<Emphasis Type="Italic">In vitro</Emphasis> nitrogen nutrition and hormonal pattern in bromeliads

Summary Four cytokinins (CKs), indole-3-acetic acid (IAA) and its ester and amino conjugates, and abscisic acid (ABA) levels of two bromeliads, Ananas comosus (L.) Merril and Vriesea gigantea Gaudich., grown in 5 mM (NH₄)₂SO₄ or urea as the sole nitrogen (N) form, were investigated. In both bromeliads, zeatin (Z) and zeatin riboside (9R]Z) were the most abundant CKs. In A. comosus, CKs levels decreased drastically (≊ 12 times) after 7 and 30 d in media with ammonium and urea, respectively. After 3 d in media with N, V. gigantea CK levels decreased 30 and 20 times in the presence of ammonium and urea, respectively. N-starved A. comosus and V. gigantea exhibited similar ABA levels, but ABA decreased faster in V. gigantea when plants were transferred to media with N. Free IAA levels decreased until the 15th and 30th day when A. comosus was transferred to a medium with ammonium and urea, respectively. N-starved A. comosus amide, ester, and free IAA amounted to 81%, 14%, and 4%, respectively. There was a transient increase in the proportion of amide IAA and a corresponding decrease of the ester and the free IAA proportion when N-starved plants were transferred to media with N. The relationship between the internal hormonal patterns and the different ecological adaptations of the two bromeliads are discussed.