The role of ethylene and carbon dioxide in differentiation of shoot buds in excised cotyledons of Pinus radiata in vitro

The production of ethylene and carbon dioxide by Pinus radiata D. Don cotyledons cultured on shoot‐forming medium in sealed Erlenmeyer flasks was studied. To establish the role of these gases on morphogenesis three experimental approaches were used: (1) capping the flasks with serum caps on various days, and removing the serum caps at different stages of morphogenesis, (2) absorbing the gases by setting up traps singly and in combination during the various stages of differentiation and (3) incubating the cultures under continuous flow of constant gas mixtures. The results indicate that both ethylene and carbon dioxide, which build up during the first 10 to 15 days of culture, promote morphogenesis. Excessive accumulation after the initiation of buds causes some degree of dedifferentiation. When both the gases were eliminated from the flasks, bud formation and growth were inhibited. In the absence of oxygen, ethylene and carbon dioxide fail to influence growth and morphogenesis.