Fruit Malformation of Satsuma Mandarin (Citrus unshiu Marc.) Infected by Citrus Yellow Vein Clearing Virus

In 2013–2014, malformed young Satsuma mandarin (Citrus unshiu Marc.) fruits were found in Xunwu County, Jiangxi Province, China. Common disease symptoms include slightly curled and backward‐twisted spring leaves, cracked and deformed leaf edges, thickly grown spring twigs with twisted and slightly bent shoots, and malformed young fruits where groovelike depression forms from the upper portion and resembles a pumpkin. On the basis of the morphological characteristics, sequencing results and phylogenetic analysis of the infected plant, we identified the disease as citrus yellow vein clearing, which is caused by Citrus yellow vein clearing virus (CYVCV). To our knowledge, this study is the first to report CYVCV infecting Satsuma mandarin.     

Alleviation of salt stress by plant growth regulators in Triticum aestivum L.

Seedlings of the salt sensitive wheat cultivar C-306 evolved more ethylene than the salt tolerant cultivar Kharchia-65 under different levels of both chloride- and sulphate-dominated types of salinity. Pre-sowing seed soaking treatments with kinetin, gibberellic acid and to a lesser extent indole-3-acetic acid alleviated salt stress effects as apparent from seedling dry mass. Treated seedlings also evolved more ethylene both under saline and non-saline conditions. Ethrel did not affect seedling growth as well as ethylene production. Abscisic acid inhibited seedling growth and ethylene production under both types of salinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Arginase activity in the cotyledons of soybean seedlings

The influence of naphthylacetic acid, abscisic acid, gibberellic acid and kinetin on the formation of aerenchyma in seedling roots of Zea mays L. cv. Capella has been studied in relation to reported changes of their concentration in poorly aerated roots, which readily form aerenchyma, and to the effects of these hormones on the production of ethylene, a major factor promoting aerenchyma formation. Because the absence of nitrate accelerates aerenchyma formation in aerated roots, their influence on these roots was compared. The growth regulators were added to roots growing in non-aerated and aerated nutrient solutions, and aerenchyma formation and the production and endogenous concentration of ethylene were measured. Naphthylacetic acid prevented aerenchyma formation in both aerated roots without nitrate and in non-aerated roots although it enhanced the ethylene concentration of the roots. Abscisic acid also prevented aerenchyma formation, but without affecting the ethylene concentration. Gibberellic acid promoted aerenchyma formation in aerated roots only, but ethylene production in both aerated and non-aerated roots. Kinetin promoted aerenchyma formation in both aerated and non-aerated roots. It stimulated ethylene production in aerated roots, but slightly inhibited it in non-aerated roots. Co²⁺ and Ag⁺, which suppress ethylene production and action, respectively, reduced the promoting effects of gibberellic acid, but not those of kinetin. It is concluded that the effects of the plant growth regulators on aerenchyma formation in maize roots were, with a possible exception for gibberellic acid, not the result of altered ethylene concentrations in the roots. Their influence on aerenchyma formation is discussed in relation to their reported actions on cell membranes.     

Maintenance of the diurnal petiolar movement by exogenous indole-3-acetic acid under day-night cycles in Mimosa pudica

Effects of plant hormones on the diurnal movement of the petiole of Mimosa pudica L. were examined under the conditions of day-night cycles. Surgical removal of the leaf at the middle of the petiole led to gradual loss of the movement. Aqueous solutions of indole-3-acetic acid (IAA) applied as a pulse each day 10 μl at (10⁻⁶−10⁻⁵ M ) or continuously (10⁻⁸−10⁻⁶ M ) to the cut end of the petiole maintained a diurnal movement that has the same phase of oscillation as that shown in the intact leaf. Pulse treatments given at different times of the day had no effect on the phase of the oscillation. Higher concentrations of the acid gave larger amplitudes. Other hormones such as gibberellic acid, kinetin and [R,S]-abscisic acid or 1-aminocyclopropane-1-carboxylic acid did not show diurnal movement-maintaining activities of IAA. Gibberellic acid disturbed the phase of the diurnal movements and kept the petiole elevated at very high positions. A possible action mechanism of IAA is discussed.     

