Effect of Gibberellic Acid on Dwarf and Normal Pea Plants

Gibberellic acid at concentrations between 10 and 100 mg/1 greatly stimulated the elongation growth of intact dwarf pea plant but showed little or no effect on that of Alaska pea. It showed no effect on the elongation growth of excised stem segments of either dwarf or normal pea when given alone. Indole-3-acetic acid stimulated the elongation of excised segments of both varieties. Gibberellic acid synergistically enhanced the indole-3-acetic acid-induced elongation of excised segments. Tryptophan also stimulated the elongation of these segments. Gibberellic acid showed a synergistic effect on the tryptophan-induced elongation, as on the indole-3-acetic acidinduced one. Gibberellic acid reduced the lag period of tryptophan-induced elongation, suggesting that gibberellic acid promotes the conversion of tryptophan to auxin.     

The Stimulation by Gibberellic Acid of Cell Wall Synthesis in the Dwarf Pea Plant

Gibberellic acid (GA) brought about an increase in the rateof dry-weight incorporation into expanding internodea of intactdwarf pea seedlings. The amount of water present in expandinginternodes was closely correlated with internode dry weight,and the slope of the relation was unaffected by GA treatment.It is proposed that the effect of GA upon internode expansionis mediated through the change in dry weight. Part of the increasein dry weight brought about by GA was attributable to an increasein the weight of cell wall material. The amount of water presentin expanding internodes was found to be correlated with theamount of wall material present. It is possible that the increasedrate of wall synthesis which follows GA treatment allows anincrease in the rate of cell expansion.     

Effects of Gibberellic Acid on Growth and Parthenocarpy in the Dwarf Telephone Pea

Growth in height and production of seedless pods wore studied in Dwarf Telephone pea seedlings treated with relatively large amounts of the potassium salt of gibberellic acid applied in solution to leaflets. Such treatment produced a saturation in growth in height with 2 mg or more per plant when the plants were allowed to grow to maturity. Larger amounts caused no inhibitory effects on growth. Maximum growth with 1 mg per plant was attained only if the treated leaflets were left on the plant for about 14 days, at least, but increasing numbers of weekly 10-mg applications produced no additional growth affects beyond two applications. Increasing age of plants from 10 to 59 days of age at the time of single 10-mg applications per plant resulted in decreasing final heights. Gibberellic acid caused the formation of seedless pods a number of weeks after application, and deformed flower petals, elongated peduncles, and conspicuously inflated pods were associated with seedlessness. GA was most effective in inducing parthenocarpy when applied to the first true leaves of young seedlings and became progressively less effective with age. A complete absence of seeds in pods formed on the main plant axis was produced by one application of 10 mg GA per plant, while six applications were required for the suppression of seed formation on side branches.     

Physiological Responses of Pea Plants to Salinity and Gibberellic Acid

Pea is a seed legume. It is rich in cellulose fibre and protein. It is also a significant source of minerals and vitamins. In this paper, we set out to better characterize the physiological responses of Pisum sativum L. to the combined effects of NaCl, 100 mM and gibberellins (GA3). Our analysis revealed that NaCl caused a decrease in growth resulting in a reduction in root elongation, distribution and density, leaf number and leaf area, and a decrease in dry matter of roots and shoots. However, the contribution of GA3 in the salty environment induced an increase in these different parameters suggesting an improving effect of this hormone on growth of pea in presence of salt. NaCl also led to a disturbance of the photosynthetic machinery. Indeed, level of chlorophyll pigments (a and total) and photosynthetic activity were decreased compared to the control plants. However, the exogenous supply of GA3 restored this decrease in net CO₂ assimilation, but not in chlorophyll content. Additional analyses were performed on the effect of salinity/GA3 interaction on osmolytes (soluble sugars and starch). Our results showed an increase in sugars and a decrease in starch in the presence of 100 mM NaCl. The salt-GA3 combination resulted in compensation of soluble sugar contents but not of starch contents, suggesting a beneficial effect of GA3 under saline stress conditions. Level of three main polyamines putrescine, spermidine, and spermine increased significantly in all organs of salt-treated plants.     

