Petiole Sections Research Articles

The effects of salinity and gibberellic acid on blackheart disorder in celery (Apium graveolensL.)

SummaryBlackheart of celery is known to be a Ca deficiency-related disorder. The present study shows that blackheart is greatly attenuated in plants adapted to salinity (NaCl) in which the Ca content in young susceptible leaves is significantly reduced. The application of GA3 to untreated plants enhanced blackheart development, but GA3 sprayed on salinized plants has no effect although the Ca level in the young leaves was further reduced by this treatment. GA3 supplied to either untreated or salinity-adapted plants substantially enhanced the elongation of mature leaves but only slightly increased the elongation of young leaves which are the ones most susceptible to blackheart. The same was observed in similarly treated plants the inner leaves of which were covered to encourage blackheart development. GA3 increased electrolyte leakage from sections of petioles from mature and young leaves. However, the most affected sections were those from mature leaves of salinized plants which are not prone to blackhear...

Initiation of callus and somatic embryos from explants of mature cotton (Gossypium klotzschianum Anderss)

Stem and petiole sections from a diploid species of cotton (Gossypium klotzschianum Anderss.) were longitudinally sliced and placed on a callus induction medium. Explants with the cut surface in contact with the medium either browned or produced a slow growing red callus which could not be subcultured. Explants oriented with the epidermis in contact with the medium produced a rapidly growing, friable, green callus which could be subcultured biweekly and has been maintained for 12 months. Globular and torpedo embryos were obtained 2 weeks after transfer of the callus to a liquid medium containing the auxin, 2,4-dichlorophenoxyacetic acid. Following subculture to an auxin-free medium, the embryos underwent additional development but plantlets were not obtained. Attempts to consistently regenerate plants from embryos are currently under way.

Petiole growth in Ranunculus sceleratus: the role of growth regulators and the leaf blade

In the presence of the leaf blades, excised petioles of the semiaquatic celery-leaved buttercup Ranunculus sceleratus L. elongate when submerged, or when treated in air with indoleacetic acid (IAA), gibberellin A3 (GA3), or C2H4 alone or in combination, responses that are similar to those obtained using intact plants. Isolated petiole sections do not respond to C2H4, but are responsive in the presence of low levels (10−6 mol L−1) IAA. Gibberellin A3 is less active than IAA in promoting growth or in sensitizing the petiole tissue to C2H4.

In Vivo Measurement of Indole-3-acetic Acid Decarboxylation in Aging Coleus Petiole Sections

The concentration of indoleacetic acid (IAA) in plant tissues is regulated, in part, by its rate of decarboxylation. However, the commonly used in vitro assays for IAA oxidase may not accurately reflect total in vivo decarboxylation rates. A method for measuring in vivo decarboxylation was utilized in which (14)CO(2) is collected following uptake of [1-(14)C]IAA by excised tissue sections. After a 30-minute equilibration period, the evolution of (14)CO(2) was found to follow an approximately linear course with respect to both time and tissue weight.Decarboxylation rates were measured by this method in petiole sections of the Princeton clone of Coleus blumei Benth. Both the (14)CO(2) evolved per milligram tissue and the percent of [1-(14)C]IAA uptake decarboxylated were highest in sections from the youngest petioles tested, and declined in the older tissue. Thin layer chromatography of acetonitrile extracts from the [1-(14)C]IAA-treated petioles showed a decreasing amount of free IAA and an increase at the retardation factor of indoleacetylaspartate in the older sections. The decreased decarboxylation rates in the older petioles may be attributable to a generally lower metabolic rate and increased protection of the IAA by conjugation.

Adventitious shoot formation from sections of sweet potato grown in vitro

Sweet potato ( Ipomoea batatas Lam.) root sections were obtained from the cultivars ‘Centennial’, ‘Redmar’ and ‘Jewel’ with a No. 6 cork borer. These sections were cut into 2–3-mm discs and explanted on to modified Murashige and Skoog (MS) medium consisting of MS high mineral salts, myo-inositol (100 mg l −1), Staba vitamins, 6-benzyl-aminopurine (2.0 mg l −1), naphthaleneacetic acid (0.1 mg l −1), sucrose (30 g l −1) and agar (10 g l −1). Root discs from internal regions of the tuberous roots gave rise to calli and meristematic bud-like centers (MBLC's). A small percentage of ‘Centennial’ MBLC's burst open to reveal plantlets which grew and rooted well on the medium. Some of the ‘Jewel’ MBLC's contained only roots, while those of ‘Redmar’ did not differentiate. MBLC-formation occurred most often on discs taken from fresh (unstored) roots of ‘Centennial’. Petiole sections taken from in vitro-cultured plants of all 3 cultivars developed plants quite readily on the medium. Shoots of all 3 cultivars grew rapidly, to yield whole rooted plants which could easily be moved to soil and grown in the greenhouse and field.

