Stabilization of Cortical Microtubules in Maize Mesocotyl Cells by Gibberellin A3

Effects of GA₃ on the stability of cortical microtubules (MTs)were studied in mesocotyl cells of etiolated maize seedlings.Propyzamide, an MT-disrupting agent specific for plant tubulin,disrupted cortical MTs in cells in the upper regions of mesocotylsof GA₃-untreated seedlings and caused swelling of the cells.GA₃ prevented propyzamide from disrupting MTs and from causingsuch swelling. Chilling of mesocotyls at 4°C for 60 minbrought about the disruption of cortical MTs in cells in theupper regions of mesocotyls of GA₃-untreated seedlings, butnot in cells in corresponding regions of GA₃-treated seedlings,suggesting that treatment with GA₃ increased the stability ofcortical MTs in maize mesocotyl cells. Cortical MTs in protoplastsisolated from mesocotyls of GA₃-untreated seedlings failed towithstand chilling at 0°C for 90 min, while those in protoplastsisolated from mesocotyls of GA₃-treated seedlings withstoodchilling successfully. It appears that the cell wall is notinvolved in the stabilization of cortical MTs by GA₃ in maizemesocotyl cells. (Received July 6, 1993; Accepted November 29, 1993)     

Effects of a Plant Growth Regulator, Prohexadione Calcium (BX-112), on the Elongation of Rice Shoots Caused by Exogenously Applied Gibberellins and Helminthosporol, Part II

Prohexadione calcium (BX-112) is a novel plant growth regulatorthat inhibits the late stages of the biosynthesis of gibberellinsin plants. Fourteen kinds of gjbberellin, helminthosporol and'helminthosporic acid were applied simultaneously with BX-112to rice seedlings (Oryza sativa L. ), and their growth-promotingactivities in terms of shoot elongation were examined. The growth-promotingactivities of GA₁, GA₄, GA₁₈, GA₂₂, GA₂₃, GA₃₈, helminthosporoland helminthosporic acid were not inhibited by BX-112, but thoseof GA₅, GA₉, GA₁₅, GA₁₉, GA₂₀, GA₃₁, GA₄₄ and GA₅₃ were inhibited.These results suggest that 3ß-hydroxylation is animportant and necessary step in the biosynthesis of gibberellinsthat promote shoot elongation in rice seedlings. The weak promotionof shoot elongation by GA₂₂ in the presence of BX-112 suggeststhat the effect of a hydroxyl group at C-18 of GA₂₂ might beable to mimic the effect of the 3ß-hydroxyl groupof GA₁. Helminthosporol and helminthosporic acid may promotethe shoot elongation of rice by mimicking physiologically activegibberellins and not by stimulating their biosynthesis. ¹Part I is the previous paper by Nakayama et al. (1990a) ³Present address: Frontier Research Program RIKEN, Wako-shi,Saitama, 351-01 Japan. (Received June 26, 1991; Accepted September 4, 1991)     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)     

Stimulation of the Flowering of Pharbitis nil Chois. by Gibberellin A3 : Time Dependent Action at the Apex

Gibberellin A₃ (GA₃) stimulated flowering when it was appliedto the shoot apex of seedlings of Pharbitis nil, dwarf strainKidachi; but, not when it was applied to the cotyledons. GA₃applied to the plumule before or shortly after the start ofan inductive dark period promoted both flowering and shoot elongation;but, the later the time of application during the dark periodless the promotion of flowering, although marked promotion ofshoot elongation always took place. The variation with time in the response of flowering to GA₃indicates that early floral processes at the apex are stimulatedby GA₃, but that subsequent processes are insensitive to it.The early processes of floral stimulus produced by a 16 hr inductivedark period probably are completed within 20 hr at 28°Cafter the end of the dark period. At low temperatures, suchas 15 and 20°C, early floral processes continued for morethan 40 hr. When cotyledons were removed at various times, the export ofthe floral stimulus to the shoot apex was apparent within hoursof the generation of the floral stimulus in the cotyledons,which started with the passage of the critical 9-hr dark period. (Received February 18, 1981; Accepted March 24, 1981)     

Long-Day Induced Bud Break in Salix pentandra Is Associated with Transiently Elevated Levels of GA1 and Gradual Increase in Indole-3-Acetic Acid

