Gibberellins and parthenocarpic ability in developing ovaries of seedless mandarins

Satsuma (Citrus unshiu [Mak] Marc.) and Clementine (Citrus reticulata [Hort.] Ex. Tanaka, cv Oroval) are two species of seedless mandarins differing in their tendency to develop parthenocarpic fruits. Satsuma is a male-sterile cultivar that shows a high degree of natural parthenocarpy and a high fruit set. Seedless Clementine varieties are self-incompatible, and in the absence of cross-pollination show a very low ability to set fruit. The gibberellins (GAs) GA53, putative 17-OH-GA₅₃, GA₄₄, GA₁₇, GA₁₉, GA₂₀, GA₂₉, GA₁, 3-epi-GA₁, GA₈, GA₂₄, GA₉, and GA₄ have been identified from developing fruits of both species by full-scan combined gas chromatography-mass spectrometry. Using selected ion monitoring with [²H₂]- and [¹³C]-labeled internal standards, the levels of GA₅₃, GA₄₄, GA₁₉, GA₂₀, GA₁, GA₈, GA₄, and GA₉ were determined in developing ovaries at anthesis and 7 days before and after anthesis, from both species. Except for GA8, levels of the 13-hydroxy-GAs were higher in Satsuma than in Clementine, and these differences were more prominent for developing young fruits. At petal fall, Satsuma had, on a nanograms per gram dry weight basis, higher levels of GA₅₃ (10.4x), GA₄₄ (13.9x), GA₁₉ (3.0x), GA₂₀ (11.2x), and GA₁ (2.0x). By contrast, levels of GA₈ were always higher in Clementine, whereas levels of GA₄ did not differ greatly. Levels of GA₉ were very low in both species. At petal fall, fruitlets of Satsuma and Clementine contained 65 and 13 picograms of GA₁, respectively. At this time, the application of 25 micrograms of paclobutrazol to fruits increased fruit abscission in both varieties. This effect was reversed by the simultaneous applications of 1 microgram of GA₃. GA₃ alone improved the set in Clementine (13x), but had little influence on Satsuma. Thus, seedless fruits of the self-incompatible Clementine mandarin may not have adequate GA levels for fruit set. Collectively, these results suggest that endogenous GA content in developing ovaries is the limiting factor controlling the parthenocarpic development of the fruits.     

Self‐pollination and parthenocarpic ability in developing ovaries of self‐incompatible Clementine mandarins (Citrus clementina)

This study aimed to determine if self‐pollination is needed to trigger facultative parthenocarpy in self‐incompatible Clementine mandarins (Citrus clementina Hort. ex Tan.). ‘Marisol’ and ‘Clemenules’ mandarins were selected, and self‐pollinated and un‐pollinated flowers from both cultivars were used for comparison. These mandarins are always seedless after self‐pollination and show high and low ability to develop substantial parthenocarpic fruits, respectively. The time‐course for pollen grain germination, tube growth and ovule abortion was analyzed as well as that for carbohydrates, active gibberellins (GA₁ and GA₄), auxin (IAA) and abscisic acid (ABA) content in the ovary. ‘Clemenules’ showed higher pollen grain germination, but pollen tube development was arrested in the upper style 9 days after pollination in both cultivars. Self‐pollination did not stimulate parthenocarpy, whereas both un‐pollinated and self‐pollinated ovaries set fruit regardless of the cultivar. On the other hand, ‘Marisol’ un‐pollinated flowers showed greater parthenocarpic ovary growth than ‘Clemenules’ un‐pollinated flowers, i.e. higher ovule abortion rate (+21%), higher fruit set (+44%) and higher fruit weight (+50%). Further, the greater parthenocarpic ability of ‘Marisol’ paralleled higher levels of GA₁ in the ovary (+34% at anthesis). ‘Marisol’ ovary also showed higher hexoses and starch mobilization, but lower ABA levels (?64% at anthesis). Self‐pollination did not modify carbohydrates or GA content in the ovary compared to un‐pollination. Results indicate that parthenocarpy in the Clementine mandarin is pollination‐independent with its ability to set depending on the ovary hormone levels. These findings suggest that parthenocarpy in fertile self‐incompatible mandarins is constitutively regulated.     