Low temperature influence on flowering in Citrus. The separation of inductive and bud dormancy releasing effects

The flowering response of Owari Satsuma mandarin ( Citrus unshiu Marc) to low temperature treatments has been determined using potted trees and in vitro bud cultures. In potted trees the chilling treatments released bud dormancy and enhanced both sprouting and flowering, but these two responses could not be separated. However, bud cultures showed no dormancy, and a specific effect of low temperature on flower induction was demonstrated. Low temperature appears to have a dual effect, releasing bud dormancy and inducing flowering. Potential flower buds have a deeper dormancy than vegetative buds, and the first stages of flower initiation seem to occur before the winter rest period.     

Effects of growth regulators on fatty acids of soybean suspension cultures

Soybean suspension cultures were grown for 24 weeks in the absence of plant growth regulators and in the presence of 1 ppm levels each of an auxin (indole-3-butyric acid), a cytokinin (kinetin) and a gibberellin (gibberellic acid), individually and in all possible combinations. Cells grown in the presence of the auxin with and without gibberellin contained relatively greater amounts of palmitic and smaller amounts of polyunsaturated acids than did cells grown under other regimens. The combination of cytokinin and gibberellin caused a higher proportion of linoleic and a lower proportion of linolenic acids than in cells of the other groups. Neither of these regulators by itself produced the effect, and addition of auxin to the other two diminished the effect.     

The effect of some growth regulators on light-induced germination of Paulownia tomentosa seeds

Grubišié, D., Konjevié, R. and Neškovié, M. 1988. The effect of some growth regulators on light-induced germination of Paulownia tomentosa seeds. - Physiol. Plant. 72: 525–528.
The germination of Paulownia tomentosa Steud. (Empress tree) seeds can be induced either by red light (R) or by exogenously applied gibberellic acid (GA₃). The R induced germination is completely suppressed by far red irradiation, abscisic acid (ABA) or by growth retardants such as ancymidol, tetcyclacis and paclobutrazol, though not by AMO 1618 or chloro-choline chloride (CCC). The inhibition caused by far red light (FR) and growth retardants can be overcome by GA₃, while the ABA-induced inhibition can be reversed by fusicoccin (FC), which does not reverse the inhibition caused by FR or growth retardants. It is noteworthy that the germination of light insensitive wheat, corn, alfalfa and mung bean seeds is not inhibited by growth retardants.     

Induction of Parthenocarpy in Rosa Canina and Diospyros Lotus by the application of growth regulators

The effect of indole-3-acetic acid (IAA) and gibberellic acid (GA₃) applications on parthenocarpic fruit set in Rosa canina and Diospyros lotus was investigated. GA₃ induced parthenocarpic fruit set in both plants, but IAA only in D. lotus. Maturation of seedless fruits was earlier than the seeded fruits. GA₃ caused a decrease in the fresh mass and size of both fruits. IAA induced an increase in the fresh mass and size in parthenocarpic fruit of D. lotus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Production of somatic hybrids between satsuma mandarin (Citrus unshiu) and navel orange (Citrus sinensis) by protoplast fusion

We have regenerated altotetraploid plants that are interspecific somatic hybrids between Citrus sinensis Osbeck cv. Yoshida navel orange and Citrus unshiu Marc cv. Okitsu satsuma mandarin. Protoplasts isolated from ‘Yoshida’ leaves were chemically fused with call us-derived protoplasts from ‘Okitsu’. After 6 months of culture, 102 plants were obtained. These hybrids were identified by differential leaf morphology, DNA fluorescence intensity, and DNA analysis. Ploidy analysis via the flow cytometry revealed that 15 of the 102 plants were tetraploids, with the rest being diploids that morphologically resembled their mesophyll parent. SRAP analysis confirmed that 9 of the tetraploid plants were allotetraploid somatic hybrids. These will be utilized as a possible pollen parents for improving seedy citrus cultivars, e.g., ponkan, mandarin, lemon and kumquat, in order to produce triploid seedless hybrids.     