Clonal propagation in vitro of red beet (Beta vulgaris ssp.) by multiple adventitious shoot formation

An efficient procedure is described for the rapid in vitro clonal propagation of red beets (Beta vulgaris ssp.) from cultured shoot tips. Propagation was through a tillering response of the rosette plantlets or through multiple adventitious bud formation on the petioles. Histological analysis of petiole sections indicated that buds arise from single cells of the upper epidermis.

A hydroxyproline-rich bacterial agglutinin from potato: its localization by immunofluorescence

Potato tubers (cv. Katahdin) contain a hydroxyproline-rich glycoprotein (HPRG) that agglutinates certain avirulent strains of the bacterial wilt pathogen, Pseudomonas solanacearum. This and similar agglutinins are thought to play an important rôle in the immobilization of incompatible bacteria in potato and tobacco tissues. The agglutinin from potato tubers was purified by ion exchange chromatography. Antisera to the intact or deglycosylated agglutinin were obtained from New Zealand white rabbits after multiple intradermal and intramuscular injections. Immunoglobulins were precipitated with (NH4)2SO4 and antibodies specific for the agglutinin were purified by affinity chromatography. Frozen sections of petiole or leaf tissue from tobacco and potato were treated firstly with sheep normal immunoglobulin and then with either anti-agglutinin antibodies or normal rabbit immunoglobulin for 20 min. The sections were rinsed and then treated with fluorescein isothiocyanate-conjugated sheep anti-rabbit immunoglobulin. When the sections were examined by fluorescence microscopy, it was determined that anti-agglutinin antibodies bound only to the cell walls, particularly those of parenchyma. Fluorescence was also evident on the cell walls of tobacco and potato xylem vessels, epidermis, and collenchyma. Control sections treated with normal rabbit immunoglobulin did not bind the labelled anti-rabbit immunoglobulin. Cell walls in tissue sections from non-solanaceous plants such as soybean, corn, or begonia, treated in the same manner, were also stained by the labelled antibodies. Antibodies to both intact and deglycosylated potato agglutinin bound to these plant cell walls, indicating that the receptors are proteins with antigenic determinants which are similar to those of proteins from potato or tobacco cell walls. Such proteins (HPRGs) are common components of plant cell walls and may play a rôle in immobilizing bacteria that gain access to the intercellular spaces.

Induction, ultrastructure, isolation, and tissue culture of chlorophyll mutants in carrot

Seeds ofDaucus carota “Danvers” were treated with ethyl methanesulfonate (EMS) for 6-hr periods at concentrations of 0.01, 0.03, 0.1, 0.3, 1.0, and 3.0% to induce plastid mutants. In these treatments, there was a gradual decrease in percent germination from control up to 1.0% EMS and no germinations at 3.0%. The number of chlorophyll mutants increased with dose of mutagen. One mutant plant was isolated from the 0.1% treatment and it had leaf sections of green, white layered on green and pure white; and white and green striped petioles. Histogenic analysis of this mutant showed it to be a GGW chimera, the “all-white” sectors being GWW, arising from displacement of L-II by L-III. Electron micrographs of the white sections showed plastids that had dilated thylakoids typical of PS-I mutants. So called “mixed cells” of normal and mutant plastids were found, suggesting a plastome mutation. Leaf and petiole sections have been successfully cultured through the development of callus, and both green and white plants have been regenerated. Regenerated white plantlets were insensitive to 10 mM methyl viologen (paraquat), whereas green tissues were killed by the herbicide.

