Increasing Auxin Concentration Research Articles

Auxin- and pH-induced guttation in Phycomyces sporangiophores: relation between guttation and diminished elongation growth.

Guttation, the formation of exudation water, is widespread among plants and fungi, yet the underlying mechanisms remain largely unknown. We describe the conditions for inducing guttation in sporangiophores of the mucoracean fungus, Phycomyces blakesleeanus. Cultivation on peptone-enriched potato dextrose agar elicits vigorous guttation mainly below the apical growing zone, while sporangiophores raised on a glucose-mineral medium manifest only moderate guttation. Mycelia do not guttate irrespective of the employed media. The topology of guttation droplets allows identifying the non-growing part of the sporangiophore as a guttation zone, which responds to humidity and medium composition in ways that become relevant for turgor homeostasis and thus the sensor physiology of the growing zone. Apparently, the entire sporangiophore, rather than exclusively the growing zone, participates in signal reception and integration to generate a common growth output. Exogenous auxin applied to the growing zones elicits two correlated responses: (i) formation of guttation droplets in the growing and transition zones below the sporangium and (ii) a diminution of the growth rate. In sporangiophore populations, guttation-induction by exogenous control buffer occurs at low frequencies; the bias for guttation increases with increasing auxin concentration. Synthetic auxins and the transport inhibitor NPA suppress guttation completely, but leave growth rates largely unaffected. Mutants C2 carA and C148 carA madC display higher sensitivities for auxin-induced guttation compared to wild type. A working model for guttation includes aquaporins and mechanosensitive ion channels that we identified in Phycomyces by sequence domain searches.

Integrative analysis of transcriptome reveals the possible mechanism of delayed leaf senescence in pak choi (Brassica rapa subsp. chinensis) following melatonin treatment

Abstract Melatonin (MT) is a low molecular weight compound with a wide variety of biological functions in plants. It is known to delay senescence in various fruits and vegetables. This study demonstrates that MT (100 μmol/L) delayed the senescence of pak choi stored at 20 °C. A total of 1121 differentially expressed genes (DEGs) were identified in an MT-treated group in comparison to untreated pak choi. Analysis of DEGs revealed that MT-induced delay in senescence involved reduction in the expression of chlorophyll metabolism genes and regulation of the expression of hormone-related genes and leaf senescence-related transcription factors. MT decreased the activity of chlorophyll metabolism-related enzymes Mg-dechelatase, pheophytinase, and pheide a oxygenase, decreased the concentrations of abscisic acid and jasmonic acid, and increased auxin concentration. MT delayed the impact of senescence-related transcription factors BcNAC41 and BcNAC87 on tobacco leaf senescence. This study provides an insight into the molecular mechanisms of MT-induced delay of postharvest senescence in pak choi and confirms its potential as a preservation technique.

Effect of the media type and auxin concentration on the growth of cuttings seedlings of pepper (Piper nigrum)

