The hormonal regulation of bud outgrowth in Phaseolus vulgaris L.

Summary Aqueous solutions of indole acetic acid, kinetin, gibberellic acid and abscisic acid were applied singly and in combination to the decapitated stem stump of Phaseolus seedlings. Application of indole acetic acid will not completely replace the intact stem apex with regard to the inhibition of lateral bud extension. The greatest inhibition of bud growth is obtained when indole acetic acid is applied in combination with both kinetin and abscisic acid. Treatment with gibberellic acid causes massive bud growth even in the presence of indole acetic acid, kinetin and abscisic acid. Although both abscisic acid and kinetin have only a slight promoting effect on bud outgrowth when applied singly, these hormones will modify the effects of indole acetic acid and gibberellic acid.     

Apical dominance in Phaseolus vulgaris. The triggering effect of shoot decapitation and leaf excision on growth of the lateral buds

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node of Phaseolus vulgaris (L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth.
Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral buds.     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L.--Influence of the Environment

The influence of various environmental factors upon main stemand lateral bud growth has beeninvestigated using Phaseolusvulgaris, with the object of discovering why there is variabilityin the response of lateral buds on decapitated plants to apically-appliedIAA. Light intensity, light quality and temperature had differentand specific effects on main stem and lateral bud growth inintact plants and on the effectiveness of IAA in inhibitingprimary leaf axillary bud growth in decapitated plants. Photoperiod,on the other hand, was apparently ineffective. It is concluded that environmental factors, as well as contributingto the normal regulation of apical dominance, could also partlyor wholly account for the variation in effectiveness of appliedIAA found by different workers. IAA was least effective whenthe temperature was lower at night than during the day.     

Apical Dominance in Phaseolus vulgaris L.

Although determinations of the ABA content of lateral buds ofPhaseolus vulgaris revealed no difference between decapitatedand intact control plants in the first 12 h following decapitation,a relative decrease in the ABA content of lateral buds of decapitatedplants was detectable 24 h following decapitation. Shoot decapitationwas also observed to result in a decrease in the ABA contentof stem tissue. The application of IAA to the stem of decapitatedplants prevented these changes and increased the ABA contentof stem tissue relative to that of intact plants. The levelsof IAA and ABA were also determined in the stem tissue fromthe nodes of intact bean plants. The possible interdependenceof these two plant hormones was further investigated by a studyof [2_–14ClABA metabolism. The results are discussed inrelation to the possible role of these hormones in apical dominance. Key words: Apical dominance, Abscisic acid, Indole-3-acetic acid     

Cytokinin metabolism in Phaseolus vulgaris L.

The major cytokinins in stems of decapitated, disbudded bean plants have been identified by enzymic degradation, Sephadex LH20 and reversed phase high performance liquid chromatography, and by combined gas chromatography-mass spectrometry as 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9--D-ribofuranosylpurine (zeatin riboside), 6-(4-hydroxy-3-methylbutylamino)-9--D-ribofuranosylpurine (dihydrozeatin riboside), and the 5-phosphates of these compounds (zeatin ribotide and dihydrozeatin ribotide). Minor cytokinins in this tissue were tentatively identified as dihydrozeatin-O--D-glucoside and zeatin ribotide-O--D-glucoside. [8-¹⁴C-]Dihydrozeatin appeared to be rapidly metabolized to dihydrozeatin ribotide when supplied to segments of stems from decapitated plants. These results are discussed in relation to the metabolism and distribution of cytokinins in the whole plant.Abbreviations TEAB triethyl ammonium bicarbonate - UV ultra-violet - GCMS gas chromatography-mass spectrometry - HPLC high performance liquid chromatography - TMS trimethyl silyl     

Tissue Cultures of Phaseolus vulgaris L.

