SOLUTE LEAKAGE FROM DETACHED PLANT-PARTS OF WINTER-WHEAT - INFLUENCE OF MATURATION STAGE AND INCUBATION-TEMPERATURE

Plant pans from field-grown wheat were detached and immersed in distilled water for several hours in the dark at 4 degrees C (very low metabolic activities) and at 20 degrees C. The release of amino acids, potassium, sodium, calcium and magnesium was measured repeatedly throughout the incubation period of 48 h. Such leakage experiments were started at four different maturation stages between ear emergence and harvest. Cations (except sodium, which was retained in the plant parts) were released immediately from senesced plant material, regardless of the temperature. In the incubation medium of green or yellowing plant parts, cations appeared only after several hours at 20 degrees C, but essentially no release was detected at 4 degrees C. Major quantities of amino acids were released only from green leaves or those in an early phase of senescence after incubation for several hours at 20 degrees C. At 4 degrees C, hardly any amino acids leaked out, regardless of the senescence stage. Consequently, metabolic activities were relevant for the delayed leakage at 20 degrees C. Our results suggest that changing properties of the leaf surface, the intactness of membranes, and compartmentation play an import role in the leakage of solutes. Leakage of solutes from senescing organs during a rain period must be considered as a relevant factor for the nutrient balance of crop plants.