Induction of Swelling in Pea Internode Tissue by Ethylene

Ethylene inhibits polar cell expansion of etiolated pea (Pisum sativum) internode tissue and results in a radial cell expansion, swelling. A special gas-tight growth chamber was developed to monitor continuously the induction of cell expansion inhibition of excised internode segments in the presence of ethylene. Following a complex induction period which lasts about 3 hours, a low, but steady-state growth rate is achieved. Ethylene removal experiments indicate that the gas induces an irreversible change in the cell expansion mode. If the tissue was transferred to an ethylene-free chamber after the steady-state rate had been achieved, this rate continued in the absence of the gas. If the gas was removed during an intermediate phase, that intermediate rate of growth continued after removal. In other experiments, segments were incubated with intact apical hooks and the induction period was much shorter than with isolated segments. Changes in imino acid metabolism have been correlated with the induction of swelling. Although total proline and hydroxyproline levels were not affected by ethylene treatment, incorporation of [(14)C]proline into a wall-associated protein was inhibited during the period when swelling occurred. These results suggest that ethylene is affecting proline pool sizes.