Abstract

Callus production and plant regeneration from different explants of Phaseolus vulgaris L. cv. Giza are reported. Calli cultures were induced from leaf, hypocotyl, embryo and root explants. Rapid growth of callus was achieved by leaf explants cultured on MS salts, B5 vitamins and supplemented with 2,4— dichlorophenoxyacetic acid (2, 4—D)+0.5 mg/l kinetin (kin). Addition of casein hydrolysate at 2 g/l to maintenance medium enhanced callus growth and hindered the early appearance of necrotic parts. This report also provides a detailed method for production of multiple shoots directly from the wounded edges of immature cotyledon explant via organogenesis on 1 mg/l benzyladenine (BA) or indirectly on 0.5 mg/l naphthaleneacetic acid (NAA)+2 mg/l BA. The regeneration of bean plants through the two ways described here (direct or indirect) may be of use in genetic improvement of bean.     

Xylem changes in the correlative inhibition of lateral bud growth in flax (Linum usitatissimum L.)

Xylem or tracheary changes at the base of the cotyledonary buds of flax seedlings (Linum usitatissimum L.), released from inhibition by decapitation of the main apex were studied. The differentiation of xylem strands and/or tracheary elements was correlated with the growth in length of the lateral buds, especially 48–72 hr after the removal of the main apex. The xylem strands, connected to the hypocotylary stele or not, and the tracheary elements increased with age within and outside the strands of both non-decapitated and decapitated seedlings. In the latter, the differentiation of these structures, however, occurred much earlier and in greater abundance in the same regions. The early growth in length of lateral buds, 1 or 2 hr after decapitation, was correlated with the early development of tracheary perforations in the xylem strands. The xylary strands with perforated elements are known to be more efficient than those without them. Therefore, it is suggested that the inhibition of lateral-bud growth was due, in fact, to a lack of appropriate tracheary perforations in the bud xylem strands that were connected with the hypocotylary stele of flax seedlings.     

Correlative Growth in Seedlings of Phaseolus vulgaris L. : Inhibition of Stem Growth by the Primary Leaves

Primary leaves of one-week-old seedlings of dwarf beans effectivelyinhibit stem elongation either in natural daylight or in continuousdarkness. Stem elongation is promoted by exogenous gibberellicacid and kinetin and inhibited by indol-3-ylacetic acid (IAA)or abscisic acid, and it is suggested that IAA is the inhibitorysubstance emanating from the primary leaf blades which affectsthe growth of the stem.     

Ureide Metabolism in Non-nodulated Phaseolus vulgaris L.

The distribution of ureide-N was studied throughout vegetativeand reproductive growth of non-nodulated Phaseolus vulgarisL. (bushbean) grown in nitrate nutrient solution. Largest increasesin ureide-N per plant were correlated with flowering and earlypod formation and with seed filling. Highest amounts of ureidesper organ were measured in stems and axillary trifoliates. Highestconcentrations (µmol ureide-N g^–1 fr. wt.) weremeasured in young developing organs and stems. Seeds did notaccumulate ureides until the ureide content of pods had reacheda maximum. Results obtained using the inhibitor of xanthine oxidase, allopurinol,are consistent with the origin of ureides via purine degradationbut alternative pathways cannot be discounted. Leaves and stems were shown to have the ability to degrade allantoatevia an enzymic process.     

Isozymes of Glutamine Synthetase in Phaseolus vulgaris L. and Phaseolus lunatus L. Root Nodules

