Influence of growth regulator treatments on dry matter production,fruit abscission,and14C-assimilate partitioning in citrus

Experiments were performed to monitor (1) uptake and translocation of foliar-applied microdroplets of¹⁴C hormones and (2) effects of multiple growth regulator sprays on foliar and fruit growth variables and photosynthate partitioning in Valencia orange trees (Citrus sinensis (L.) Osbeck). The uptake of¹⁴C-sucrose,¹⁴C-paclobutrazol (PP333), and¹⁴C-napthaleneacetic acid (NAA) in 6-month-old greenhouse-grown trees exceeded that of¹⁴C-abscisic acid (ABA) and¹⁴C-benzyladenine (BA) 48 h after microdroplet application.¹⁴C-sucrose transport from the application site was much greater than any other source, especially¹⁴C-BA. In a second study, 2-year-old Valencia orange trees were maintained under field conditions and were sprayed to foliar runoff (3 × /week for 3 weeks) with BA, NAA, ABA, PP333, and gibberellic acid (GA₃) at 100 M during flowering and early fruit set. Select branches were then briefly exposed to¹⁴CO₂ and harvested 24 h later. Both GA₃ and BA sprays promoted foliar growth. BA also stimulated fruit growth, whereas GA₃ sharply increased fruit dry weight while fruit number decreased. BA and GA₃ enhanced¹⁴C assimilate export by the foliage to the developing fruit, and GA₃ was especially active in promoting fruit sink intensity (¹⁴C/dry wt). The other compounds (NAA, ABA, PP333) restricted foliar and fruit growth. They also inhibited transport of¹⁴C assimilate from the leaves to the fruit. Results indicate that foliar-applied growth regulators can influence source-sink relations in citrus early in reproductive development by manipulating photoassimilate production and partitioning.     

Responses of ivy (Hedera helix L.) to combinations of gibberellic acid,paclobutrazol and abscisic acid

A reduction in concentration of gibberellins has been implicated in the phase change from juvenile to mature forms of ivy (Hedera helix L.). Attempts were made to increase the effective internal concentration of gibberellins by exogenous application of GA₃, and to decrease them by various applications of abscisic acid (ABA) and paclobutrazol (PP333), alone or in combination with GA₃. ABA and GA₃ were fed directly into the xylem of ivy plants by a wick system (a less drastic procedure than the defoliation or decapitation used by earlier workers) whereas PP333 was applied as a soil drench.Mature ivy responded to the application of GA₃ by reversion to the juvenile form, although this reversion was incomplete with respect to leaf lobing and red (anthocyanin) pigmentation and could occur spontaneously without the application of GA₃. Contrary to expectation, applications of ABA and PP333 caused the stimulation of growth in juvenile ivy. No adult characteristics were induced. As similar concentrations of ABA and PP333 produced severe retardation of growth (which could be alleviated by the application of GA₃) in other species, it is suggested that ivy may be an unsuitable model system for the investigation of phase change in woody plants.     

Embryogenesis and plant regeneration from unpollinated ovary culture of <Emphasis Type="Italic">Psoralea corylifolia</Emphasis>

Embryogenesis and plant regeneration was achieved from callus cultures derived from unpollinated ovaries of Psoralea corylifolia L. Callus was initiated from unpollinated ovaries on Murashige and Skoog (MS) medium supplemented with 2.2 μM N ⁶-benzyladenine (BA) and various concentrations of α-naphthaleneacetic acid (NAA (2.7 to 10.7 μM) or 2,4-dichlorophenoxyacetic acid (2,4-D (2.3 to 9 μM) alone or in combination. Highly organized embryogenic callus induction, embryo development, proliferation and maturation were achieved on transfer of callus clumps to MS medium supplemented with NAA (0.27 μM) or 2,4-D (0.23 μM) alone or in combination with BA (2.2 to 8.8 μM). Addition of abscisic acid (ABA) (0.95 to 5.8 μM) to the medium enhanced average numbers of cotyledonary stage embryos, the maximum number (34.6 ± 0.7) being obtained on MS medium containing 0.27 μM NAA, 2.2 μM BA and 3.8 μM ABA. Embryos germinated on MS medium supplemented with BA (0 to 8.8 μM). MS medium containing gibberellic acid (GA₃ (0.29 to 5.8 μM) enhanced embryo germination frequency, the highest frequency (66.7 %) occurring on MS medium containing 2.2 μM BA and 4.3 μM GA₃. Effect of several concentrations (3.0 to 6.0 %) of sucrose or maltose was also observed on germination of embryos. MS medium enriched with maltose supported high frequency of embryo germination.     