Induced parthenocarpy—a way of changing the levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 1. Extractable hormones

Ethylene, indol-3-acetic acid (IAA), gibberellin-like substances (GAs) and abscisic acid (ABA) were analysed in extracts from normal, seed-containing and parthenocarpic tomato fruits throughout fruit development. Parthenocarpic fruit growth was induced with an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃) and compared with that of pollinated control fruits. Fruit growth was only affected by the treatment with GA₃, decreasing size and fresh weight by 60%. The peak sequence of hormones during fruit development was ethylene-GAs-IAA-ABA. Seeded fruits contained the highest levels of IAA and ABA but the lowest levels of GAs. Also, in seeded fruits, a high proportion of IAA and ABA was found in the seeds whereas this was not the case for GAs.Hormone levels of tomato fruits may be successfully, easily and reproducibly altered by inducing parthenocarpic fruit growth and thus eliminating development of seeds which are a major source of hormone synthesis. In spite of markedly changed hormone levels, there was no obvious relationship between fruit growth and extractable hormones per se. However, the results indicate that a high ratio of GAs: auxins is unfavourable for growth of tomato fruits.     

Induced parthenocarpy-a way of manipulating levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 2. Diffusible hormones

Indol-3-acetic acid (IAA), gibberellin-like substances (GAs), and abscisic acid (ABA) were measured throughout the first 35 days of fruit development in agar diffusates from seeded and parthenocarpic tomato fruits. Parthenocarpic fruit growth was induced with either an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃). IAA and GAs were at their highest levels in diffusates during the early stages of fruit growth, whereas diffusible ABA increased later. Most IAA was found in diffusates from auxin-induced and seeded fruits, whereas GAs were at their lowest levels in seeded fruits. There were only minor differences in ABA concentrations regardlesss of the treatments.Levels of diffusible hormones of tomato fruits may be easily manipulated by inducing parthenocarpic fruit growth. In spite of no obvious relationship between fruit growth and hormone levels in this study, induced parthenocarpy is considered a useful tool to further elucidate the role of hormones in fruit development and sink-source interactions.     

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.     

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.     

Hormonal regulation of fruit set, parthenogenesis induction and fruit expansion in Japanese pear

The effects of applied gibberellins (GAs), GA₁, GA₃, GA₄ and GA₇ with a cytokinin, N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) and indole-3-acetic acid (IAA) on fruit set, parthenogenesis induction and fruit expansion of a number of Rosaceae species were assessed. These included Japanese pear cv. ‘Akibae’ (self-compatible) and cv. ‘Iwate yamanashi’ (a seedless cultivar). Other Rosaceae species (Pyrus communis, Chaenomeles sinensis, Cydonia oblonga, and Malus pumila) were also investigated. GA₄, GA₇ and CPPU are very effective in inducing parthenocarpic fruit growth, whereas GA₁, GA₃ and IAA, have no ability to induce parthenogenesis in Japanese pear. GA₄- and GA₇-induced parthenocarpic fruit tended to be smaller in size, higher in flesh hardness, and showed advanced fruit ripening in comparison to pollinated fruit and to parthenocarpic fruit induced by CPPU. GA₄- and GA₇-induced parthenocarpic fruit also had an increased pedicel length and fruit shape index and also showed a slight protrusion of the calyx end. CPPU, GA₄ and GA₇ alone or combination with uniconazole were also active in inducing parthenogenesis in three other Rosaceae species, although final fruit set was extremely low. GA₁ was essentially inactive in promoting fruit expansion unlike the other bioactive GAs, whose effectiveness in promoting fruit cell expansion was as follow: GA₄ ≈ GA₇ > GA₃ > GA₁.     

Cytokinin-Induced Parthenocarpic Fruit Development in Tomato Is Partly Dependent on Enhanced Gibberellin and Auxin Biosynthesis

Fruit set of plants largely depends on the biosynthesis and crosstalk of phytohormones. To date the role of cytokinins (CKs) in the fruit development is less understood. Here, we showed that parthenocarpic fruit could be induced by 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU, an active CK) in tomato ( Solanum lycopersicum cv. Micro-Tom). The fresh weight of CPPU-induced parthenocarpic fruits was comparable with that induced by GA₃. Importantly, CPPU-induced parthenocarpy was found to be compromised by simultaneous application of paclobutrazol (a GA biosynthesis inhibitor), and this effect could be restored by exogenous GA₃. Like pollination, CPPU-induced fruit showed enhanced accumulation of GA₁₊₃ and indole-3-acetic (IAA), which were accompanied by elevated expression of GA biosynthesis genes like SlGPS, SlGA20ox1, SlGA20ox2 and SlGA3ox1, and IAA biosynthesis gene ToFZY. Elevated GAs level in CPPU-induced fruits was also associated with down-regulation of GA inactivation genes, namely SlGA2ox1,2,3,4,5 in comparison with untreated control. These results suggested that CKs may induce parthenocarpy in tomato partially through modulation of GA and IAA metabolisms.     

