Relations Between Indoleacetic Acid, Calcium Ions and Ethylene in the Regulation of Growth and Cell Wall Composition in Picea abies

Effects of indoleacetic acid, calcium ions and ethylene on thegrowth of and deposition of different cell wall fractions inthe hypocotyl of Norway spruce (Picea abies (L.) Karst.) seedlingswere investigated. Indoleacetic acid progressively stimulated cellulose depositionas the amount of added Ca²⁺ increased. In contrast, indoleaceticacid promoted lignification and the deposition of non-cellulosicpolysaccharides only in the absence of added Ca²⁺ . When Ca²⁺was added, the indoleacetic acid effect disappeared. Similarly,indoleacetic acid promoted non-cellulosic polysaccharide depositiononly in the absence of ethylene. At increasing ethylene levelsthe effect of indoleacetic acid on non-cellulosic polysaccharidedeposition disappeared and indoleacetic acid instead promotedcellulose deposition. The response to indoleacetic acid depended on the Ca²⁺ concentrationand on the rate of ethylene production. The relationship betweenindoleacetic acid and Ca²⁺ seemed complex, but clearly indoleaceticacid could partially overcome a Ca²⁺ deficiency. The resultssuggest that ethylene may be a factor of particular importancefor the type of polysaccharide deposition during cell wall formation. Key words: Calcium, cell wall, conifers, ethylene, indoleacetic acid