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.     

Effects of hypergravity on the elongation growth in radish and cucumber hypocotyls

The elongation growth of the hypocotyls of radish and cucumber seedlings was examined under hypergravity in a newly developed centrifuge (Kasaharaet al. 1995). The effects of hypergravity on elongation growth differed between the two species. The rate of elongation of radish hypocotyls was reduced under basipetal hypergravity (H+20g) but not under acropetal hypergravity (H-13g), as compared to growth under the control conditions (C+1g and C-1g). In cucumber hypocotyls, elongation growth was inhibited not only by basipetal but also by acropetal hypergravity. Under these conditions, the reduction in the elongation growth of both radish and cucumber hypocotyls was accompanied by an increase in their thickness. Although no distinct differences in relative composition of neutral sugars were found, the amounts of cell-wall components (pectic substances, hemicelluloses and cellulose) per unit length of hypocotyls were increased by exposure to hypergravity.     

Comparative Potency of Nine Gibberellins

Gibberellins A₁ to A₉ have been compared, each at several doselevels, in bioassays based on extension of stems of dwarf gardenpea (Pisum sativum), dwarf bean (Phaseolus vulgaris) and Lunariaannua, of hypocotyls of cucumber (Cucumis sativus) and lettuce(Lactuca sativa), and of leaf sheaths of three dwarf mutants(d–1, d–3, d–5) of maize (Zea mays). GibberellinsA₃ (gibberellic acid) and A₇ are of high potency in most bioassays.A₈ is of negligible potency in all and is probably not a functionalhormone. The other gibberellins show a more or less marked tendencyto specificity. The plants used as bioassay material also differin the specificity of their response. Some, for example, maizedwarfs d–3 and d–5 and lettuce, respond well tomost gibberellins; others, for example, cucumber, respond onlyto a few; extreme specificity is shown by Lunaria annua which,in the unvernalized condition, responds by stem elongation onlyto gibberellin A₇. Dose/response curves of the various gibberellinsare usually parallel, but certain exceptions to this have beenfound. Possible explanations of specificity are discussed inrelation to the results obtained, and it is concluded that insufficientevidence is available to make it possible to draw any validconclusions. Current definitions of gibberellins, whether basedon chemical structure or biological activity, are unsatisfactory.     

Intergeneric Translocation of Floral Stimulus across a Graft in Monoecious Cucurbitaceae with Special Reference to the Sex Expression of Flowers

The effect of floral stimulus on flower sex expression in monoeciouscucurbits was examined using a qualitative short-day plant,Sicyos angulatus L. Sicyos was induced to flower not only bygrafting it onto a flower-induced plant of the same speciesbut also by intergeneric grafting Onto the day-neutral plantCucumis sativus L. or the quantitative short-day plant Luffacylindrica Roem under noninductive long-day conditions. Sicyosplant grafted onto various cucumber varieties having differentgenetic backgrounds for their sex expression developed bothstaminate and pistillate inflorescences with similar sex expression.When the availability of floral stimulus was restricted as inthe case of grafting of Sicyos onto young cucumber seedlingsat the cotyledonary stage, most inflorescences appearing onthe Sicyos were staminate ones. Pistillate flowers formed onthe cucumber receptors substantially increased when they weregrafted onto Sicyos donors which had a sufficient number ofleaves induced by short-days as compared with those graftedonto noninduced ones. These results suggest that the availabilityof floral stimulus participates in the sex expression of flowersin Cucurbitaceae. Undeveloped pistillate inflorescences, whichoccasionally appear on Sicyos scion, flowered normally whenN⁶-benzylaminopurine was directly applied to the inflorescence. (Received February 27, 1981; Accepted October 16, 1981)     

