respiration de creases and eventually ceases.…”