Abstract. Amanah S, Budiastuti MTHS, Sulistyo A. 2022. Effect of the media type and auxin concentration on the growth of cuttings seedlings of pepper (Piper nigrum). Cell Biol Dev 6: 32-40. Pepper (Piper nigrum L.) is an export commodity and has become one of the Indonesian sources of income. It is necessary to develop the best cultivation for increasing pepper production. Vegetative propagation has been chosen in this research, using manure as part of the media and auxin as a growth hormone. The research aims to find the best media and auxin concentration for the ideal growth of pepper grafting. The research conducted in Manyaran Wonogiri, Indonesia, with RCB design consists of two factors arranged in the factorial method. The first factor is the kind of media (soil, soil + manure, soil + manure + husk), and the second is auxin's concentration (0 g/L, 12.5 g/L, 25 g/L, 37.5 g/L; 50 g/L). Observation variables are bud growth time, number of buds, length of bud, number of leaves, leaf width, number of roots, length of root, and life percentage of cuttings. Data were analyzed by F test at 1% and 5% and continued with DMRT at 5% if the treatment had a significant effect. It is also continued with regression if there was an interaction between treatments. The longest bud was found on soil + manure + husk (12.28 cm) and followed by soil + manure (10.57 cm) and soil (6.15 cm) in the low level, respectively. The study revealed that the bud length and the number of roots were influenced by auxin concentration. The longest bud was found using 12.5 g/L of auxin (15.14 cm), followed by 50 g/L, 25 g/L, 0 g/L, and 37.5 g/L in the low level, respectively (12.05 cm, 7.72 cm, 7.67 cm, 5.75 cm). The highest number of roots was found on 0 g/L and 12.5 g/L of auxin (7.78), followed by 50 g/L, 25 g/L, and 37.5 g/L in the low level, respectively (4, 3.43, 2.33). The number of roots and percentage of life cuttings showed an interaction between the two factors. The number of roots on the soil shows a parabolic response with auxin. In the beginning, the number of roots decreased and then increased with increasing auxin concentration. The number of roots on soil + manure and soil + manure + husk showed the same pattern with auxin concentration. Almost 100% of life cuttings have been found on all media and auxin concentrations. Soil + manure with 25 g/L auxins and soil + manure + husk with 50 g/L auxins caused 33.33% and 66.67% life cuttings, respectively.

A system for rapid gene introgression into cassava immature leaves and subsequent recovery of transformed lines

Friable embryogenic callus (FEC) currently forms the tissue of choice for gene transfer to cassava tissues. However, this technology has not been sufficiently adopted in most laboratories, partly because of the challenging protocols involved in FEC production. Therefore, the development of transformation systems targeting readily accessible explants could enable the rapid improvement of this essential root tuber. This study developed a simple, efficient, and rapid transformation protocol for three elite cassava cultivars (TMS 60444, 08/354, KME 1) using immature leaf lobes (ILLs). Factors affecting callus and somatic embryo formation, such as auxin concentration and culture photoperiod, were optimized. Cassava transformation was achieved by co-cultivation of ILLs and callus with Agrobacterium strain EHA101 harboring pTF102 plasmid. We report a positive interactive effect between dark treatment and an increasing auxin concentration. Exposure to light was found to negatively affect the formation and viability of SEs by promoting tissue browning. The results further show that cassava transformation success depends on the cultivar, explant type, and age. Using this simple protocol, transgenic plants of TMS 60444, 08/354, and KME 1 with an average transformation frequency of 0.4% (0.5, 0.4, and 0.4%, respectively) were obtained in 6 months. Reverse transcription PCR, Southern blot, and histochemical GUS staining confirmed the stable integration of the gusA gene into the regenerated plantlets. This optimized transformation system for cassava is rapid, efficient, and simple to operate and will facilitate more genetic applications in cassava research.

Effects of Phosphate Shortage on Root Growth and Hormone Content of Barley Depend on Capacity of the Roots to Accumulate ABA.

Although changes in root architecture in response to the environment can optimize mineral and water nutrient uptake, mechanisms regulating these changes are not well-understood. We investigated whether P deprivation effects on root development are mediated by abscisic acid (ABA) and its interactions with other hormones. The ABA-deficient barley mutant Az34 and its wild-type (WT) were grown in P-deprived and P-replete conditions, and hormones were measured in whole roots and root tips. Although P deprivation decreased growth in shoot mass similarly in both genotypes, only the WT increased primary root length and number of lateral roots. The effect was accompanied by ABA accumulation in root tips, a response not seen in Az34. Increased ABA in P-deprived WT was accompanied by decreased concentrations of cytokinin, an inhibitor of root extension. Furthermore, P-deficiency in the WT increased auxin concentration in whole root systems in association with increased root branching. In the ABA-deficient mutant, P-starvation failed to stimulate root elongation or promote branching, and there was no decline in cytokinin and no increase in auxin. The results demonstrate ABA’s ability to mediate in root growth responses to P starvation in barley, an effect linked to its effects on cytokinin and auxin concentrations.

