INTRACELLULAR LOCALIZATION OF NATIVE AUXIN IN AVENA COLEOPTILE

Intracellular localization of the native auxin in the Avenacole-optile tip was investigated by separating cellular fractionsby differential centrifugation. Each fraction was extractedwith ether and the auxin activity was measured by the sensitizedAvena curvature test. After the removal of the native free auxin,each fraction was alkaline-hydrolyied, and from these hydrolyzatesthe bound auxin was extracted with ether and its activity wasmeasured. Both the native free auxin and the native bound auxinin these extracts were identified as IAA by paper chromatography.The results show that the native free auxin occurs only in thesupernatant soluble cytoplasm, and that the native bound auxinlocalizes also in the supernatant. The distribution of the externallyapplied IAA was also investigated. (Received February 27, 1962; )     

EFFECT OF AUXIN AND OXALIC ACID ON THE CELL WALL PROPERTY OF AVENA COLEOPTILE

In accelerating the elongation of excised Avena coleoptile cylinders,the effect of oxalic acid was found to be additive to that ofindole-3-acetic acid. Elastic and plastic extensions of the coleoptile cylinder weremeasured by using the plasmolytic method. Both indole-3-aceticacid and oxalic acid increased the elastic extension quickly,while their effect in increasing the plastic extension appeared2 hours after their application. The mechanism of auxin action is discussed in connection withthe effect of removal of calcium from the pectic substance ofthe primary cell wall. (Received November 15, 1960; )     

ON THE RELATION BETWEEN GROWTH AND RESPIRATION IN THE AVENA COLEOPTILE

1. The growth of Avena coleoptile sections in sucrose and auxin solutions is inhibited by various substances which are known to act as dehydrogenase inhibitors. 2. Iodoacetate, which is particularly active in this connection, inhibits all growth at a concentration of 5 x 10^–5 M, but produces only a slight inhibition of oxygen uptake. 3. The growth inhibition by iodoacetate is completely removed by malate and fumarate, and to a lesser extent by succinate and pyruvate. 4. These acids themselves increase the effect of auxin on growth and also increase the respiration of the coleoptile sections, but only if auxin is present. 5. When sections have been soaked in malate or fumarate, the addition of auxin considerably increases the total respiration. Further, the concentration range over which this increase takes place parallels that active in promoting growth. 6. The four-carbon acids provide a respiratory system which is part of the chain of growth processes, and which is in some way catalyzed by auxin. It represents a small but variable fraction of the total respiration.     

THE GROWTH AND RESPIRATION OF THE AVENA COLEOPTILE

1. Transport of the plant growth hormone into the Avena coleoptile as well as the action of the hormone on cell elongation in the coleoptile are shown to depend upon aerobic metabolism. 2. Crystalline auxine, in contrast with impure preparations, affects neither the magnitude nor the respiratory quotient of coleoptile respiration. 3. Increasing age of the coleoptile cell decreases its rate of elongation much more than its rate of respiration. HCN or phenylurethane on the other hand decrease the two processes to the same extent, in spite of the fact that only a small portion of the energy liberated by respiration can be used in the mechanical process of growth. 4. From 2 and 3 it is concluded that processes of a respiratory nature but of relatively small magnitude form one or more integral steps in the chain of reactions by which the plant growth hormone brings about cell elongation.     

EFFECT OF AUXIN ON β-1, 3-GLUCANASE ACTIVITY IN AVENA COLEOPTILE

When the homogenate of Avena coleoptile segments was fractionated, the specific activity of β-1, 3-glucanase was remarkably associated with the cell wall, partly to be released from it by a detergent. The cell wall-bound glucanase activity was increased by the treatment of coleoptile segments with auxin. Only in 10 min of the treatment the glucanase activity and the incorporation of labeled leucine into the proteins were found to be increased in the fraction to be liberated by detergent from the cell wall fraction. These effects of auxin were inhibited by 10 μg/ml cycloheximide.     

MODE OF ACTION OF MALEIC HYDRAZIDE ON THE GROWTH OF ESCHERICHIA COLI AND AVENA COLEOPTILE SECTIONS

1. MH was found to suppress the growth and respiration of E. colias well as the IAA-induced growth of Avena coleoptile sections.
2. These suppressions could be reversed more or less strikinglyby the addition of a trace of heavy metals such as Co, Mn, Ni,Zn, Cu, or Mo.
3. The reversal could also be achieved by cysteine,thioglycollate,or fumarate, the latter two substances being,however, lesseffective.
4. The inhibition of the growth of E.coli by MH was completelyrelieved by the addition of IAA. Conversely,the inhibitionof the microbial growth by high concentrationsof IAA couldbe relieved by the addition of MH.
5. It was inferredthat MH may block certain heavy metal-catalyzedprocess, inwhich some thiol substance and IAA are participating,probablyby combining with the heavy metal.

(Received June 23, 1960; )     

EFFECT OF LIGHT ON AUXIN TRANSPORT AND ELONGATION OF AVENA MESOCOTYL

The present work was undertaken to find if there are relations between light and auxin action on elongation of coleoptilar node and mesocotyl with Avena seedlings. Red light inhibited the elongation of mesocotyl and simultaneously decreased the rate of transport of diffusible auxin through the node. Red light also inhibited the transport of exogenously given IAA through the nodal region. The light inhibition of IAA transport was closely related to the increase of IAA immobilization. As the age proceeds, the ability of IAA immobilization increased with the decrease in the rate of mesocotyl elongation, even if the seedling was grown in complete darkness. The nature of radioactive substances found in the IAA-C¹⁴ treated tissue was examined by paper chromatography. The above results strongly suggested that the increase of IAA immobilization might result in the inhibition of mesocotyl elongation.