Accumulation Of IAA Research Articles

Immunohistochemical localization of IAA and ABP1 in strawberry shoot apexes during floral induction

By using an anti-indole-acetic acid (anti-IAA) monoclonal antibody and an anti-auxin-binding protein 1 (anti-ABP1) polyclonal antibody, IAA and ABP1 were immunohistochemically localized in strawberry (Fragaria ananassa Duch.) shoot apexes during floral induction. The spatial distribution patterns of endogenous IAA and ABP1 and their dynamic changes during floral induction were investigated. In addition, the affect of 1-N-naphthylphtalamic acid (NPA) on IAA distribution during floral induction was also analyzed. The results showed that IAA was present in the shoot apexes throughout the floral induction process, gradually concentrating in the shoot apical meristem (SAM). The distribution of ABP1 and its dynamic changes were similar to those of IAA. In addition, the ABP1 immune signal in SAM gradually increased as floral induction developed. On a morphological level, these results indicate both the spatial distribution and dynamic changes in endogenous IAA and ABP1 during the floral induction process. The close correlation found between IAA and ABP1 indicates that a cooperation occurs during the regulation of floral induction. The results also suggest that IAA was the significant agent for floral induction, and that SAM might be the place of the main action. Treatment with NPA during floral induction prevented the accumulation of IAA in the SAM, delayed the process of floral differentiation and induced an abnormal flower development. It is likely that IAA in the shoot apex is produced in young leaves and transported through the vascular tissues to the SAM and other places of function. Finally, an appropriate amount of IAA in the SAM and normal polar auxin transport are essential for floral induction and differentiation in strawberries.

Hormonal Status in Wheat and Rice Seedlings under Anoxia

A comparative analysis of the effects of anoxia on growth, fresh weight gain, and phytohormones in wheat (Triticum aestivum L.) and rice (Oryza sativa L.) seedlings was performed. In both plant species, a total cessation of root growth occurred during the initial hours of anoxia. In an anaerobic environment, the fresh weight of wheat seedlings decreased. An increase in the shoot length and weight under the stress conditions was found only in rice seedlings. During the initial hours of anoxia, the level of free ABA in wheat and rice tissues increased manifold, and the accumulation of a free ABA form occurred at the expense of the hydrolysis of its bound forms. The IAA content in plant tissues also increased. In wheat, the accumulation of IAA was short, but in rice, a high hormone level was retained during the entire experiment, and, as a result, its concentration exceeded that of ABA. A level of cytokinins in the tissues of both plant species was affected by anoxia to a lesser extent than that of other phytohormones. This level somewhat decreased under anoxia similarly to the level in darkness under aeration. It is suggested that IAA accumulation in hypoxia-tolerant rice seedlings under anoxia favors maintenance of shoot growth and simultaneous inhibition of root growth. At the same time, in the hypoxia-sensitive wheat, an increase in the ABA level resulted in growth cessation.

Effect of PEG-treatment on the leaf growth response and auxin content in shoots of wheat seedlings

Addition of Polyethylene glycol(PEG) to the nutrient medium of wheatseedlings led to a rapid cessation of leaf growth and shrinkage, measured withahighly sensitive growth sensor, followed by a partial restoration of extensionin the subsequent 40 min. This osmotic shock resulted in IAAaccumulation in the shoots. Leaf extensibility, measured by addition of 5g as a counterweight to an extensiometer, did not change for 20min after the start of the treatment, but then increased andbecametwice as high as the initial value. Changes in leaf extensibility coincidedwitha restoration of leaf growth. Leaf shrinkage, which was observed immediatelyafter addition of the osmoticum, suggests that the initial growth response wasdue to a water deficit, which led to a decrease in cell turgor. Howeverrestoration of growth during water stress could be due to changes in cell wallrheological properties, which could be triggered by IAA accumulation.

Indole-3-acetic acid biosynthesis in isolated axes from germinating bean seeds: The effect of wounding on the biosynthetic pathway

A facile radiotracer method for discriminating between the activities of tryptophan-dependent and tryptophanindependent pathways for IAA biosynthesis is described. This method utilized the simultaneous exposure of plants to [ 14 C]anthranilate in the presence or absence of excess unlabeled tryptophan in order to determine if tryptophan feeding can affect the relative enrichment of the IAA pool. Using this radiotracer method, the activities of the two biosynthetic pathways were analyzed in isolated axes of germinating bean seedlings at various times after cotyledon excision. Unlabeled tryptophan suppressed [ 14 C]anthranilate conversion into IAA in isolated axes of different ages immediately following cotyledon excision. On the other hand, tryptophan feeding did not inhibit [ 14 C]IAA accumulation in isolated axes 36 or 120 h after cotyledon excision. Thus, this method was able to resolve time-dependent differences following cotyledon excision in the biosynthetic activities of the two pathways. Moreover, the present results lend further support to the emerging consensus that the tryptophan-dependent pathway acts to maintain very high IAA levels required for mediating rapid cell proliferation in wounded tissues and, as previously shown, young embryos.