Effects of growth regulators on light-dependent anthocyanin production in Zea mays seedlings

Rengel, Z. and Kordan, H. A. 1987. Effects of growth regulators on light-dependent anthocyanin production in Zea mays seedlings.
The effects of ethylene, indolyl- and naphthylacetic acids, zeatin, benzyladenine, gib-berellic acid and triiodobenzoic acid on anthocyanin production in seedlings of Zea mays L. cv. Golden Bantam were investigated. Endogenously produced and exogen-ously supplied ethylene, as well as the other growth regulators tested markedly suppressed anthocyanin formation. Except for triiodobenzoic acid, the other growth regulators stimulated ethylene production, the amounts produced in the light being larger than those in the dark. Absorption of ethylene by permanganate as well as inhibition of ethylene production or action by Co²⁺ or Ag⁺ increased anthocyanin formation in maize seedlings above the level found in the control plants. The inhibiting effect of auxins and cytokinins on anthocyanin production was reversed by Co²⁺ or Ag⁺. In contrast, decreased anthocyanin formation caused by gibberellic acid or triiodobenzoic acid seemed unrelated to ethylene and could not be alleviated by Co²⁺ or Ag+.     

Gibberellic acid and kinetin partially reverse the effect of water stress on germination and seedling growth in chickpea

The percent germination and seedling growth of chickpea (Cicer arietinum L. cv. PBG-1) decreased with increasing concentrations of exogenous polyethylene glycol 6000 (PEG). With 15% PEG in the growth medium germination was only 33% while with 10% PEG it was 58% as compared to 93% in control. Addition of gibberellic acid (GA₃) and kinetin to medium containing 10% PEG increased the germination and seedling growth and the effect was maximum with 6 µM GA₃ which was a better inducer of growth and germination under reduced water potential than kinetin. However, indole acetic acid (IAA) inhibited germination and growth of stressed seedlings. The activity of amylase in cotyledons under stress was significantly increased with GA₃ while kinetin and IAA were less effective. Gibberellic acid also enhanced the mobilization of starch from cotyledons of stressed seedlings resulting in low starch levels in cotyledons compared with stressed seedlings.     

Abscisic acid increases in non-growing and paclobutrazol-treated fruits of seedless mandarins

Clementine ( Citrus reticulata [Hort.] Ex. Tanaka cv. Oroval) is a self-incompatible mandarin with a slow rate of fruit growth and high percentage of fruit abscission. Seedless Satsuma ( Citrus unshiu [Mak] Marc. cv. Clausellina) shows natural parthenocarpy and higher fruit set. Application of 25 μg fruit⁻¹ of paclobutrazol (PP333), an inhibitor of gibberellin biosynthesis, reduced the rate of growth and accelerated fruit abscission in both varieties. In contrast, gibberellin A₃ (GA₃) stimulated fruit growth only in the self-incompatible mandarin. Clementine fruits, in the absence of pollination, showed an approximately 2-fold transient increase in the free abscisic acid (ABA) content shortly after petal fall. In Satsuma, a very small accumulation of ABA was detected. Paclobutrazol treatment induced a 3-fold increase in ABA in Satsuma fruits but did not substantially affect the pattern of ABA accumulation in Clementine. In this variety, GA₃ suppressed the ABA increase observed in untreated fruits. These effects were observed 24 h after treatment. However, in Satsuma fruits, the effect of GA₃ on the ABA content was negligible. In addition, a comparative analysis of growing and non-growing fruits of Clementine showed that ABA, on a per unit weight basis, was always higher in the non-growing fruits. Treatment with 85 μM fluridone, an inhibitor of carotenoid biosynthesis and thus indirectly of ABA, delayed fruit abscission in Clementine, but also decreased fruit growth. Collectively, these observations indicate a relationship between high ABA content and a reduced rate of fruit growth and an acceleration of fruit abscission.     

Periodicity of bud bursting in willow (Salix viminalis) as affected by growth regulators

Saunders, P. F. and Barros, R. S. 1987. Periodicity of bud bursting in willow ( Salix viminalis ) as affected by growth regulators.
Lateral vegetative buds of willow ( Salix viminalis L.) were only innately dormant for 3–5 weeks in October; during this time their apices were correlatively inhibited by the bud leaflets. Exogenous gibberellins stimulated the opening of cultured buds when the plants were dormant or entering dormancy. As dormancy was being released, however, cultured buds became more responsive to exogenous cytokinins. Thus the demand for gibberellins and cytokinins for bud opening seemed to be sequential rather than simultaneous. Dormant buds cultured in the presence of abscisic acid remained unopened, but they opened after a chilling treatment. Subsequent growth of such buds as measured by dry matter accumulation, was observed only if a cytokinin was added to the medium.     