Starch Grain Casts and Moulds in Eocene (Tertiary) Fossil Mangrove Hypocotyls

Further examples of the recently reported fossil starch graincasts and moulds in the fossil mangrove Ceriops cantiensis Chandlerfrom the London Clay (Eocene) of the Isle-of-Sheppey, Kent,England have now been discovered. In addition, similar structureshave been found in the fossil hypocotyls of Palaeobruguieraelongata Chandler from Herne Bay, Kent and also in four recentlycollected hypocotyls of a new species of fossil mangrove fromSheppey. Starch grains from herbarium material of the extantmangrove genera, Bruguiera and Ceriops, have been examined forcomparison with the fossil forms. starch grain casts, fossil, mangrove, hypocotyls, palaeobotany, Eocene, framboids, Rhizophoraceae, Bruguiera sexangula, Ceriops cantiensis, Palaeobruguiera elongata     

Variation in the Content and Composition of Sterols in Alfalfa Seedlings Treated with Compactin (ML-236B) and Mevalonic Acid

Compactin (ML-236B), a specific inhibitor of 3-hydroxy-3-methylglutarylCoA reductase, inhibited the elongation of roots and hypocotylsof Medicago sativa seedlings when it was applied to the roots.Addition of mevalonic acid, the direct product of the enzyme,together with compactin relieved the growth inhibition of roots. The contents and compositions of sterols were studied in threeparts of M. sativa seedlings—roots, hypocotyls and cotyledons.Compactin (20 µM) decreased the sterol contents of rootsand hypocotyls by about a half but did not affect that of cotyledons.On the other hand, mevalonic acid (2 mM) increased the sterolcontent of roots more than threefold the nontreated controllevel but not the contents of hypocotyls and cotyledons. Mevalonicacid added in combination with compactin had a similar effecton the sterol content of roots as when it was added alone. The major sterol in all three parts was stigmasterol whetheror not compactin or mevalonic acid was present. However, thevariation of the sterol composition in the roots was distinct;mevalonic acid-treated roots markedly accumulated ⁷-sitosterol,24-methylenecycloartanol and squalene. (Received October 16, 1986; Accepted April 2, 1987)     

The RHG Gene Is Involved in Root and Hypocotyl Gravitropism in Arabidopsis thaliana

In higher plants, shoots show negative gravitropism and rootsshow positive gravitropism. To elucidate the molecular mechanismsof root and hypocotyl gravitropism, we segregated the secondmutation from the original phyB-1 mutant line which impairedboth root and hypocotyl gravitropism and characterized thisnovel mutation named rhg (for root and hyzypocotyl gravitropism).The rhg is a single recessive nuclear mutation and it is mappedon the lower part of the chromosome 1. Analyses on the gravitropicresponses of the rhg mutant indicate that root and hypocotylgravitropism are severely impaired but inflorescence stem gravitropismis not affected by the rhg mutation. In the rhg mutant seedlings,amyloplasts (statoliths for gravity-perception) were presentin the presumptive statocytes of roots and hypocotyls. Phototropismby roots and hypocotyls was not impaired in the rhg mutant.These results suggest that the RHG gene product probably actson the gravity-perception and/or the gravity-signal transductionin root and hypocotyl gravitropism. This is the first reportabout the genetic locus specifically involved in both root andhypocotyl gravitropism but not inflorescence stem gravitropism,supporting our hypothesis that the mechanisms of gravitropismare genetically different between hypocotyls and inflorescencestems. (Received March 11, 1997; Accepted April 17, 1997)     

Effects of hypergravity on growth and cell wall properties of cress hypocotyls

Elongation growth of etiolated hypocotyls of cress (Lepidiumsativum L.) was suppressed when they were exposed to basipetalhypergravity at 35 g and above. Acceleration at 135 g causeda decrease in the mechanical extensibility and an increase inthe minimum stress-relaxation time of the cell wall. Such changesin the mechanical properties of the cell wall were prominentin the lower regions of hypocotyls. The amounts of cell wallpolysaccharides per unit length of hypocotyls increased underthe hypergravity condition and, in particular, the increasein the amount of cellulose in the lower regions was conspicuous.Hypergravity did not influence the neutral sugar compositionof either the pectin or the hemicellulose fraction. The amountof lignin was also increased by hypergravity treatment, althoughthe level was low. The data suggest that hypergravity modifiesthe metabolism of cell wall components and thus makes the cellwall thick and rigid, thereby inhibiting elongation growth ofcress hypocotyls. These changes may contribute to the plants'ability to sustain their structures against hypergravity. Key words: Cell wall extensibility, cellulose, hypergravity, Lepidium sativum L., lignin     

