A Rapid, Postillumination Deceleration of Respiration in Green Leaves.

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: Discussionmentioning

confidence: 92%

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

Hew¹,

Krotkov²,

Canvin³

1969

“…Thus decreasing the photorespiratory rate by about one-half increased net photosynthesis by 38%. The results suggest that diminishing photorespiration, in an otherwise suitable genetic background, will result in large increases in net photosynthesis and plant productivity.Leaves of species with high rates of photorespiration often evolve CO2 at rates three to five times faster during illumination than in darkness (2,3,12). These observations suggested that photorespiratory CO2 largely accounts for the slower rate of net CO2 assimilation during photosynthesis normally found in many species, including tobacco, in comparison with efficient species such as maize (12,13,15).…”

mentioning

confidence: 81%

The Effect on Net Photosynthesis of Pedigree Selection for Low and High Rates of Photorespiration in Tobacco

Zelitch¹,

Day²

1973

A normal appearing plant with a low rate of photorespiration (ratio of UCO2 released light/dark = 1.6) was found in an unselected tobacco (Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net C02 assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of "4CO2 released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of C02 dm 2 hr-1) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25 % ) than did selfing inefficient plants (about 6% ), but this proportion did not increase in successive generations.Wide variations in photorespiration and photosynthesis were observed within populations of normal appearing plants grown in the same greenhouse environment. Several plants had photosynthetic rates as great as 25 mg of CO2 dm-2 hr-1 coupled with light/dark ratios below 2.0.The characteristics of two representative contrasting plants were studied more extensively and were fairly constant, irrespective of leaf position on the stalk, leaf size, or time of sampling within approximately a 2-week period. One plant with a mean light/dark ratio of 1.7 showed a mean net photosynthesis of 23.4 mg of CO2 dm 2 hr-', while an inefficient plant with a light/dark ratio of 3.7 had an average photosynthetic rate of only 17.0 mg CO2 dm-2 hr-'. The dark respiration was similar in these plants. Thus decreasing the photorespiratory rate by about one-half increased net photosynthesis by 38%. The results suggest that diminishing photorespiration, in an otherwise suitable genetic background, will result in large increases in net photosynthesis and plant productivity.Leaves of species with high rates of photorespiration often evolve CO2 at rates three to five times faster during illumination than in darkness (2,3,12). These observations suggested that photorespiratory CO2 largely accounts for the slower rate of net CO2 assimilation during photosynthesis normally found in many species, including tobacco, in comparison with efficient species such as maize (12,13,15).The view that photorespiration might be decreased and thereby CO2 uptake might be enhanced within a species was supported by our finding (16) (12), we therefore sought normal appearing tobacco plants with slower rates of photorespiration for this species. A plant was found in the standard tobacco variety Havana Seed with about one-half of the normal rate of photorespiration. We describe here the results obtained on net CO2 assimilation and photorespiration in progeny of three generations derived from self-pollinations of individual plants selected for having an unusually low or a high rate of photorespiration. Normal appearing plants with lower than usual rates of photorespiration and exceedingly rapid rates of CO2 uptake showed ...

“…Since In the light, leaves of many higher plants evolve carbon dioxide and take up oxygen. This apparent reversal of the photosynthetic process is called photorespiration (3,4,13). It is easily detectable in, and perhaps restricted to, higher plants which fix carbon dioxide via the enzymes of the CalvinBenson cycle (13).…”

mentioning

confidence: 99%

Changes of Photorespiratory Activity with Leaf Age

Salin¹,

Homann²

1971

We have discovered that younger leaves do not exhibit the same large increase in photosynthesis as do older ones when the oxygen tension is lowered. This phenomenon was observed in various tobacco and citrus species and indicated less photorespiration in young leaves. Activities of glycolate oxidase and of glyoxylate reductase were found to be significantly lower in younger leaves than in more mature ones from the same plant. Measurements of the dark respiration were done manometrically. Leaf slices were placed over water on small wire coils as described by Schmid (17). The side arm contained 0.2 ml of 20% KOH.