Ethylene, indoleacetic acid and apical dominance in peas: A reappraisal

Decapitation of peas ( Pisum sativum L. cv. Greenfeast) promoted sprouting of the lower buds with the most active growth in the first week occurring in the bud at the lowest fully expanded leaf node. Addition of 3‐indolyl acetic acid (IAA; a 0.03 M solution, applied al 10 and 25 μg/plant) inhibited bud outgrowth whether added to the cut stump or injected above or below the lowest leaf node. Ethylene evolution by the nodal region decreased following decapitation, but increased greatly if IAA was added to the cut stump. Ethylene gas (3, 15 and 1 500 ul/l) or the precursor ACC (l‐aminocyclopropane‐I‐carboxylic acid) reduced bud outgrowth while factors which scrub ethylene (mercuric perchlorate). inhibit ethylene synthesis (canaline), or prevent its action (silver nitrate), enhanced bud growth on decapitated plants, It was concluded that auxin‐induced inhibition of bud growth through an increase in ethylene synthesis is a more logical hypothesis than the direct inhibition by auxin per se since a) acropetal movement of the inhibitory principle occurred whereas [ 14 C] IAA movement in stems was basipetal, b) a decline in the levels of ethylene evolution was correlated with bud outgrowth in decapitated plants and c) exogenous application of chemical agents which increase or decrease ethylene level or response lead to correlative decreases or increases in bud outgrowth, respectively.