Transorgan Tissue pH Gradients and Their Significance for the Maize Plant Functioning as a Whole in the Process of Nutrient Uptake During Ontogenesis

N. I. MITREVA

N. Poushkarov Research Institute of Soil Science and Agroecology, BG-1380 Sofia, Bulgaria

Abstract

MITREVA, N. I., 1999. Transorgan tissue pH gradients and their significance for the maize plant functioning as a whole in the process of nutrient uptake during ontogenesis. Bulg. J. Agric. Sci., 5: 741-752

Pot experiments were conducted with maize (Zea mays L.) grown in nutrient solutions and on soil substrate. The following indices were studied: 1. Variations of H+ and OH- excretion (changes in pH of the substrate). 2. Differences in tissue pH between plant organs (transorgan tissue pH gradients). 3. The NRA (nitrate reductase activity) of organs. 4. Cation-anion balance in the shoot. All the indices were studied as a function of N source and plant age. The introduction gives proof of the understanding, that the excretion of H+ from the roots of intact plants is the result of the function of an auxin dependent ATPase (H+ pump) in the cells of the leaves and that there exist extra stelar transport pathway to the roots for the H+ produced in the leaf cells.

Key words: maize, tissue pH, transorgan gradients, driving force, whole plant functioning