Initiation of dormancy in woody species is induced by a shortphotoperiod. In the early stages of dormancy development, growthcan be initiated by long days. To study the possible involvementof gibberellins and indole-3-acetic acid in bud break in Salixpentandra, effects on levels of these plant hormones of transferof seedlings in an early stage of dormancy to a growth-inductivelong photoperiod was investigated. The bud break and initiationof growth correlated with a rapid transient increase in GA₁in defined zones of shoot tips to levels twice of that in continuouslyelongating long day-grown control seedlings, followed by a rapiddecrease to levels similar to in these control plants. Also,the contents of GA₅₃, GA₁₉, GA₂₀, GA₈ increased upon transferfrom short to long days. Levels of indole-3-acetic acid showeda gradual decline under short days, and increased graduallyupon transfer to long days up to a level of continuously elongatingplants. The present data suggest an interaction between gibberellinand indole-3-acetic acid in the photoperiodic control of dormancydevelopment and bud break in S. pentandra. (Received October 14, 1996; Accepted February 18, 1997)     

Effects of a New Plant Growth Regulator Prohexadione Calcium (BX-112) on Shoot Elongation Caused by Exogenously Applied Gibberellins in Rice (Oryza sativa L.) Seedlings

The effects of a novel plant growth regulator (PGR) prohexadionecalcium (BX-112; calcium 3,5-dioxo-4-propionylcyclohexanecarboxylate)on shoot elongation caused by exogenously applied GA₁, GA₃,GA₄₎ GA₁₉ and GA₂₀ were investigated in rice (Oryza sativa L.cv. Nihonbare and cv. Tan-ginbozu) seedling test. Dependingon the dose, BX-112 reduced shoot elongation in both cultivarscaused by GA₁₉ and GA₂₀, but not by GA₁. When a high dose ofBX-112 (e.g. 250 ng/plant and over) was applied with GA₁, orGA₄, shoot elongation was even promoted. This promotive effect,however, was not observed with GA₃. These results suggest thatBX-112 inhibits gibberellin (GA) biosynthesis in the rice plantat the 3ß- and 2ß-hydroxylation of GAs,namely steps of activation and inactivation, respectively. (Received September 6, 1989; Accepted November 27, 1989)     

Gibberellins, Amylase, and the Onset of Heterosis in Maize Seedlings

Rood, S. B. and Larsen, K. M. 1988. Gibberellins, amylase, andthe onset of heterosis in maize seedlings.—J. exp. Bot.39: 223–233. The possible involvement of gibberellins and amylase in heterosisof maize seedlings was investigated in two parental inbreds,CM7 and CM49, and their single cross F₁ hybrid, CM7xCM49. Germinationof all three genotypes was complete within 36 h after the onsetof imbibition. By 48 h, heterosis (hybrid vigour) for increasedshoot and root length was consistently observed. The endogenousconcentration of gibberellin A₁ (GA₁) was measured in 48 h seedlingsby gas chromatography-mass spectrometry with selected ion monitoring(GC-SIM) using [²H₂]-GA₁ as an internal standard. The GA₁ concentrationwas highest in the hybrid (59 ng g^–1 dry wt.), intermediatein CM49 (9.0 ng g^–1), and lowest in CM7 (<5.0 ng g^–1).Amylase activities in all three genotypes were very low at 24h, but increased during the next 24 h, after which time amylaseactivity in the hybrid was significantly higher than that ofeither parental inbred. Inhibitors of gibberellin (GA) biosynthesis,AMO-1618 or CCC, inhibited germination, shoot and root growth,and amylase activity in all three genotypes. Conversely, exogenousgibberellic acid (GA₃) increased amylase activity, particularlyin the inbred CM7. Amylase isozymes were separated through polyacrylamidegel electrophoresis and generally similar profiles of starchdegrading enzymes were observed in the three genotypes. SinceGA is known to control a-amylase biosynthesis in some cereals,these results are consistent with the hypothesis that GAs areinvolved in the regulation of heterosis in maize. A higher endogenousGA₁ concentration in the hybrid could result in increased amylaseactivity in the hybrid seedlings and consequently, more rapidstarch hydrolysis which fuels heterosis for early growth. Key words: Amylase, germination, gibberellic acid, Gibberellin A₁, heterosis, hybrid vigour, Zea mays     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Gibberellin Control of Microtubule Arrangement in the Mesocotyl Epidermal Cells of the d5 Mutant of Zea mays L.