Rooting stimulation of “Victoria” and “Korinka russkaya” grape hardwood cuttings as influenced by potassium salt of Indolyl-3-Acetic Acid (KIAA)

Relevance. Applying exogenous auxins to the cuttings of grapevines is a common practice in viticulture to improve the rooting process. The potassium salt formulations of auxins have been documented to be more, less, or equally efficient as acid formulations in rooting stimulation of cuttings depending on the genetic features of the plant, type and concentration of auxin, type of cuttings, and many other factors.Methods. The present study aimed at evaluating the effect of potassium salt of indolyl-3-acetic acid (KIAA) on rooting of the hardwood cuttings of two grape cultivars namely, Korinka russkaya and Victoria, which are commonly planted by grape growers of the Tatarstan Republic. The study was conducted in 2018 and 2019 under hydroponic conditions in a controlled-environment growth chamber in Kazan State Agrarian University. The cuttings were treated with 1) KIAA at two concentrations (5,000 and 10,000) ppm; 2) β-indolyl-butyric acid (IBA) 3,000 ppm (as a check treatment) and 3) distilled water as a control.Results. Based upon the overall results, KIAA significantly improved the rooting process of both investigated cultivars. Rooting percentage, average number of roots on cuttings as well as the quality of the root system was enhanced with increasing auxin concentration up to 10,000 ppm. IBA also improved the rooting quality parameters over the controls. The two grape cultivars differed significantly in their rooting capacity: cuttings of Korinka russkaya in both years had greater values of all the studied parameters compared with those of Victoria cultivar except for the callusing percentage, which was higher in Victoria.

Influence of girdling on flower sex ratio, biochemical constituents, and fruit set intensity in mango (Mangifera indica L.)

The study was conducted in mango to understand the relationship of various metabolites with flower sex ratio (hermaphrodite/male) and fruit set using stem girdling technique. Girdling one year old branches was carried out in two cultivars, Mangifera indica 'Alphonso' and 'Totapuri' to retain 50, 100 and 150 leaves to vary the content of hormones, sugars, total carbohydrates, and amino acids. The increased leaf number was found to increase the total carbohydrates, glucose, fructose, and other sugars. Girdling also significantly increased the concentration of abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), indole acetic acid, indole butyric acid but decreased gibberellins and cytokinins. Amino acids also increased in the girdled branches. Girdling improved the flower sex ratio as well as fruit set more efficiently in 'Alphonso' than in 'Totapuri'. Results indicate that the increase in production of hermaphrodite flowers may be more related to the higher production of growth inhibitors, like ABA, SA, and JA along with increased concentration of sugars. Increased auxin concentration also might play an important role in increasing the fruit set.

Arabidopsis Type II Phosphatidylinositol 4-Kinase PI4Kγ5 Regulates Auxin Biosynthesis and Leaf Margin Development through Interacting with Membrane-Bound Transcription Factor ANAC078.

Normal leaf margin development is important for leaf morphogenesis and contributes to diverse leaf shapes in higher plants. We here show the crucial roles of an atypical type II phosphatidylinositol 4-kinase, PI4Kγ5, in Arabidopsis leaf margin development. PI4Kγ5 presents a dynamics expression pattern along with leaf development and a T-DNA mutant lacking PI4Kγ5, pi4kγ5–1, presents serrated leaves, which is resulted from the accelerated cell division and increased auxin concentration at serration tips. Studies revealed that PI4Kγ5 interacts with and phosphorylates a membrane-bound NAC transcription factor, ANAC078. Previous studies demonstrated that membrane-bound transcription factors regulate gene transcription by undergoing proteolytic process to translocate into nucleus, and ANAC078 undergoes proteolysis by cleaving off the transmembrane region and carboxyl terminal. Western blot analysis indeed showed that ANAC078 deleting of carboxyl terminal is significantly reduced in pi4kγ5–1, indicating that PI4Kγ5 is important for the cleavage of ANAC078. This is consistent with the subcellular localization observation showing that fluorescence by GFP-ANAC078 is detected at plasma membrane but not nucleus in pi4kγ5–1 mutant and that expression of ANAC078 deleting of carboxyl terminal, driven by PI4Kγ5 promoter, could rescue the leaf serration defects of pi4kγ5–1. Further analysis showed that ANAC078 suppresses the auxin synthesis by directly binding and regulating the expression of auxin synthesis-related genes. These results indicate that PI4Kγ5 interacts with ANAC078 to negatively regulate auxin synthesis and hence influences cell proliferation and leaf development, providing informative clues for the regulation of in situ auxin synthesis and cell division, as well as the cleavage and functional mechanism of membrane-bound transcription factors.