The glutamine synthetase (GS) isozymes in the plant fraction of nodule extracts from 62 cultivars of Phaseolus vulgaris L. and one cultivar of Phaseolus lunatus L. were analyzed by polyacrylamide gel electrophoresis. All P. vulgaris nodule extracts displayed two GS activity bands: a nodule-specific band (GS_n1) and a band (GS_n2) similar to the single band (GS_r) present in root extracts. In nodule extracts of P. lunatus, the GS_n1 band was detected, but the GS_n2 band was barely detectable. In contrast to P. vulgaris, the GS_n2 band and the GS_r band of P. lunatus appeared to be different. The electrophoretic mobility of the GS_n1 band in P. vulgaris was governed by both the plant cultivar and the development stage of the nodule. In nodule extracts of P. vulgaris and P. lunatus, the zone of GS_n1 activity coincided with six to nine distinct protein bands as revealed after treatment of gels, which had previously been stained for GS activity, with Coomassie blue. All these protein bands were shown to consist of polypeptides of identical molecular weight (approximately 47,000 daltons) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our results indicate that P. vulgaris continuously generates isozymes of GS_n1 of increasing electrophoretic mobility during the course of nodule development.     

Phaseolus vulgaris RbohB functions in lateral root development

Respiratory burst oxidase homologs (RBOHs) catalyze the reduction of oxygen to generate superoxide anion, a kind of reactive oxygen species (ROS). The ROS produced by RBOHs play essential roles in diverse processes, such as root hair development, stomata closure and signaling mechanisms in response to abiotic stimuli and during plant-pathogen interactions. Recently, we found that PvRbohB silencing in transgenic Phaseolus vulgaris roots had a negative impact on lateral root density. In this work, we show that the downregulation of PvRbohB affects both the growth and ROS levels in recently emerged lateral roots. In addition, we found that the PvRbohB promoter was activated during lateral root primordium initiation in the pericycle, and remained active throughout lateral root development. This study identifies RBOHs as potentially important players in lateral root development in P. vulgaris.     

Compensation among root classes in Phaseolus vulgaris L.

The activity of soil pathogens, competition for assimilates, and the changing availability of below-ground resources make root systems subject to a continuous and dynamic process of formation and loss of both fine and coarse roots. As hypocotyl borne roots appear later than other root classes, they may serve to functionally replace basal and primary roots lost to biotic and abiotic stress. Using common bean (Phaseolus vulgaris L.), we conducted experiments in solution and solid media culture with treatments involving the removal of part of the root system (basal, hypocotyl borne or primary roots), phosphorus availability, and depth of seeding to test the hypothesis that there are compensation mechanisms among basal, hypocotyl borne and primary roots to cope with the loss of part of the root system. The root system was highly plastic in response to root excision, which resulted in the maintenance of below-ground biomass accumulation. In most cases, this compensation among root classes was enough to maintain plant performance in both phosphorus sufficient and phosphorus stressed plants. Removal of a specific root class induced an increase in the growth of the remaining root classes. All root classes, but especially the primary root, contributed to the compensation mechanism in some way. Primary roots represented around 10% of the root system in control plants and this proportion increased dramatically (up to 50%) when other root classes were removed. In contrast, negligible compensatory re-growth was observed following removal of the primary root. Greater planting depth increased the production of hypocotyl borne roots at the expense of basal roots. The proportion of hypocotyl borne roots increased from 25% of the whole root system when seeds were placed at a depth of 2 cm to 30% when they were placed at 5 cm and to 38% when placed at 8 cm, with corresponding decreases in the proportion represented by basal roots. The common feature of our observations is the innate ability of the root system for its own regeneration. Total root biomass maintained strict allometric relationships with total shoot biomass in all treatments. Re-stabilization of root to shoot balance after partial root loss is governed by overall plant size following allometric relationships similar to undisturbed plants. However, the pattern of this root regeneration was not uniform since the way the three root classes compensated each other after the removal of any one of them varied among the different growth media and phosphorus supply conditions. The resulting changes in root architecture could have functional significance for soil resource acquisition.     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L. Ethylene and the Physical Restriction of Apical Growth