Long-term effects of plant hormones on K+ levels and transport in young wheat plants of different K+ status

Long-term effects of 1-naphtaleneacetic acid (NAA), benzyladenine (BA), gibberellic acid (GA₃), abscisic acid (ABA) and ethylene on K⁺ levels, K⁺ uptake and translocation to the shoot were studied in young wheat plants (Triticum aesticum L. cv. Martonvásári-8) grown at different K⁺ supplies. Na⁺ levels and K⁺/Na⁺ selectivity were also investigated. Both in shoots and roots, NAA, BA and ABA decreased K⁺ and Na⁺ levels more effectively in high-K⁺ plants than in low-K⁺ plants. GA, and ethylene did not influence K⁺ and Na⁺ levels. K⁺/Na⁺ selectivity in roots of low-K⁺ plants was increased in favour of K⁺ by BA, NAA and to a lesser extent by ABA. In high-K⁺ plants only BA increased the K⁺/Na⁺ ratio, whereas the effects of the other hormones were the opposite (NAA) or less pronounced (ABA). K⁺(⁸⁶Rb) uptake was inhibited by NAA and BA in low-K⁺ plants but not in high-K⁺ plants. K⁺(⁸⁶Rb) uptake was inhibited throughout by 10 μM ABA. K⁺(⁸⁶Rb) translocation to the shoot was influenced by the hormones similarly to the uptake patterns, with the exception of ABA, which inhibited translocation in low-K⁺ plants but not in high-K⁺ plants. The results show that hormonal effects may quantitatively and qualitatively be modified by K⁺ levels in the plant and that internal K⁺ concentration may play a role in the mechanisms regulating the effects of NAA, BA and ABA but probably not in those of GA₃ or ethylene.     

The effect of plant growth regulator treatments on the levels of ethylene emanating from excised turgid and wilted wheat leaves

Abscisic acid (ABA) inhibits the production of ethylene induced by water stress in excised wheat leaves and counteracts the stimulatory effect of 6-benzyladenine (BA) on this process. The stimulatory effect of BA and the inhibitory effect of ABA were equally pronounced whether external or endogenous ethylene levels were determined. When leaves were sprayed or floated on solutions of BA, indole-3-acetic acid (IAA), gibberellic acid (GA₃), or ABA, the relative activities of these growth regulators on stress-induced ethylene at 10^-4 mol l^-1 were BA>IAA >GA₃>controls>ABA. In non-stressed leaves, however, where the levels of ethylene produced were 2–20 times smaller, the relative activities were IAA >BA>GA₃>controls>ABA. The effects of BA and ABA spray treatment on water stress induced ethylene were closely similar whether the solutions were applied 2 or 18 h prior to the initiation of water stress. The relationships between the levels of endogenous growth regulators in the plant and ethylene release induced by water stress are discussed.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - GA₃ gibberellic acid - ABA abscisic acid - GLC gas-liquid chromatography - _leaf leaf water potential     

The Interaction of Plant Growth Regulators and Vernalization on the Growth and Flowering of Cauliflower (Brassica oleracea var. botrytis)

