Indole-3-acetic Acid Treatment Research Articles

Some quantitative effects of indoleacetic acid on the wood production and tracheid dimensions of Picea

The diameter and wall thickness of tracheids produced after indoleacetic acid treatment were not significantly different from those of the intact controls, for the first few weeks after treatment of disbudded shoots of Picea abies Karst. and Picea sitchensis (Bong.) Carr. However, lateral application of indoleacetic acid (IAA) to intact shoots increased both tracheid diameter and wall thickness; it is suggested that IAA acted synergistically with another endogenous growth regulator, which was also removed by disbudding. Increase in wall thickness after exogenous IAA was associated with increase in duration of the wall thickening phase of tracheid differentiation; this is discussed in relation to the seasonal change from early to latewood. Cambial dormancy was induced by disbudding during active wood production. Since this occurred with or without the presence of current leaves, it is concluded that in Picea continued cambial activity depends upon supply of auxin from the buds, and cannot be supplied from expanded leaves or from the internode itself. Neither indoleacetic acid nor gibberellic acid stimulated renewed cambial activity when applied after the cessation of wood production. With both disbudded and intact shoots, the effectiveness of exogenous IAA declined with time, probably due to decreasing penetration through callus developing at the wounded surface. It is suggested that this apparent change in IAA effectiveness may explain some discrepancies between the results of previous observers.

Ultrastructural Alteration of Plant Plasma Membranes Induced by Auxin and Calcium Ions

Ultrastructural changes in isolated and in situ plasma membranes of etiolated soybean hypocotyls (Glycine max L. cv. Wayne) were induced by indole-3-acetic acid (IAA), other auxins, and calcium chloride. Fixed and embedded preparations were stained by a phosphotungstate-chromate procedure to identify and accentuate plasma membrane. Measurements were on micrographs obtained with an electron optical system calibrated and corrected for reproducible and accurate size measurements. Plasma membranes treated for 20 minutes with 1 mum IAA were 10 to 15% thinner than controls. The response to IAA was rapid, reproducible, auxin-specific, temperature-dependent, and reversible. Comparable responses were obtained with isolated and in situ membranes. Membranes treated with 0.5 m calcium chloride for 20 minutes were 15 to 20% thicker than controls. Multiple cycles of alternating calcium and IAA treatments yielded membranes with dimensions that reflected the last treatment of the series. The findings show a direct response of plasma membranes to growth regulating agents and provide evidence for a cell-free response of isolated plasma membranes to a hormone.

Bound Auxin Formation in Growing Stems

The term "bound auxin" is herein used to describe auxin conjugates insoluble in organic solvents which dissolve indoleacetic acid (IAA) and its derivatives, but hydrolyzable by NaOH to release IAA. Bound auxin from pea stems was fractionated into water-soluble, water-insoluble/NaOH-hydrolyzable, and insoluble components. Formation of bound auxin commenced with 15 minutes of applying exogenous labeled IAA, and progressively increased in amount, relative to IAA uptake, over 6 hours. Formation was not restricted to any particular zone of the stem and occurred in both light- and dark-grown stems. A greater quantity of bound auxin was formed in light-grown stems, reaching 4.2 and 7.7%, of the IAA taken up, in the water-soluble and water-insoluble/NaOH-hydrolyzable fractions after 6 hours. The presence of sucrose, during either the IAA treatment or an aging pretreatment had no effect, though 6 hours aging did cause a subsequent increase in the water-insoluble fraction of the bound auxin. Bound auxin formation in light-grown stems was dependent on respiratory metabolism, being reduced by KCN. It was also reduced, compared to total uptake, by inhibitors of RNA, and protein synthesis (6-methylpurine and cycloheximide) but only when the inhibitors preceded auxin addition and were present for a 4-hour period. Addition of inhibitors following auxin had no effect, suggesting an early inductive effect of auxin on bound auxin formation. Inhibitors of cell elongation had no effect. Deoxyglucose, an inhibitor of glucan synthesis, had only a small effect on the water-soluble fraction. Bound auxin is an important auxin product in growing plants. Its function is unknown, but some possibilities are discussed.