Endogenous Phytohormones and Regulation of Morphogenesis of Arabidopsis thalianaby Blue Light

We studied the effects of blue light (BL) on the levels of endogenous phytohormones (IAA, ABA, gibberellins, and cytokinins) and morphogenesis of the 7-day-old Arabidopsis thaliana(L.) Heynh seedlings of wild type (Ler) and its hy4mutant with a disturbed synthesis of cryptochrome 1 (CRY1), which is a receptor for BL. In darkness, the mutant contained considerably less free IAA and zeatin, but much more ABA as compared to the wild-type seedlings. BL retarded the hypocotyl growth in the wild-type seedlings but stimulated it in the mutant. Elongation of mutant hypocotyls was accompanied by accumulation of free IAA and a decrease in the content of free ABA; the level of cytokinins did not change. We believe that the response of the hy4hypocotyls to BL is mediated by a BL receptor distinct from cryptochrome 1. The conclusion is that light and hormonal signals interact in the control of the hypocotyl growth in A. thalianaseedlings.

Transport of [1-14C]-indole-3-acetic acid in Abies balsamea shoots ringed with Ethrel

The terminal (1-year-old) shoot of dormant, 2-year-old Abies balsamea (L.) Mill. seedlings was ringed with 0 or 10 mg Ethrel g–1 lanolin. After 5 weeks of culture under environmental conditions favorable for growth, some of the treated shoots were harvested to measure tracheid number by microscopy and ethylene evolution by gas chromatography-flame ionization detection. The remaining shoots were used to measure basipetal IAA transport in the cambial region by decapitating the shoot apex, applying a pulse of [1-14C]-IAA to the cut surface, and monitoring the subsequent distribution of radioactivity. Ringing with 10 mg Ethrel g–1 lanolin, compared with lanolin alone, stimulated cambial region ethylene evolution about 26-fold at, and 3-fold above and below the ringing site, but promoted tracheid production at the ringing site only. Ethrel ringing also increased the velocity, after 26 h transport, at which the front of the [1-14C]-IAA pulse moved below the ringing site. After 72 h of [1-14C]-IAA transport, when only immobilized radioactivity was present, the amount of radioactivity recovered in shoots ringed with 10 mg Ethrel g–1 lanolin was higher than with lanolin alone at the ringing site but lower below it. No difference was observed above the ringing site. The distribution of radioactivity was the same in shoots ringed with lanolin alone and in unringed shoots. The results support the hypothesis that an abnormally high cambial region concentration of ethylene derived from Ethrel ringing inhibits the capacity of basipetal IAA transport at the ringing site, resulting in a local accumulation of IAA that stimulates tracheid production.