Restriction of apical growth in Phaseolus by enclosing the upperpart of the shoot in sealed or ventilated tubes induced developmentof axillary buds beneath the enclosure. Enclosed parts of shootsshowed a reduction of leaf growth and, in experiments wherethe tubes were sealed, of internode extension. Enclosure ofthe shoots in large vessels that did not restrict leaf expansion,but which contained 0?5 vols 10^–6 ethylene, similarlyinduced axillary bud growth. Analysis of the gaseous extractof physically restricted shoots showed a 2?5-fold increase inethylene concentration. The results suggest involvement of ethylenein the release of correlative inhibition brought about by physicalrestriction of apical growth.     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L. Isolation of Indoleacetic Acid from the Inhibitory Region

The young, growing leaves have been shown by excision treatmentsto be responsible for the correlative inhibition of lateralbud growth in Phaseolus vulgaris. The presence of indoleaceticacid in apical portions of the stem bearing young leaves hasbeen demonstrated by extraction and collection in agar (‘agardiffusion’) followed by purification and analysis by bioassay,chromogenic assay, and gas chromatography-mass spectrometry.The relevance of these results to the possible involvement ofindoleacetic acid in correlative phenomena is discussed     

Effect of water stress on growth and proline metabolism of Phaseolus vulgaris L.

Summary The effect of water stress on growth (fresh weight, dry weight), water relations (water saturation deficit, water potential, osmotic pressure), and proline metabolism in Phaseolus vulgaris were studied.Experimentally, water deficit was produced by reduced watering of the bean plants. This resulted in a decrease in water potential and leaf fresh and dry weight. Increases in the water saturation deficit and the osmotic pressure of the sap were, however, recorded. Water stress was also induced by treatment of the plants with polyethylene glycol, but its effects on the above mentioned parameters were different. In addition, necrosis of the foliage was observed. According to the present results, polyethylene glycol seems to be suitable only for the induction of short-termed water stress conditions.The effects of water stress on growth and on water relations of the plants were accompanied by a marked increase in the free amino acid content, especially that of the free proline content of the plants. The activities of the proline dehydrogenase and glutamate dehydrogenase were stimulated under water stress conditions, indicating that proline accumulation in water stressed plants is not attributed to an inhibited proline breakdown. The accumulated proline was metabolized rapidly once the water deficit of the plant was relieved by watering. The ability of the plant to accumulate proline might be of ecological importance for the plant and might be an adaption mechanism of the plant to overcome short periods of drought.Abbreviations -Kg -ketoglutarate - GDH glutamate dehydrogenase - PDH proline dehydrogenase - P5C -pyrroline-5-carboxylic acid - PEG polyethylene glycol - WSD water saturation deficit     

Correlative Inhibition of Lateral Bud Growth in Pisum sativum L. and Phaseolus vulgaris L.: Studies of the Role of Abscisic Acid

The possibility has been investigated that abscisic acid (ABA)might act as a correlative inhibitor of lateral bud growth inPisum sativum and Phaseolus vulgaris. Application of ABA insmall quantities (2µg) to axillary buds on decapitatedplants of P. sativum caused appreciable inhibition of theirgrowth, and induced a compensatory growth of the bud on an adjacentnode. Application of this same quantity of ABA to axillary budson decapitated plants of Phaseolus vulgaris was without effect,but a high concentration in lanolin (1 mg g^–1) did substantiallyreduce bud outgrowth. Endogenous ABA-like substances in Phaseolusvulgaris, detected by bioassay and electron capture g.l.c.,were present in similar concentrations in shoot tips, lateralbuds on intact plants and lateral buds on plants decapitated24 h earlier. The effects of applied ABA suggested that it might be involvedin the mechanism of correlative inhibition in Pisum sativum,but it was not possible to test this hypothesis by determiningendogenous ABA levels in axillary buds because of their smallsize. The evidence presented here suggests that ABA is not acorrelative inhibitor in Phaseolus vulgaris even though at highconcentration it can inhibit the growth of axillary buds.     

Actin expression in germinating seeds of Phaseolus vulgaris L.