Ultrastructure of wilt syndrome caused by Verticillium dahliae. VII. Correlated light and transmission electron microscope identification of vessel coatings and tyloses

Thin cross sections of petioles from wilted leaves of chrysanthemums infected with Verticillium dahliae were fixed in glutaraldehyde + FeCl3 and embedded for electron microscopy. Alternate thick (LM) and thin (TEM) sections were cut. The thick sections were stained with (1) the Prussian blue reaction, (2) Sudan black B, (3) toluidine blue O, or (4) Schiff s reagent. Correlated LM and TEM of exactly the same vessels showed that tylosis walls, smooth coating, fibrillar coating, and bubbly coating stained differentially. The tyloses are more abundant than formerly anticipated but are restricted to the primary vessels; fungal cells and coating on vessel walls are confined to smaller secondary vessels.

Genotypic Differences for Reduction in Carbon Exchange Rates as Associated with Assimilate Accumulation in Soybean Leaves1

Six soybean [Glycine max (L.) Merrill] genotypes which differed in growth characteristics were selected to test the hypothesis that genotypes differed in their capacity to maintain carbon exchange rates (CER) at original levels as assimilate accumulated. Chilling (4 C) a 3 cm section of the leaf petiole for 3 hours created a 5.3‐fold increase for sucrose and 1.4‐fold increase for starch in the leaf relative to the control leaves with nonchilled petioles. Levels of sucrose and starch continued to increase with an additional 4 hours of chilling the petiole. Sucrose and starch levels increased in the leaf blade primarily as compared with the petiole and leaf veins. Transpiration rates and stomatal diffusive resistances were similar for chilled and nonchilled petiole treatments. All genotypes had similar decreases in stomatal diffusive resistances during 3 hours of chilled petiole treatment. Differences in reduction of carbon exchange rates (CER) were found among genotypes when petioles were chilled for 3 hours. Those genotypes whose CER were unaltered by chilling did not accumulate more sucrose and starch in the leaves than genotypes whose CER declined. In a 7‐hour chilled petiole study, the change in CER was inversely proportional to level of sucrose in the leaf blade. Genotypic differences for maintaining CER with assimilate accumulation in the leaf were not found.

Movement of Kinetin and Gibberellic Acid in Leaf Petioles during Water Stress-induced Abscission in Cotton

Movement of [(14)C]kinetin and [(14)C]gibberellic acid was examined in cotton (Gossypium hirsutum L.) cotyledonary petiole sections independent of label uptake or exit from the tissue. Sections 20 millimeters in length were taken from well watered, stressed, and poststressed plants. Transport capacity was determined using a pulse-chase technique. Movement of both kinetin and gibberellic acid was found to be nonpolar with a velocity of 1 millimeter per hour or less, suggesting passive diffusion. Neither water stress nor anaerobic conditions during transport of labeled material affected the transport capacity of the petioles.Results suggested strong kinetin binding but weak gibberellic acid binding in the tissue sections. Apparent binding of both growth regulators was unaltered by the experimental conditions. Movement of these two growth regulators within cotton cotyledonary petioles plays a minor role in the stress-induced, foliar abscission process.

Relationship of Phloem Size to Leaf Size and Position1

Prior studies have shown that phloem cross‐sectional area in leaf bases or petioles may influence the rate of export of photosynthetic products from leaves. Since information could not be found on the variability in phloem size due to leaf size and position, an experiment was conducted to study phloem area in the leaf bases of two grass species and in petioles of two dicots. Leaves were removed from several nodes on each stem when the leaf at each node became fully expanded. Tall fescue (Festttca arundinacea Schreb.), sugarcane (Saccharum officinmrum L.), soybean (Glycine max Merr.), and peanut (Arachis hypogaea L.) were grown outside during the summer in full sunlight. Soybean and peanut were also grown under 50% shade. Lamina base or petiole sections were embedded in paraffin, sectioned, and stained for measurements of phloem cross‐sectional area under the light microscope.Leaf area increased with leaf position from the stem base toward the top. In peanut, soybean, and tall fescue, however, the distal one or two leaves were smaller than the one just below. Phloem area in the leaf bases or petioles followed a pattern similar to that for leaf area and the two parameters were closely correlated. The increased phloem area in larger leaves was due mainly to an increase in the number of vascular bundles per leaf in tall fescue and sugarcane. In soybean larger leaves had more and larger bundles per petiole and in peanut increased phloem in larger leaves was due to more phloem per bundle, since bundle number was constant at 5. Shading reduced phloem size in soybean even though leaf area was increased. Leaf area was barely affected by shading in peanut, but phloem size was reduced. Leaf weight was reduced to a greater extent than phloem size by shading, so that phloem per unit of leaf weight was increased in peanut and soybean. It is concluded that leaf position, size, and environment have an effect on phloem size that may complicate comparisons of species in studies of photosynthate translocation and anatomy.

