Deficiencies in the supply of nitrogen and phosphorus brought about the cessation of shoot extension and the formation of terminal resting buds in seedlings of Acer pseudoplatanus maintained under long days, whereas seedlings of Betula pendula maintained under the same conditions continued extension growth of the main axis over a long period, although they showed symptoms of nitrogen deficiency, including a reduced chlorophyll content. The endogenous cytokinin levels of the base/nucleoside fraction in leaves of B. pendula were significantly lower in the nitrogen-deficient plants than in the controls only 3 d after transfer to deficient conditions. Similar, though less marked, changes were observed in response to phosphorus deficiency. Changes in the levels of cytokinin activity in the nucleotide fraction in response to nitrogen deficiency were much less marked. No significant changes in cytokinin levels of the base/nucleoside or nucleotide fractions could be detected in leaf material from seedlings of A. pseudoplatanus, even after a nitrogen or phosphorus deficiency treatment of 4 weeks. Application of exogenous benzyladenine to seedlings of B. pendula subjected to nitrogen deficiency resulted in a rapid regreening and to outgrowth of inhibited lateral buds after only 2 d.
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Horgan et al. (1980) studied this question.