Changes in osmotic pressure and cell wall properties during auxin‐ and ethylene‐induced growth of intact coleoptiles of rice

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Abstract
Indole‐3‐acetic acid and 1‐aminocyclopropane‐1‐carboxylic acid, the precursor of ethylene, stimulated elongation of coleoptiles of seedlings of intact rice (Oryza sativa L. cv. Sasanishiki) submerged in buffer solution with constant air‐bubbling. The osmotic pressure of the cell sap decreased during elongation of coleoptiles. In the presence of 30 μM aminooxyacetic acid, an inhibitor of ethylene biosynthesis, in‐dole‐3‐acetic acid at 30 μM accelerated the decrease in the osmotic pressure in the early stage of growth. 1‐Aminocyclopropane‐1‐carboxylic acid at 30 μM did not influence the decrease in the osmotic pressure.Both indole‐3‐acetic acid and 1‐aminocyclopropane‐1‐carboxyIic acid decreased the minimum stress‐relaxation time and the relaxation rate of the cell wall, suggesting that both auxin and ethylene induce elongation of rice coleoptiles by stimulating cell wall loosening. These growth regulators caused an increase in the level of glucose in hemicelluloses in the early stage of growth and a decrease in the level in the subsequent last growth phase. Indole‐3‐acetic acid decreased the hydroxyproline and glucosamine levels per unit dry weight of the cell wall. These changes in the level of cell wall components may be associated with the changes in the mechanical properties of the cell walls caused by auxin and ethylene.