Appearance of a Host Protein in Cucumber Plants Infected with Viruses, Bacteria and Fungi

Electrophoretic analyses of extracts of cucumber leaves infectedwith Colleiotrichum lagenarium, Fusarium oxysporum f. sp. cucumerinum,Pseudomonas lachrymans, Erwinia tracheiphila, tobacco necrosisvirus or cucumber mosaic virus revealed the presence of a proteinband with an R_F value of 0.55–0.60 (based on mobilityof bromophenol blue) on 10% polyacrylamide gel. This band wasnot evident in extracts of healthy or mechanically wounded leaves.The protein was not detected in uninfected leaves of infectedplants, but it was detected in similar amounts in infected leavesand in secondarily challenged leaves of infected plants eventhough symptoms were not apparent on the latter. The proteinhad a molecular weight of approximately 16 000 d, was adsorbedon DEAE-cellulose, did not react with Schiff's reagent, anddid not have ribonuclease activity. When injected into cucumberleaves, it did not inhibit germination of conidia of C. lagenariumor induce resistance against disease caused by the fungus.     

Stress relaxation properties of the cell wall of growing intact plants

The cell wall of dark-grown Avena coleoptiles and the epidermisof light-grown mungbean hypocotyls was subjected to stress-relaxationanalysis and the following results were obtained. 1. Actively growing apical regions of the organs, either coleoptilesor hypocotyls, had certain threshold values of minimum stress-relaxationtime, T_O, 0.04 sec for coleoptile cell wall and 0.03 sec forthe epidermal cell wall of hypocotyls. The cell wall of thebasal region of the organs, which were mature and not growing,had a higher value of To. 2. When the apical regions of the organs, either coleoptilesor hypocotyls, ceased to grow, their cell walls showed T_O valuesabove these thresholds. 3. The relaxation rate, b, was small in the cell wall of activelygrowing regions of the organs, compared with that of non-growingregions. 4. The maximum relaxation time, T_m, was variable and no significantrelationship with growth capacity was found. 5. The extensibility, mm/gr, was large not only in activelygrowing regions of the organs but also in fully grown regions,suggesting that the value represents complex properties of thecell wall including the history of cell wall extension. From these results, we concluded that biochemical modificationsoccur in the cell wall matrix of actively growing organs ofeither monocots or dicots, and these are the bases of the capacityof the cell wall to extend and are represented chiefly by T_oand possibly by b. (Received August 12, 1974; )     

棉花型和瓜型棉蚜产生有性世代能力的分化

为了明确寄主专化性是否会影响棉蚜的繁殖策略或生活史对策,采用低温和短光照组合（18℃,L∶D=8∶16）分别对棉花型和瓜型棉蚜进行有性世代的诱导,比较两寄主专化型棉蚜产生有翅蚜、雄性母、雌性母及无翅孤雌蚜的能力。结果表明：两寄主专化型棉蚜在产生有性世代能力上存在显著差异,表现为棉花型棉蚜在诱导后代中产生有翅蚜、雄性母和雌性母的比率显著高于瓜型棉蚜,并且雌、雄性母产生的时间明显早于瓜型棉蚜。瓜型棉蚜在诱导条件下产生无翅孤雌蚜的比率显著高于棉花型棉蚜,并且发现有不产生有性世代的营专性孤雌生殖个体,而在棉花型棉蚜中没有发现。产生性母蚜的棉花型和瓜型棉蚜均可同时产生孤雌胎生后代。寄主型与诱导时间长短对棉蚜有性世代的产生存在交互作用。采集于田间棉花和黄瓜上的棉蚜,也表现为棉花上的易产生有性世代,在诱导的第2代中产生性母蚜的比率显著高于黄瓜上的棉蚜,并且性母蚜比率在诱导的第2代与第3代间无显著差异; 但黄瓜上的棉蚜性母蚜产生比率第3代显著高于第2代。由此推测,棉蚜寄主专化性的形成与生活史特性的分化有关。     

