Sexual differentiation in cucumber: Abscisic acid and gibberellic acid contents of various sex genotypes

The AbA content of cucumber shoot tips was determined by GLC.Shoot tips of monoecious plants had a higher AbA content thanthose of gynoecious ones, and SD conditions caused higher AbAcontent than LD conditions. AbA content per unit dry weightof young floral buds was 5- to 9-fold higher than in older ones. A GLC method was developed to allow parallel identificationand quantitative determinations of GA₃ and AbA with the samesample. The shoot tip contents of both growth substances weredetermined at four developmental stages of the monoecious plant.Both significantly increased until the 12th day after plantingthen decreased; the GA₃ content decreased markedly. A general hypothesis for the role of growth substances in regulatingsex expression of cucumber is presented and discussed. (Received January 7, 1977; )     

The level of phytohormones in monoecious and gynoecious cucumbers as affected by photoperiod and ethephon

The endogenous levels of auxin, gibberellin, and inhibitors were followed in monoecious and gynoecious cucumber (Cucumis sativus L.) plants, and in plants treated with the ethylene-releasing compound Ethephon (2-chloroethyl phosphonic acid). Higher auxin inhibitor and lower gibberellin levels were associated with female tendency. The endogenous level of gibberellin and auxin decreased in Ethephon-treated plants. Application of Ethephon induced a rise in abscisic acid. Root application of abscisic acid promoted female tendency of gynoecious cucumbers grown under conditions which increase maleness. High CO₂ levels, which are known to antagonize ethylene, increased maleness of gynoecious cucumbers. The possibility of interrelationship between gibberellin, auxin, ethylene, and abscisic acid on sex expression are discussed.     

Involvement of abscisic acid in the regulation of sex expression in the cucumber

The interaction between abscisic acid (ABA), gibberellin (GA)and ethephon on sex determination in cucumber (Cucumis sativusL.) flowers was examined. ABA promoted the female tendency ofgynoecious plants, but did not change the sex expression ofmonoecious ones. When ABA was applied together with GA₄₊₇ thepromoting activity of the GA on male flower formation in thegynoecious line was reduced. ABA also inhibited tendril appearanceand internode length, characteristic of GA treatments. A combinedABA and ethephon treatment resulted in a synergistic activityinhibiting growth and increasing the period of female flowerappearance in the monoecious line. It is suggested that ABAparticipates in the sex regulation of the cucumber by inhibitingGA activity. (Received March 8, 1974; )     

The M locus and ethylene-controlled sex determination in andromonoecious cucumber plants.

Sex determination in cucumber (Cucumis sativus L.) plants is genetically controlled by the F and M loci. These loci interact to produce three different sexual phenotypes: gynoecious (M-F-), monoecious (M-ff), and andromonoecious (mmff). Gynoecious cucumber plants produce more ethylene than do monoecious plants. We found that the levels of ethylene production and the accumulation of CS-ACS2 mRNA in andromonoecious cucumber plants did not differ from those in monoecious plants and were lower than the levels measured in gynoecious plants. Ethylene inhibited stamen development in gynoecious cucumbers but not in andromonoecious ones. Furthermore, ethylene caused substantial increases in the accumulation of CS-ETR2, CS-ERS, and CS-ACS2 mRNA in monoecious and gynoecious cucumber plants, but not in andromonoecious one. In addition, the inhibitory effect of ethylene on hypocotyl elongation in andromonoecious cucumber plants was less than that in monoecious and gynoecious plants. These results suggest that ethylene responses in andromonoecious cucumber plants are reduced from those in monoecious and gynoecious plants. This is the first evidence that ethylene signals may influence the product of the M locus and thus inhibit stamen development in cucumber. The andromonoecious line provides novel material for studying the function of the M locus during sex determination in flowering cucumbers.     