Strong synergistic effects of gibberellins with the synthetic cytokinin N-(2-chloro-4-pyridyl)-N-phenylurea on parthenocarpic fruit set and some other fruit characteristics of apple

The induction of parthenocarpic fruit set was investigated using the apple cvs. Golden Delicious and Jonagold. The gibberellins GA₃, GA₄, GA₅ and GA₇ and the synthetic phenylurea-type cytokinin CPPU (N-(2-chloro-4-pyridyl)-N-phenylurea), were applied alone and in combination to unpollinated flowers at the end of petal fall. Gibberellins induced only a marginal final set of parthenocarpic fruits. CPPU sprays were more effective, particularly in the first year. When applied in combination, CPPU and gibberellins had a positive synergistic effect on parthenocarpic fruit set and fruit size, but a negative effect on flower induction the next year. After CPPU + GA sprays, percent fruit set was similar, or greater, compared to natural pollinated trees. The parthenocarpic fruits induced by CPPU + GA had an increased length to diameter ratio. CPPU stimulated, and GA₄ and GA₇ reduced, the russeting of the parthenocarpic fruits. The internal quality of the fruits was hardly affected, but Ca-deficiency symptoms occurred more frequently in parthenocarpic fruits.     

扁桃生理落果期不同组织激素浓度的动态变化及其对落果的影响

为探明扁桃幼果生理脱落与GA3、IAA和ABA等3种激素的关系,以新疆‘纸皮’扁桃为试材,分析新梢、结果枝组、幼果和果柄(包括正常发育幼果和果柄、即将脱落幼果和果柄)中3种内源激素浓度的动态变化规律,并分别涂抹3种外源激素调查其对坐果率的影响。结果表明:(1)‘纸皮’扁桃幼果脱落期和新梢生长期重合,扁桃生理落果期不同组织中3种内源激素浓度变化趋势与新梢生长期和幼果脱落期的动态特征基本一致。(2)扁桃生理落果期间,正常的和即将脱落的幼果及其果柄中内源激素浓度呈规律性变化,即:GA3和IAA浓度表现为正常果和正常果果柄始终大于相应的落果和落果果柄,而内源ABA浓度表现则与之相反,同时对应外源涂抹试验也印证了幼果和幼果果柄中高GA3和IAA浓度、低ABA浓度有利于扁桃坐果。(3)新梢和幼果中对应内源激素之间的浓度平衡关系也是调控扁桃幼果生理脱落的重要因素,即:新梢与幼果的GA3比值和IAA比值增大、而ABA比值减少将会促进幼果脱落,反之则减缓幼果脱落。     

Identification and quantitative analysis of gibberellins inCitrus

Nine gibberellins (GAs) have been identified from tissues of Valencia orange (Citrus sinensis Osbeck) using gas chromatography—mass spectrometry and gas chromatography-selected ion monitoring of high-performance liquid chromatography (HPLC)-fractionated extracts. These GAs are GA₁, GA₃, GA₈, GA₁₉, GA₂₀, GA₂₉, 3-epi-GA₁, 2-epi-GA₂₉, and iso-GA₃. Selected-ion monitoring and stable-isotope dilution assays have been used to estimate levels of some of these GAs in vegetative and reproductive tissues. GA₂₉ was found to be the most abundant GA measured. GA₁ was found in all samples examined, and there was always less 3-epi-GA₁ than GA₁. GA₂₀ was present in most extracts. Leaves of developing inflorescence shoots contained six times more GA₂₉ than did leaves of comparable vegetative shoots. Levels of GA₂₉ increased during the early stages of fruit development. GA₂₀ may be more abundant in growing fruitlets than in those about to abscise; however, there were no consistent differences in the relative amounts of the other GAs. No major differences were found between tissues of immature seeded and seedless fruit, and developing seeds did not contain high levels of any of the GAs measured. It is concluded that seed-produced GAs are not essential for normal fruit development in Valencia orange.     

