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

Abstract

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 ...

Comparative Growth Analyses of Panicum Species with Differing Rates of Photorespiration

“…Trin., is intermediate between C3 and C4 plants with respect to photorespiration. In contrast to other reports in the literature of C3 species with altered rates of photorespiration (4,12,14,(21)(22)(23), this observation has been independently confirmed in several laboratories based on a variety of CO2 exchange parameters, including reductions in the 02 inhibition of net photosynthesis, the CO2 compensation concentration (F)2, and the rate of CO2 evolution in the light (2,3,8,10,12).…”

“…Trin., is intermediate between C3 and C4 plants with respect to photorespiration. In contrast to other reports in the literature of C3 species with altered rates of photorespiration (4,12,14,(21)(22)(23), this observation has been independently confirmed in several laboratories based on a variety of CO2 exchange parameters, including reductions in the 02 inhibition of net photosynthesis, the CO2 compensation concentration (F)2, and the rate of CO2 evolution in the light (2,3,8,10,12).Although leaf anatomical studies of P. milioides have revealed some features of Kranz anatomy characteristic of C4 plants (2, 3, 9), biochemical investigations (8)(9)(10)(11)13) indicate that this species has not reduced photorespiration and the associated 02 inhibition of photosynthesis by a C4-like CO2 concentrating mechanism (5). For example, the primary products of photosynthesis in 14CO2-air are 3-P-glycerate and glycerate rather than C4 dicarboxylic acids (8,9,11).…”

Metabolic Regulation of Glycolate Synthesis, Photorespiration, and Net Photosynthesis in Tobacco by L-Glutamate

“…When the discs were exposed to glutamate, 27,700 cpm were released in the light in 30 min and 66,400 cpm in 60 min of darkness. The resulting ratios of 14C02 released in light/dark were 2.6 for the discs on water (a reasonable ratio for tobacco [28]) and 0.8 for the discs on glutamate. Glutamate supplied under these conditions decreased the rate of CO2 released by leaf discs in the light about 60% and had no substantial effect on dark respiration.…”

“…These experiments with glutamate raise the question of whether changes in the ratio of photosynthetic CO2 fixation to photorespiratory CO2 release normally occur in C3 plants by the mechanism induced by adding glutamate or other metabolites. Individual tobacco plants with slower rates of photorespiration and increased net photosynthesis have been observed (27,28), but the extent of normal fluctuations in the pool sizes of glutamate, aspartate, and related compounds during photosynthesis is not known. The inhibition of glycolate synthesis (23) and photorespiration (25), always found in leaves of C4 species such as maize, may be brought about in part by the higher concentration of aspartate present in the bundle sheath cells (9).…”

“…Photorespiration was measured in leaf discs as the release of previously fixed 14CO2 into a stream of C02-free air in the light, compared to the dark as described previously (19,28).…”