Die Wirkung von Atrazin auf den Stoffwechsel von Phaseolus vulgaris L. II. Kohlenhydrate und Organische Sauren

Abstract

Summary Stems and successively more highly inserted leaves of seven week old bush bean plants ( Phaseolus vulgaris L. {itvar. nanus «Sabo») grown in the field and in a growth chamber were analysed independently for their starch, soluble carbohydrate and organic acid contents three days after treatment with Atrazine (2-chloro-4-ethylamino-6-isopropylamino-striazine). 1. Starch content in treated plants was reduced by 75.8 % - 99.4 % depending on the part of the plant. In the growth chamber losses from 17.7 % (stem) - 97.6 % occurred, indicating a diminished effect of the herbicide under increased humidity. 2. Sugars disappeared almost completely after treatment, while the concentration of myo-inositol was hardly affected. Plants from the growth chamber showed similar effects, but to a lesser extent. 3. The greatest effects on carbohydrates took place in leaves inserted at the second and third internodes which are the most active respective of net photosynthesis. 4. Malonate concentration was not remarkably different in treated plants and controls. 5. Malate concentration was strongly reduced at the upper internodes after treatment (38.9-88.4 % loss). 6. Citric acid content was increased at the upper internodes by 29.2-504.0 %. 7. Respective of organic acid content, plants from the growth chamber reacted like those of the field experiment whereby the increase in citric acid was emphasized. 8. As photosynthesis is blocked by the herbicide, carbohydrates are channelled into respiration and amino acid synthesis. 9. The losses in carbohydrates - mostly through respiration - did not influence the dry weight, which was used as the base of reference. 10. Increased citric acid and decreased malic acid contents can be explained by the action of a citrate-malate-shuttle which uses malate to promote Krebs-cycle-reactions. Also in treated plants, citrate would be stored rather than converted to fat via acetyl-CoA. 11. Another mechanism - a malate-α-ketoglutarate-shuttle - normally used to transport NADH into the mitochondria draws on malic acid pools within the cytoplasm and the vacuoles to produce oxaloacetate, the forerunner of asparagine, the main nitrogen-compound accumulated in treated plants. Again, NADH can be used as explained.