Mutual interaction of auxin and cytokinins in regulating correlative dominance

Correlative dominance requires correlative signals from a dominant to a dominated organ. Auxins, particularly IAA, and cytokinins are obviously important components of this correlative system. Using a vegetative pea shoot and a generative apple and tomato fruit system it can be demonstrated that dominant organs always export more IAA and have a higher 3H-IAA transport capacity and velocity compared to dominated organs. In both systems the dominant organ can be replaced by the application of auxin, e.g. NAA, which maintains the differences in IAA export. This is an indication that similar regulatory mechanisms control dominance in both of these diverse systems. The possibility of replacing a dominant organ by auxin also makes it unlikely that growth of that organ or allocation of nutrients regulates the correlative inhibition of the dominated organ.It is suggested that differences in IAA export from, and transport capacities of, dominant and dominated shoots, may be explained by a mechanism of auxin transport autoinhibition (ATA), whereby the earlier and stronger export of IAA from the dominant shoot inhibits auxin export from the dominated shoot at the point where the two auxin streams converge. This hypothesis was tested with explants of pea, apple and tomato. It was shown that the basal application of cold IAA significantly reduced endogenous as well as exogenous IAA transport through these explants.Since the reduced IAA transport of dominated organs was not followed by an accumulation of IAA in the auxin producing subtending organ, it was concluded that IAA biosynthesis was possibly reduced and/or IAA conjugation stimulated. This could have been one of the determinants of their growth inhibition. ATA might also explain how the unidirectional IAA signal may affect the growth rate of organs even lateral or acropetal to its transport pathway and thus polar IAA-transport becomes a ``multidirectional'' signal. From the experiments demonstrated it seems that ATA is a sufficient mechanism to impose growth inhibition in the dominated organ, without the need of other regulators.However, to release dominated organs from dominance cessation of ATA may not be sufficient and cytokinins are obviously a powerful antagonist to auxins. Their repeated exogenous application turns dominated lateral buds into strongly growing organs which ultimately may even dominate the previously dominant apex. These lateral shoots finally gain a strong IAA export capacity and inhibit, by ATA, IAA export from the hitherto dominant apex.In other experiments it was shown that interruption of polar IAA transport leads to a strong increase in root derived cytokinins. This can largely be prevented, in a concentration dependent manner, by the application of auxin, indicating that basipolar auxin may control cytokinin production in the roots and its possible delivery to lateral buds. In turn, the increased delivery of cytokinins to the lateral buds promotes a strong increase in IAA production and export. Thus there is a strong mutual interaction between auxin production in the shoots and cytokinin production in the roots, which may be important in regulating the balance between root and shoot growth.

Increased Production of IAA by Rhizoctonia solani is Induced by Culture Filtrate from Rice Suspension Cultures

To investigate the role of the plant hormones produced by fungi, we tried to construct a system to examine the interaction between Rhizoctonia solani Kühn MAFF305219 and rice cells in suspension culture (Oc). R. solani was previously found to produce IAA, with the main biosynthetic pathway via the indole-3-pyruvate pathway. The amount of IAA in the medium produced by R. solani was increased by cocultivation with rice cells (Oc) and by culture filtrate (CF) of Oc. Further analysis revealed that the factor(s) that induced the enhanced accumulation of IAA was sensitive to heat, to freezing and thawing and lyophilization, and the molecular weight was estimated to more than 10,000. These results suggest that the active agent(s) in the medium was (a) protein or a proteinous substance. Among suspension cultures of various plants, Oc and another line of rice cells (Ok) had the ability to induce the accumulation of IAA in the fungal medium 4 h after inoculation but other cultures of plant cells were ineffective. The promotive effect of rice CF on the accumulation of IAA was also observed with some strains of R. solani that belong to a different anastmosis group from MAFF305219. Thus, the accumulation of IAA was not related to the host specificity.

Embryogenic Competence of Immature Wheat Embryos: Genotype, Donor Plant Environment, and Endogenous Hormone Levels

The genotype and the environment in which donor plants grow influence embryogenic competence of immature wheat (Tritium Estevan L.) embryos and levels of endogenous hormones in kernels. We studied relationships between embryonic competence and hormone levels in kernels and Calli of PC YT 10 (highly competent) and Yaqui 50 (nearly incompetent) wheat grown at 15 and 25°C. Endogenous levels of abscissa acid (ABA), in dole‐3‐acetic acid (AA), and stockings were determined for kernels at 0, 4, 8, and 12 d past an thesis (DOPA). Immature embryos were cultured at 12 DOPA and hormone content of Calli was determined at 7, 14, 21, and 28 d past culture initiation (DP|). Somatic embryos were counted at 28 DIP. Embryonic competence was associated with low AA and ABA levels in kernels from 0 to 12 DOPA, high seating to AA ratios in kernels at 4 DOPA, and high stoking to auxin ratios in Calli. Incompetence in Yaqui 50 may be due to low stoking to auxin ratios in kernels at 4 DOPA and sharp increases in kernel AA and/or ABA levels prior to embryo excision (12 DOPA). Low temperatures during donor plant growth delayed the rise in AA and ABA in Yaqui 50 kernels and significantly increased the embryogenic response from both Yaqui 50 and PCYT 10 embryos. It may be possible to increase competence of nearly nonembryogenic wheat lines by growing donor plants in cool conditions, which appear to delay the accumulation of IAA and ABA in kernels.

Mycorrhizal formation by Paxillus involutus strains in relation to their IAA-synthesizing activity.

