ABSCISIC ACID AND DORMANCY IN ROOT-NODULATED ALNUS GLUTINOSA (L.) GAERTN

Treatment of three-month or six-month-old water culture plants of Alnus glutinosa with 0.1 mol m^-3 (±) abscisic acid (ABA) induced formation of resting buds after 30 to 60 d. Leaf dry weight per plant decreased by 40 to 45 % during this period but root and nodule dry weights were unchanged relative to control plants. [2-¹⁴ C] ABA was taken up by the root system within 5 d and after 30 or 60 d the ABA content of plants fed 01 mol m^-3 ABA was 60 and 119 times that of control plants. In control plants, the levels of 'free'cis(Z) ABA were similar to or exceeded 'free'trans(E) ABA in all plant parts while, in general, the converse was true for these isomers in 'bound' form. In ABA-treated plants, all isomeric forms of ABA were present at much higher amounts than in the controls but, whereas in leaves and shoot apices the amount of cis ABA in both 'free' and 'bound' forms was much greater than the trans isomer, in roots and nodules trans ABA was the dominant isomer in both 'bound' and 'free' forms. Most biologically active 'free'cis ABA thus accumulated in the leaves and shoot apex, where effects of ABA treatment on growth were most evident, whereas in roots and nodules where biologically inactive 'free' and 'bound'trans ABA were dominant, growth was relatively unaffected. Amounts of 'free' ABA in nodules were several times those recorded previously in nodules of dormant plants, in keeping with earlier suggestions that ABA is unlikely to have a precise regulatory role in growth and dormancy of nodules.