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.     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

Hormonal Control of Sex Differentiation of Potentially Female Floral Buds of Lagenaria siceraria var. hispida In Vitro

In the present study, several kinds of phytohormones were used for the control of sex differentiation of the potentially female floral buds of Lagenaria siceraria var. hispida in vitro. It was shown that both GA3 and STS (silver thiosulphate) could effectively change the direction of sex differentiation of the potentially female floral buds in vitro. In the MS medium, supplemented with IAA, BA and ACC(1-aminocyclopropane-l-carboxylic acid) at l nmol/L, male flowers would be induced from the potentially female floral buds by the addition of GA3 (1–500μmol/L). Herein the male flowers were induced more effectively by GA3 within 5–-20 μmol/L but it was not as effective as STS. In the MS medium supplemented with IAA, BA and ACC at 1 nmol/L and with GA3 at 20 nmol/L more male flowers were differentiated from the potentially female floral buds with the addition of STS within 100–500 μmol/L. On the contrary, when the MS medium were supplemented with IAA and ACC at 1 nmol/L and with BA increased to 100 nmol/L more female flowers were differentiated from the potentially female floral buds, even with addition of 10–50 nmol/L of GA3.     

棉花胚珠纤维发育的研究

将未受精的棉花胚珠漂浮培养在加有不同植物激素的BT培养基上,培养48小时或96小时后,用扫描电镜观察纤维发育情况,以及测定胚珠内IAA氧化酶活性变化及内源ABA的含量变化,并和同一时期的大田生长的胚珠进行比较。结果表明:IAA+GA_3是最佳激素组合。在这种激素组合的培养基中培养的未受精胚珠,在纤维发育、酶活性变化等方面,均与大田生长的胚珠相似。这一激素组合还能抑制离体胚珠内源ABA的增长,但同一时期的大田生长的胚珠,其内源ABA含量却相对要高。     

Development of fertilized ovules and their role in the growth of the pea pod

The histological development of fertilized ovules during fruit-set and development in pea ( Pisum sativum L. cv. Alaska) has been investigated. Killing the ovules on day 0 (anthesis) or day 1 prevented fruit-set and resulted in ovary degeneration. When the ovules were destroyed at later stages the ovaries developed, though the rate of growth of the pod was reduced significantly. Pollination in pea occurs normally the day before anthesis, and fertilization of the egg cell 32 to 48 h later. The first divisions of the zygote and endosperm nuclei started simultaneously (ca 48 h after pollination) but the endosperm developed more rapidly than the embryo; the embryo sac cavity was lined with free endosperm nuclei at the time of beginning suspensor elongation. Extracts of endosperm and ovule coats from ovules at day 7 after anthesis showed fruit-set activity in pea, the latter material having about 3 times more activity than the former per ovule basis. These results indicate that fertilization of the ovule is necessary for fruit-set in pea, and that compounds which induce fruit-set are probably synthesized in the ovules following fertilization.     

LABILE SEX EXPRESSION IN ANDROMONOECIOUS SOLANUM HIRTUM: FLORAL DEVELOPMENT AND SEX DETERMINATION

Sex expression (the proportions of hermaphrodite and staminate flowers produced) of the andromonoecious species Solatium hirtum is labile, and this lability of whole plant sex expression is due to labile sex expression of individual floral buds. In this paper I examine the developmental processes that underlie the differences in floral sex expression of hermaphrodite and staminate flowers of Solarium hirtum, focusing particularly on the processes responsible for the observed lability of floral sex expression. Differences in bud growth rate and relative growth of floral organs in these buds are evident at about the time of megasporocyte meiosis (11–12 days before anthesis). However, gynoecial sterility in staminate buds does not occur until just 6–7 days before anthesis. At this time, abnormalities in ovule development occur in staminate buds: the ovules begin to appear necrotic, the integumentary tapetum collapses, and the megagametophytes of many ovules cease normal development. These observations are consistent with the predictions of labile floral development.     