Changes in levels of gibberellins,their putative conjugates,and ABA in zygotic embryos during late maturation and dry seed stages of <Emphasis Type="Italic">Brassica napus</Emphasis> cv Topaz

Two late stages [days 35 and 40 after pollination (DAP)] in zygotic embryo (ZE) development of Brassica napus were utilized to quantify, by the stable isotope-labeled dilution method, levels of “free” and “aglycone” gibberellins (GAs), as well as abscisic acid (ABA), during the programmed dehydration of the seed. GAs from both the early 13 hydroxylation and early non-hydroxylation pathways were present in these ZEs of B napus. Between 35 and 40 DAP endogenous ABA dropped precipitously (almost 30-fold) and this drop in ABA was accompanied by a significant reduction in levels of GA₁ and even in levels of the inactive GA catabolites, GA₈ and GA₂₉. Levels of GA₄ and putative GA₈₅ also dropped appreciably, though not significantly. In contrast, the levels of GA₂₀ and GA₉ (the immediate precursors of GA₁ and GA₄, respectively) did not change in the ZEs during this transition. A fungal-derived cellulase was used to hydrolyze the highly water-soluble fraction, which will contain GA conjugates. Relatively high levels of several GAs (GA₉, GA₂₀) were thus quantified after hydrolysis as the aglycones, e.g., 56 and 25 ng/g DW of GA₂₀ and 23 and 5 ng/g DW, of GA₉, respectively at DAP 35 and DAP 40. Other GAs found after hydrolysis of the highly water-soluble fraction remained relatively constant between 35 and 40 DAP. An exception was the putative GA₈₅ aglycone, which increased sixfold (free GA₈₅ decreased by ca. half). The transition to the dry seed stage for ZEs of B. napus is thus accompanied not only by the expected reduction in ABA, but also by reduced levels of many “free” GAs, especially the bioactive, 3β-hydroxylated GAs. In contrast, levels of 3-deoxy GAs remain relatively high, implying a partial block in the 3β-hydroxylation “activation” step of GA biosynthesis.     

Estimation of endogenous contents of phytohormones during internode development in <Emphasis Type="Italic">Merremia emarginata</Emphasis>

During the entire period of internode growth of Merremia emarginata contents of gibberellic acid (GA₃), phenyl-acetic acid (PAA), indole-3-acetic acid (IAA, free and conjugated) and abscisic acid (ABA, free and conjugated) were estimated by ELISA using polyclonal antibodies raised against each hormones. At the time of internode elongation free auxin content was low and increased with the decrease in the rate of elongation. In contrast, conjugated IAA showed declining trend where free IAA content was remarkably high, suggesting thereby that conjugated IAA might have mobilized during the later phase of internode development. The endogenous GA₃ contents were high as compared to other hormones; however, no significant role of GA₃ was discernible in elongation growth. Conjugated ABA contents remained very low during the elongation growth and increased thereafter.     

Pleiotropic effects of the<Emphasis Type="Italic"> male sterile33</Emphasis> (<Emphasis Type="Italic">ms33</Emphasis>) mutation in<Emphasis Type="Italic"> Arabidopsis</Emphasis> are associated with modifications in endogenous gibberellins,indole-3-acetic acid and abscisic acid

Earlier, we reported that mutation in the Male Sterile33 (MS33) locus in Arabidopsis thaliana causes inhibition of stamen filament growth and a defect in the maturation of pollen grains [Fei and Sawhney (1999) Physiol Plant 105:165–170; Fei and Sawhney (2001) Can J Bot 79:118–129]. Here we report that the ms33 mutant has other pleiotropic effects, including aberrant growth of all floral organs and a delay in seed germination and in flowering time. These defects could be partially or completely restored by low temperature or by exogenous gibberellin A₄ (GA₄), which in all cases was more effective than GA₃ Analysis of endogenous GAs showed that in wild type (WT) mature flowers GA₄ was the major GA, and that relative to WT the ms33 flowers had low levels of the growth active GAs, GA₁ and GA₄, and very reduced levels of GA₉, GA₂₄ and GA₁₅, precursors of GA₄. This suggests that mutation in the MS33 gene may suppress the GA biosynthetic pathway that leads to GA₄ via GA₉ and the early 13-H C₂₀ GAs. WT flowers also possessed a much higher level of indole-3-acetic acid (IAA), and a lower level of abscisic acid (ABA), relative to ms33 flowers. Low temperature induced partial restoration of male fertility in the ms33 flowers and this was associated with partial increase in GA₄. In contrast, in WT flowers GA₁ and GA₄ were very much reduced by low temperature. Low temperature also had little effect on IAA or ABA levels of ms33 flowers, but did reduce (>2-fold) IAA levels in WT flowers. The double mutants, ms33 aba1-1 (an ABA-deficient mutant), and ms33 spy-3 (a GA signal transduction mutant) had flower phenotypes similar to ms33. Together, the data suggest that the developmental defects in the ms33 mutant are unrelated to ABA levels, but may be causally associated with reduced levels of IAA, GA₁ and GA₄, compared to WT flowers.Abbreviations ABA Abscisic acid - GA Gibberellin - GC-MS-SIM Gas chromatography-mass spectrometry-selected ion monitoring - IAA Indole-3-acetic acid - ms33 Male sterile33 mutant - PP333 Paclobutrazol - WT Wild type     