Characterization of ethylene effects on sex determination in cucumber plants

Sex differentiation in cucumber plants (Cucumis sativus L.) appears to be determined by the selective arrest of the stamen or pistil primordia. We investigated the influence of an ethylene-releasing agent (ethephon) or an inhibitor of ethylene biosynthesis (aminoethoxyvinyl glycine) on sex differentiation in different developmental stages of flower buds. These treatments influence sex determination only at the stamen primordia differentiation stage in both monoecious and gynoecious cucumbers. To clarify the relationships between the ethylene-producing tissues and the ethylene-perceiving tissues in inducing female flowers in the cucumber, we examined the localization of mRNA accumulation of both the ACC synthase gene (CS-ACS2) and the ethylene-receptor-related genes (CS-ETR1, CS-ETR2, and CS-ERS) in flower buds by in situ hybridization analysis. CS-ACS2 mRNA was detected in the pistil primordia of gynoecious cucumbers, whereas it was located in the tissues just below the pistil primordia and at the adaxial side of the petals in monoecious cucumbers. In flower buds of andromonoecious cucumbers, only CS-ETR1 mRNA was detected, and was located in the pistil primordia. The localization of the mRNAs of the three ethylene-receptor-related genes in the flower buds of monoecious and gynoecious cucumbers overlap but are not identical. We discuss the relationship between the mRNA accumulation patterns and sex expression in cucumber plants.     

Sex expression in cucumber plants as affected by mechanical stress

Sex expression in cucumber plants, as affected by mechanicalstress, was examined using 4 cultivars with different geneticbackgrounds for sex expression. Mechanical stress given to theplant greatly reduced growth and increased the number of pistillate(female) flowers in the monoecious type, but it had no effecton the sex expression of the gynoecious type. The effect ofmechanical stress on the growth and sex expression of the monoecioustype was nullified by the foliar application of gibberellinA₄₊₇. Silver nitrate also was effective in nullifying the effectof mechanical stress on sex expression, but not the effect ofgrowth retardation. Pistillate flowers in a gynoecious strainwere reduced by silver nitrate. (Received October 18, 1979; )     

Peroxidase and IAA Oxidase Activity and Isoenzyme Patterns in Cucumber Plants, as Affected by Sex Expression and Ethephon

Peroxidase and IAA-oxidase activity, electrophoretic patterns of total proteins and isoenzymes and the effect of Ethephon (= Ethrel, 2-chloroethane phosphonic acid) on these patterns were compared in extracts of monoecious and gynoecious cucumber plants. The activity of both peroxidase and IAA oxidase was greater in gynoecious than in monoecious plants. Ethephon treatments given at the 2-leaf stage increased peroxidase activity, especially in monoecious plants, and decreased IAA-oxidase activity. Ethephon treatment did not affect total protein or isoenzyme patterns, but increased band intensity, especially that of one band in monoecious plant extracts. No differences between monoecious and gynoecious plants were found in total protein, peroxidase and IAA-oxidase isoenzyme patterns. Peroxidase and IAA-oxidase activity sites on the gel were similar.     

The Interaction of Genetic, Environmental, and Hormonal Factors in Stem Elongation and Floral Development of Cucumber Plants

Hypocotyl length was found to vary between cucumber plants carryingdifferent genes controlling sex expression. Among lines havingonly unisexual flowers (genotype M/M), the homozygous monoeciousplants (st⁺/st⁺) had significantly longer hypocotyls than theirgynoecious counterparts (st/st), heterozygous gynoecious plants(st+/st) being intermediate. Similarly, hypocotyls of plantsof an andromonoecious line (st⁺/st⁺ m/m) were significantlylonger than in their hermaphrodite counterparts (st/st m/m).Differences in intemode length were also significant and inthe same direction. Since stem and particularly hypocotyl elongationin cucumber is known to be very sensitive to applied gibberellin,these findings suggest the existence of differences in the effectivelevels of endogenous gibberellins in the different sex types,higher levels being correlated with stronger male tendency.This conclusion is in good agreement with the known effect ofapplied gibberellin on sex expression (enhancement of the maletendency) in cucumber. Application of gibberellin (GA₄+GA₇) and exposure to ‘summer’conditions (long days and relatively high temperature) inhibitedthe development of pistillate flowers while ‘winter’conditions (short days, lower temperature) had a similar effecton staminate flowers. The effect was in either case specific,that is, limited to flower development. It is concluded thatexogenous and endogenous gibberellins affect not only the initiation,but also the further development, of flowers in the cucumber.     

Contents and recovery of gibberellins in monoecious and gynoecious cucumber plants

Diffusates from seedlings and root exudates from 6-week-old plants of a monoecious line of cucumber, Cucumis sativus L., contained considerably higher levels of gibberellin-(GA-) like substances than did those from plants of an isogenic gynoecious line. Most of the GA-like activity was found in a chromatogram region typical of GA₁ and GA₃; some activity, particularly in root exudates, appeared also at an R_F similar to that of GA₄ and GA₇.