Organogenesis from shoot segments and via callus of endangered Kosteletzkya pentacarpos (L.) Ledeb.

Efficient plant regeneration systems both from shoot segments and via callus organogenesis were developed for Kosteletzkya pentacarpos (L.) Ledeb., a rare and endangered Eurasian species. In the experiments with existing meristems, factors affecting shoot proliferation, including explant type, i.e. decapitated and intact shoots, and plant growth regulators, indole-3-acetic acid or kinetin, were investigated. Shoot proliferation was significantly affected by the type of explant, the hormones and their interaction. The highest shoot multiplication rate was obtained from decapitated shoots. Increasing kinetin concentration promoted shoot elongation regardless of explant type. In intact shoots, shoot length was also affected by increasing auxin concentration, although this effect tends to decrease with higher concentration. Decapitated shoots were not responsive to the addition of auxin. Micropropagation through organogenesis from callus was also investigated. Calli were obtained from leaf, stem internode and root explants. Only the leaf-derived calli produced shoots and indole-3-acetic acid favoured increased numbers of shoots. A number of experiments were conducted for rooting of in vitro produced shoots. All of them induced high rooting frequency, the number and the length of roots being dependent on the strength of the basal medium. The use of 1–2 mg l−1 indole-3-butyric acid resulted in refining the optimal concentration for root elongation. The regenerated plants (70%) survived and flowered in their first vegetative period.

Sodium Cellulose Glycolate as a Thickening Agent for Liquid Auxin Formulations can Enhance Rooting of Stem Cuttings

Abstract Stem cuttings of Abelia ‘Edward Goucher’, Buxus sinica var. insularis ‘Wintergreen’, Hedera helix, Hibiscus syriacus ‘Collie Mullens’, Ilex vomitoria ‘Nana’, Juniperus conferta ‘Blue Pacific’, and Rosa ‘Red Cascade’ received a basal quick-dip in solutions of Dip ‘N Grow at concentrations of 0 + 0, 50 + 25, 250 + 125, 500 + 250, 750 + 375, and 1000 + 500 ppm IBA + NAA prepared with and without 13.5 g/liter sodium cellulose glycolate (SCG) as a thickening agent. Cuttings of Ilex vomitoria ‘Nana’ exhibited increased rooting with increasing auxin concentration with inclusion of SCG. The other six taxa exhibited similar rooting percentages among all treatments, but exhibited an increase in root number and/or total root length with inclusion of SCG. Initial shoot growth on rooted cuttings of Abelia ‘Edward Goucher’ showed some reduction with increasing auxin concentration with inclusion of SCG, suggesting cuttings absorbed more auxin from solutions containing SCG owing to their extended period of exposure to the auxin. Otherwise, there were no negative responses to solutions containing SCG. The greater viscosity of solutions prepared with SCG can help reduce the possibility of spillage and evaporation of alcohol during use of the auxin solutions.