IAA production by the ectomycorrhizal fungus Paxillus invotutus grown in pure culture was investigated by testing IAA accumulation or IAA-synthesizing activity. All the Paxillus involutus strains studied released indole compounds either when incubated with 0.5 mM tryptophan or in its absence. HPLC analyses of indole compounds all yielded two main peaks identified by reference to controls as being IAA and indole-3-carboxylic acid and a small peak of indole-3-aldehyde. Mass spectrometry unequivocally confirmed IAA production in the culture filtrates and in the incubation solution used to study in vitro IAA-synthesizing activity. The IAA-synthesizing activity was found to vary widely, from 7.6 to 137.4 nmol IAA h-1 g-1 f. wt, between strains. The mycorrhizal activity of these strains with seedlings of Pinus sylvestris cultured under aseptic conditions was tested. Fungal strains that were characterized in pure culture conditions by high LAA-synthesizing activity induced more fine roots and significantly higher numbers of mycorrhizas than strains which showed a low activity of IAA synthesizing enzymes. The increased ectomycarrhiza formation was generally accompanied by an increased growth of seedlings.

Changes in IAA responsiveness in the elongation region of graviresponding mung bean roots.

IAA responsiveness of sections of root tissue taken from the top and bottom of mung bean roots was assessed prior to and at varying times following gravistimulation. Prior to gravistimulation, root tissue sections from the sides of the elongation zone responded similarly to IAA. After gravistimulation (within 5 min), root sections from the bottom of the elongation zone became more responsive to IAA than sections collected from the upper side of the elongation zone. The change in IAA responsiveness of these tissue sections was transient with root sections from both the top and bottom of the elongation zone again exhibiting similar responsiveness to IAA following 15 minutes of gravistimulation. These studies also examined if the root tip is required for the gravity-induced shift in IAA responsiveness in the tissues of the elongation zone. The IAA responsiveness of top and bottom sections of the elongation zone from decapped mung bean roots was assessed at varying times following gravistimulation. The responsiveness to IAA of top and bottom sections changed rapidly in decapped roots, just as had been previously found for intact roots. Although the alteration in responsiveness was transient in decapped roots (just as intact roots), the time it took for the sections to recover previous responsiveness to IAA was extended. The results suggest that the initial growth response of graviresponding roots may be due to a change in the IAA responsiveness of tissues in the elongation zone and not an asymmetric accumulation of IAA on the lower side of the elongation zone. The results also indicate that the gravity-induced shift in IAA responsiveness in the elongation zone occurs independently of the root cap, suggesting that the cells in the elongation region can perceive and respond to gravity independently of the root cap during the initial phases of the gravity response.

Relations between auxin and cytokinin contents and in vitro rooting of tree Peony (Paeonia suffruticosa Andr.)

In this work, a combined HPLC-ELISA technique was used to associate in vitro rooting capacity of tree peony micro-cuttings with contents of cytokinin and auxin; the cytokinin mainly detected corresponded to the N6-benzyladenine which had been added to the multiplication medium. Rooting capacity of explants was favoured by a preliminary accumulation of endogenous IAA only when levels of the BA absorbed from the multiplication medium had decreased. Main shoots coming from a 5-weeks subculture fulfilled these hormonal conditions and were the best microcuttings for rooting (87% rooting). Main shoots coming from shorter cycles or axillary shoots coming from a 5-weeks cycle always contained high benzyladenine levels and had a low rooting capacity (25–55% rooting). Root induction was associated with an early peak of indole-3-acetic acid followed by a 10-fold lower peak of endogenous ribofuranosyl-isopentenyladenine. Only a low and transitory accumulation of isopentenyladenine occurred during root development, and this could explain the lack of shoot development. Root development was efficient, especially in a medium containing activated charcoal, which led to an almost 3-fold decrease of IAA contents in roots.

Water stress and indol-3yl-acetic acid content of maize roots

Water-stress conditions were applied to the apical 12 mm of intact or excised roots ofZea mays L. (cv. LG 11) using mannitol solutions (0 to 0.66 M) and changes in weight, water content, growth and IAA level of these roots were investigated. With increasing stress a decrease in growth, correlated with an increased IAA level, was observed. The largest increase in IAA (about 2.7-fold) was found in the apical 5 mm of the root and was obtained under a stress corresponding to an osmotic potential of −1.39 MPa in the solution. This stress led to an isotonic state in the cells after 1 h. When the duration of water stress (−1.09 MPa) was increased to 2 or 3 h, no further increase in the IAA content was observed in the root segments. This indicated that there was no correlation between a hypothetical passive penetration of mannitol in the cells and IAA content. Indol-3yl-acetic acid rose to the same level in excised as in intact roots. In both cases, IAA accumulation was apparently independent of the hydrolysis of the conjugated form. The caryopsis and shoot seem not to be necessary to induce the increase of the IAA level in the roots during water stress (−1.09 MPa). Therefore, there seems to be a high rate of IAA biosynthesis in excised maize roots under water-stress conditions. Exodiffusion of IAA was observed during an immersion in either buffer or stress (−1.09 MPa) solution. In both cases, this IAA efflux into the medium represented about 50% of the endogenous level. Considering the present results, IAA appears to play an important part in the regulation of maize root metabolism and growth under water deficiency.

