Developing Inflorescences of Male and Female <Emphasis Type="Italic">Rumex acetosa</Emphasis> L. Show Differences in Gibberellin Content

Rumex acetosa L. (common sorrel) is a dioecious perennial in the family Polygonaceae. Gibberellins (GAs) of the early 13-hydroxylation pathway and the putative early 3, 13-hydroxylation pathway were previously identified in young R. acetosa inflorescences by GC-MS. In this investigation to examine the GA content of individual inflorescences ELISAs were used for quantitative analysis. Significant differences were revealed between the sexes in the GA content of young inflorescences, and GC-SRM was used to validate the observed trends. Males had higher levels of the 3, 13-hydroxylated C₂₀-GA GA₁₈ and the 2, 13-hydroxylated C₁₉-GA GA₂₉, whereas females had higher levels of the 13-hydroxylated C₂₀-GAs GA₅₃ and GA₁₉. It is suggested that the conversion from C₂₀-GAs to C₁₉-GAs is under tighter control in the inflorescences of females compared to male plants and therefore there is accumulation of the C₂₀-GAs in the females. Results from flowering bioassays using authentic GAs indicate that differences in GA content between the sexes are unlikely to be a consequence of sex determination.     

A plant growth retardant related to chlamydocin and its proposed mechanism of action

A comparison of the plant growth retardant activity of the chlamydocin analogues, compound 1, six derivatives from 1 and 2, and two synthetic analogues revealed that there are two types of retardant in chlamydocin analogues. One, for example in compound 1, requires an oxygen atom at C-8 of the 2-aminodecanoic acid moiety to show retardant activity. The other, for example in compound 8, requires no oxygen atom at C-8 but requires a specific alkyl group chain length for activity. To determine the differences in mode of action of both types of retardant, rice seedlings were separately treated with compounds 1 and 8, and after appearance of dwarfism, their endogenous ABA and GA(1) levels were determined and compared to those of the control. Treatment with 1 (10 nmol/plant) increased ABA levels 4 times higher than that of the control and decreased GA(1) levels to 20% of that of the control. Treatment with 8 (30 nmol/plant) did not affect the ABA level but decreased GA(1) content to 5% of that of the control.     

Effect of exogenous gibberellins on flowering in Pinus sylvestris grafts

Ethanolic sprays of gibberellins were applied to developing shoots of about 12-year-old Scots pine (Pinus sylvestris L.) grafts during the shoot elongation period in two consecutive years. Both male and female flowering was increased by these treatments in both years. The effect was particularly distinct in male flowering. However, different clones showed varying responses to the treatment. This variation was associated with both the genotype and the environmentally determined year-to-year fluctuation in flowering. Differences among clones were analysed further by introducing a model earlier developed for comparisons of the growth rhythm in various woody and herbaceous species.     

One for All and All for One: Cross-Talk of Multiple Signals Controlling the Plant Phenotype

The plant hormone ethylene plays a pivotal role in steering various processes by regulating the biosynthesis, distribution, or signal transduction of other hormones. Ethylene also mediates the effects of other hormones. Similarly, hormones control the ethylene synthesis and signalling pathway. Eventually, integration of this network of signals leads to an appropriate morphological or biochemical response. Consequently, this cross-talk results in the characteristic plasticity associated with plant development. Here, the interplay of ethylene with other hormones is described for germination and seedling growth, stomatal control, and tissue elongation. The mechanisms by which this occurs are discussed in more detail.     

The Effects of Gibberellin4+7 on the Vase Life and Flower Quality of Alstroemeria Cut Flowers

Leaf yellowing is a major problem in Alstroemeria and absence of leaf senescence symptoms is an important quality attribute. Two Alstroemeria cultivars ‘Yellow King’ and ‘Marina’ were sourced from a commercial farm and harvested when sepals began to reflex. Stems were re-cut under water and kept in vase solutions of gibberellin A₄₊₇ (0, 2.5, 5.0, 7.5, 10.0, 12.5 or 15.0 mg l⁻¹ [Provide^r]). Treatments and cultivars were combined in a factorial fashion and arranged in a completely randomised design. Application of GA₄₊₇ in the holding solution at 2.5–10.0 mg l⁻¹ significantly delayed the onset of leaf senescence by around 7 days and significantly increased days to 50% petal fall by ca. 2 days. Additionally, these GA₄₊₇ concentrations resulted in higher retention of leaf nitrogen, leaf chlorophyll and also increased leaf water content, while reducing leaf dry weight, all relative to untreated controls. Cultivar ‘Yellow King’ had significantly longer vase life and a better retention of leaf quality than ‘Marina’. Our results suggest that a concentration of 10 mg l⁻¹ GA₄₊₇ can be used to prolong vase life, delay leaf senescence and enhance post-harvest quality of Alstroemeria cut flowers during their transport to market.     