PHYSIOLOGICAL ACTIVITIES OF HELMINTHOSPOROL AND HELMINTHOSPORIC ACID: I. EFFECTS ON GROWTH OF INTACT PLANTS

Helminthosporol (H-ol) and helminthosporic acid (H-acid) wereeffective in promoting elongation of leaf sheaths of rice, Japanesebarnyard grass and dwarf maize (d-2 and d-5) and of hypocotylsof taisai (Brassica chinensis), but inactive in leaf sheathsof oat and wheat, hypocotyls of sesame and morning glory (Pharbitisnil) and epicotyls of Pharbitis and dwarf and tall peas. Onthe elongation of the leaf sheath of maize d-1, H-ol was promotivebut the activity of H-acid was doubtful. On hypocotyls of lettuceand daikon (Raphanus sativus), only H-acid was active. Multiplicationrate and size of fronds of Lemna perpusila were not affectedby either of the substances. Compared with gibberellic acid for the effect on the shoot growth,H-ol and H-acid were weak in activity and narrower in the scopeof plants that responded. H-ol and H-acid characteristicallypromoted the elongation of the primary root. Comparative effectivenessof H-ol and H-acid varied with plant species or parts examined. ¹ This study was supported in part by grant-in aid of the Ministryof Education (No. 0417). The results reported here were presentedat the Annual Meeting of the Botanical Society of Japan at Kanazawain 1964 (S).     

Effects of Osmotic Stress, Ionic Stress and IAA on the Cell-Membrane Resistance of Vigna Hypocotyls

The cell-membrane resistance (R_m) of Vigna hypocotyls was examined,and the effects of osmotic stress, ionic stress and IAA on R_mwere investigated. R_m decreased by 64 to 77% under osmotic stressin the presence of absorbable solutes (40 mM sorbitol, 15 mMKC1, 30 mM sucrose; or 40 mM sorbitol, 15 mM KC1, 30 mM sucroseplus 10^–4 M IAA) or under ionic stress (50 mM NaCl or50 mM KC1). R_m was not changed by perfusion with 10^–4M IAA. Therefore, the hyper-polarizations of the membrane potentialobserved in both cases should be ascribed totally to the activationof the electrogenic proton pump. Although R_m showed an increaseof 1.6 fold when the hypocotyls were subjected to osmotic stress(100 mM sorbitol or 100 mM sorbitol plus 10^–4 M IAA),83.6% or 92.4% of the hyperpolarization of the membrane potential(V_px was also the result of the activation of the pump. Theresults, calculated on the basis of the current source model,support the viewpoint that the hyperpolarization of the cellmembrane potential of Vigna hypocotyls under osmotic stress,ionic stress or in the presence of IAA is an expression of theactivation of the proton pump, and is not caused by an increasein R_m. ¹ Present address: Researchers and Planners of Natural Environment, Yotsugi Bldg. (2F), 1-5-4 Horinouchi, Suginami-Ku, Tokyo,166 Japan ² Present address: Graduate School of Integrated Science, YokohamaCity University, 22-2 Seto, Kanazawa-Ku, Yokohama, 236 Japan (Received February 14, 1991; Accepted July 24, 1991)     

Promotive effect of chrysanthemic acids on adventitious root formation in some plants

