Glycolate Pathway and Serine Synthesis in Relation to CO_2 Concentration in Tomato Leaves

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Isotopic trapping of the carbon flowing through the glycolate pathway by exogenous glycolate, glycine and L-serine was investigated during ^<14>CO_2 photosynthesis at different CO_2 concentrations in tomato leaves. L-Serine markedly trapped the carbon flowing from ^<14>CO_2. The amounts of ^<14>C incorporated into serine decreased at a high CO_2 concentration, but increased with an increase in the CO_2 concentration in the presence of exogenous serine during 10-min photosynthesis in ^<14>CO_2. When ^<14>CO_2 was fed for 5 to 40 sec at 1300 ppm CO_2 to tomato leaves which had been given L-serine, an increase in the accumulation of ^<14>C-serine began after 20 sec, and the ^<14>C-serine molecules formed at 20 and 40 sec were labeled uniformly. In the presence of exogenous serine during 10-min photosynthesis in 1300 ppm CO_2, isonicotinic acid hydrazide increased the incorporation of ^<14>CO_2 into glycine with a corresponding decrease in the accumulation of 14C-serine, but it did not inhibit serine accumulation completely; an evidence for that some serine was formed by a pathway other than the glycolate pathway. The effect of the CO_2 concentration on the glycolate pathway is discussed in terms of serine synthesis in the presence of exogenous serine.
日本植物生理学会の論文