植物生长调节剂影响沙田柚内源激素水平的研究

研究了植物生长调节剂优康唑和CPPU对沙田柚生理落果期间幼果和新梢叶片内源IAA、GA1 3和ABA水平的影响.研究结果表明:优康唑处理降低新梢叶片内源IAA和GA1 3水平,提高细胞分裂素含量.优康唑对叶片ABA含量和(IAA GA1 3 CTKs)/ABA比值影响不明显;优康唑处理下幼果IAA、GA1 3和ABA含量均有不同程度的下降,以GA1 3下降幅度最大.果实中CTKs含量和CTKs/ABA比例上升,结合优康唑和CPPU促进沙田柚座果的效应,提示细胞分裂素对座果有重要作用,而CTKs/ABA比例升高有助于缓解生理落果;CPPU处理降低果实ABA含量,提高果实CTKs水平和CTKs/ABA比值.这可能是CPPU促进座果和果实膨大的生理基础.     

ANATOMY AND DEVELOPMENT OF THE FLOWER AND FRUIT OF PERESKIA PITITACHE

Boke, Norman H. (U. Oklahoma, Norman.) Anatomy and development of the flower and fruit of Pereskia pititache. Amer. Jour. Bot. 50 (8): 843–858. Illus. 1963.—Flowers of P. pititache are about 6 cm in diameter and perigynous. The receptacle bears numerous broad bracts; the inner perianth segments are orange and deeply cleft; the numerous stamens develop centrifugally. The fundamentally superior gynoecium is broad and flat and consists of 10–18 connate carpels, the fertile portions of which are involute and adnate to the conical floral axis. The 8–16 ovules in each of the pocket-like locules are borne in 2 rows along the zone of adnation; placentation is axile. The short style and the style branches are lined with stigmatic tissue, which extends downward among the ovules. There is no definite stigma. The tip of the floral axis retains its meristematic characteristics beyond anthesis. In early fruit development, the rim of the floral cup grows in height, while the residual floral axis becomes a conspicuous peg-like columella. Concomitantly, the formation of numerous mucilage cells and cavities causes the ovary partitions and parts of the ovary roof to disintegrate. As a result, the seeds are contained in a single, moat-like cavity, which appears inferior. Late fruit development is characterized by the differentiation of numerous fiber sclereids in association with the extensive and complex vascular system.     

Variability in the developmental stage of apricot ovules at anthesis and its relationship with fruit set

The stage of ovule development at anthesis and its relationship with fruit set was studied in several apricot cultivars growing in Mediterranean climatic conditions. Although generally the ovule was immature at anthesis, a great variability was found in the stage of development of the ovules from different cultivars. Considering functional ovules to be those with an embryo sac with at least four nuclei at anthesis, the earliest flowering varieties frequently showed more than 50% of functional ovules. Though these results could suggest that there is an influence of the chilling requirement on the percentage of functional ovules at anthesis, data recorded from two cultivars, ‘Goldrich’ and ‘Colorao’, with high chilling requirements, contrast with this suggestion. These results indicate that in apricot flowers the development of the embryo sac at anthesis is genotype dependent. The fact that a high frequency of functional ovules at anthesis was found, in cultivars with more than 50% of fruit set, suggests that, to be fertilised, a certain level of development of the apricot ovules at this time is necessary.     

Chromoplast Biogenesis in Cucumis sativus Corollas (Rapid Effect of Gibberellin A3 on the Accumulation of a Chromoplast-Specific Carotenoid-Associated Protein)

The development of cucumber (Cucumis sativus L.) corollas is accompanied by the accumulation of chromoplasts. In mature corollas, chromoplasts, but no chloroplasts, were detected by electron microscopy. Chlorophyll was also undetectable in corollas at anthesis. The contents of carotenoids and a carotenoid-associated, chromoplast-specific, 35-kD protein in corollas increased in parallel with flower development, peaking concomitantly at anthesis. The involvement of phytohormones and light in the regulation of their expression was studied. When gibberellin A3 (GA3) was added to an in vitro bud culture system, accumulation of both carotenoids and the 35-kD protein was markedly enhanced. The specific up-regulation of the 35-kD protein was very rapid: after only 2 h of culture, increased levels were detected in GA3-treated versus untreated corollas. During this period, corolla fresh weight and total protein and carotenoid contents remained unchanged. Inclusion of abscisic acid in the culture medium counteracted the effect of GA3. Accumulation of the 35-kD protein was also enhanced when flower buds on plants were sprayed with GA3 or etiolated.     