Physiological characteristics and related gene expression of after‐ripening on seed dormancy release in rice

After‐ripening is a common method used for dormancy release in rice. In this study, the rice variety Jiucaiqing (Oryza sativa L. subsp. japonica) was used to determine dormancy release following different after‐ripening times (1, 2 and 3 months). Germination speed, germination percentage and seedling emergence increased with after‐ripening; more than 95% germination and 85% seedling emergence were observed following 1 month of after‐ripening within 10 days of imbibition, compared with <45% germination and 20% seedling emergence in freshly harvested seed. Hence, 3 months of after‐ripening could be considered a suitable treatment period for rice dormancy release. Dormancy release by after‐ripening is mainly correlated with a rapid decline in ABA content and increase in IAA content during imbibition. Subsequently, GA₁/ABA, GA₇/ABA, GA₁₂/ABA, GA₂₀/ABA and IAA/ABA ratios significantly increased, while GA₃/ABA, GA₄/ABA and GAs/IAA ratio significantly decreased in imbibed seeds following 3 months of after‐ripening, thereby altering α‐amylase activity during seed germination. Peak α‐amylase activity occurred at an earlier germination stage in after‐ripened seeds than in freshly harvested seeds. Expression of ABA, GA and IAA metabolism genes and dormancy‐related genes was regulated by after‐ripening time upon imbibition. Expression of OsCYP707A5, OsGA2ox1, OsGA2ox2, OsGA2ox3, OsILR1, OsGH3‐2, qLTG3‐1 and OsVP1 increased, while expression of Sdr4 decreased in imbibed seeds following 3 months of after‐ripening. Dormancy release through after‐ripening might be involved in weakening tissues covering the embryo via qLTG3‐1 and decreased ABA signalling and sensitivity via Sdr4 and OsVP1.     

不同成花量金花茶花果期果枝叶内源激素的变化

该研究采用ISSR分子标记,对黄枝油杉7个自然种群的遗传多样性进行了分析。结果表明：用12条ISSR引物对218个黄枝油杉个体进行扩增,共扩增出125个位点。在物种水平上,多态性位点百分数( PPL)为100.00％,Shannon信息多样性指数( I)为0.4177,Nei’ s基因多样性指数( H)为0.2666;在种群水平上,多态性位点百分数(PPL)在71.20％~92.00％之间,平均值为80.69％,Shannon信息多样性指数(I)在0.3273~0.3886之间,平均值为0.3548,Nei’ s基因多样性指数( H)在0.2139~0.2478之间,平均值为0.2291。这说明黄枝油杉在物种水平和种群水平上均显示出较高的遗传多样性。 Nei’ s遗传多样性分析( Gst＝0.1433)和AMOVA分析(Φst＝17.91％)表明,黄枝油杉的遗传变异主要存在于种群内,种群间的遗传分化程度较低,种群间保持一定的基因交流( Nm＝2.9890>1)。 Mantel分析显示,黄枝油杉种群间的遗传距离和地理距离之间不存在显著的相关关系( r＝0.4567, P＝0.0610>0.05)。     

Gibberellins inCitrus sinensis: A comparison between seeded and seedless varieties