The mesocotyl length of dark-grown maize seedlings is much shorterin the dwarf (d₅) than in the normal. The elongating zone ofd₅ mesocotyl is restricted to 1 mm below the coleoptilar node,while that of the normal extends to almost 4 mm. When the 4mm portion below the node was marked at 1 mm intervals and designatedas A, B, C and D from the top, gibberellin (GA₃) particularlystimulated elongation of the A–B region of d₅ and alsoC to some extent. Electronmicroscopic observation of microtubulesin the epidermal cells of these regions of d₅ showed that microtubuleswere longitudinally and/or randomly oriented in all other regionsexcept the region immediately below the node. Following 100µM GA₃ treatment for 21 h, the microtubule arrangementbecame transverse to the cell axis in A and B. Even in C a significantnumber of transversely oriented microtubules were observed.On the other hand, in normal seedlings microtubules were orientedtransversely to the cell axis in all four regions regardlessof GA₃ treatment. Results indicate that the dwarf habit of d₅seedlings can be ascribed to their possession of a small populationof elongating cells, the microtubules of which are predominantlyoriented transversely to the cell axis as a result of insufficientsupply of endogenous gibberellin. ¹Present address: Department of Cell Biology, National Institutefor Basic Biology, Myodaiji, Okazaki 444, Japan. (Received December 17, 1985; Accepted March 10, 1986)     

Distribution of Endogenous Gibberellins in Vegetative Shoots of Rice

Levels of endogenous gibberellins in rice seedlings (Oryza sativaL., cv. Nipponbare) were compared between young and old leavesat the 4- and 5-leaf stages. The levels of GA₁, GA₁₉ and GA₅₃were higher in the youngest leaf than in older leaves at the5-leaf stage, but they did not differ significantly betweenthe leaf sheath and the leaf blade. At the 4-leaf stage, thelevel of GA₁, was highest in the third leaf sheaths which containedyoung elongating tissues. These results indicate that gibberellinsare synthesized in young vegetative tissues to promote theirelongation growth. The levels of GA₁ in the youngest leaf sheathsof two cultivars of dwarf rice, Tan-ginbozu and Waito-C, wereapproximately 10% of that in the normal rice at the 5-leaf stage.This result could explain the retardation of shoot elongationin these dwarf cultivars. (Received February 15, 1995; Accepted June 1, 1995)     

Gibberellin A3 and Abscisic Acid Cause the Reorientation of Cortical Microtubules in Epicotyl Cells of the Decapitated Dwarf Pea

To determine whether or not the changes in the orientation ofmicrotubules (MTs) that are induced by GA₃ and ABA result fromchanges in the rate of epicotyl elongation caused by these hormones,we examined the effects of GA₃ and ABA on the orientation ofMTs in epidermal cells of decapitated epicotyls of the dwarfpea (Pisum sativum cv. Little Marvel), in which neither GA₃nor ABA causes changes in the rate of epicotyl elongation. Cuttings taken from GA₃-pretreated seedlings were decapitatedand treated with ABA. ABA eliminated the GA₃-induced predominanceof transverse MTs and treatment with ABA resulted in a predominanceof longitudinal MTs in the decapitated cuttings. However, ABAdid not reduce the rate of epicotyl elongation in these samples.Cuttings taken from ABA-pretreated seedlings were decapitatedand treated with GA₃. GA₃ caused the orientation of MTs to changefrom longitudinal to transverse in the decapitated cuttings.However, GA₃ had no promotive effect on elongation of theseepicotyls. The results indicate that both ABA and GA₃ have the abilityto change the orientation of MTs by mechanisms that do not involvechanges in the rate of cell elongation. (Received August 18, 1992; Accepted January 18, 1993)     

Interaction between Hormones, Light, and Nutrition on Extension of Lateral Buds in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indol-3yl-acetic acid (IAA)contained in lanolin were applied in various combinations andconcentrations to decapitated stems and petioles and to budsof Phaseolus vulgaris L. GA₃ applied alone usually promotedgrowth of main stems and laterals but this was by no means consistentand occasionally it acted in the opposite way. IAA applied alonereduced lateral bud extension slightly, but not consistently;however, when applied with GA₃ or GA₃ plus kinetin, it oftenmarkedly inhibited the promotion caused by these compounds.On occasions, however, GA₃ and IAA acted synergistically topromote and sometimes to inhibit lateral shoot growth. Kinetinalone showed few significant effects on lateral shoot growthbut applied with GA₃ it often dramatically increased GA₃-inducedgrowth of main stems and laterals. The diversity of these results,which parallels that found in the literature, was shown to bepartly dependent on the point of hormone application and ageof the plant or bud, on concentration of hormone and on lightintensity or nutrition. However, no meaningful relationshipswere found and it is concluded that growth of laterals and mainstems is dependent on a hormone balance which can be criticallymodified by a wide range of internal and external factors thenature of which is still to be determined.     

