Die Veränderungen des Chlorophyllgehaltes in ontogenetisch verschiedenen Blättern von Phaseolus vulgaris var. nanus L. nach Behandlung mit Atrazin

Abstract

Summary By measurement of physiological variables, of 7 week old bush beans (“Sabo”), three physiologically delimited zones could be distinguished: 1. the catabolic region; 2. the productive region and 3. the growth region. In younger plants, the catabolic region is essentially absent, as is the growth region in older plants. During it's ontology and continuing throughout senescence, each leaf exhibits, with minor variations, every physiological condition characteristic of the three major physiological zones. These zones represent individual stages of leaf development which otherwise can only be observed over an extended time interval. The effect of the herbicide atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) is manifested after a few hours by photosynthesis inhibition; and after a few days, the total chlorophyll content decreases distinctly, with a slight disproportionate loss of chlorophyll a. A typical pattern of injury, which can be modified by ecological factors, subsequently occurs. Onset of symptoms is for every leaf of the three regions at least in time distinguishable. Through investigation of darkened green plants as well as non-green seedlings, loss of chlorophyll in leaves of zones 2 and 3 can be explained by synthesis inhibition. The yellowing of leaves from the catabolic region implies a triggering of the normal catabolic processes of chlorophyll degeneration, both by darkness and atrazine treatment. Since the toxic effect of atrazine can be demonstrated only in light, the question arises as to whether the initiation and effect of atrazine's herbicidal activity is a result of the initial photosynthesis inhibition, or whether it is induced by the activation of the herbicide through chlorophyll and light. The full spectrum of atrazine activity cannot be appropriately explained by any known theory.