Studies on Plant Growth Hormones: III. APPLICATION OF ENZYME REACTION KINETICS TO CELL ELONGATION IN THE AVENA COLEOPTILE

1. Previous reports that Michaelis enzyme kinetics may be appliedto the system controlling cell elongation in Avena coleoptilesare confirmed.
2. Substrate (applied hormone) and enzyme arenot in direct contactwith each other. Active transport of theapplied hormone incoleoptile sections, and permeability ofcells to hormone, regulatethe intracellular substrate concentration,thereby markedlyinfluencing the value of K₅, a parameter givinga measure ofthe affinity of substrate for enzyme.
3. The effectof permeability and transport factors on calculatingK₁ valuesof competitive hormone inhibitors is considered. Dataof otherworkers are used to show that observed K₁ values arenot necessarilyindependent of the hormone used.
4. Auxin-induced inhibitionof cell elongation results primarilyfrom a toxic action ofhormones on cell protoplasm leading finallyto cellular disorganization,shrinkage, and death. The datado not decisively support thehypothesis of inhibition resultingfrom steric hindrance totwo-point attachment between substrateand enzyme.