Growth and Development in NaCl-Treated Plants. II. Do Na⁺ or Cl^- Concentrations in Dividing or Expanding Tissues Determine Growth in Barley?

Abstract

Plants of barley (Hordeum vulgare cv. Clipper) were grown in solutions containing 0, 100 or 175 mol m^-3 NaCl from leaf 3 emergence until anthesis. Na⁺ and Cl^- concentrations in various growing tissues of the shoot were measured concurrently with increases in dry weight. The tissues on which the study focused were the basal 30 mm of leaves 4 and 7 (mainly expanding cells), and the primordial stage of leaf 7 and the floral apex (mainly dividing cells). Although leaf growth was reduced by the higher NaCl treatments, apex growth was initially increased. Na⁺ and Cl^- concentrations were high in the expanding tissues (150 mol m^-3), but there was no consistent relation between the concentrations and the growth rate. Na⁺ and particularly Cl^- concentrations were much lower in the dividing tissues, and again did not correlate with the rate of development of the tissue, or the final size of the organ. These data strongly indicate that the growth of the shoot is not directly controlled by local concentrations of Na⁺ or Cl^- of the growing tissues, but by some influence originating elsewhere in the plant.