Measurement of Indole-3-Acetic Acid in Peach Fruits (Prunus persica L. Batsch cv Redhaven) during Development

The amount of indole-3-acetic acid (IAA) was measured in peach fruits by gas chromatography-mass spectrometry-selective ion monitoring using an isotope dilution assay with [¹³C₆]IAA as an internal standard throughout the growing season. Ethylene evolution of the fruit was also measured. IAA levels were 25 nanograms per gram fresh weight, 18 days after anthesis. Both IAA levels and rates of ethylene evolution declined to their lowest levels (7 nanograms IAA per gram fresh weight and 0.01 nanoliter ethylene per gram per hour) in the second stage of fruit growth. Endogenous levels of free-IAA and ethylene evolution increased in the last stage of peach fruit development to 32 nanograms per gram fresh weight and 0.27 nanoliter per gram per hour, respectively. IAA amounts peaked in the ovules 67 days after anthesis.     

无核白葡萄胚挽救育种技术研究

无核白葡萄在授粉后20－50d,将胚珠接种在含不同激素的Nitsch培养基上,培养80－90d后转入胚荫发培养基中,待胚萌发20d左右,再转入成苗培养基中使其发育成正常幼苗。结果表明,胚萌发适宜的培养基是附加0．5mg/L IAA,1.5mg/L BA和0.5mg/LGA3的Nitsh培养基,在所试10个接种时期中,无授粉后39d胚的发育率最高。     

The relative importance of architecture and resource competition in allocation to pollen and ovule number within inflorescences of Hosta ventricosa varies with the resource pools

Background and Aims

Allocation of resources to floral traits often declines distally within inflorescences in flowering plants. Architecture and resource competition have been proposed as underlying mechanisms. The aim of the present study is to assess the relative importance of resource competition and architectural effects in pollen and ovule production on racemes of Hosta ventricosa, an apomictic perennial herb.

Methods

Combinations of two defoliation treatments (intact and defoliated) and two fruit-set treatments (no-fruit and fruit) were created, and the roles of architecture and resource competition at each resource level were assessed.

Key Results

Pollen and ovule number per flower increased after defoliation, but pollen to ovule ratio per flower did not change. Pollen, ovules and the pollen to ovule ratio per flower declined distally on racemes at each resource level. In the intact treatment, fruit development of early flowers did not affect either pollen or ovule number of late flowers. In the defoliated treatment, fruit development of early flowers reduced both pollen and ovule numbers of late flowers due to over-compensation caused by defoliation. Late flowers on defoliated fruit racemes produced less pollen than intact fruit racemes but the same number of ovules; therefore, the reduction in pollen number was not caused by over-compensation. In addition, the fruit-set rate of early flowers during flowering was higher in intact racemes than in defoliated racemes.

Conclusions

In flowering plants, the relative importance of architecture and resource competition in allocation to pollen and ovules may vary with the resource pools or the overall resource availability of maternal plants.     

TRANSPORT OF IAA AND ACC IN FLORAL ORGANS OF IPOMOEA NIL (CONVOLVULACEAE)

The involvement of the stamens as transporters of plant growth regulators in flowers was examined by measuring the movement of ¹⁴C-indole-3-acetic acid (IAA) and ^l4C-l-aminocyclopropane-1-carboxylic acid (ACC) through floral organs of Ipomoea nil. During the transport of ¹⁴C-IAA through isolated filament segments, the polar accumulation of ¹⁴C-IAA in receiver blocks increased with time during filament development, which correlated with polar efflux rates at older stages of filament development. An inhibitor of polar IAA transport, 2,3,5-triiodobenzoic acid, disrupted the polarity of auxin transport by reducing the movement of ¹⁴C- IAA from filaments into receiver blocks. Transport of both ¹⁴C-IAA and ^l4C-ACC through filaments into other floral organs also was monitored in isolated flower buds in the laboratory and intact buds in the greenhouse. In isolated and intact buds 21 hr before anthesis, substantially higher levels of isotope were recovered in corolla tissue when ¹⁴C-ACC was transported through the filaments than when ¹⁴C-IAA was transported from the filaments. In isolated buds, substantial levels of both isotopes accumulated in the pistil (69 hr and 45 hr before anthesis), but minimal amounts were observed in receptacle and calyx tissues (69 hr to 21 hr before anthesis). In intact buds, high levels of both isotopes were recovered in receptacle, calyx, and pistil tissues (69 hr to 21 hr before anthesis). The results from this study support the hypothesis that Ipomoea stamens are transporters for ACC and IAA to regulate ethylene production in the corolla and other floral tissues.     