Gibberellic Acid and Starch Breakdown in Pea Cotyledons

The stimulation of starch breakdown in the cotyledons of dwarfpea cultivars (Progress No. 9 and Dark Skin Perfection) whentreated with gibberellic acid (GA³) is mediated through theremoval of metabolites by the axis. When applied to excisedcotyledons, GA³ had only a minor effect on starch breakdown,as it did in the cotyledons of a tall pea (cv. Alaska) irrespectiveof whether they were attached to the plant or excised. Enzyme activity appears to be controlled by the level of solublesugars in the cotyledons, and GA³delays the increase in amylolyticactivity in the cotyledons through a direct effect on cotyledonmetabolism.     

The Stability and Movement of Gibberellic Acid in Pea Seedlings

The stability and movement of gibberellic acid (GA) in intactdwarf pea seedlings growing in the light was studied by meansof both unlabelled GA and GA labelled with isotopic carbon (¹⁴C).After ¹⁴C-GA had been applied to the mature leaves of pea seedlingsmuch remained in association with the treated leaflets, but¹⁴C-GA was also extractable from the young shoots. The yieldwas approximately the same 5 to 96 hours after treatment. GApenetrated leaf surfaces only while the application solventwas moist (about 1 hour), but moved from the treated leafletsinto the shoots for at least 24 hours. Some hours after treatmentthere was an abrupt increase in the growth-rates of the plants,and crude estimates suggest that an effective dose of GA movedto the elongating tissue at about 5 cm/hr. The pattern of distributionof ¹⁴C was examined by autoradiography. The data suggest thatGA which enters the plant is redistributed from maturing leavesto immature leaves, passing through the elongating tissue, foras long as any of the substance is present. The hypothesis remainstenable that GA produces its growth effects by acting only uponexpanding tissue     

Pit-field Distribution in Relation to Cell Growth in Dwarf Peas, as Affected by Gibberellic Acid

Data are given relating cell length and pit-field frequencyto internode length, as influenced by the application of gibberellicacid. Both cell extension and cell division are affected, thelatter especially in internodes developing later after treatment.Where enhanced cell extension only occurs, existing pit-fieldsmerely become spaced out. Where cell division is involved, thisis accompanied by an increase in pit-field numbers so that daughtercells of the same type tend to have a characteristic number.This is in accordance with earlier observations on other plantsand confirms the suggestion made previously of the existenceof rather different patterns of cell-wall extension in dividing,as distinct from merely enlarging, cells.     

The Effect of Gibberellic Acid on Cell Width and the Cell-wall of Some Phloem Fibres

Treatment of plants of Cochorusoiltorius L., Hibiscus cannabinusL., and Cannabis sativa L. with gibberellic acid induced highlysignificant increases in cell diameter and wall thickness ofproblem fibres. This difference varies along the shoot and ismaximal in the middle region, internodes 10–15. The ratio is higher in treated plants. Gibberellic acid reduces the angle of orientation of the pits to the cellwall and also the pit frequency. Pits in treated plants arelonger and narrower in surface view.     

Effect of Gibberellic Acid and Ethylene on Peroxidase in Pea Internodes

Ethylene at 5–80 µl l^–1 inhibited elongationand induced swelling in internodes of light-grown normal anddwarf pea plants; GA₃ did not prevent swelling in response toethylene. GA₃ neither inhibited nor enhanced the activity of isoperoxidasesin the internodes, regardless of its effect on their elongation.Ethylene at 80 µl l^–1 enhanced peroxidase in GA₃-untreatedand treated normal and dwarf plants. At 5 µl l^–1,ethylene had only a weak effect on peroxidase activity or none.The enzyme enhancement by ethylene was not related to its effecton cell expansion and seems do be due, at least in part, tochemical injury. Electron microscopy revealed peroxidase activity in the roughER and cell walls, including intercellular spaces. Stainingof walls in ethylene-treated tissues was more pronounced thanin untreated ones. Golgi vesicles did not seem to be involvedin the assembly of the enzyme carbohydrate moiety in ethylene-treatedcells. The peroxidase fraction extracted with 20 mM phosphate buffer,pH 6, and that extracted from wall debris with 1 M NaCl accountedfor 98% of total enzyme activity. Both fractions contained thesame six cathodic isoforms which comprised 85–90% of theiractivity. Electrophoresis did not reveal differences in thequalitative isoenzyme patterns in relation to variety, age,GA₃, or ethylene. The only observed quantitative differenceswere age-dependent. Procedural artefacts during separation of protoplast and wallionically bound peroxidase fractions are discussed.     

