Cellular Processes Limiting Leaf Growth in Plants under Hypoxic Root Stress

Abstract

The effects of root hypoxia on leaf growth of a Populus trichocarpa x deltoides hybrid have been assessed. Clonal plants were subjected to hypoxic root conditions in pot culture by flooding and in solution culture by gassing with nitrogen. The rate of leaf expansion declined within 8 h and was suppressed for the duration of the treatment. Final leaf size was reduced by 35% to 60% compared to aerated plants. Final epidermal cell size and number depended both on the developmental stage of the leaf at the onset of stress and on the duration of the treatment. No differences in bulk leaf water potential were measured between the hypoxic and aerated plants. Cell wall extensibility was lower, leaf solute potential was more negative and turgor potential was higher in leaves of hypoxia-treated plants than of aerated plants. These data suggest that leaf growth of hypoxia-stressed plants is limited by cell wall extensibility. The mechanism by which the root stress induces changes in leaf cell wall characteristics is not known.