2,4‐D‐induced parthenocarpy in pear is mediated by enhancement of GA4 biosynthesis

Parthenocarpy, the productions of seedless fruit without pollination or fertilization, is a potentially desirable trait in many commercially grown fruits, especially in pear, which is self‐incompatible. Phytohormones play important roles in fruit set, a process crucial for parthenocarpy. In this study, 2,4‐dichlorophenoxyacetic acid (2,4‐D), an artificially synthesized plant growth regulator with functions similar to auxin, was found to induce parthenocarpy in pear. Histological observations revealed that 2,4‐D promoted cell division and expansion, which increased cortex thickness, but the effect was weakened by paclobutrazol (PAC), a gibberellin (GA) biosynthesis inhibitor. Phenotypic differences in pear may therefore be due to different GA contents. Hormone testing indicated that 2,4‐D mainly induced the production of bioactive GA₄, rather than GA_3. Three key oxidase genes function in the GA biosynthetic pathway: GA20ox, GA3ox and GA2ox. In a pear group treated with only 2,4‐D, PbGA20ox2‐like and PbGA3ox‐1 were significantly upregulated. When treated with 2,4‐D supplemented with PAC, however, expression levels of these genes were significantly downregulated. Additionally, PbGA2ox1‐like and PbGA2ox2‐like expression levels were significantly downregulated in pear treated with either 2,4‐D only or 2,4‐D supplemented with PAC. We thus hypothesize that 2,4‐D can induce parthenocarpy by enhancing GA₄ biosynthesis.     

Changes in Amide-Linked and Ester Indole-3-Acetic Acid in Cotton Fruiting Forms during Their Development

The concentration of free indoleacetic acid (IAA) is high in cotton (Gossypium hirsutum L.) fruiting forms before anthesis, but is low at and for a few days after anthesis. Amide-linked and ester IAA were measured in fruiting forms at 9, 6, and 3 days before anthesis; at anthesis; and at 2, 4, 7, and 9 days after anthesis to determine if free IAA decreased because it was converted to a conjugated form. That did not appear to be the case. While the major decrease in free IAA occurred during the 6 days before anthesis, ester IAA increased only a small amount and amide-linked IAA decreased even more than free IAA. During the 6 days before anthesis free IAA decreased from 0.62 to 0.12 micrograms per gram and amide-linked IAA decreased from 19.14 to 1.16 micrograms per gram dry weight. No evidence was found that a large amount of amide-linked IAA was converted to an insoluble form; flowers contained less than 1 microgram per gram of insoluble IAA. The free and amide-linked IAA must have been converted to other forms, perhaps by oxidation. Soluble amide-linked IAA remained low after anthesis. No ester IAA was detected 6 days before anthesis and only 0.08 microgram per gram dry weight was measured at anthesis. The concentration of ester IAA increased thereafter to 4.43 micrograms per gram at 9 days after anthesis. Therefore, amide-linked IAA was the major form of IAA in flower buds and ester IAA was the major form in young fruits (bolls). Minimum concentrations of free and total IAA occurred during the 4 days after anthesis, a stage when cotton fruiting forms are most likely to abscise. The large decreases in free and amide-linked IAA during the 6 days before anthesis may indicate a rapid turnover of IAA in flower buds. But, the decrease in free IAA was not accompanied by a comparable increase in ester or amide-linked IAA.