Common and distinct responses in phytohormone and vitamin E changes during seed burial and dormancy in Xyris bialata and X. peregrina

Temperature and humidity are the main factors influencing seed viability, dormancy and longevity of buried seeds. Unfortunately, very little is known about such processes in species of tropical regions, where temperature does not show major seasonal variations. The extent to which germination capacity, phytohormones and vitamin E levels were altered after burial of seeds of Xyris bialata and X. peregrina (Xyridaceae), two species endemic to rupestrian fields of Brazil, was examined. After 2 months of burial, seed germination capacity remained constant, which is associated with decreases in ABA and IAA content in both species. During this period, zeatin levels also decreased in X. bialata, but not in X. peregrina, the latter showing much lower levels of ABA. During the summer (rainy season), seeds of both species experienced a progressive, but severe, decrease in germination capacity, which reversed at the end of the winter (dry season), thus suggesting secondary dormancy. This dormancy appeared to be caused by drastic decreases in GAs, rather than increases in ABA. Levels of GA(4) decreased to non-detectable values during dormancy in both species. Furthermore, zeatin levels decreased in X. bialata but not in X.peregrina during this period. Both species accumulated γ-tocopherol as the major vitamin E form, and levels of this antioxidant remained constant or even increased during seed burial; however, X. bialata seeds showed a significant decrease in α-tocopherol during seed burial and dormancy. It is concluded that in X. peregrina and X. bialata, (i) burial causes significant changes in the phytohormone levels of seeds; (ii) secondary dormancy is induced in seeds; (iii) a GA(4) decrease, rather than an ABA increase, seems to be involved in the induction of secondary dormancy; and (iv) reductions in α-tocopherol in buried seeds are not necessarily indicative of reduced germination capacity.     

Transport and metabolism of exogenously applied gibberellins to Malus domestica Borkh. cv. Jonagold

The radio-labeled gibberellins GA₁, GA₃,GA₄, and GA₇ were applied to intact developing applefruits (Malus domestica Borkh. cv. Jonagold) during theperiod when GAs are suggested to inhibit flower bud induction for the followingyear. Radioactivity from these compounds was found to be transported intoadjacent tissues as there are pedicels and bourses (4%). Application topedicels, after removal of the fruits, enhanced the transport into adjacentbourses up to 11%. The bud-carrying lateral bourse shoots contained onlyminor amounts of radioactivity on average 0.4% in both cases. Theseexport rates were identical, 1 or 5 days after application.After application of the corresponding deuterium-labeled GAs and analyses bymass spectrometry the specific metabolization of GA₁ toGA₁ 13-O-glucoside and of GA₃ to GA₃13-O-glucoside was demonstrated. Additional metabolites of GA₁ andGA₃ were not detected. After fruit application of GA₃ theratio of GA₃ to GA₃ 13-O-glucoside was found to be 1:2 inthe fruit. Pedicel application led to ratios of 1:4 and 1:5, respectively, inthe pedicel and in the adjacent bourse. After the application of GA₄and GA₇, neither glucosylation products nor other GA-like metabolitescould be identified.This is the first report of the metabolism of GAs to GA 13-O-glucosides indeveloping apple fruits. The possible function of the GAs as a signal in flowerbud formation for the following year is discussed.     

Lack of effect of photoperiod on metabolism of exogenous GA19 and GA1 in Salix pentandra seedlings