The growth and flowering response of a cold-requiring cauliflower (Brassica oleracea var. botrytis cv. 60 day) to a range of temperatures under 10 h photoperiod and to growth regulator application were investigated. Endogenous gibberellin A₁(GA₁) concentrations were also assessed under these treatments. Flowering and growth of the inflorescence stalk were correlated with plant developmental stage at the time of a vernalizing cold treatment. Temperature and its duration also affected flowering and inflorescence development. The most effective temperature for inflorescence induction was 10 °C. Flowering did not occur in non-vernalized plants (25 °C) even though they had been treated with GA₃. Application of GA₃ promoted inflorescence stalk elongation greatly in vernalized plants (10 °C), but less so in partially vernalized plants (15 °C or 20 °C). Paclobutrazol (PP₃₃₃) sprayed at the 8–9 leaf stage significantly suppressed inflorescence stalk length and slightly delayed flower bud formation and anthesis. Vernalization at 10 °C increased endogenous GA₁ content in both leaves and the inflorescence stalk irrespective of GA₃ or PP₃₃₃ treatment. Application of GA₃ tended to increase GA₁ levels, while PP₃₃₃ significantly reduce GA₁, both irrespective of vernalization. Vernalization is an important factor for flowering, but not curd formation in this cauliflower cv. 60 day and GA₁ is likely a causal factor in inflorescence stalk elongation.     

Influence of plant growth regulators and water stress on ramet induction,rosette engrossment,and fructan accumulation in <Emphasis Type="Italic">Agave tequilana</Emphasis> Weber var. Azul

Agave tequilana Weber var. Azul plants reproduce asexually by producing ramets. Continuous production of ramets throughout the vegetative cycle of the parent delays the time of harvesting of heads for tequila production. Little is known about the factors influencing their emergence. Heads are engrossed rosettes where fructans are stored. We show here that, in plantlets grown in vitro, growth regulators such as 2,4-dichlorophenoxyacetic acid (2,4-D), a combination of 1-naphthaleneacetic acid (NAA)/6-benzyladenine (BA), or abscisic acid (ABA) increased the production of ramets, whereas BA, NAA, gibberellic acid (GA₃), glycerol, or a combination of glycerol/ABA decreased ramet production. Plantlets that developed ramets did not form heads. Head formation was improved on solid media in the presence of BA, NAA, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), or the water stress inducer polyethylene glycol (PEG). Basal Murashige–Skoog (MS) liquid media also enhanced rosette engrossment, which was further increased by addition of ACC or PEG. In contrast, CoCl₂, an ethylene biosynthesis inhibitor, reduced rosette engrossment. Furthermore, heads from A. tequilana plantlets grown in tissue culture in MS media, or in MS media supplemented with NAA, ACC or PEG, showed fructan concentrations 10–30 times higher than in leaves from greenhouse-grown plants. Our results indicated that BA, NAA, water stress, and ethylene are critical regulators of rosette engrossment, whereas asexual reproduction in A. tequilana seems to be controlled by a complex hormonal network.     

Micropropagation of Albuca bracteata and A. nelsonii — Indigenous ornamentals with medicinal value

In this study, two species from the genus Albuca (Hyacinthaceae) with ornamental and medicinal properties were micropropagated. Adventitious bulblets of Albuca bracteata were cut into quarters and used as explants to examine the effect of temperature (10, 15, 20, 25, 30 or 35 °C), carbohydrates (glucose, fructose or sucrose at 0, 87.5, 175, 262.5 or 350 mM) and hormones (BA, mTR, NAA, IAA, GA₃, ABA or methyl jasmonate each at 0, 0.1, 1.0 or 5.0 mg/L) on the induction and growth of bulblets. Temperatures above 35 °C completely inhibited bulb formation, while induction at all other temperatures was high. Heaviest and largest bulbs formed at 20 °C. Low concentrations (87.5 mM) of all tested carbohydrates increased bulb induction compared to media without a carbohydrate source, while higher levels decreased bulblet induction. The cytokinins mTR and BA inhibited bulb induction, diameter and mass at moderate (1.0 mg/L) and high (5.0 mg/L) concentrations. GA₃, NAA and particularly IAA promoted bulblet induction, while ABA and methyl jasmonate had no significant effect on the induction or bulblet growth. Leaf material and young inflorescences of A. nelsonii were removed, decontaminated, and dissected into seven explant types: leaves, peduncles, pedicels, whole flowers, tepals, ovaries and anthers. These were placed on MS media without hormones, or containing 0.5 mg/L mTR, 0.5 mg/L NAA or 0.5 mg/L mTR + 0.5 mg/L NAA to establish which explant type and hormone combination promoted shoot formation. Some tepal and pedicel explants were capable of shoot production on media with both mTR and NAA, but peduncle explants produced the most shoots when mTR and NAA were both present in the culture medium. Flowers, leaves, ovaries and anthers were completely unresponsive, irrespective of medium composition. These techniques will aid the further horticultural development of these plants, and can be easily adjusted for other species within the genus to promote conservation.     