Vegetative Propagation of Mature Eastern and Carolina Hemlocks by Rooted Softwood Cuttings

This study tested the effects of cutting length and auxin (NAA) concentration on adventitious root formation in softwood stem cuttings from mature eastern hemlock, Tsuga canadensis (L.) Carr., and carolina hemlock, T. caroliniana Engelm. Overall rooting percentage (41%) and percent mortality (22%) were higher for eastern hemlock compared with carolina hemlock (10% rooting and 13% mortality). Rooting percentage of each species responded differently to varying auxin concentrations (0, 1, 2, 4, 8 mm NAA). Maximum rooting (56%) for eastern hemlock occurred at 0 mm NAA; then decreased with increasing auxin concentration. Carolina hemlock rooting percentage increased from the control to a maximum (16%) at 1 mm NAA; then decreased with increasing auxin concentration. For both species, the lowest mortality occurred at the same auxin concentration as maximum rooting. The highest rates of mortality coincided with the same concentrations as the lowest rooting percentages. At all auxin concentrations, eastern hemlock had a higher number of roots and greater total root length relative to carolina hemlock. Mortality among 6-cm stem cuttings was twice that observed for 3-cm cuttings of both species. However, 6-cm cuttings of eastern hemlock that did form adventitious roots had more roots and longer total root length compared with 3-cm cuttings. Chemical name used: 1-naphthalenacetic acid.

CUTTING PROPAGATION WITH AUXIN APPLIED VIA THE ROOTING SUBSTRATE

Stem cuttings of golden euonymus (Euonymus japonicus `Aureo-marginatus'), shore juniper (Juniperus conferta `Blue Pacific'), white indian hawthorn (Rhaphiolepis indica `Alba'), and `Red Cascade' miniature rose (Rosa `Red Cascade') were successfully rooted in plugs of a stabilized organic substrate that had been soaked in aqueous solutions of the potassium salt of indole-3-butyric acid (K-IBA) at 0 to 75 mg·L–1 before inserting the cuttings. Cuttings were rooted under intermittent mist in polyethylene-covered greenhouses with rooting periods appropriate for each species. Rooting percentages showed some increase with increasing auxin concentration with juniper cuttings, but were similar among treatments for the other three species. Number of roots per rooted cutting increased with increasing auxin concentration with cuttings of juniper, Indian hawthorn, and rose, and was greatest using around 60 mg·L-1 K-IBA for cuttings of juniper and Indian hawthorn and 30 to 45 mg·L-1 K-IBA for cuttings of rose.

A Comparison of Irrigation System, Basal Temperature and Auxin Concentration on Rooting of Stem Cuttings of Ilex glabra L.

Abstract Basal stem temperature and auxin treatment effects on rooting percentage, root number, length of the longest root, and basal stem necrosis of hardwood stem cuttings of Ilex glabra L. (inkberry holly) were compared between a recirculating subirrigation propagation system and a conventional intermittent mist propagation system. Recirculating subirrigation maintained basal temperature and medium moisture content better than conventional intermittent mist. While rooting percentages were significantly greater for cuttings rooted in the recirculating subirrigation system, root number, and length of the longest root were higher for cuttings rooted under intermittent mist. A basal temperature of 32C (90F) was supra-optimal, resulting in significantly lower rooting percentages. However, rooting temperature had no effect on root number or basal stem necrosis. Basal stem necrosis of rooted cuttings was greater in the recirculating subirrigation system, and increased with temperature in both irrigation treatments, but appeared to have no significant effect on root number. Increasing auxin concentration increased rooting percentage, root number, and length of the longest root of rooted cuttings, though the response differed with irrigation treatment. Cuttings of Ilex glabra L. can be rooted successfully in a recirculating subirrigation propagation system where the rooting process appears to be less sensitive to rooting temperature and auxin concentration than for cuttings rooted under intermittent mist. However, overall root growth was greater on cuttings rooted under intermittent mist, perhaps because of the lower medium moisture content in that system. This suggests that optimal rooting of hardwood cuttings can be achieved without intermittent mist using a recirculating subirrigation system with modifications to the moisture content of the rooting medium.

