Effects of Ethylene, Kinetin, and Calcium on Growth and Wall Composition of Pea Epicotyls

Abstract

Ethylene supplied with indoleacetic acid at 0.1 and 1 mum inhibited elongation and enhanced swelling in epicotyls of decapitated and derooted pea seedlings (Pisum sativum L., var. Alaska). These growth responses were correlated with the development of cell walls rich in weak acid-extractable materials and pectic uronic acids. Ethylene had no effect on the formation of hemicellulose, or hemicellulosic uronic acid. Ethylene stimulated the formation of residual materials at 0.1 mum indoleacetic acid but had little effect at 1 mum. With indoleacetic acid at 10 mum, ethylene modified neither the growth or wall composition appreciably. Growth and wall composition in intact seedlings were modified in similar fashion by ethylene. In intact seedlings ethylene promoted the development of walls high in weak acid-extractable materials and pectic uronic acid. These effects were less impressive in the first 24 hours than in the second 24 hours when the control plants suffered a net loss of these constituents. Ethylene considerably inhibited the formation of hemicellulose and residual wall materials in the apical sections but promoted it in the basal sections of the intact seedlings.Measurements of ethylene production by decapitated and derooted pea seedlings suggest that Ca(2+) and kinetin do not promote swelling through an effect on the formation of ethylene.We propose that cells of ethylene-treated pea epicotyls lack polarity because their walls are abnormally rich in pectic substances.