Movement and Endogenous Levels of Abscisic Acid during Water-Stress-induced Abscission in Cotton Seedlings

In an effort to investigate possible involvement of abscisic acid (ABA) in foliar abscission processes, its movement and endogenous levels were examined in cotyledons taken from cotton seedlings (Gossypium hirsutum L.) subjected to varying degrees of water deficit, a condition which initiates leaf abscission. Using a pulse-labeling technique to avoid complications of uptake and exit from the tissue, ABA-1-(14)C movement was observed in both basipetal and acropetal directions in cotyledonary petioles taken from well watered, stressed, and rewatered plants. The label distribution patterns obtained after 1 and 3 hours of transport under all situations of water supply were diffusive in nature and did not change when tested under anaerobic conditions. The transport capacity of the petioles ranged from 3.6 to 14.4% ABA-1-(14)C transported per hour at estimated velocities of 0 to 2 millimeters per hour. Comparison of basipetal and acropetal movement indicated a lack of polarity under all conditions tested. These low transport capacities and slow velocities of movement, when compared to the active transport systems associated with auxin movement, as well as the lack of anaerobic effects and polarity, suggest that ABA movement in cotton cotyledonary petiole sections is facilitated by passive diffusion. Increases in free and bound ABA in the lamina with increased water stress did not correlate with patterns of cotyledonary abscission. Thus, no evidence was found to suggest that ABA is directly involved in stress-induced abscission processes.

Auxin Transport as Related to Leaf Abscission during Water Stress in Cotton

Plant water deficits reduced the basipetal transport of auxin in cotyledonary petiole sections taken from cotton (Gossypium hirsutum L.) seedings. A pulse-labeling technique was employed to eliminate complications of uptake or exit of (14)C-indoleacetic acid from the tissue. The transport capacity or the relative amount of radioactivity in a 30-minute pulse which was basipetally translocated was approximately 30% per hour in petioles excised from well watered seedlings (plant water potentials of approximately -4 to -8 bars). No cotyledonary leaf abscission took place in well watered seedlings. Plant water potentials from -8 to -12 bars reduced the transport capacity from 30 to 15% per hour, and although the leaves were wilted, cotyledonary abscission did not increase appreciably at these levels of stress. The threshold water potential sufficient to induce leaf abscission was approximately -13 bars and abscission increased with increasing stress while the auxin transport capacity of the petioles remained relatively constant (15% per hour). The basipetal transport capacity of well watered petioles tested under anaerobic conditions and acropetal transport tested under all conditions were typically less than basipetal transport under the most severe stress conditions. Cotyledonary abscission took place during and 24 hours after relief of stress with little or no abscission taking place 48 hours after relief of stress. Although the water potential returned to -4 bars within hours after rewatering the stressed plants, partial recovery of the basipetal transport capacity of the petioles was not apparent until 48 hours after rewatering, and at least 72 hours was required to return the transport capacity to near normal values. These data support the view that decreased levels of auxin reaching the abscission zone from the leaf blade influence the abscission process and further suggest that the length of time that the auxin supply is maximally reduced is more critical than the degree of reduction.

Failure of Ethylene to Change the Distribution of Indoleacetic Acid in the Petiole of Coleus blumei X frederici during Epinasty

The effect of ethylene on the distribution of applied indoleacetic acid in the petiole of Coleus blumei Benth. X C. frederici G. Taylor has been investigated during the development of epinastic curvature. Using intact plants, (14)C-IAA was applied to the distal region of the leaf lamina and the accumulation of label in the abaxial and adaxial halves of 5 mm petiole sections was determined after 1.5, 3, and 6 hours. Over this period the label was transported out of the lamina into the petiole at a rate of at least 66 mm hr(-1). Of the total amount of label in the petiole sections, 24 to 30% was located in the adaxial half and this distribution was not altered significantly by exposing plants to an atmosphere containing 50 mul/l ethylene. Thus when epinastic curvature is induced by ethylene there is no associated increase in the IAA content of the expanding adaxial half. The role of endogenous IAA in petiole epinasty was studied by restricting its movement with DPX 1840 (3,3a-dihydro-2-[p-methoxyphenyl]-8H-pyrozolo{5,1-a}isoindol-8-one). The leaf petioles still showed an initial epinastic response to ethylene. It is concluded that ethylene-induced epinasty is not dependent upon either any change in the transport of IAA or its redistribution within the petiole.

