Stimulation of oat and rice mesocotyl growth by ethylene

A low concentration of ethylene stimulated growth of intact oat and rice mesocotyls in darkness. Combined application of ethylene and gibberellin A3 produced an evident additive effect on the elongation of rice mesocotyls. Ethylene usually acts as a growth inhibitor (/), for coleoptile growth in wheat (2) and oat (3, 4). However, ethylene stimulates growth of intact (5) and excised (6) rice coleoptiles although the latter requires the presence of exogenous auxin. 2-Chloroethylphosphonic acid (Ethrel, CEPA), an ethylene releasing agent, stim-ulates elongation of intact rice coleoptiles but inhibits that of wheat, barley, oat and rye (7). This report gives evidence showing that ethylene stimulates growth in intact oat and rice mesocotyls. Materials and methods Seeds of oat (cv. Victory) and rice (cv. Nato) were soaked for 1 or 2 days in darkness at 27 °C. Germinated seeds were selected for uniformity of coleoptile length (1 mm). To treat seedlings with ethylene two methods were employed: (1) Ten seeds were transferred into 2 ml of distilled water or into various con-centrations of gibberellin A3 (GA3) (obtained from the Gibberellin Research As-sociation) in a 50-ml Erlenmeyer flask. The flask was stoppered with a vaccine cap and ethylene was injected through the cap with a gas-tight syringe. This method is called the "flask method". (2) Twenty seeds were planted on a 0.95% agar prepared in the center well (5 cm in diameter and 4 cm in depth) of a glass-made capsule (500 ml in volume), designed especially for ethylene treatment. In this case, ethylene was introduced through a vaccine cap fitted to the lower mouth of the capsule with a gas-tight syringe as shown in Fig. 1. This method is called the "capsule method". In some cases, a small tube (18x35 mm) containing either 5 ml of 20 % KOH to remove evolved CO2 or 5 ml of mercuric perchlorate to remove evolved ethylene was placed in the agar of the center well. In other cases, 50-ml Erlenmeyer flasks having one or two center well(s) were used. The center well contained either 2 ml of 20 % KOH or 2 ml of mercuric perchlorate