Localization of target cells and improvement ofAgrobacterium-mediated transformation efficiency by direct acetosyringone pretreatment of carrot root discs

Localization of target cells forAgrobacterium-mediated transformation in the carrot root disc model has been achieved after inoculation with a disarmedA. tumefaciens strain harbouring a GUS-intron construct. The first GUS positive cells could be detected on both sides of the discs 48 h after inoculation. The transformed cells were always more numerous on the apical side, mainly localized in the intrafascicular cambium and in the immature phloem strands. The kinetics of free endogenous IAA levels on both sides after wounding have been determined, indicating that rapid IAA accumulation on the apical side was not simply due to polar migration from the basal side. Attempts to optimize transformation efficiency were made by pretreating the discs with various concentrations of acetosyringone (AS) and/or naphthalene acetic acid (NAA). Surprisingly, while 25 μM AS applied to bacteria prior to the inoculations was ineffective, the same AS concentration applied as a pretreatment to the discs strongly increased the number of transformed cells in the target tissues and decreased the lag time for the appearance of the first GUS positive cells. NAA pretreatment on the basal side enhanced the AS effect. AS pretreatment was found both to advance the reentry of competent cells with a potential for cell division into the S phase of the cell cycle and to stimulate bacterial attachment to the cell walls. The relationship between transformation efficiency and DNA synthesis in the host cells is discussed. AS treatment of plant tissues prior to inoculation is proposed as a means of increasing the transformation rates.

Phytotropin-binding sites and auxin transport in Cucurbita pepo: evidence for two recognition sites

Two properties of phytotropins, their ability to bind to 1-N-naphthylphthalamic acid (NPA) receptors located on microsomal vesicles isolated from Cucurbita pepo L. hypocotyls, and to stimulate auxin (indol-3-yl acetic acid, IAA) accumulation into such vesicles by blocking its efflux from them, were assessed in double labelling experiments using [2,3,4,5-(3)H]1-N-naphthylphthalamic acid and 3-indolyl-[2-(14)C]acetic acid. Two sites of differing affinities and activities on IAA accumulation were found. 1-N-Naphthylphthalamic acid was found to have high affinity (KD at 10(-8)mol·l(-1)) for one site and low affinity (KD at 10(-6) mol·l(-1)) for the other, whereas 2-(1-pyrenoyl)benzoic acid displaced NPA with high efficiency (KD below 10(-8) mol·l(-1)) from both sites. Other phytotropins had intermediate affinities for either site. Occupation of the site with low affinity for NPA stimulated auxin accumulation, while occupation of the high-affinity site with a phytotropin did not interfere with auxin accumulation into vesicles.

Pisum sativum epicotyls inoculated with agrobacterium rhizogenes agropine strains harbouring various T-DNA fragments: morphology, histology and endogenous indole-3-acetic acid and indole-3-acetamide content

In the present paper we correlate endogenous IAA and IAM levels with morphological and histological changes of decapitated Pisum sativum epicotyls after inoculation with pA-303,d16Agrobacterium derived strains. Callus and subsequent root formation in the infected region are correlated with endogenous IAA accumulation as a result of expression of the TR aux genes, concomitant with IAM accumulation. Irrespective of the bacterial strain analyzed IAA synthesis by the bacteria themselves was found to be constitutive and therefore not related to root proliferation. Inoculation with strains harbouring the aux genes (TR or TR + TL) induced callus formation, root initiation and histological changes such as tracheid differentiation and development of cribrovascular nodules surrounded by cambial-like layers. The presence of TL largely abolished the geotropic growth of the neoformed roots. Inoculations with strains harbouring only TL DNA or the Eco15 fragment covering orf10 to 12 lead to limited histological effects and root initiation. Morphology and growth pattern of root clones obtained from inoculations with the wild type A4 pA-303,d16oculations with strains containing either TL or TR alone differed greatly and could be related to varying endogenous IAA levels. High endogenous IAA and IAM levels were found in root clones obtained after inoculation with bacterial strains carrying only TL DNA.