The gibberellin (GA) content of the reproductive organs ofCitrus sinensis (L.) Osb., cv. Bianca Comuna and the seedless variety, Salustiana, were examined by combined gas chromatography-mass spectrometry (GC/MS) at different stages of development. Gibberellins A₁, A₂₀, and A₂₉ were identified in the reproductive buds of both cultivars 21 days prior to anthesis and in fruits 35 days after anthesis by comparison of their mass spectra and Kovats retention indices with those of standards. In addition, three uncharacterized isomers of GA₁ were detected, one in buds and two in fruits. The presence of GA₄ in both tissues, and of GA₈ in the reproductive buds, was indicated by the occurrence of characteristic ions at the expected retention times, although their spectra were too weak for full identification. Vegetative shoots of cv. Salustiana contained gibberellins A₁, A₁₉, A₂₀, and A₂₉, and the unidentified isomer of GA₁ present in reproductive buds. The presence of trace amounts of gibberellins A₈ and A₁₇ was also indicated. Although the two varieties did not differ qualitatively in the GAs present during flower and fruit development, the seedless variety contained slightly greater amounts. The concentrations of gibberellins A₁, A₄, and A₂₀ were determined by gas chromatography-selected ion monitoring (GC/SIM) throughout ovary development and early fruit growth. In both varieties, the maximum GA₁ concentration occurred at anthesis. Highest concentrations of gibberellins A₂₀ and A₄ were found in fruit 35 days after anthesis, although the GA₁ concentration at this stage remained low.     

Gibberellic acid impairs fertilization in Clementine mandarin under cross-pollination conditions

We investigated the effect of gibberellic acid (GA₃) in the fertilization of Clementine mandarin cv. ‘Clemenules’ (Citrus clementina Hort. ex Tan.), a parthenocarpic variety that produces seedless fruit due to its self-incompatible nature, but yields seedy fruits when grown under cross-pollination conditions.Experiments were conducted with on-tree ‘Clemenules’ flowers and ‘Fortune’ mandarin pollen (C. clementina Hort. ex Tan. × C. reticulata Blanco), which is sexually compatible with the former. Preanthesis treatment at −2 days after anthesis (−2 DAA) enhanced ovule abortion in both unpollinated and cross-pollinated (at +2 DAA) flowers. In the latter, the number of pollen tubes reaching the ovules was significantly reduced although pollen grains were not treated; thus, fertilization was partially avoided and seed set was reduced. When GA₃ was applied at anthesis (0 DAA) at the time of pollination, ovule abortion was again enhanced, and pollen tube growth was completely arrested; thus, fertilization was prevented and seed set was impeded. When GA₃ was applied 24 h after pollination (+1 DAA in flowers pollinated at anthesis), pollen tube growth was impaired but not arrested and ovule abortion was enhanced; therefore, fertilization was not prevented but impaired.We conclude that, when applied the days around anthesis, GA₃ (10 mg l⁻¹) impairs fertilization by either enhancing ovule abortion or reducing pollen tube growth, in ‘Clemenules’ flowers under cross-pollination conditions. The intensity of the response depends on the physiological flower state at the moment of treatment.     

Hormones in zygotic and microspore embryos of Brassica napus

A number of studies have used microspore-derived embryos (MDEs) as amodel for examining a range of processes, including hormonal regulation ofembryo development. We examined the hormonal physiology of MDEs with theprimaryobjective of testing the validity of using the MDE system as a model forhormonally-regulated development in zygotic embryos, through late stages. To dothis we identified and quantified endogenous levels of abscisic acid (ABA),indole-3-acetic acid (IAA) and a number of gibberellins (GAs), includingGA₁₉, GA₂₀, GA₁ and GA₈ in bothMDEsand zygotic embryos. The presence of GA₁₉, together with itsC₁₉ metabolites indicates that the early-13 hydroxylation pathway isoperative in both embryo systems. Gibberellins A₄ and GA₉were also identified, thereby confirming the presence of the earlynon-hydroxylation pathway in B. napus MDEs and zygoticembryos. In general, the pattern of change of hormone (ABA, IAA, GA₁and GA₂₀) content per embryo through embryogenesis was similar forMDEs and zygotic embryos. Indole-3-acetic acid and GA₁ increased toamaximum at day 30 after culture (DAC) before decreasing. Abscisicacid levels increased to a maximum at day 35, and declined in zygoticembryos but not in MDEs. GA₂₀ increased to the final harvest atmaturity, or day 40. The absolute content (g/embryo) of each hormone, howeverwas appreciably lower (5- to 15- fold) in the MDEs. This was not the result ofdilution into surrounding medium for ABA or IAA; GA₁, however, didaccumulate in the medium. Although there were absolute quantitative differencesin the levels of IAA and ABA found in the two embryo systems, the similaritiesin the pattern of hormone changes suggests that the MDE system can serve as auseful model for examining the physiological roles of hormones duringembryogenesis.