The effect of 5-azacytidine on the growth and thymidine kinase activity of coleoptile sections ofTriticum

The growth of coleoptile sections ofTriticum and its stimulation by indole-3-acetic acid (IAA) are inhibited by 5-azacytidine added into the cultivation medium. 50 per cent depression of the elongation was observed at 2×10−3M 5-azacytidine concentration. Thymidine kinase activity in cell-free extracts prepared from coleoptile sections treated with 5-azacytidine, and caleulated per 10 mg of their wet weight, is increased while IAA administration resulted in its depression. The observed changes in thymidine kinase activity can be explained assuming the different uptake of water due to 5-azacytidine and IAA treatment.

Alachlor and 1,8-Naphthalic Anhydride Effects on Corn Coleoptiles

More force was required to induce leaf slippage in coleoptiles from corn (Zea maysL. ‘Tenn 5009′) plants grown in the presence of 25 ppmw alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] than in the controls, or in coleoptiles from plants grown in the presence of 25 ppmw alachlor in combination with 150 ppmw 1,8-naphthalic anhydride (hereafter referred to as NA). NA alone reduced the force required to induce leaf slippage below that of all treatments. Incubation for 16 hr in 10 ppmw IAA (indoleacetic acid) did not lower the force required to induce leaf slippage in coleoptiles from plants grown in the presence of 25 ppmw alachlor even though the length of the coleptiles increased 30% more than coleoptiles not receiving the IAA treatment. Percent dry matter, dry matter per 100 plants, and percent protein increased in coleoptiles from alachlor treated plants, while percent cellulose and lignin decreased. The extent of variation in these parameters was lessened when NA was applied in combination with alachlor, with the exception of percent lignin which was further decreased by the combination treatment. Percent hemicellulose was not affected by alachlor, NA, or their combination.

Activation of Avena Coleoptile Cell Wall Glycosidases by Hydrogen Ions and Auxin

Several cell wall-bound glycosidases present in Avena sativa coleoptiles were assayed by following the hydrolysis of p-nitrophenyl-glycosides. Particular emphasis was placed on characterizing some parameters affecting the activity of beta-galactosidase. The pH optimum of this enzyme is 4.5 to 5.5; it is sensitive to copper ions and p-chloromercuribenzoate treatment and apparently has an exceptionally low turnover rate. Indoleacetic acid treatment enhanced in vivo beta-galactosidase activity of coleoptile segments by 36% over control after 60 minutes. This enhancement was prevented by abscisic acid and cycloheximide. High buffer strengths and low pH reduced the indoleacetic acid-enhanced increase in enzyme activity. These data lend support to the following proposed model of indoleacetic acid action. Indoleacetic acid enhances the release of hydrogen ions into the cell wall which promote the activities of cell wall glycosidases, some of which may participate in the cell extension process.

The regulation of peroxidase activity by gibberellin and auxin in pea stem segments

Peroxidase activity in excised stem segments of Pisum sativum L. cv. Progress No. 9 increases linearly during incubation in buffered medium. Gibberellic acid (GA) causes a slight reduction in activity whereas indoleacetic acid (IAA) treatment completely prevents this rise. Excision produces two new cathodic isoperoxidases near the cut ends. Their appearance is prevented by cycloheximide, actinomycin D, and IAA; G A enhances this IAA-induced repression. GA alone stimulates one of the isozymes but does not affect the other one. Peroxidase leakage is stimulated by GA and inhibited by IAA treatment. The activity is entirely confined to the isoperoxidases produced in response to injury.IAA oxidase activity in incubated segments was slightly elevated over that of freshly cut ones. However, differences in activity among hormone treatments were small. IAA oxidase was also demonstrated in growth media and only IAA treatment reduced activity. Both peroxidases in the medium were isolated by column chromatography. Surprisingly, the purified isozymes appear to be essentially devoid of IAA oxidase activity.