Effects of Gibberellin on the Arrangement and the Cold Stability of Cortical Microtubules in Epidermal Cells of Pea Internodes

Longitudinal microtubules are predominant in epidermal cellsof the 3rd internodes of dwarf pea (Pisum sativum L. cv. LittleMarvel) seedlings. In more than 50% of the cells, cortical microtubulesare running parallel to the cell axis. GA₃ promotes elongation of the internodes and gives rise toa predominance of transverse microtubules. In more than 60%of the GA₃-treatd cells, cortical microtubules are running transverseto the cell axis. Longitudinal microtubules in the GA₃-untreated cells are resistantto low-temperature treatment, but transverse microtubules inthe GA₃-treated cells are sensitive to it. Longitudinal microtubulesare present in GA₃-treated epidermal cells with low frequency.They are resistant to low-temperature treatment. Longitudinal, oblique and transverse microtubules are presentwith almost the same frequency in epidermal cells of the 3rdinternodes of tall pea (cv. Early Alaska) seedlings. GA₃ promoteselongation of the internodes also in tall pea seedlings, butit does not alter the direction of cortical microtubules sodistinctly as it does in dwarf pea seedlings. As in dwarf pea seedlings, longitudinal microtubules are resistantto low-temperature treatment, and transverse microtubules aresensitive to it in tall pea seedlings. (Received September 19, 1986; Accepted December 26, 1986)     

Actinomycin D Inhibits the GA3-Induced Elongation of Azuki Bean Epicotyls and the Reorientation of Cortical Microtubules

Actinomycin D inhibited the elongation of epicotyl segmentsfrom azuki bean seedlings that was induced by simultaneous treatmentwith IAA and GA₃. The drug also inhibited the elongation ofthe segments that was caused by IAA alone when it was appliedtogether with IAA. When the segments were pretreated with GA₃and then incubated with IAA, GA₃ promoted the elongation causedby IAA and brought about a predominance of transverse corticalmicrotubules (MTs) in the epidermal cells of the segments. Thechange in the arrangement of MTs caused by pretreatment withGA₃ was evident 1 h after the start of subsequent incubationwith IAA when the effect of pretreatment with GA₃ on the elongationhad not yet become apparent. Pretreatment with GA₃ did not causeany change in the arrangement of MTs when GA₃-pretreated segmentswere not incubated subsequently with IAA. Although actinomycinD applied before treatment with IAA did not inhibit the IAA-inducedelongation, the drug diminished the promotion of the elongationcaused by pretreatment with GA₃ and prevented GA₃ from bringingabout a predominance of transverse MTs when the drug was appliedduring the pretreatment with GA₃. GA₃-induced synthesis of mRNA seems to be involved in the promotionby GA₃ of IAA-induced elongation and in the GA₃-induced rearrangementof cortical MTs. (Received June 15, 1993; Accepted August 16, 1993)     

Enhancement of Gibberellic Acid-stimulated Hypocotyl Elongation of Lettuce (Lactuca sativa L. cv. Grand Rapids) by Phlorizin and Light

The interaction of light, gibberellic acid (GA₃), and phlorizinin the growth of lettuce (Lactuca sativa L. cv. ‘GrandRapids’) hypocotyls was investigated. At all concentrationsof GA₃, phlorizin enhanced GA₃-induced growth at luminous intensitiesabove 50 ft-c (continuous light). Without GA₃, phlorizin hadno effect on hypocotyl growth in the light but it inhibitedgrowth in the dark. Both seedlings and hypocotyl sections respondedto phlorizin in the presence of GA₃. There was no iteractionbetween phlorizin and KCl. Water-growth was severly inhibitedby light. GA₃,-induced growth was slightly inhibited by light,and then only at luminous intensities above 50 ft-c. Thus, relativeto H₂O-growth, GA₃-induced growth increased with increasingluminous intensity up to 450 ft-c, where it reached saturation.It seems that a synergism may exist between light and GA₃ aswell as between phlorizin and GA₃. Lactuca sativa L, lettuce, hypocotyl elongation, gibberellic acid, phlorizin, light     

Effect of ABA and GA3 on tuberization and some chemical constituents of potato

The effects of abscisic acid (ABA) and gibberellic acid (GA₃)on the chemical composition of and tuberization in the potatowere studied. GA₃ at 10^–6 M inhibited and ABA at an equimolarconcentration promoted tuberization. The inhibitory effect ofGA₃ was relieved by the addition of ABA. The fresh weight ofthe shoot, chlorophyll content and the total glycoalkaloidslevel were increased by GA₃ treatment, but decreased by ABAtreatment. In contrast, total proteins were increased by ABA,but decreased by GA₃ treatment. ¹This work was supported by a PL-480 research grant (FG-Pa-262)from the United States Department of Agriculture widi co-ordinationby the Agriculture Research Council, Pakistan. (Received August 29, 1980; )     