Gibberellic Acid-Promoted Lignification and Phenylalanine Ammonia-lyase Activity in a Dwarf Pea (Pisum sativum)

The effects of gibberellic acid on lignification in seedlings of a dwarf and a tall cultivar of pea (Pisum sativum) grown under red or white light or in the darkness, were studied. Gibberellic acid (10⁻⁶-10⁻⁴ m) promoted stem elongation in both light and dark and increased the percentage of lignin in the stems of the light-grown dwarf pea. The gibberellin had no effect on the lignin content of the tall pea although high concentrations (10⁻⁴ m) promoted growth of the tall plants. Time course studies indicated that the enhanced lignification in the gibberellin-treated dwarf plants occurred only after a lag period of several days. It was concluded that gibberellic acid-enhanced ligmification had no direct relation to gibberellic acid-promoted growth. The activity of phenylalanine ammonia-lyase (E.C. 4.3.1.5) was higher in gibberellin-treated dwarf plants grown under white or red light than in untreated dwarf plants. Gibberellic acid had no detectable effect on the activity of this enzyme when the plants were grown in darkness, just as it had no effect on lignification under dark conditions. The data suggest that in gibberellin-deficient peas the activity of phenylalanine ammonia-lyase is one of the limiting factors in lignification.     

The Promotion of Indole-3-acetic Acid Oxidation in Pea Buds by Gibberellic Acid and Treatment

Terminal buds of dark-grown pea (Pisum sativum) seedlings have an indole-3-acetic acid oxidase which does not require Mn(2+) and 2,4-dichlorophenol as cofactors. Oxidase activity is at least 50 times higher in buds of tall peas than in dwarf seedlings. Administration of gibberellic acid to dwarf peas stimulates both growth and indoleacetic acid oxidase activity to the same levels as in tall seedlings. By contrast, indoleacetic acid oxidation assayed in the presence of Mn(2+) and 2,4-dichlorophenol proceeds at similar rates regardless of gibberellin application. Treatment of tall peas with the growth retardant AMO-1618 reduces growth and oxidase activity. Such treated seedlings are indistinguishably dwarf. The enzyme does not appear to be polyphenol oxidase, nor do the results suggest that reduced activity in dwarf buds is due to higher levels of a dialyzable inhibitor. The peroxidative nature of the oxidase is probable.     

Relations between DNA, RNA and Protein Synthesis, and the Cellular Basis of the Growth Response in Gibberellic acid-Treated Pea Internodes

1. A study was made of the influence of gibberellic acid (GA₂)on nucleic acid, protein, and cell-wall synthesis in pea internodesin vivo. 2. GA₃-treated fifth internodes finally contained more thantwice as much total RNA and protein as comparable untreatedones, and the contents of RNA and protein were closely relatedto the length of internode cortical cells. 3. Cell elongation, RNA, protein, and cell-wall synthesis werestimulated 24–48 h before there was any demonstrable GA₃effect on DNA synthesis and cell division. 4. Treated fifth internodes finally contained twice as manycortical cells as control internodes, a response that was matchedby a proportionate increase in the amount of DNA. 5. Internodes treated with actinomycin D or cycloheximide failedto elongate in response to GA₃ treatment, indicating that bothRNA and protein synthesis are essential for gibberellin-stimulatedcell elongation to occur in this tissue. 6. 5-fluorodeoxyuridine at concentrations which completely blockcell division did not prevent cells from elongating in the presenceof GA₃. 7. With the possible exception of pectic substances there wasno change in the relative proportions of each of the major cell-wallconstituents in treated, as compared to control internodes.     