DOSE RESPONSE CURVES AND CARRIER EFFECTS ON ROOTING

Auxins are indispensable for vegetatively propagating many woody plants. The rooting of stem cuttings treated with auxin varies with shoot maturation, phenological age and stock plant nutrition. Sensitivity to applied auxin is important both practically and for understanding the physiology of root formation. Applying optimal auxin concentrations is often the key to successful cutting propagation. Auxin dose-response curves for rooting usually show increased rooting with increasing auxin concentration to an optimum, followed by rooting inhibition and phytotoxicity at supra-optimal rates. These curves will be used to analyze dose response kinetics for common rooting hormones and carrier formulations. Dose-response curves were developed, using cuttings of Ilex glabra — inkberry holly, to evaluate IBA and NAA dissolved in 50% aqueous ethanol (EtOH) or 40% aqueous polyethylene glycol (PEG). Few differences were evident in the response curves of auxin dissolved in EtOH or PEG at concentrations of 0 to 75 mM. PEG yielded higher root numbers at the optimal concentrations of 10-20 mM NAA and 30-50 mM IBA. Both the stimulation and inhibition of rooting were more sensitive to NAA than IBA. Decreasing root length and increasing basal rooting inhibition were good indicators of auxin toxicity. These results further our knowledge of carrier effects on rooting and the potential of dose response analysis for studying adventitious root formation in cuttings.

Stevioside biosynthesis by callus, root, shoot and rooted-shoot cultures in vitro

Leaf explants of Stevia rebaudiana Bertoni (Compositae), an herb which produces the sweet ent-kaurene glycoside stevioside, were cultured in Murashige and Skoog medium with vitamins, sucrose (30 g l−1), agar (0.9% w/v) and supplemented with naphthaleneacetic acid (NAA, 0.5 mg l−1) and benzylaminopurine (BAP, 0.5 mg l−1). These conditions yielded friable callus cultures. Differentiation of the callus tissue was then achieved by eliminating the agar and modulating the medium's hormone concentrations. Thus, medium containing increased auxin concentration (1.0 mg l−1) and no cytokinin or increased cytokinin (1.0 mg l−1) and no auxin yielded root or shoot cultures respectively. Supplementation of the shoot medium with NAA (1.0 mg ml−1) induced shoot cultures to grow roots thereby differentiating into rooted-shoot cultures. Only the rooted-shoot cultures tasted sweet. Feedings of [2-14C]acetic acid to callus, shoot or rooted-shoot cultures demonstrated that only the rooted-shoot cultures are capable of de novo biosynthesis of the aglycone moiety of stevioside (steviol). In addition, [methyl-3H(N)steviol feedings to shoot or rooted-shoot cultures illustrated that both types of cultures are capable of the glycosylation reaction. The ability of these tissues to glycosylate steviol to stevioside was also demonstrated employing crude enzyme preparations derived from shoot or rooted-shoot cultures. These results suggest that stevioside biosynthesis is a function of tissue differentiation since both roots and leaves are required for cultured S. rebaudiana to biosynthesize stevioside from acetate, while the final biosynthetic steps can be performed at all levels of differentiation.

Gravitropism in higher plant shoots. V. Changing sensitivity to auxin.

An alternative to the Cholodny-Went, auxin-transport hypothesis of gravitropic stem bending was proposed as early as 1958, suggesting that gravistimulation induces changes in sensitivity to auxin, accounting for differential growth and bending. To test the sensitivity hypothesis, we immersed marked, decapitated sunflower (Helianthus annuus L.) hypocotyl sections in buffered auxin solutions over a wide concentration range (0, 10(-8) to 10(-2) molar IAA), photographed them at half-hour intervals, analyzed the negatives with a digitizer/computer, and evaluated surface-length changes in terms of Michaelis-Menten enzyme kinetics. Bending decreases with increasing auxin concentration; above about 10(-4) molar IAA the hypocotyls bend down; increasing auxin inhibits elongation growth of lower surfaces (which is high at zero or relatively low auxin levels) but promotes upper-surface growth (which is low at low auxin levels). Thus, lower surfaces have a greater Km sensitivity to applied auxin than upper surfaces. At optimum auxin levels (maximum growth), growth of bottom surfaces exceeds that of top surfaces, so bottom tissues have a greater Vmax sensitivity. Vmax sensitivity of vertical controls is slightly lower than it is for either horizontal surface; Km sensitivity is intermediate. Clearly, gravistimulation leads to significant changes in tissue sensitivity to applied auxin. Perhaps these changes are also important in normal gravitropism.