The Influence of Humidity and Gibberellic Acid on Movement and Immobilization of Radiocarbon within Petioles of Coleus blumei Benth. after Application of Indole-3- (Acetic Acid-2-14C) to Leaves of Intact Plants )

Summary Auxin transport and immobilization of radiocarbon in petioles of intact plants of Coleus blumei Benth. as influenced by the humidity of the atmosphere and by preceding and simultaneous treatment with GA 3 were followed 14 h after application of IAA-[2- 14 C] as droplets to the blades of leaves #3 and # 5. The auxin uptake, the fraction remaining transportable and being immobilized within the petioles were much smaller under low humidity (RH ~ 75%) than under high humidity (RH 100%); the differences were larger in leaf # 5 than in leaf # 3. With all treatments and in both leaves the amount of transportable and immobilized radiocarbon was high in the apical part of the petioles; the values decreased toward the middle of the petioles and increased to the level of the apical region toward the base of the petioles which includes the abscission layer. The low auxin supply observed under low humidity led to a steeper initial decrease of the transport characteristics in both leaves. GA treatment did not alter the distribution pattern along the petioles in general, neither did it significantly affect the transport characteristics under low humidity conditions; however, under high humidity, GA reduced auxin uptake and the radiocarbon fractions remaining transportable and being immobilized within the sections of both petioles; GA pretreatment was more effective than application simultaneously with IAA. The reduction of the immobilized fractions was strongest near to the base of the # 3 petioles; this may explain the speeding action of GA on abscission observed by Jacobs and Kirk (1966) in # 3 leaves of Coleus . The results have been discussed in connection with a previously developed (Kaldewey and Jacobs 1974) auxin transport and immobilization model which assumes there is a competition between the transport and immobilization systems for the auxin molecules, and GA weakens the transport system.

Apical Correlative Effects in Leaf Epinasty of Tomato

The influence of the stem apex on leaf curvature was investigated using debudded tomato (Lycopersicon esculentum Mill. cv Anahu) plants and petiole explants, consisting of a section of petiole attached to a section of stem.Decapitation of the main shoot of tomato plants induced hyponasty of petioles in young leaves. Application of auxin in place of the removed apex or fumigation of intact tomato plants with ethylene produced epinastic curvature at the base of the petiole. Simultaneous carbon dioxide treatments prevented the development of petiolar epinasty due to auxin and ethylene treatments. Application of ethylene gas to the decapitated shoot or injection into the stem, induced petiolar epinasty. In a saturating level of ethylene gas, tomato petioles did not respond to indole-3-acetic acid applied to the cut apex. Auxin-induced ethylene production in petiole explants preceded the development of epinasty. Application of indoleacetic acid in lanolin to the entire lower side of the petioles of leaves in situ produced petiole epinasty. Petiolar epinasty due to apically applied indoleacetic acid resulted from differential cell elongation.The auxins indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, and naphthalene-1-acetic acid induced epinasty when applied apically to decapitated tomato plants, while gibberellic acid, kinetin, abscisic acid, and auxin or gibberellin antagonists had no effect. When such compounds were applied to petiole explants, only indole-3-acetic acid and kinetin caused an increase in ethylene production and the effect of kinetin was relatively weak.Application of 2,3,5-triiodobenzoic acid around the stem did not change the effect on petiolar epinasty of auxin applied to the decapitated shoot or around the stem. Radioautography showed that the label from (14)C-indoleacetic acid applied apically entered the petiole and midrib tissue; however, extraction showed that only a fraction of the label in these tissues was in the form of indoleacetic acid.Removal of leaflets from leaves induced hyponasty in the midrib region, and application of auxin to the leaflet stubs produced midrib epinasty; carbon dioxide did not block the action of auxin in this type of epinasty. Removal of leaflets from leaves did not alter the effect of apically applied auxin on petiolar epinasty.The data are consistent with the hypothesis that the oblique orientation of leaves in tomato plants is influenced by two epinastic responses. Petiolar epinasty is controlled by the apical region on the stem and is due to the action of auxin-induced ethylene; and midrib epinasty is due to an action of auxin other than through ethylene.