Adventitious root formation in excised cucumber (Cucumis sativus L.) cotyledons was significantly promoted by (±)-cis-chrysanthemic acid at 0.006–1.8 mM. The effect of (±)-cis-chrysanthemic acid on indole-3-acetic acid (IAA)-induced rooting was additive. Rooting in excised cucumber cotyledons was significantly promoted by several isomers of chrysanthemic acid and sodium (±)-cis-chrysanthemate at 0.18 mM. Rooting in mung bean (Phaseolus radiatus L.) hypocotyls was also stimulated by the sodium salt at 0.06–0.6 mM. Rooting of kidney bean (Phaseolus vulgaris L.) hypocotyls was also clearly enhanced by sodium (±)-cis-chrysanthemate at 0.18–6 mM.     

Effects of Deoxygibberellin C (DGC) and 16-Deoxo-DGC on Gibberellin 3{beta}-Hydroxylase and Plant Growth

Deoxygibberellin C (DGC), a C/D ring-rearranged isomer of GA₂₀,was shown to inhibit the conversion of [2,3-³H₂]GA₉ to [2-³H]GA₄by gibberellin 3ß-hydroxylase from immature seedsof Phaseolus vulgahs. Deoxygibberellin C inhibited the promotionof growth by exogenously applied GA₂₀ of rice (Oryza sativaL.) seedlings. Evidence is also presented that DGC is a competitiveinhibitor of the 3ß-hydroxylase from P. vulgaris.However, DGC only weakly inhibited the conversion catalyzedby the 3ß-hydroxylase from Cucurbita maxima at highconcentrations, and it did not inhibit the promotion of growthby exogenously applied GA₉ of cucumber (Cucumis sativus) seedlings.These results suggest that the 3ß-hydroxylases fromP. vulgaris and C. maxima have different structural requirementswith respect to their substrates. 16-Deoxo-DGC also inhibitedcatalysis of the same conversion by 3ß-hydroxylasefrom P. vulgaris, and it slightly inhibited the conversion catalyzedby the enzyme from C. maxima. Application of 16-deoxo-DGC causedthe promotion of the growth of seedlings of both rice and cucumber. ³ Present address: Genetic Engineering Center, Korea Instituteof Science and Technology, Daejeon 305–606, Korea ⁴ Present address: Department of Agricultural Chemistry, UtsunomiyaUniversity, Utsunomiya-shi, Tochigi, 321 Japan (Received September 25, 1990; Accepted December 17, 1990)     

The relationship between xyloglucan endotransglycosylase and in-vitro cell wall extension in cucumber hypocotyls

It has been proposed that cell wall loosening during plant cell growth may be mediated by the endotransglycosylation of load-bearing polymers, specifically of xyloglucans, within the cell wall. A xyloglucan endotransglycosylase (XET) with such activity has recently been identified in several plant species. Two cell wall proteins capable of inducing the extension of plant cell walls have also recently been identified in cucumber hypocotyls. In this report we examine three questions: (1) Does XET induce the extension of isolated cell walls? (2) Do the extension-inducing proteins possess XET activity? (3) Is the activity of the extension-inducing proteins modulated by a xyloglucan nonasaccharide (Glc₄-Xyl₃-Gal₂)? We found that the soluble proteins from growing cucumber (cucumis sativum L.) hypocotyls contained high XET activity but did not induce wall extension. Highly purified wall-protein fractions from the same tissue had high extension-inducing activity but little or no XET activity. The XET activity was higher at pH 5.5 than at pH 4.5, while extension activity showed the opposite sensitivity to pH. Reconstituted wall extension was unaffected by the presence of a xyloglucan nonasaccharide (Glc₄-Xyl₃-Gal₂), an oligosaccharide previously shown to accelerate growth in pea stems and hypothesized to facilitate growth through an effect on XET-induced cell wall loosening. We conclude that XET activity alone is neither sufficient nor necessary for extension of isolated walls from cucumber hypocotyls.     

