The cytokinin content of stem tissues, primary genetic tumours (excised from 2‐month‐old plants) and 3‐week‐old in vitro cultured genetic tumour tissues derived from Nicotiana glauca (Grah.) × langsdorffii (Weinm.) and N. suaveolens (Lehm.) × langsdorffii (Weinm.) hybrids and stem tissues derived from 2‐month‐old N. suaveolens and N. langsdorffii plants has been analysed by radioimmunoassay. Stem tissues of tumour‐prone hybrids contain high cytokinin levels (3–3.7 nmol g −1 ). This increase is caused mainly by increased levels of cytokinin nucleotides, particularly those of zeatin nucleotide (0.5 nmol g −1 ) in stem tissues of parent plants and 2.4 nmol g −1 in stem tissues of hybrids). All other tissues contain lower cytokinin levels (0.7–1.7 nmol g −1 ). Cytokinin bases and ribosides are major compounds in cultured tumour tissues while the nucleotides are dominant cytokinins in all freshly excised tissues from parent plants and their hybrids. In a separate study, the metabolic fate of supplied [ 3 Hj‐zeatin riboside. which is inactivated mainly by sidechain cleavage, has been studied. The results collectively suggest that cytokinins may be involved in tumourigenesis.
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Nandi et al. (1990) studied this question.