Influence of plant growth regulators on micropropagation and in vitro flowering of Trichodesma indicum (Linn) R. Br

An efficient protocol for micropropagation and in vitro flowering of Trichodesma indicum (Linn) R. Br. was developed using shoot tip explants. The physiological role of cytokinin and its combination with auxins on micropropagation and in vitro flowering was investigated. The highest number of shoots (9.94 ± 0.10) and the maximum average shoot length (5.56 ± 0.35 cm) were recorded on Murashige and Skoog (MS) medium supplemented with benzylaminopurine (BAP) (4.44 μM) and naphthaleneacetic acid (NAA) (2.69 μM). The effect of sucrose concentration on in vitro floral development was studied in plantlets cultured on MS medium supplemented with gibberellic acid (GA₃) and BAP. The highest percentage of flowering (93.2%) was obtained on MS medium supplemented with GA₃ (1.44 μM), BAP (1.33 μM) and sucrose (30 g l^?1). Root formation from the adventitious shoots was easily achieved on MS medium containing indole-3-butyric acid (IBA) (2.46 μM). The regenerated plantlets showed 86% survival rate and were phenotypically normal. The described method can be successfully employed for large-scale multiplication and in vitro flowering of T. indicum.     

Role of growth regulators in the senescence of Arabidopsis thaliana leaves

A homozygous, dominant, C₂H₄-resistant line of Arabidopsis thaliana (L.) Heynh (cv. Columbia; er ) was selected from ethylmethylsulfonate-mutagenized seed, and used to test the role of C₂H₄ and other growth regulators in senescence of mature leaves. Chlorophyll (Chl) loss from disks excised from leaves of er was much slower than that from wild-type (WT) disks, whether they were held in the light or in the dark. C₂H₄ accelerated Che loss from WT disks but had no effect on the yellowing of mutant disks. C₂H₄ biosynthesis was higher in disks from the mutant plants, particularly in the light. In the dark, treatment with the cytokinin, 6-benzyladenine (BA), reduced Chl loss from wild-type disks, but had no effect on mutant disks. In the light, BA treatment stimulated chlorophyll breakdown in both wild type and mutant disks. Treatment with abscisic acid (ABA) stimulated chlorophyll loss in wild-type and mutant disks, whether they were held in the light or the dark. C₂H₄ production was stimulated in ABA-treated disks, but they still yellowed even when C₂H₄ production was inhibited by application of aminooxyacetic acid (AOA). These data indicate that C₂H₄ is only one of the factors involved in leaf senescence, and that the promotion of senescence by ABA is not mediated through its stimulation of C₂H₄ production.     

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.     

Karrikins: A new family of plant growth regulators in smoke

Karrikins are a chemically defined family of plant growth regulators discovered in smoke from burning plant material. Karrikins are potent in breaking dormancy of seeds of many species adapted to environments that regularly experience fire and smoke. The recent discovery that karrikins trigger seed germination and control seedling growth in taxa that would rarely experience fire indicates that their significance could extend far beyond fire ecology. This is exemplified by new studies showing that seeds of Arabidopsis thaliana respond sensitively and specifically to karrikins in smoke. These exciting discoveries might be explained if karrikins are produced in the environment by processes other than fire, such as by chemical or microbial degradation of vegetation in response to disturbance of the soil or removal of the plant canopy. Another hypothesis is that plants contain endogenous karrikins that function naturally in the control of seed germination and that species from fire-prone habitats have evolved to respond also to exogenous karrikins. A variant on this hypothesis is that karrikins mimic endogenous plant hormones such as terpenoids that control seed germination. The evidence for these hypotheses is discussed, but whatever the explanation karrikins are now firmly established as an important family of naturally occurring plant growth regulators.     