Evidence for the accumulation of a germination inhibitor during progressive thermoinhibition of seeds of celery (Apium graveolens L.)

The germination of seeds of celery (Apium graveolens L.) becomes progressively thermoinhibited on incubation in the dark at high temperatures, the inhibitory temperature being dependent on the cultivar used. In two high-dormancy cultivars of celery, the production of germination inhibitors in seeds incubated in the dark at 26°C gradually increased over a 7-day period. Inhibitor production was measured by incubating seeds of the low-dormancy cultivar Florida 683 in homogenates of the thermoinhibited seeds of the high-dormancy cultivars and recording germination either in the light or with the gibberellins A₄ and A₇ (GA_4/7) in the dark. Most Florida 683 seeds which failed to germinate in the homogenates after 15 days were induced to germinate by addition of N⁶-benzyladenine (BA). The presence of BA in addition to GA_4/7 throughout incubation in the dark completely overcame the inhibitory effects of homogenates. This indicates that thermoinhibition of celery seeds is associated with the accumulation of a germination inhibitor which interacts with cytokinins. This does not appear to be abscisic acid (ABA) since ABA levels in thermoinhibited seeds were lower than in untreated seeds and did not increase with duration of high temperature treatment.Abbreviations ABA Abscisic acid - BA N⁶-benzyladenine - GA_4/7 a mixture of the gibberellins A₄ and A₇ - HTP high-temperature pretreatment     

Efficient in vitro germination and shoot proliferation of chilling-treated water chestnut (Trapa japonica Flerov) embryonal explants

Summary Embryonal explants from water chestnut (Trapa japonica Flerov) seeds germinated with high efficiency following a 40-d cold treatment at 5°C on half-strength MS (Murashige and Skoog) medium supplemented with 2.7 μM N⁶-benzyladenine (BA), 0.5 μM 1-naphthaleneacetic acid (NAA) and 0.5 μM gibberellic acid (GA₃). Control and chill-treated (different durations) embryonal explants were cultured onto media which contained half-strength MS medium supplemented with different concentrations and combinations of cytokinins [BA, thidiazuron (TDZ), kinetin, zeatin], auxin (NAA) and GA₃. A liquid half-strength MS medium with 1.1 μM BA and 0.5 μM NAA resulted in the best shoot proliferation of control or chill-treated explants, and the addition of 0.5 μM GA₃ stimulated axillary shoot elongation. Germination and shoot proliferation were always greater for chill-treated explants compared with control explants under the same culture conditions. Shoots produced in vitro rooted 100% of the time in a liquid half-strength MS medium with 1.1 μM BA, 0.5 μM NAA and 1.1 μM indole-3-butyric acid, and the regenerated plantlets were established successfully in a water chestnut paddy field.     