The effect of photoperiod on metabolism of 16,17-[³H₂]GA₁₉, and 1.2-[³H₂]GA₁ applied to intact seedlings of Salix pentandra, was investigated. No difference was found in conversion of 16,17-[³H₂]GA₁₉ to 16,17-[³H₂]GA₂₀, and 16,17-[³H₂]GA₁, or in metabolism of 1,2-[³H₂]GA₁ to [³H]GA₈ between plants grown in continuous light and plants exposed for 14 days to a 12-h photoperiod. Also, leaf discs from plants grown in long or short days, converted 16,17-[³H₂]GA₁₉ both in light and darkness. These data on metabolism of 16,17-[³H₂]GA₁₉, contrast with previous results, which have indicated a photoperiodic control of the metabolism of GA₁₉ to GA₂₀ in S. pentandra. Presence of these applied labelled GAs and their metabolites in different parts of seedlings was recorded, after application to intact seedlings as well as to isolated plant parts. When 16,17-[³H₂]GA₁₉ was applied through the roots of intact plants, the relative amounts of 16,17-[³H₂]GA₁ present in leaves and shoot apices were higher than in roots and stems. In corresponding experiments with 1,2-[³H₂]GA₁, relatively higher amounts of [³H₂]GA₈ were found in roots and stems than in leaves and shoot apices. Twenty-four hours after application of 16,17-[³H₂]GA₁₉ to isolated plant parts, 16,17-[³H₂]GA₂₀ and 16,17-[³H₂]GA₁ were found in leaves and roots, but not in internodes. Incubation of isolated plant parts with 1,2-[³H₂]GA₁ for 24 h resulted in presence of [³H]GA₈ in all parts. The results mentioned above were obtained by monitoring metabolites by HPLC with on-line radio counting. The conversions of 17-[²H₂]GA₁₉ to 17-[²H₂]GA₂₀ and 17-[²H₂]GA₁ in shoot apices and whole seedlings, and of 17-[²H₂]GA₈ in whole seedlings, were confirmed by GC-MS.     

Distribution of Gibberellins A7 and A4 in Tobacco Proembryos Using Immunoelectron Microscopy

The ovules of Nicotiana tabacum var. macrophylla 8 days after pollination were fixed successively with 2% EDC (1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide) and a mixture solution of paraformaldehyde and glutaraldehyde, then slightly postfixed in 0.5 % osmium solution. UI- trathin sections of 6-, 9- or 12- celled proembryos embedded in Epon 812 resin were stained in an anti-GA MAb and sheep anti-mouse IgG-colloidal gold (10 nm). This MAb specifically recognizes methyl esters of GA7 and GAn. Therefore, it could be used as a probe to localize GA7 and GAn in cells after EDC fixation. The 12-celled proembryo is composed of a 9-celled embryo and a 3-celled suspensor. Wide distribution of GA7 and GAn was observed in all proembryo cells and most organelles at subeellular level, including walls, plasmodesmata, plasma membrane, cytoplasmic matrix, mitochondria, plastids, vacuoles, endoplasmic reticulum and nuclei. Clusters of gold granules were found in nuclear envelope, nucleomatrix, nucleolus, chromosome, cytoplamic matrix. In a region composed of cytoplasmic matrix, a vacuole and a mitochondrium, such concentrated gold granules were particularly obviously observed. There appeared a gradient distribution of GA7 and Gan from embryo cells decreasingly to suspensor cells. GA7 and GAn could be translocated via intercellular walls, plasmodesmata and vesicles between embryo and suspensor. 1he authors suspect the direction of GA translocation in proembryo may be from suspensor to embryo. To author's knowledge, this is the first report to indicate subcellular and gradient distributions of bioactive gibberellins in plant proembryos.     

Delay of early fruitlet abscission by branch girdling in citrus coincides with previous increases in carbohydrate and gibberellin concentrations

Current evidence in citrus indicates that gibberellins (GAs) are main determinants of early fruit set while subsequent growth of developing fruits is mostly dependent upon carbohydrate availability. In this work, branch girdling performed at anthesis in Satsuma mandarin (Citrus unshiu (Mak.) Marc.) cv. Okitsu transitorily reduced early abscission rates (12–32 days after anthesis, DAA) delaying initially the process of natural fruitlet drop. The effects of girdling on growth, gibberellin (GA) and carbohydrate concentrations in developing ovaries and fruitlets were assessed during this initial growth stage (0–69 DAA). In girdled branches, abscission rate reduction was preceded by elevated concentrations of carbohydrate and GA in developing ovaries and fruitlets. Girdling at anthesis stimulated higher hexose (21 DAA) and starch (6–20 DAA) concentrations and also higher GA₁ (6 DAA), GA₁₉ (13–20 DAA) and GA₂₀ (6–20 DAA). The results established a relationship between the reduction of early abscission rates and higher concentrations of carbohydrates and GAs induced by girdling in developing fruitlets. These findings revealed that girdling certainly increased GA concentration and strongly suggested that its effect on early fruitlet abscission delay is likely mediated by both GA and carbohydrates.