When seedlings were treated with ³H-labeled GA₁, more radioactivity was found in the diffusates from monoecious seedlings than from gynoecious ones. The same was true of biological activity in root diffusates from older plants which had been treated with gibberellin A₄₊₇.

In conjunction with evidence present in literature, these results support the idea that endogenous GAs play a part in the regulation of sex expression in cucumber, relatively high levels favoring the formation of staminate flowers.

     

Ethylene evolution from cucumber plants as related to sex expression

Ethylene evolved from monoecious and gynoecious cucumber (Cucumis sativus) plants grown under short and long day conditions was determined. More ethylene was evolved from floral buds and apices bearing buds than from whole seedlings of comparable weight. More ethylene also was evolved from apices of the gynoecious than from those of the monoecious type. Furthermore, quantities evolved from female buds were greater than from male ones and plants grown under short day conditions which promote femaleness evolved more ethylene than those grown under long day conditions. The data suggest that ethylene participates in the endogenous regulation of sex expression by promoting femaleness.     

黄瓜茎端ABA/GA_4比值与花芽性别分化的关系(英文)

在同一环境条件下,单雌性株茎端ABA含量显著高于雌雄同株的,而GA_4水平却正好相反。 较高的ABA/GA_4比值有利于黄瓜雌性分化,反之则有利于雄性分化。促进黄瓜雄性分化的生长物质GA_3和AgNO_3会引起黄瓜茎端ABA/GA_4比值的下降,而促进其雌性分化的生长物质乙烯利(Ethrel)则会引起ABA/GA_4比值的上升。     

Auxin,biosynthesis of ethylene and sex expression in cucumber (Cucumis sativus)

Ethylene production, level of 1-aminocyclopropane-1-carboxylic acid (ACC) and activity of the ethylene forming enzyme (EFE) were higher in apices of gynoecious cucumber (Cucumis sativus cv. Alma) as compared to monoecious cucumber (C. sativus cv. Elem). Application of indole-3-acetic acid (IAA) enhanced ethylene and ACC production in both cultivars. The stimulatory effect of IAA was more pronounced in gynoecious apices. Induction of ethylene production and accumulation of ACC resulting from treatment with IAA were effectively blocked by aminoethoxyvinylglycine (AVG). Content of endogenous IAA, measured by an enzyme immunoassay, was lower in gynoecious cucumber as compared to monoecious one. Treatment of gynoecious plants with the antiauxins -(p-chlorophenoxy)isobutyric acid (PCIB) and -naphthaleneacetic acid (-NAA) did not inhibit female sex expression.It appears that although exogenous IAA enhances ACC and ethylene production, endogenous IAA might not have a major role in the control of sex expression in cucumber of the Beit-Alfa type.Prof. Rudich passed away in May 1986.     

Adventitious staminate flower formation in gibberellin treated gynoecious cucumber plants

Single gibberellin (A₄₊₇) treatments induced the appearanceof staminate floral buds in several consecutive nodes on themain stem of genetically female cucumber (Cucumis sativus L.).The staminate buds appeared next to pistillate buds which showedvarious degrees of degeneration. Similarly, repeated GA treatmentsinduced the appearance of staminate flowers in otherwise strictlyhermaphrodite plants, next to bisexual flowers. However, thebisexual buds, unlike the pistillate ones, did not show anydeleterious effects of the GA treatment. Therefore, it is inferredthat the hormonally induced staminate buds did not develop bysexual reversion of would-be pistillate or bisexual buds, butrather, represent adventitious buds which, in normally grownfemale or hermaphrodite plants, never develop. It thus seemsthat predetermined pistillate or bisexual buds do not changeinto staminate ones, while change in the reverse direction hasbeen demonstrated in the past (at least for the gynoecious ones). The effectiveness of the GA treatment in the gynoecious plantsshowed an acropetal gradient both within the affected region,as well as along the main stem. Autoradiographic histologicalexaminations showed that the course of development of the inducedstaminate floral bud did not differ from that of normally developingbuds. (Received June 16, 1977; )     

