IODOACETATE INHIBITION OF PHOTOSYNTHETIC CARBON DIOXIDE ASSIMILATION IN SUGAR BEET AND SOYBEAN LEAVES

1960 ◽  
Vol 38 (4) ◽  
pp. 623-634 ◽  
Author(s):  
D. C. Mortimer
Keyword(s):  
Carbon Dioxide ◽  
Sugar Beet ◽  
Aspartic Acid ◽  
Glyceric Acid ◽  
Carbon Dioxide Assimilation ◽  
Alternate Pathway ◽  
Acid Incorporation ◽  
Photosynthetic Carbon ◽  
Phosphoglyceric Acid ◽  
Soybean Leaves

When the petioles of freshly excised sugar beet or soybean leaves were immersed in dilute iodoacetate solutions, the rates of photosynthetic carbon dioxide assimilation were reduced and characteristic changes in the distribution of assimilated C14 were observed. Inhibited sugar beet leaves accumulated C14 in phosphoglyceric acid (PGA) and aspartic acid, but did not incorporate C14 into glyceric acid. Inhibited soybean leaves continued to form glyceric acid, but did not incorporate C14 into PGA and only trace amounts into aspartic acid. Incorporation of C14 into sucrose by the sugar beet leaf ceased when the assimilation of carbon dioxide was reduced below 1/10th of normal, while soybean leaves still formed sucrose at that level of inhibition. It was concluded from these and other data that the mechanisms for photosynthetic carbon dioxide assimilation in the two species were different. The iodoacetate-sensitive, PGA-glyceraldehyde-3-phosphate reduction, which could account for only part of the assimilation by sugar beet leaves, did not appear to be utilized by soybean leaves. An alternate pathway for the reduction of carbon dioxide to the carbohydrate level is postulated to account for the assimilation patterns observed in the two species.

THE ROLE OF KETO ACIDS IN PHOTOSYNTHETIC CARBON DIOXIDE ASSIMILATION

1956 ◽  
Vol 34 (1) ◽  
pp. 511-519 ◽  
Author(s):  
G. H. N. Towers ◽  
D. C. Mortimer
Keyword(s):  
Carbon Dioxide ◽  
Amino Acids ◽  
Sugar Beet ◽  
Aspartic Acid ◽  
Pyruvic Acid ◽  
Carbon Dioxide Assimilation ◽  
Free Air ◽  
Keto Acids ◽  
Photosynthetic Carbon

Of the keto acids identified in leaves of sugar beet and other plants exposed to C14O2, pyruvic acid was found to be the only one labelled in light periods up to 45 sec. α-Ketoglutaric and glyoxylic acids became radioactive after about 45 sec. Radioactive hydroxypyruvate was not identified under these conditions and labelled oxaloacetate was detected only in trace amounts after 60 sec. in Scenedesmus. In contrast glycine and serine were labelled after 10 sec. under comparable conditions and aspartic acid was appreciably labelled after 30 sec. The effect on the radioactivity of the keto acids of an additional period intracer-free air, with and without light, as well as the dark incorporation of C14O2 was studied. These results are discussed in relation to the role of the ketoacids in photosynthesis. It is concluded that the synthesis of amino acids such as glycine, serine, and aspartic acid may be effected by mechanisms other than transamination in green leaves in the light.

THE ROLE OF KETO ACIDS IN PHOTOSYNTHETIC CARBON DIOXIDE ASSIMILATION

1956 ◽  
Vol 34 (3) ◽  
pp. 511-519 ◽  
Author(s):  
G. H. N. Towers ◽  
D. C. Mortimer
Keyword(s):  
Carbon Dioxide ◽  
Amino Acids ◽  
Sugar Beet ◽  
Aspartic Acid ◽  
Pyruvic Acid ◽  
Carbon Dioxide Assimilation ◽  
Free Air ◽  
Keto Acids ◽  
Photosynthetic Carbon

Of the keto acids identified in leaves of sugar beet and other plants exposed to C14O2, pyruvic acid was found to be the only one labelled in light periods up to 45 sec. α-Ketoglutaric and glyoxylic acids became radioactive after about 45 sec. Radioactive hydroxypyruvate was not identified under these conditions and labelled oxaloacetate was detected only in trace amounts after 60 sec. in Scenedesmus. In contrast glycine and serine were labelled after 10 sec. under comparable conditions and aspartic acid was appreciably labelled after 30 sec. The effect on the radioactivity of the keto acids of an additional period intracer-free air, with and without light, as well as the dark incorporation of C14O2 was studied. These results are discussed in relation to the role of the ketoacids in photosynthesis. It is concluded that the synthesis of amino acids such as glycine, serine, and aspartic acid may be effected by mechanisms other than transamination in green leaves in the light.

scholarly journals Photosynthesis by isolated chloroplasts. Inhibition by dl-glyceraldehyde of carbon dioxide assimilation

1972 ◽  
Vol 128 (5) ◽  
pp. 1147-1157 ◽  
Author(s):  
D. M. Stokes ◽  
D. A. Walker
Keyword(s):  
Carbon Dioxide ◽  
Carbon Assimilation ◽  
Photosynthetic Electron Transport ◽  
O2 Evolution ◽  
Appreciable Effect ◽  
Carbon Dioxide Assimilation ◽  
Photosynthetic Carbon ◽  
Photosynthetic Carbon Assimilation ◽  
Isolated Chloroplasts ◽  
Spinach Leaves

Photosynthetic carbon assimilation and associated CO2-dependent O2 evolution by chloroplasts isolated from pea shoots and spinach leaves is almost completely inhibited by 10mm-dl-glyceraldehyde. The inhibitor is without appreciable effect on photosynthetic electron transport, photophosphorylation, the carboxylation of ribulose 1,5-diphosphate or the reduction of 3-phosphoglycerate, but apparently blocks the conversion of triose phosphate into ribulose 1,5-diphosphate.

SOME OBSERVATIONS ON THE FORMATION OF GLYCERIC ACID DURING PHOTOSYNTHESIS EXPERIMENTS

1961 ◽  
Vol 39 (1) ◽  
pp. 1-5 ◽  
Author(s):  
D. C. Mortimer
Keyword(s):  
Enzymatic Activity ◽  
Glyceric Acid ◽  
Short Term ◽  
Alternate Pathway ◽  
Phosphoglyceric Acid ◽  
Soybean Leaf ◽  
Photosynthetic Assimilation ◽  
Hydrolysis Of

The dephosphorylation of phosphoglyceric acid was tested under a variety of conditions. Hydrolysis of the ester by leaf homogenates was relatively slow, even when conditions favored enzymatic activity, and was not detected when frozen homogenate was extracted by boiling 80% ethanol. The results suggest that glyceric acid recovered in ethanol-soluble extracts of leaves following short-term photosynthesis experiments is not normally derived from phosphoglyceric acid. The route proposed for the synthesis of glyceric acid is related, with particular reference to soybean leaf, to an alternate pathway for photosynthetic assimilation which does not utilize phosphoglyceric acid.

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