J Integr Plant Biol. ›› 1963, Vol. 11 ›› Issue (4): -.

• Research Articles •    

Studies on Plant Respiration VI.

L. F. Yen, F. C. Wang, K. L. Kuan and P. S. Tang   

Abstract: (2-C14)-acetate was fed to etiolated rice seedlings and the respiratory pathways of the acetate in them were studied. The following results were obtained from feeding experiments: 1. 5-day old etiolated rice seedlings were extracted with 80% alcohol. The extract was passed through the anion exchange resin Amberlite IRA-400 and the eluant was collected for chromatography on Sin Hua no. 1 filter paper. The paper chromatogram showed that citric, isocitric, α-ketoglutaric, succinic, fumaric and malic acids were present in the rice tissues. It demonstrates that the intermediates of the tricarboxylic acid cycle exist in the intact rice seedling. 2. The rice seedlings were fed with (2-C14)-acetate, incubated in various time intervals from 2 to 40 or 60 minutes and then extracted with 80% hot alcohol. The extracts were passed through cation exchange resin Zerolite 225 and anion exchange resin Amberlite IRA-400 to separate them into organic acids, amino acids and sugars. The estimation of the three kinds of compounds indicates that radio activity appeared first in the organic acids, followed by amino acids and rarely appeared in the sugars. 3. The above organic acids were fractionated with ion exchange chromatography of Zerolite FF. The fractions were collected and concentrated for radioactivity determination. The results showed that citric, isocitric, succinic, fumaric and malic acids are labelled with Cl4. When malonate was added to the substrate solution, the incorporation of acetate into the organic acids was reduced to below 50%, while the radioactivity of the labelled succinate increased correspondingly. The radiochromatogram indicates the accumulation of succinate in the rice seedlings fed with labelled acetate and malonate. 4. The radioactivities of the organic acids isolated from the rice seedlings showed that succinate appeared in the initial 2 minutes in quite measurable quantity, and ma- late and citrate increased in amount until 10 minutes later. Radiochromatogram con- firmed this result. 5. When arsenite and α,α′-dipyridyl were added to the media, the incorporation of acetate into organic acid was inhibited to 68 % and 44% respectively, but the amount in- corporated into succinate was depressed 46% and 29% respectively. It means that some labelled succinate accumulates even as the inhibitors are operative. 6. The radiochromatogram of the amino acids extracted from the seedlings fed with (2-C14)-acetate shows that the radioactivities of aspartate and glutamate approach 17% and 20% of the total radioactivity of amino acids respectively. If malonate was added, the incorporation of C14 into amino acids was reduced to 50%. It means that the labelled acetate incorporates into those amino acids which are assiociated with the tricarboxylic acid cycle. 7. The following conclusion may be drawn from the above experimental results. Tricarboxylic acid cycle is present in the intact rice seedlings. From the facts that large amounts of succinate was labelled during the first moment of feedings and that some amount of succinate was still accumulated even after inhibition by arsenite and α,α′- dipyridyl, it is suggested that besides the tricarboxylic acid cycle as the main route for the utilization of acetate, it is probable that glyoxylate cycle and dicarboxylic acid cycle may be operative in these rice seedlings.

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