Flower Formation in Excised Tobacco Stem Segments

A method has been developed that extracts DNA from stem tissue of flowering tobacco plants, Nicotiana tabacum cv. Wis. 38. The DNA content of stem tissue from a flowering tobacco plant is correlated with its capacity to flower in vitro. Stem segments known to form 100% floral buds contain 10 times more DNA per gram fresh weight than segments that form 5% floral buds and 95% vegetative buds, and in the uppermost 28 centimeters of flowering tobacco plant stems the DNA content decreases roughly in parallel with the floral gradient.((3)H)-Thymidine incorporation into DNA in the internodes is inhibited by attached leaves in flowering tobacco plants but promoted in vegetative plants. Low indoleacetic acid concentrations (2.8 and 5.7 mum) inhibit DNA synthesis in internodes of defoliated stems of flowering tobacco plants to the same extent as attached leaves, whereas the same concentrations of indoleacetic acid promote DNA synthesis in internodes of defoliated stems of vegetative plants. The optimal concentration (11.4 mum) of indoleacetic acid supplied to defoliated stems of vegetative plants increased the rate of DNA synthesis to 4 times the rate in defoliated stems without indoleacetic acid treatment. This increase more than compensates for the promotion of DNA synthesis by the young leaves. Thus, the opposite effects of young leaves on DNA synthesis in internodes of flowering and vegetative tobacco plants may be related to their auxin content.

Effects of Cycloheximide on Indoleacetic Acid-induced Ethylene Production in Pea Root Tips

Cycloheximide inhibited ethylene production in excised pea root tips treated with high levels of indoleacetic acid (100 mum and 10 mum). In contrast, cycloheximide did not inhibit ethylene production induced by a lower concentration (1 mum) of indoleacetic acid unless it was added 2 hours before the indoleacetic acid treatment. These observations suggest that indoleacetic acid has two effects on the enzyme system involved in ethylene synthesis. At low concentrations (1 mum) indoleacetic acid increases ethylene production without protein synthesis, whereas at the higher concentrations, the synthesis of new protein is associated with increased ethylene production.

Effect of indole acetic acid and gibberellic acid on histone composition in the nucleoprotein of dark grown pea epicotyls

Summary Histones from gibberellic acid and indole acetic acid treated etiolated pea epicotyls have been compared with histones from untreated epicotyls by Polyacrylamide gel electrophoresis. The histone components were found to be altered in relative quantity of individual fractions by both gibberellic acid and indole acetic acid treatment. Gibberellic acid specially increased the relative quantity of the 3 fastest moving fractions, indole acetic acid specially increased the quantity of the 2 fastest moving fractions, by comparison with the samples of untreated epicotyls.

Increase in Indoleacetic Acid Oxidase Activity of Winter Wheat by Cold Treatment and Gibberellic Acid

The activity of indoleacetic acid oxidase increased 10-fold during 40 days of cold treatment of winter wheat seedlings. Puromycin and 6-methyl purine inhibited indoleacetic acid oxidase development in the cold. Addition of gibberellic acid stimulated indoleacetic acid oxidase development during germination at room temperature and during cold treatment. Amo-1618 inhibited indoleacetic acid oxidase development before and during cold treatment. Indoleacetic acid treatment increased indoleacetic acid oxidase activity during germination at room temperature while no significant effect on activity was observed during cold treatment.