Growth of apical and lateral buds of papaw (Carica papaya, L.) as affected by nutritional and hormonal factors

SummaryStudies were made of nutritional and hormonal factors affecting shoot and callus growth from apical and lateral bud explants of Carica papaya. Both high concentrations of minerals and the addition of 10 μM riboflavin to the culture medium reduced callus growth and improved shoot growth and quality. The promotion of shoot growth by cytokinin was greatly reduced when riboflavin was absent. Increasing auxin concentration reduced shoot growth; however this effect was removed when riboflavin was added. Six auxins (IAA, IBA, NAA, NOA, pCPA and 2,4-D) and five cytokinins (kinetin, 2iP, zeatin, PBA and BAP) were applied individually over a range of concentrations and the resultant growth was observed and recorded. Best shoot growth occurred when 1 μ mol l−1 of both NAA and BAP were added to a modified de Fossard et al. (1974) basal medium. High concentrations of auxin in the medium caused deformed shoot growth, whereas high concentrations of BAP and PBA caused excessive callus production.

Effect of Ethrel on the IAA Content and on its Distribution in Cucumber Seedlings

Summary Ethrel inhibits the apical growth of cucumber seedlings and provokes abnormal morphological alterations. These growth disorders are correlated with the changes in IAA metabolism taking place on the effect of ethrel. In the hypocotyls and roots treated with ethrel the amount of IAA, IAAsp and IAGlu is increasing to a great extent. In contrast to the control, in the hypocotyls treated with ethrel only a small proportion of the total free IAA is distributed in the relatively thinner apical part and a large proportion is present in the swollen basal part. On the effect of ethrel the amounts of IAAsp and IAGlu are decreasing i.e. the binding of IAA into conjugates is of a smaller extent in the lower hypertrophic part of the stem. In the seedlings with 2,4-D a similar growth inhibition and morphological abnormalities can be obtained as with ethrel of higher concentration. Thus the growth disorders caused by ethrel can be ascribed to the abnormally increased auxin concentration.

Stem Cutting Propagation of Big Sagebrush (Artemisia tridentata Nutt.)

Vegetative propagation of big sagebrush (Artemisia tridentata Nutt.) is often desirable to preserve valuable characteristics of ecotypes for use in disturbed site rehabilitation and range research. Previous research is not clear with regard to procedures for sagebrush propagation. Three experiments were designed to define the influence of synthetic auxin rates, plant dormancy and individual source plants on rooting performance of big sagebrush stem cuttings. Cuttings obtained in the winter during plant dormancy showed greater rooting activity than those collected from actively growing plants. Synthetic auxin, Indolebutyric acid (IBA) treatment, increased root formation as a function of increased auxin concentration but was unable to overcome factors causing seasonal dormancy in cuttings. Source plants varied in the rootability of cuttings. Care should be exercised in selecting only plants that have a high capability for rooting of cuttings.

Initial phases of indoleacetic acid induced growth in coleoptile segments of Avena sativa L.

The intial phases of auxin-induced growth in coleoptile segments of Avena sativa L. were investigated using a high resolution growth recording technique, based on an angular position sensing transducer. The first response to the hormone is a slight, transient reduction of the growth rate lasting about 5 min. After this phase growth rate increases to a maximum. The duration of the increase and the maximum clearly depend on the concentration of the hormone. With increasing auxin concentration the duration of the growth rate increase is reduced from about 80 min in 10(-9) M indoleacetic acid (IAA) to about 14 min in 10(-4) M IAA. After the maximum the growth rate declines. Looking at the maximum of the growth rate, we obtained a dose-response curve with a sharp increase between 10(-9) M and 10(-6) M IAA and a slight decline between 10(-6) M and 10(-4) M IAA. This result is confirmed by growth rates measured one and two hours after the application of the hormone.