Antagonistic Changes between Abscisic Acid and Gibberellins in Citrus Fruits Subjected to a Series of Different Water Conditions

The relationship between absicisic acid (ABA) and gibberellin (GA) changes in developing fruitlets from both Clementina (Citrus clementina, Hort ex Tan) and Okitsu (Citrus unshiu, (Mak) Marc.) trees subjected to changing water conditions was investigated. The treatments consisted of a series of water stress, rainfall, and re-irrigation periods. To confirm the effectiveness of the imposed water changes, leaf water potential and soil moisture were measured. The data indicated that there were antagonistic changes between ABA and GA₂₀, because in both species ABA increased and GA₂₀ decreased during water stress, whereas re-hydration via either rainfall or irrigation reduced ABA but increased GA20. In addition, the data indicated that during water stress GA1 also decreased, whereas GA₈ did not change. After re-hydration, however, levels of GA₂₀ products, in general were rather dependent upon the hormonal levels induced in the previous water status. In conclusion, the results showed the occurrence of antagonistic changes between the levels of ABA and GA₂₀ in developing citrus fruitlets subjected to changing water conditions. The data might suggest that gibberellin 20-oxidase is regulated by water stress in citrus fruits.     

Cold-acclimation induced changes in freezing tolerance and translatable RNA content in Citrus grandis and Poncirus trifoliata

Cold-acclimation-induced changes in freezing tolerance and translatable RNA content were compared in seedlings of a relatively cold sensitive citrus species, Citrus grandis L. Osb. cv. Thong Dee (pummelo), and the cold-hardy citrus relative, Poncirus trifoliata L. Raf. cv. Pomeroy (trifoliate orange). Cold acclimation of pummelo (10 days at 15°C followed by 4 weeks at 10°/5°C, day/night) resulted in a decrease in LT₅₀ from −6 to −8°C, while in trifoliate orange (acclimated for 7 weeks at 5°C), the LT₅₀ decreased from −9 to −18°C. Qualitative changes in the in vitro translation profile, revealed by two-dimensional gel electrophoresis, were observed following cold acclimation in both species. An mRNA for a large polypeptide (ca 160 kDa) was detected following cold acclimation of trifoliate orange. A similar change was not observed in pummelo following cold acclimation.     

Plant regeneration from pea protoplasts via somatic embyogenesis

Plant regeneration via somatic embryogenesis was obtained from pea protoplasts. Strong auxins (picloram or 2.4-D) and increased osmolarity of the medium were necessary for embryo induction. Relatively high amounts of embryogenic calli could be obtained in 2 genotypes. After a period on hormone-free medium, a second induction of somatic embryos was possible. Further development of somatic embryos was accomplished on GA₃ — containing medium.Abbreviations ABA abscisic acid - BA 6-benzylaminopurine - 2.4-D 2.4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - Kin kinetin - NAA naphthaleneacetic acid - Pic Picloram, 4-amino-3,5,6-trichloropicolinic acid     

The reduction of naringin content of grapefruit by applications of gibberellic acid

Four different plant growth regulators, gibberellic acid (GA₃), naphthaleneacetic acid (NAA), benzyladenine (BA) and abscisic acid (ABA), were individually mixed in a lanolin paste and applied to immature fruit on grapefruit trees beginning soon after fruit set. The treated fruit was allowed to mature on the tree. Application of 1000 ppm GA₃ in this manner generally increased fruit size, decreased the concentration of the total acid in the juice and decreased the concentration of naringin in the juice sacs compared to that of the controls. GA₃ increased the total soluble solids (brix) in the juice in some experiments. Treatment of fruit with 1000 ppm ABA and BA significantly decreased the size of the fruit and increased the naringin concentration, but had variable effects on the soluble solids content and the acid content. Treatment with 1000 ppm NAA did not produce any significant changes in size, acid content, brix or naringin concentration.RetiredReference to a company or product name does not imply approval or recommendation of the product by the U.S. Department of Agriculture to the exclusion of other products that may be suitable.     

<Emphasis Type="Italic">Ptcorp</Emphasis> gene induced by cold stress was identified by proteomic analysis in leaves of <Emphasis Type="Italic">Poncirus trifoliata</Emphasis> (L.) Raf.