Germination of Tea Seeds (Part 3)

An abnormal thickening growth of plumule in tea seeds has been observed for several years on the germination bed which was warmed up artificially in order to accelerate the seed germination.The leaf primordium of this plumule is white and grows abnormally and loses the function of cell division.A series of experiments was carried out with regard to the abnormal thickening of plumule varied with the varieties used, storage and germination temperature, pre-treatment of seed coat, gibberellin (GA) and indole acetic acid (IAA) treatment, etc.It was confirmed that the abnormal growth was caused by a high temperature on the seed bed and also more or less affected by storage temperature. The varietal difference was observed in the rate of occurrence of the abnormal plumule too. The removal of the seed coat and IAA treatment, however, did not influence the occurrence of the thickened plumule.It was found that the abnormal growth was perfectly cheched by the GA pre-treatment, even though the germination temperature was high.From the results, it was concluded that the seed bed for tea plant should be always kept under 25°C, and the GA per-treatment was very useful for checking the abnormal growth.

Effects of indoleacetic acid on intracellular distribution of β-glucanase activities in the pea epicotyl

β-1,4-Glucanase (cellulase) and β-1,3-glucanase activities were estimated in various subfractions of the growing region of decapitated Pisum sativum epicotyls. Treatment of the epicotyl apex with the hormone indoleacetic acid (IAA) caused total and specific cellulase activity to increase, first and most markedly, in a microsomal fraction containing membrane-bound ribosomes and eventually in fractions containing soluble enzyme and wall material. The responses did not occur in the presence of actinomycin D or during growth after treatment with other hormones. In the absence of IAA, cellulase activity disappeared within a few days from microsomal and wall fractions. It is concluded that cellulase is synthesized via an IAA-dependent mechanism and is inactivated extracellularly. In the same system, β-1,3-glucanase activity increased greatly with time but microsomes failed to show preferential enrichment at any stage of development and IAA treatment failed to affect the increase unilaterally.

Indoleacetic Acid and the Synthesis of Glucanases and Pectic Enzymes

Indoleacetic acid (IAA) and/or inhibitors of DNA, RNA or protein synthesis were added to the apex of decapitated seedlings of Pisum sativum L. var. Alaska. At various times up to 4 days, enzymic protein was extracted from a segment of epicotyl immediately below the apex and assayed for its ability to hydrolyse polysaccharides or their derivatives. With the exception of amylase, the total amounts per segment of all of the tested enzymes increased due to IAA treatment. The development of beta-1,4-glucanase (cellulase) activity per unit of protein or fresh weight proceeded according to a typical sigmoid induction curve. Pectinase was formed for about 2 days in control segments and IAA treatment resulted in continued synthesis for at least another 2 days provided cell division took place. beta-1,3-glucanase and pectinesterase activities were only enhanced by IAA to the extent that total protein levels increased. Reaction mechanisms for these effects and functions for the enzymes during growth are discussed.

Studies on the Role of RNA Synthesis in Auxin Induction of Cell Enlargement

Selective inhibitors were used to study the connection between nucleic acid synthesis and indoleacetic acid (IAA) induction of cell enlargement. Actinomycin D (act D) and azaguanine (azaG) almost completely inhibit IAA-induced growth in aged artichoke tuber disks when they are added simultaneously with IAA. In contrast, when they are added 24 hours after the hormone, these inhibitors have little or no effect on the induced growth which continues for 48 hours or more with little or no inhibition. Inhibitors of protein synthesis still stop growth when applied 24 hours after the IAA, thus protein synthesis and presumably supporting metabolism are still essential.In corn coleoptile sections auxin-induced growth did not show any pronounced tendency to become less sensitive to act D as the IAA treatment progressed. Act D did not completely inhibit the response to IAA unless the sections were pretreated with act D for 6 hours. In contrast to act D, cordycepin produced almost complete inhibition of IAA-induced growth when added with the IAA.Although IAA has a very large and very rapid stimulatory effect (within 10 min) on incorporation of (32)P-orthophosphate into RNA in disks, it did not cause a detectable change in the base composition of the RNA synthesized. Furthermore, the promotive effect could be accounted for through increased uptake of the (32)P. That much of the RNA synthesis in these tissues is not necessary for auxin action is indicated by the results with fluorouracil (FU). FU strongly inhibits RNA synthesis, probably acting preferentially on ribosomal RNA synthesis, without inhibiting auxin-induced growth in the disks or coleoptile sections. FU also strongly inhibited respiration in auxin-treated disks indicating that the large promotion of respiration by auxin likewise may not be entirely necessary for growth.At least in the artichoke disks, RNA synthesis is required for auxin induction of cell enlargement and not for cell enlargement itself.The possible relationships of auxin induction of cell enlargement and RNA synthesis are discussed.

