The Effect of Auxin on Growth and Respiration of Artichoke Tissue

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Abstract
Artichoke disks were prepared and maintained aerobically on nets to detn. the uptake of water and oxygen under the influence of indoleacetic acid (IAA) and of IAA with metabolic inhibitors. In 12 expts. the mean value of the increase in fresh weight of disks in IAA (10 mg./l.) for 4 days was 60%, whereas the corresponding increase in pure water averaged only 6%. Naphthaleneacetic acid (10 mg./l.) and 2,4-dichlorophenoxyacetic acid (1 mg./l.) gave comparable results in one expt, but atypical results in 3 others. Disks in IAA solns. apparently underwent a large amt. of cell division as shown by their thickness and irregular outlines. The effect of various inhibitors on IAA-induced water uptake during 4 days was detd. The concn. of inhibitor required to give 50% inhibition was 1 x 10-5 [image] for arsenite, 3 x 10-5 for 2,4-dinitrophenol, 1 x 10-4 [image] for azide, 3 x 10-3 [image] for fluoroacetate and 3 x 10-4 [image]. for iodoacetate. IAA (10 mg./l.) caused a significant increase in oxygen uptake through a 6-day period, with a 400% increase from the 2d to the 6th day, indicating that the auxin exerted its effect primarily on oxidative metabolism. The IAA-induced water uptake seems to involve the participation of-SH-containing enzymes, phosphorylation reactions, a heavy-metal oxidase and acetate metabolism. A quantitative comparison of the 50% inhibiting concns. for water uptake by potato and artichoke disks gave similar values, indicating the same basic processes. The stimulating effects of IAA on respiration and on water uptake are comparable.

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