黄瓜植株性别表现与3种氧化酶同工酶的关系

采用同工酶电泳技术分析了二叶期纯雌株和雌雄株黄瓜（Ｃｕｃｕｍｉｓ ｓａｔｉｖｕｓ Ｌ．）子叶和真叶过氧化物酶、多酚氧化酶和超氧化物歧化酶同工酶,结果发现：给株比雌雄株酶活性强、酶带数量多,这种差异酶带大多与雌性或雌雄性别紧密相关,经检验可以作为黄瓜雌性株早期鉴定的生化标记,尤其以真叶中多酚氧化酶同工酶Ｒｆ０．２８７表现稳定,鉴定成功率高。等电聚焦电泳垂直平板聚丙烯酰胺凝胶电泳分辨效果好。     

Germination and Dormancy in Immature and Fresh-mature Lettuce Seeds

The effects of red light, far-red light, Gibberellin A₃, andethephon were studied on the germination of lettuce seeds cv.Grand Rapids harvested at different stages of development. Seeds did not become capable of germination until 8 days afteranthesis. Red light promoted seed germination from the age of8–9 days following anthesis up to the newly mature stage.Ten or 11 days following anthesis, a large percentage of seedsbecame capable of germination in the dark and therefore couldbe considered not dormant. They were affected by far-red light,but less so than the mature seeds. The effect of light on the germination of developing seeds appearedto be similar to the known light effect on mature lettuce seedgermination. Gibberellin A₃ and ethephon had no effect on immatureand fresh seed germination. Lactuca sativa L., Lettuce, germination, dormancy, red light, far-red light, gibberellin A₃, ethephon     

Femaleness in breeding glasshouse cucumbers

In growing parthenocarpic cucumber varieties the occurrence of bullnecks due to pollination by bees is a problem. To prevent the formation of these bullnecked cucumbers the possibilities of breeding female-flowered varieties were explored. Use was made of material derived from the gynoecious line MSU 713-5. Femaleness is caused by the gene Acr, which accelerates the production of female flowers. Within the type which, genetically, must be regarded as female, a variation occurs from total absence of male flowers to rather numerous axils with male flowers, mainly on the lower part of the stem. On the one hand this variation is also genetically controlled, and we may speak of “weakly” female and “strongly” female. On the other, environmental factors play an important part. The formation of male flowers in preponderantly female-flowered material is promoted by a long day, high night temperature and particularly, at least with our material, low light intensity; furthermore by a low pH of the soil and rich dressings of nitrogen. In order to be able to distinguish during selection between the weakly and strongly female plants, the environmental conditions should be favourable for the formation of male flowers. The maintenance of female plants is possible, because the formation of male flowers can be induced by spraying with gibberellin, after which selfing can be practised. Old plants respond less readily to gibberellin than young plants. Also, the response from strongly female plants is less pronounced than that from weakly female ones, which offers another possibility of selection. The extent to which male flowers may occur when growing female varieties depends on the cultivation method used. With the conventional method fruiting is forced to begin mainly on the laterals and any male flowers, if confined to the main stem, could be removed early. However, in view of fluctuations caused by the environment a rather pronounced female character will be desirable. Other cultivation methods are conceivable, e.g. short-term cultivation of larger numbers of plants per area unit, allowing the plants to come into bearing rapidly. The total absence of male flowers is then indispensable. With the aid of the femaleness it is also possible to simplify the production of hybrid seed, as hand pollination can be replaced by bee pollination. The combination gynoecious × monoecious, which in itself is the most favourable for this purpose, has the drawback that the resulting hybrid is usually insufficiently female. Therefore, use will generally have to be made of the combination gynoecious × gynoecious, spraying the latter parent with gibberellin.     

Some Morphogenic Differences between Monoecious and Gynoecious Cucumber Seedlings as Related to Ethylene Production

Exposure of gibberellic acid-treated seedlings of a monoecious cucumber cultivar `Chipper' (Cucumis sativus L.) to ethylene caused thickening of the hypocotyl, inhibited longitudinal growth, and had no effect on fresh weight. Downward curvature of cotyledons was increased by the presence of ethylene. A gynoecious breeding line, `Gy 3,' had thicker hypocotyls and displayed its cotyledons in a more downward position than `Chipper'. Excised hypocotyls of the gynoecious seedlings produced three times as much ethylene as did the monoecious Chipper hypocotyls. Thus, ethylene may play a role in the regulation of cucumber seedling morphology.