Actin was present at very low levels in the seeds of common bean (Phaseolus vulgaris L.) compared with those from other species, and was observed mostly in the embryo. A time-course of actin expression in germinating bean seeds revealed an induced expression of both the mRNA and protein. Initially, the actin mRNA in seeds was barely detectable by northern blot analysis. However, there was a substantial increase in the expression of the actin mRNA at 24, 48 and 72 h after imbibition, compared with an internal control consisting of a late-embryogenesis-abundant (LEA) type IV gene from P. vulgaris. An increase in the amount of actin in total seed extracts that parallelled that of the mRNA was detected by western blotting starting at 24 h after imbibition. This increase was more apparent when the embryo alone was analyzed. Two-dimensional western blots initially revealed three actin isoforms with isoelectric points (pIs) of approximately 5.6, 5.7 and 5.8, the amounts of which increased within a 48-h period, when a new minor isoform of pI approximately 5.5 appeared; however, after 72 h, the pI-5.8 isoform had almost disappeared and the pI-5.5 isoform had disappeared completely, indicating that these two minor isoforms are expressed transiently. These results indicate that actin is at very low levels in the dry seed but undergoes an increased and differential expression during imbibition, an event probably required to carry out all the necessary functions for germination. Received: 21 July 1998 / Accepted: 1 September 1998     

The influence of aluminium availability on phosphate uptake in Phaseolus vulgaris L. and Phaseolus lunatus L.

Aluminium toxicity is one of the major limiting factors of crop productivity on acid soils. High levels of available aluminium in soil may induce phosphorus deficiency in plants. This study investigates the influence of Aluminium (Al) on the phosphate (P_i) uptake of two Phaseolus species, Phaseolus vulgaris L. var. Red Kidney and Phaseolus lunatus L. The two bean species were treated first with solutions of Al at different concentrations (0, 25, 50 and 100 μM, pH 4.50) and second with solutions of P_i (150 μM) at pH 4.50. The higher the Al concentration the higher the Al concentration sorbed but P. vulgaris L var. Red Kidney adsorbed significantly more Al than P. lunatus L. Both species released organic acids: P. vulgaris L var. Red Kidney released fumaric acid and P. lunatus L. fumaric and oxalic acids which could have hindered further Al uptake.The two bean species showed a sigmoid P_i uptake trend but with two different mechanisms. P. vulgaris L var. Red Kidney showed a starting point of 3 h whereas P. lunatus L. adsorbed P_i immediately within the first minutes. In addition, P. vulgaris L var. Red Kidney presented significantly higher P_i uptake (higher uptake rate ‘k’ and higher maximum adsorption ‘a’ of the kinetic uptake model). The Al treatments did not significantly influence P_i uptake. Results suggest that P. lunatus L. might adopt an external Al detoxification mechanism by the release of oxalic acid. P. vulgaris L var. Red Kidney on the other hand seemed to adopt an internal detoxification mechanism even if the Al sorbed is poorly translocated into the shoots. More detailed studies will be necessary to better define Al tolerance and/or resistance of Phaseolus spp.     

Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indole-3yl-acetic acid(IAA) were applied to roots of Phaseolus vulgaris under twodifferent light intensities and when either young or old leaveswere removed In all cases GA₃, promoted stem and lateral growth,especially when light intensity was reduced. Promotion by GA₃,of stem growth under reduced light was reduced if IAA and kinetinwere present; promotion of lateral growth under reduced lightwas reduced if IAA was added and eliminated if kinetin or kinetinplus IAA were added to GA₃. Removal of young and mature leavesreduced main stem growth; removal of young leaves promoted,and of mature leaves reduced, lateral shoot growth. We suggestthat shoot growth and apical dominance are governed by the balanceof hormones present in elongating internodes. There may be twoways of modifying this balance; firstly by altering light, temperature,or nutrients, or by applying hormones generally to the plant.Secondly, local modifications can be made by removing apicesor young leaves, or applying hormones in lanolin to specificareas. Knowledge of both the general and local conditions maybe necessary for a complete understanding of apical dominance.