A proteomic approach was employed to investigate the cold stress-responsive proteins in trifoliate orange (Poncirus trifoliata (L.) Raf.), which is a well-known cold tolerant citrus relative and widely used as rootstock in China. Two-year-old potted seedlings were exposed to freezing temperature (−6°C) for 50 min (nonlethal) and 80 min (lethal), and the total proteins were isolated from leaves of the treated plants. Nine differentially accumulated proteins over 2-fold changes in abundance were identified by two-dimensional gel electrophoresis and mass spectrometry. Among these proteins, a resistance protein induced by the nonlethal cold treatment (protein spot #2 from P. trifoliata) was selected as target sequence for degenerated primer design. By using the designed primers, a PCR product of about 700 bp size was amplified from P. trifoliata genomic DNA, which was further cloned and sequenced. A nucleotide sequence of 676 bp was obtained and named Ptcorp. Blast retrieval showed that Ptcorp shared 88% homology with an EST of cold acclimated Bluecrop (Vaccinium corymbosum) library (Accession number: CF811080), indicating that Ptcorp had association with cold acclimation. Semiquantitative RT-PCR analysis demonstrated that Ptcorp gene was up-regulated by cold stress which was consistent with the former result of protein expression profile. As the resistance protein (NBS-LRR disease resistance protein family) gene was up-regulated by cold stress in trifoliate orange and satsuma mandarin, it may imply that NBS-LRR genes might be associated with cold resistance in citrus.     

ABA and GA3 affect the growth and pigment composition in Andrographis paniculata Wall.ex Nees., an important folk herb

In this study, 5 μmol·L⁻¹ abscisic acid (ABA) and gibberellic acid (GA₃) were used to study the effect of both growth regulators on the morphological parameters and pigment composition of Andrographis paniculata. The growth regulators were applied by means of foliar spray during morning hours. ABA treatment inhibited the growth of the stem and internodal length when compared with control, whereas GA₃ treatment increased the plant height and internodal length. The total number of leaves per plant decreased in the ABA-treated plants, but GA₃ treatment increased the total number of leaves when compared with the control. Both growth regulators (ABA and GA₃) showed increased leaf area. ABA and GA₃ treatments slightly decreased the total root growth at all the stages of growth. The growth regulator treatments increased the whole plant fresh and dry weight at all stages of growth. ABA enhanced the fresh and dry weight to a larger extent when compared with GA₃. An increase in the total chlorophyll content was recorded in ABA and GA₃ treatments. The chlorophyll-a, chlorophyll-b, and carotenoids were increased by ABA and GA₃ treatments when compared with the control plants. The xanthophylls and anthocyanin content were increased with ABA and GA₃ treatments in A. paniculata plants.     

Involvement of phytohormones in germination of dormant and non-dormant oat (Avena sativa L.) seeds

Oat seeds are susceptible to high temperature dormancy. Dormant grainsdo not germinate at 30 °C unless afterripened, dry, for severalweeks. Isolated embryos of dormant grains do germinate, especially ifGA₃ is added to the germination medium. ABA inhibits germinationproportionally to the concentration applied and GA₃ can overcome theABA inhibitory effect. Measurements of endogenous ABA and several GAs revealedthat the initial levels of ABA in dormant and non-dormant grains were quitesimilar. But, endogenous ABA in non-dormant seeds almost disappeared within thefirst 16 h of imbibition, while the amount in dormant grains haddecreased by less than 24%. The level of GA₁₉ in non-dormant seedswas higher, and GA₁₉ appears to be converted to GA₂₀ within the first 16h. The GA₂₀ was converted to GA₁ at leastduring the first 48 h of the germination process. Bothphytohormones thus appear to be involved in the germination process ofnon-dormant seeds. ABA first declines, while GA₁ is producedduring the first 16 h of imbibition to allow proper germination.Indormant grains the level of ABA remained high enough to prevent germinationduring at least a week and precursor GAs were not converted to GA₁.