The stage of leaf maturity implicates the response of the photosynthetic apparatus to cadmium toxicity

The first leaves of rye seedlings exposed to toxic concentration of Cd in the nutrient medium were chosen to study the relationship between the stage of leaf maturity and the response of the photosynthetic apparatus to this heavy metal. Because of growth characteristics of leaves of monocotyledonous plants all stages of leaf maturity are represented along this organ - from the youngest cells at the base to the oldest at the tip of the leaf. Some recent studies carried on dicotyledonous plants proved the level of heavy metals toxicity to be related to the leaf age and its stage of growth. We decided to test this hypothesis on monocotyledonous plants where one can observe all stages of maturity within different sections of one leaf. Basic growth analysis (total leaf length, FW content of leaf sections), determination of Cd content and chloroplast pigment levels in individual leaf sections, measurements of the photosynthetic apparatus efficiency using chlorophyll fluorescence techniques, were carried out. We have shown a close relation between the stage of leaf maturity and the efficiency of the photosynthetic apparatus in rye plants with the Calvin cycle being the most sensitive to Cd toxicity. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.