Effect of ABA and GA3 on tuberization and some chemical constituents of potato

The effects of abscisic acid (ABA) and gibberellic acid (GA₃)on the chemical composition of and tuberization in the potatowere studied. GA₃ at 10^–6 M inhibited and ABA at an equimolarconcentration promoted tuberization. The inhibitory effect ofGA₃ was relieved by the addition of ABA. The fresh weight ofthe shoot, chlorophyll content and the total glycoalkaloidslevel were increased by GA₃ treatment, but decreased by ABAtreatment. In contrast, total proteins were increased by ABA,but decreased by GA₃ treatment. ¹This work was supported by a PL-480 research grant (FG-Pa-262)from the United States Department of Agriculture widi co-ordinationby the Agriculture Research Council, Pakistan. (Received August 29, 1980; )     

The Role of Gibberellins in Early Growth and Development of Sugar Beet

Two gibberellin(GA)-like compounds were found in both rootsand shoots of sugar beet plants using the barley endosperm bioassay.One had chromatographic properties similar to GA₃ and GA₁; theother was highly non-polar, relatively inactive in the endospermassay, and may be a new gibberellin. Presence of the GA_3/1-likecompound was confirmed with the dwarf rice bio-assay. The quantityof this GA was relatively high in the root compared with theshoot at the 3–4 leaf stage when the first supernumerarycambia are being formed in the root. As plants developed throughthe 8–9 leaf stage and the 15–16 leaf stage thequantity of GA per unit fresh weight of material decreased. Application of gibberellic acid (GA₃) to the roots of youngsugar beet plants caused a significant increase in root dryweight shortly after treatment and the rate at which supernumerarycambia were produced was increased. Application of GA₃ to asingle petiole caused a significant increase in both root andshoot dry weight. GA₃ applied to either root or shoot causeda reduction in the rate of leaf formation although total leafarea per plant and shoot dry weight were unaffected. The probablerole of GA-like substances in controlling the growth and developmentof young sugar beet plants is discussed.     

Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indole-3yl-acetic acid(IAA) were applied to roots of Phaseolus vulgaris under twodifferent light intensities and when either young or old leaveswere removed In all cases GA₃, promoted stem and lateral growth,especially when light intensity was reduced. Promotion by GA₃,of stem growth under reduced light was reduced if IAA and kinetinwere present; promotion of lateral growth under reduced lightwas reduced if IAA was added and eliminated if kinetin or kinetinplus IAA were added to GA₃. Removal of young and mature leavesreduced main stem growth; removal of young leaves promoted,and of mature leaves reduced, lateral shoot growth. We suggestthat shoot growth and apical dominance are governed by the balanceof hormones present in elongating internodes. There may be twoways of modifying this balance; firstly by altering light, temperature,or nutrients, or by applying hormones generally to the plant.Secondly, local modifications can be made by removing apicesor young leaves, or applying hormones in lanolin to specificareas. Knowledge of both the general and local conditions maybe necessary for a complete understanding of apical dominance.     

Effects of a Plant-Growth Regulat or, Prohexadione-Calcium (BX-112), on the Endogenous Levels of Gibberellins in Rice

The effects of the plant-growth regulator, prohexadione-calcium,on the levels of the endogenous gibberellins in rice shootswere measured by GC-SIM using ²H-labeled gibberellins as internalstandards. The compound was applied at the 4-leaf stage andshoots were harvested 5 and 12 days after treatment. Plant lengthwas reduced to 78% and 66%, respectively, relative to controlby application of the compound at 1 and 30 mg m^–2, whenplant length was measured 12 days after treatment. The levelof GA, was reduced to 36% and 18%, respectively, relative tocontrol in the treated plants. The levels of GA₁₉and GA₂₀ increasedbut that of GA₄₄ was reduced in the treated plants. The levelof GA₅₃ was unchanged. These results suggest that primary modeof action of the compound in vivo is the inhibition of the 3ß-hydroxylationof GA₂₀ to GA₁ and further support the hypothesis that GA₁ notGA₁₉ nor GA₂₀ is active in promoting shoot elongation in rice. ³Present address: Frontier Research Program, RIKEN, Wakoshi,Saitama, 351-01 Japan.