ENVIRONMENTAL RELEVANCE OF HEAVY METAL-SUBSTITUTED CHLOROPHYLLS USINGTHE EXAMPLE OF WATER PLANTS

Following experiments which studied the substitution of the central io n of isolated chlorophylls by heavy metal ions in vitro, in vivo exper iments with submersed water plants were carried out, It was discovered that the substitution of the central atom of chlorophyll, magnesium, by heavy metals (mercury, copper, cadmium, nickel, zinc, lead) in vivo is an important damage mechanism in stressed plants, This substitutio n prevents photosynthetic light-harvesting in the affected chlorophyll molecules, resulting in a breakdown of photosynthesis, The reaction v aries with light intensity, In low light irradiance all the central at oms of the chlorophylls are accessible to heavy metals, with heavy met al chlorophylls being formed, some of which are much more stable towar ds irradiance than Mg-chlorophyll, Consequently, plants remain green e ven when they are dead, In high light, however, almost all chlorophyll decays, showing that under such conditions most of the chlorophylls a re inaccessible to heavy metal ions.