Flavonoids and flavonoid sulphates as probes of auxin-transport regulation in Cucurbita pepo hypocotyl segments and vesicles

The accumulation of IAA by sealed microsomal vesicles prepared from hypocotyls of dark-grown Cucurbita pepo L. (zucchini) seedlings was stimulated by N-1-naphthylphthalamic acid (NPA: an inhibitor of carrier-mediated auxin efflux and hence of polar auxin transport) as well as by quercetin and certain other flavonoids with a specificity pattern similar to that previously shown for their NPA-like effects on auxin transport and inhibition of NPA binding to saturable sites. In contrast, putatively nonpenetrant negatively charged quercetinsulphate esters did not stimulate such auxin accumulation although they were able to oppose stimulation by NPA or quercetin itself. However, the binding of NPA to hypocotyl microsomes was 30- to 80-fold more strongly inhibited by the quercetin sulphates than by unsubstituted quercetin. As with vesicles, net IAA uptake by hypocotyl segments (2 mm) from dark-grown zucchini was stimulated less effectively by quercetin-sulphate esters than by quercetin itself. We discuss the implications of these observations for the accessibility of the NPA receptor from cell wall or cytoplasm and for the coupling of its occupancy to inhibition of the auxin efflux carrier.

Biochemical Bases for the Loss of Basipetal IAA Transport with Advancing Physiological Age in Etiolated Helianthus Hypocotyls

Basipetal transport of [(14)C]IAA in hypocotyl segments isolated from various regions of etiolated Helianthus annuus L. cv NK 265 seedlings declines with increasing physiological age. This decline was the result of a reduction in both transport capacity and apparent velocity. Net IAA uptake was greater and the abilities of auxin transport inhibitors to stimulate net IAA uptake were reduced in older tissues. Net IAA accumulation by microsomal vesicles exhibited a similar behavior with respect to age. Specific binding of [(3)H]N-1-naphthylphthalamic acid (NPA) to microsomes prepared from young and older hypocotyl regions was saturable and consistent with a single class of binding sites. The apparent affinity constants for NPA binding in microsomes prepared from young versus older tissues were 6.4 and 10.8 nanomolar, respectively, and the binding site densities for young versus old tissues were 7.44 and 3.29 picomoles/milligram protein, respectively. Specific binding of [(3)H]NPA in microsomes prepared from both tissues displayed similar sensitivities toward unlabeled flurenol and exhibited only slight differences in sensitivity toward 2,3,5-triiodobenzoic acid. These results demonstrate that the progressive loss of basipetal IAA transport capacity in etiolated Helianthus hypocotyls with advancing age is associated with substantial alterations in the phytotropin-sensitive, IAA efflux system and they suggest that these changes are, at least partially, responsible for the observed reduction of polar IAA transport with advancing tissue age.

IAA Distribution in the Hypocotyls and Primary Leaves of Phaseolus vulgaris L. Treated with Paclobutrazol in Relation to Their Rooting Capacity

The IAA content and its distribution were investigated in hypocotyls and primary leaves of bean plants treated with paclobutrazol in connection with the root formation of intact plants, stem and leaf cuttings. The amount of IAA in paclobutrazol-treated hypocotyls is higher than that of the control but more IAA accumulated in the basal part of the treated hypocotyls. Accumulation of IAA in the basal region correlates well with the increased root system of intact plants and with the more intensive rooting of stem cuttings. Although the IAA level in treated primary leaves was also higher than in the control, distribution of the hormone between the petiole and leaf blade was not favourable for the rooting process.

Dry matter accumulation at specific pod positions on field bean (Vicia faba L.) plants and possible relations with indoleacetic acid and abscisic acid levels

Seed weights at specific positions within inflorescences of field bean plants (Vicia faba L.) were varied by removal of flowers. The inflorescences of two regions (nodes 3+4 and nodes 5+6, counted from the bottom of the plant) were used for manipulations and investigations. The two proximal flowers of the manipulated inflorescence were removed in order to vary the development and seed weights of distal pods (see Fig. 1). Dry matter accumulation and IAA- and ABA-concentrations in seeds were investigated during the filling period. Treatment effects in both regions were similar during two seasons. The removal of proximal flowers prevented the usually observed drop of distal pods and favoured the accumulation of dry matter and IAA in seeds, whereas the variation of ABA-concentrations partly depended on interaction with season. Whether these effects contribute to a signal leading to the establishment of processes preceeding dry matter accumulation or are a consequence of such processes is questionable.