Some effects of X-rays on root primordia in the poplar

A series of experiments were conducted utilizing various doses of X-rays and a variety of indoleacetic acid (IAA) treatments in an attempt to determine the effect of these factors on the growth and emergence of roots from stem cuttings of the Lombardy poplar. The following facts emerged from these experiments: (1) When cuttings were exposed to X-ray treatments ranging from 0–10,000 r, and placed in darkness, it was found that the average number of roots produced per cutting varied inversely with the dose. (2) Doses of 4000 r were found to give approximately 50 per cent inhibition, and doses ranging between 8000 r and 10,000 r produced almost complete inhibition in most experiments. (3) Exogenous application of IAA was found to modify the response of this biological system to ionizing radiation. (4) Treatment of cuttings with 4000 r alone resulted in more inhibition (84%) than if 4000 r was given before or after IAA treatment (33%).

USE OF GROWTH CHARACTERISTICS IN STUDIES OF MORPHOLOGIC RELATIONS. I. SIMILARITIES BETWEEN EPIBLAST AND COLEORHIZA

Foard, Donald E., and Alan H. Haber. (Oak Ridge Natl. Lab., Oak Ridge, Tenn.) Use of growth characteristics in studies of morphologic relations. I. Similarities between epiblast and coleorhiza. Amer. Jour. Bot. 49(5): 520–523. Illus. 1962.—We compared the characteristics of wheat epiblast, coleorhiza, and leaves during germination and seedling growth. Although the epiblast and coleorhiza grow without cell division during germination, they sometimes produce hairs that resemble root hairs but are different in form and mode of origin from leaf hairs. Despite the similar orientation of the epiblast and leaves with respect to the main axis of the plant, during growth the epiblast changes shape such that the axis of greater linear extension per millimeter is perpendicular to the main axis of the plant, whereas leaves change shape such that the greater rate of linear extension per millimeter is parallel to the main axis of the plant. Indoleacetic acid treatment produces excessive and disorganized growth of both the epiblast and coleorhiza but retards leaf growth. Gibberellic acid stimulates, whereas (2‐chloroethyl)trimethylammonium chloride retards leaf growth. Neither substance significantly affects epiblast or coleorhiza. We conclude that the epiblast is not leaf‐like, but together with the coleorhiza forms a single, continuous structure. This paper illustrates how a wide variety of growth characteristics may be used to complement classical anatomic approaches in studies of morphologic relations.

Combined Effects of Potassium Supply and Growth Substances on Plant Development

1. Red kidney bean plants grown in sand culture at different levels of potassium nutrition and receiving indoleacetic acid or alpha naphthalene acetamide in the nutrient solution in a series of concentrations were compared by dry weights of top, of root, and of total plant. 2. Plants receiving different nutrition but externally appearing alike responded in a markedly different manner to indoleacetic-acid treatment. 3. Relatively high potassium in the nutrient solution was necessary to obtain increased dry weight of total plant by indoleacetic-acid treatment. 4. Under certain levels of nutrition, increases as great as 12.5 per cent in total plant dry weight were obtained by indoleacetic acid supplied at the 10-9 concentration. Significant increases were obtained at concentrations of 10-7, 10-8, and 10-9. 5. Indoleacetic acid appeared unable either to replace potassium or to enhance its utilization under deficiency conditions, as judged by total plant response. 6. The time of flowering was not hastened by i...