Changes in photosynthetic rates and growth following root treatments of tomato plants with phytohormones

The effects of root applications of kinetin, gibberellic acid (GA₃) and indoleacetic acid (IAA) on photosynthesis was measured using an open infrared CO₂ gas-exchange system. There was a 30–35% increase in the photosynthetic rates (mg CO₂/dm²/hr) of attached leaves within 8 hr following root treatment with 0.47 M kinetin. On a short-term basis (up to 2 days) 0.47 M kinetin was shown to have the optimal stimulatory effect on photosynthesis, relative growth rate (RGR) and total plant dry weight. If the roots were in contact with 0.47 M kinetin for longer than two days there was severe branching of the root system and growth was severely decreased. When plants were left in contact with the kinetin treatment for up to 7 days the optimal stimulatory concentration was considerably lower (0.0047 M) . Plants receiving a 4, 8, or 12 hr pulse with 0.47 M kinetin to the roots exhibited higher leaf photosynthetic rates than the control. Plants receiving an 8 or 12 hr pulse with 0.47 M kinetin maintained photosynthetic rates higher than the control for the duration of the experiment (8 days) while the 4 hr pulse remained higher than the control for only 5 days. A sharp decrease in the photosynthetic rate, RGR and total plant dry weight was observed two days following continual treatments with 0.47 M kinetin to the roots. At low light levels there was approximately a 100% increase in the photosynthetic rate two days following treatment with 0.47 M kinetin while at a saturating irradiance there was a 30 to 35% increase. Indoleacetic acid either showed no effect on the photosynthetic rate, RGR and total plant dry weight or an inhibitory effect was observed. Either GA₃ or kinetin alone were shown to stimulate photosynthesis, RGR and total plant dry weight, however, when GA₃ at a 1.4 M concentration was applied in combination with kinetin at a 0.0047 M concentration to the roots of tomato plants there was no additive effect. In all cases kinetin dramatically reduced leaf resistance whereas GA₃ had no effect.By supplying either GA₃ or kinetin to the roots of tomato plants a highly reproducible stimulation in the photosynthetic rate, RGR and total plant dry weight can be achieved at physiologically relevant concentrations, whereas IAA appears to have an inhibitory effect.Approved for publication on July 29, 1981 as paper number 6281 in the journal series of the Pennsylvania Agricultural Experiment Station.Research Assistant and Assistant Professor, respectively.     

Induction of vessels in cotyledons of Lycopersicon esculentum by exogenously applied plant bioregulators

Cotyledonary mesophyll cells of Lycopersicon esculentummay be induced to form vessels with exogenously applied 2,4-dichlorophenoxyacetic acid and 6-benzylaminopurine. As a basis for determining the molecular events involved in the induction of competence for xylogenesis, we have determined that the entry of the exogenous plant bioregulators into the explant is through both the cut surfaces and intact epidermis; the mesophyll cells adjacent to the vascular system are the first to be induced to form vessels, appearing to be pre-programmed for the first phase of the genetic programme for vascular differentiation and so forming one set of channels of plant bioregulator flow for the determination of some of the subsequently transformed cells; and the remainder of the mesophyll cells are induced through the exogenously applied plant bioregulators entering through the surface of the cotyledon.     

Endogenous levels of polyamines and abscisic acid in pepper fruits during growth and ripening

The levels of polyamines (PA) and abscisic acid (ABA) in the pericarp of California variety pepper fruit ( Capsicum annuum L.) were analyzed during development and ripening. Putrescine level was 2.75 μmol g⁻¹ fresh weight 7 days after fruit set and fell during the exponential stage of growth to 1.05 μmol g⁻¹ fresh weight. During the second growth stage. PA and ABA levels remained stable and fell sharply at the beginning of maturation. The levels of spermidine and spermine decreased throughout fruit development and maturation from 0.61 to 0.05 and 0.31 to 0.02 μmol g⁻¹ fresh weight, respectively, but no changes were associated with the onset of maturation. ABA levels remained high (0.70-0.80 μg g⁻¹ fresh weight) during the stages of fruit growth and fell at the beginning of maturation to 0.12 μg g⁻¹ fresh weight, before rising again during the last stages of maturation and senescence. The decrease in putrescine and ABA levels and the subsequent increase in the latter may be responsible for controlling the processes of ripening in pepper fruit.