The Action of Growth Inhibitors on Carbohydrate Metabolism in the Pea

Abstract

Sufficient evidence has accumulated in the past few years to make it certaini that growth by cell enlargement is inseparably connected with certain aspects of metabolism. In the Avena coleoptile, growth of isolated sections in simple solutions containing auxin is strongly aerobic and is inhibited by inhibitors of oxidizing and dehydrogenating enzymes. In particular the inhibiting action of iodoacetate, arsenite and fluoride on growth in presence of auxin [THIAMANN and BONNER (4) and unpublished data] suggests a relationship with carbohydrate metabolism, since these substances are all known to inhibit enzymes acting on the breakdown of carbohydrates. This paper is a preliminary report on a series of experiments designed to elucidate the relation between these three inhibitors and the metabolism of carbohydrates.Since Avena coleoptile sections only grow well in the presenice of sucrose, pea stems were used instead. Sections 20 mm. long were cut from the apical portion of 7-day-old etiolated Alaska pea plants and floated on the test solutionis in darkness at 25°C. for 24 hours. They were theni weighed, measured, and at once extracted with boiling 80% alcohol. Sugars were determined by the SHAFFER-HARTMAN-SOMOGYI procedure (3).In general such 20 mm. sections grow about four mm., or 20%, in water alone, and about 10 mm., or 50%, in indoleacetic acid (1 mg./l.). The growth is thus small but is very reproducible and has been shown to take place almost wholly in the first 12 hours. The reducing sugar content of the stem sections averaged 1.12%c of the fresh weight and after 24 hours' growth this fell to about three-fourths of the initial value. From a series of concentration curves for each inhibitor, which will be published in detail later, points corresponding to 50%/ inhibition were selected. The data for growth and reducing sugar content at this and at a higher concentration for each inhibitor are presented in table I.It will be seen first that in general the increase in fresh weight parallels the increase in length, with minor variations. Secondly, whether the sections are held in water or in auxin the disappearance of reducing sugar is the same. The data for the water and auxin controls are each the mean of 15 experiments. The concentratiolns of inhibitors needed for 50%

Relationship between Promotion of Xyloglucan Metabolism and Induction of Elongation by Indoleacetic Acid

“…The results with arsenite and fluoride imply a metabolic requirement for the phenomenon of xyloglucan release. They show that xyloglucan release is at least as sensitive to these inhibitors as is elongation, whereas total respiration and wall synthesis are known to be appreciably less sensitive to inhibition by these agents than is elongation (4,5).…”

Studies on the Growth and Inhibition of Isolated Plant Parts. Iii. The Action of Some Inhibitors Concerned With Pyruvate Metabolism

“…At a fluoride concentration sufficient only to produce 50 per cent growth inhibition, there is no appreciable inhibition of respiration in the coleoptile. At the corresponding concentration for pea stems, i.e., where growth is inhibited 50 per cent, there is a small but pronounced increase of oxygen uptake (Christiansen et al, 1949). The effect of fluoride on the respiration of coleoptiles is summarized in tables 2 and 3.…”