MOVEMENT AND DISTRIBUTION OF 14C WITHIN PETIOLES OF INTACT COLEUS BLUMEI (LABIATAE) AFTER APPLICATION OF INDOLE‐3‐(ACETIC ACID‐2‐14C) TO THE LEAF SURFACE

Auxin transport and immobilization were followed in the petioles of intact plants of Coleus blumei Benth. after application of IAA‐2‐14C at a physiological concentration as droplets to the upper surface near the base of the blades of leaves #3 and #5. After 14 hr transportable and immobilized radiocarbon was found all along the petioles. Moreover, about half the total amount of 14C detected within the plant (= uptake) had moved beyond the petioles. This was true for leaves of both ages although the younger #3 petioles were only about half as long as the older #5 petioles. Because the uptake of radiocarbon by the #3 petioles was roughly half that of the #5 petioles, the absolute amounts immobilized per unit length of section were essentially uniform in the two petioles. On the contrary, the fractions remaining transportable within the #3 petiole sections averaged half those of the #5 petiole sections. The distribution of the transportable and the immobilized radioactive fractions along the petioles was characterized by high values near the apical application point, a decrease toward the middle of the petioles, and an increase to the level of the apical part toward the base of the petioles, which includes the abscission layer. The results have been discussed in connection with measurements of the cross sectional areas and the lengths of the epidermal and subepidermal cells along the petioles. An auxin transport and immobilization model, which assumes there are two different immobilization systems of different strength in the differently aged tissues, is outlined to explain the observations.

Movement and Distribution of 14 C Within Petioles of Intact Coleus blumei (Labiatae) After Application of Indole-3-(Acetic Acid-2- 14 C) to the Leaf Surface

Auxin transport and immobilization were followed in the petioles of intact plants of Coleus blumei Benth. after application of IAA-2-14C at a physiological concentration as droplets to the upper surface near the base of the blades of leaves #3 and #5. After 14 hr transportable and immobilized radiocarbon was found all along the petioles. Moreover, about half the total amount of 14C detected within the plant (= uptake) had moved beyond the petioles. This was true for leaves of both ages although the younger #3 petioles were only about half as long as the older #5 petioles. Because the uptake of radiocarbon by the #3 petioles was roughly half that of the #5 petioles, the absolute amounts immobilized per unit length of section were essentially uniform in the two petioles. On the contrary, the fractions remaining transportable within the #3 petiole sections averaged half those of the #5 petiole sections. The distribution of the transportable and the immobilized radioactive fractions along the petioles was characterized by high values near the apical application point, a decrease toward the middle of the petioles, and an increase to the level of the apical part toward the base of the petioles, which includes the abscission layer. The results have been discussed in connection with measurements of the cross sectional areas and the lengths of the epidermal and subepidermal cells along the petioles. An auxin transport and immobilization model, which assumes there are two different immobilization systems of different strength in the differently aged tissues, is outlined to explain the observations.

THE TIME‐COURSE OF POLAR MOVEMENT OF GIBBERELLIN THROUGH ZEA ROOTS

The polarity of movement of gibberellin through sections cut from near the root tips of Zea mays L. was studied, using methods like those we previously used in roots for auxin and in petioles for auxins, cytokinins, and gibberellic acid (GA‐3). One μg GA‐3 was added in a donor agar block and gibberellin activity in the receiver agar at the opposite end of the section was measured directly with a modified barley endosperm bioassay. The movement of gibberellin was away from the root tip (basipetal) and thus opposite in direction to the polarity of auxin through such root sections. The time‐course of basipetal movement was dissimilar to that for gibberellin or auxin movement through petiole sections. It took 14‐18 hr for gibberellin activity equivalent to 6 ng GA‐3 to collect in the basal receivers on roots. Apical receivers showed activity equivalent to 1.6 ng GA‐3 at 14‐18 hr. Less than 0.01 ng equivalent GA‐3 was collected from sections to which GA‐3 was not added, so the 6 and 1.6 ng were almost entirely due to the added GA‐3. These general conclusions were confirmed with an experiment using 14C‐GA‐3. A decline in activity in receivers was found in some experiments at 18 hr, paralleling earlier results with GA‐3, IAA, and adenine in petioles and IAA in roots.