The Distribution of Substances similar to Gibberellic Acid in Higher Plants

Gibberellic-acid-like substances have been found in extractsfrom all parts of seedlings of tall and dwarf peas and in matureseeds of wheat, French bean and tall and dwarf peas. They werepresent in amounts equivalent to o‘1–0’3 µg-gibberellicacid in 100 plants (F.W. 100–200 g.). Immature runnerbean seed yielded larger quantities, equivalent to 0.25 µg.gibberellic acid per gram fresh weight, distributed betweentestas, cotyledons, and embryos.     

Growth and Nitrogen Accumulation in Young Tomato Plants Treated with Gibberellic Acid

The effects of foliar sprays of gibberellic acid (GA) on thegrowth of tomato plants cv. Potentate were studied in growthrooms and a glasshouse. Four sprays of GA (5 ppm) increasedleaf area and whole plant weight relative to water controlsgrown at constant temperatures (7, 17, 22, and 27 °C) for12 days, the largest plants being obtained with 5 ppm. Experimentsmade at four photoperiods (5, 10, 15, and 20 h) and at two lightintensities (7000 and 10 750 lx) showed that GA increased leafand whole plant weight at 15 h, leaf area at 10 and 15 h andstem height at all photoperiods; area, height, and weight increaseswere obtained at both light intensities, leaf growth being increasedmore by GA at 7000 lx and stem growth more at 10 750 lx. Four foliar sprays of GA (5 ppm) were combined with N supplementsapplied via leaf and/or root to plants in sand culture. Withlow supply to the roots (20 ppm N) GA failed to increase growth,but increased it at higher levels. Total N in leaf and stemwas increased by GA or by NH₄NO₃ (10 sprays 280 ppm N) at alllevels of N supplied to roots, but when applied together theeffect on total leaf N was more than additive except at thehighest level (540 ppm) GA increased the concentration of N(as per cent dry matter) in leaf and stem at all levels of Nsupplied to roots. GA and NH₄NO₃ together resulted in a greateramount and a higher concentration of N in the shoots (and usuallyalso in roots) than did NH₄NO₃ alone. Leaf thickness (as freshweight/unit area) could only be increased appreciably by sprayingwith a complete nutrient solution which reduced leaf area butnot dry weight. Growth increases induced by GA were detectable 43 days afterthe first of four sprays in the glasshouse and after 30 daysin the growth room. The persistence of GA effects was comparedwith those induced by sprays of NH₄NO₃.     

Effect of Protein Synthesis Inhibitors, Auxin, and Gibberellic Acid on Abscission

Chloramphenicol, actinomycin D, and other inhibitors of protein synthesis promote abscission in several plant genera. Abscission is accelerated in species where an abscission layer is present, as well as in tissue where no abscission layer develops prior to abscission. The inhibitors promote abscission in species where cell division is reported to precede the separation processes as well as in tissues where no cell division is associated with the initiation of abscission. Indoleacetic acid (IAA) or auxin precursors, when applied with chloramphenicol and aclinomycin D, overcome the promotive effects of the inhibitors on abscission. These inhibitors apparently do not promote abscission through their effects on auxin precursor conversion, IAA transport, and IAA destruction in the petiole. IAA increases the incorporation of leucine-1-¹⁴C into a trichloroacetic acid precipitable fraction of the abscission zone under conditions where abscission is retarded. A low concentration of IAA which accelerates abscission, decreases incorporation of leucine into protein. Other promoters of abscission — chloramphenicol, d-aspartic acid, and gibberellic acid —also decrease the incorporation of leucine into the protein of the abscission zone. The data indicate that enzymes required for the degradative processes associated with abscission are already present in the abscission zone whereas a continuous synthesis of protein is required for the retention of the leaf.     

Stimulation of Endomitotic DNA Synthesis and Cell Elongation by Gibberellic Acid in Epicotyls Grown from Gamma-irradiated Pea Seeds

Large doses of γ-irradiation, given to air-dried pea seeds, inhibit the endomitotic DNA synthesis in pea epicotyls during germination in darkness. The cortex cells of the etiolated epicotyls reach only the 4 C DNA level, whereas cortex cells of unirradiated seeds reach the 8 C DNA level. Epicotyl elongation and cell elongation are also reduced.