Effect of Vanadate on Microsomal ATPase Activity, Acidification of the Medium and Auxin-stimulated Growth in Pea and Cucumber

The relationship between ATPase activity, medium acidificationand auxin-stimulated growth in segments of pea stem (Pisum sativumL., cv. Alaska) and cucumber hypocotyl (Cucumis sativus L.,cv. Long Green Ridge) was investigated using sodium orthovanadate,widely used as a selective inhibitor of plasma membrane-associatedATPase activity. ATPase activity of cucumber microsomal preparationswas about seven times lower than similar preparations from pea(on a mg microsomal protein basis) and was much more effectivelyinhibited by vanadate. Similarly, acidification of the mediumby abraded cucumber segments occurred to a lesser extent thanwith pea and showed a greater inhibition by vanadate. Both growthin controls and auxin-stimulated growth of cucumber segmentswere strongly inhibited by vanadate, whereas in pea auxin-stimulatedgrowth was reduced by only half and controls showed little inhibition.Acidification of the medium by segments of both species wasfound to occur readily even in controls and showed little promotionin the presence of IAA, although growth in both species wasrapidly and significantly promoted by IAA. These results indicatethat acidification is brought about by a plasma membrane-associatedATPase, and suggest that while acidification is an essentialfactor for auxin-stimulated growth it may not be the mechanismby which the growth rate is controlled. ATPase, Cucumis sativus, indole-3-acetic acid, Pisum sativum, vanadate     

Isolation of xyloglucans from etiolated Glycine max and Vigna sesquipedalis hypocotyls

Xyloglucans isolated from cell walls of etiolated Glycine maxand Vigna sesquipedalis hypocotyls were subjected to fragmentationanalysis with cellulase for structural comparison with thosederived from Phaseolus aureus hypocotyls. The xyloglucans fromG. max and V. sesquipedalis had glucose, xylose, galactose andfucose in the approximate molar ratio of 10:6:4:1 and 10:7:3:1,respectively. However, the results of cellulase fragmentationanalysis of xyloglucans from the three species suggested thatthe basic structure of the xyloglucans in the cell walls ofthese bean-hypocotyls is almost the same; the structure is basedon two repeating oligosaccharide units, one of which consistsof glucose and xylose and the other of glucose, xylose, galactoseand fucose. ¹ Present address: Toppan Printing Co., Ltd., Okaji, Sendai980, Japan. (Received February 3, 1977; )     

Chitinase in cucumber hypocotyls is induced by germinating fungal spores and by fungal elicitor in synergism with inducers of acquired resistance

After root pretreatment with 2,6-dichloroisonicotinic acid (DCIA or INA), hypocotyls of etiolated cucumber seedlings acquired resistance to infection by Colletotrichum lagenarium caused by the failure of the fungus to penetrate epidermal cell walls. The hypocotyls contained only low levels of class III chitinase and its mRNA prior to infection. This pathogenesis-related (PR) gene was expressed strongly upon infection but only in resistant hypocotyls and soon after germination of the fungal spores. Chitinase was also induced early by an albino mutant strain of C. lagenarium that can barely penetrate the epidermis. Thus, early recognition of the fungus implies signal compounds able to pass, or being generated in, the hydrophobic epidermal surface. As the apoplastic chitinase accumulates timely at the site of a subsequent attack, it may contribute to disease resistance. The mechanism behind the enhanced responsiveness of epidermal cells was studied by gently abrading the cuticle of susceptible hypocotyls to allow permeation of a water-soluble polymeric fungal elicitor. Induction of chitinase occurred only when the elicitor was applied simultaneously with a resistance inducer such as DCIA, salicylic acid (SA) or a benzothiadiazole (BTH). In addition, long-term root pretreatment with DCIA conditioned the hypocotyls for enhanced elicitor responses. These results demonstrate that the above inducers of acquired resistance can affect expression of the cucumber chitinase gene not only as direct inducers. They can also act synergistically with fungal elicitors and, in addition, condition the hypocotyls in a developmental manner for potentiated elicitation.