Sodium Requirement of Monocotyledonous C4 Plants for Growth and Nitrate Reductase Activity

The effects of Na application on growth and nitrate reductaseactivity of seven C₄ plant species, Zea mays, Echinochloa crus-galli,Panicum miliaceum, Panicum coloratum, Panicum dichotomiflorum,Panicum maximum and Chloris gayana were studied. Except forZ. mays and P. miliaceum, Na application enhanced growth significantly,and concurrent increases in nitrate reductase activities weredetected in Panicum coloratum, Panicum dichotomiflorum, Panicummaximum and Chloris gayana. ¹Present address: International Research Institute, Ciba GeigyJapan Ltd., Takarazuka, Hyogo 665, Japan. ²Present address: Photobiology Lab., Research Institute forFood Science, Kyoto Univ., Uji, Kyoto 611, Japan. (Received May 2, 1988; Accepted August 22, 1988)     

Comparison of carbon dioxide fixation and the fine structure in various assimilatory tissues of Amaranthus retroflexus L

The pattern for primary products of CO₂-fixation and the chloroplaststructure of Amaranthus retrqflexus L., a species which incorporatescarbon dioxide into C₄ dicarboxylic acids as the primary productof photosynthesis, were compared in various chlorophyll containingtissues,i.e., foliage leaves, stems, cotyledons and pale-greencallus induced from stem pith. Despite some morphological differencesin these assimilatory tissues, malate and aspartate were identifiedas the major compounds labelled during a 10 sec fixation of¹⁴CO₂ in all tissues. Whereas, aspartate was the major componentin C₄-dicarboxylic acids formed in foliage leaves, malate predominatedas the primary product in stems, cotyledons and the pale-greencallus. The percentage of ¹⁴C-radioactivity incorporated intoPGA and sugar-P esters increased and ¹⁴C-sucrose was detectedin the prolonged fixation of ¹⁴CO₂ in the light, not only infoliage leaves, but also in stems and cotyledons. ¹ This work was supported by a Grant for Scientific ResearchNo. 58813, from the Ministry of Education, Japan. ² Present address: Institute of Applied Microbiology, Universityof Tokyo, Tokyo, Japan. ³ Present address: Department of Biochemistry, University ofGeorgia, Athens 30601. Georgia, U. S. A. (Received July 10, 1971; )     

Sodium Stimulates Regeneration of Phosphoenolpyruvate in Mesophyll Chloroplasts of Amaranthus tricolor

Mesophyll chloroplasts were isolated from leaves of a Na⁺-requiringNAD-malic enzyme type, dicotyledonous C₄ plant, Amaranthus tricolorL. The chloroplasts converted pyruvate to phosphoenolpyruvateunder illumination, and the conversion was stimulated by Na⁺.This observation may explain the requirement for Na⁺ of someC₄ plants. ² Present address: Institute for Life Science Research, NihonNohyaku Co., Ltd., Kawachi-Nagano, Osaka, 586 Japan     

Pathway of mannitol formation during photosynthesis in brown algae

Eisenia bicyclis, Arame, was allowed to photosynthesize in seawatercontaining H¹⁴CO₃^–, and ¹⁴C-mannitol was isolated fromits fronds. The ratio of ¹⁴C-total/¹⁴C₁ + ¹⁴C₆ in the ¹⁴C-mannitolwas found to be about 8.0 at 1 min-illumination, but graduallydecreased with time to 3.0, showing uniform radioactivity distribution.Mannitol therefore seems to be formed in brown algae throughthree carbon compounds. Enzymes which may be involved in the possible biosynthetic pathwayof mannitol, i.e. aldolase, hexose diphosphatase, mannitol-1-phosphataseand glucosephosphate isomerase were present in extracts fromseveral brown algae. Some of their properties are discussed. ¹Contribution from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 187. ²Present address: Reseach Institute, Seikagaku Kogyo Co., Ltd.,Yamato-machi, Kitatama-gun, Tokyo, Japan. (Received December 13, 1968; )     

Cloning, Expression, and Characterization of a Root-Form Phosphoenolpyruvate Carboxylase from Zea mays: Comparison with the C4-Form Enzyme

A full-length cDNA for maize root-form phosphoenolpyruvate carboxylase(PEPC) was isolated. In the coding region, the root-form PEPCshowed 76 and 77% identity with the C₄- and C₃-form PEPCs ofmaize, respectively, at the nucleotide level. At the amino acidlevel, the root-form was 81 and 85% identical to the C₄- andC₃-form PEPCs, respectively. The entire coding region was insertedinto a pET32a expression vector so that it was expressed underthe control of T7 promoter. The purified recombinant root-formPEPC had a V_max value of about 28 mol min^–1(mg protein)¹at pH 8.0. The K_m values of root-form PEPC for PEP and Mg²⁺were one-tenth or less of those of C₄-form PEPC when assayedat either pH 7.3 or 8.0, while the value for HCO^–₃ wasabout one-half of that of C₄-form PEPC at pH 8.0. Glucose 6-phosphateand glycine had little effect on the root-form PEPC at pH 7.3;they caused two-fold activation of the C₄-form PEPC. The K_i(L-malate) values at pH 7.3 were 0.12 and 0.43 raM for the root-and C₄-form PEPCs, respectively. Comparison of hydropathy profilesamong the maize PEPC isoforms suggested that several stretchesof amino acid sequences may contribute in some way to theircharacteristic kinetic properties. The root-form PEPC was phosphorylatedby both mammalian cAMP-dependent protein kinase and maize leafprotein kinase, and the phosphorylated enzyme was less sensitiveto L-malate. ¹These authors contributed equally to this work. ²Present address: Otsuka Chemical Co. Ltd., 463 Kagasuno, Kawauchi-cho,Tokushima, 771-0130 Japan. ³Present address: Sumitomo Pharmaceuticals Research Center,1-98, Kasugade, Naka 3-cho-me, Konohana-ku, Osaka, 554-0022Japan.     

Biosynthesis of Purine Alkaloids in Camellia Plants

The metabolism of [8-¹⁴C]adenine and [8-¹⁴C]hypoxanthine infour species of Camellia plants was investigated in relationto the synthesis of purine alkaloids, caffeine and theobromine.Young leaves of C. sinensis had the ability to synthesize caffeine,but in C. irrawadiensis, these labelled precursors were incorporatedinto theobromine, not caffeine. No synthesis of purine alkaloidscould be detected in C. japonica and C. sasanqua leaves. Conventional"salvage" and degradation pathways of purines were present inall species of Camellia plants examined. ¹ Present address: Research Center, Mitsubishi Chemical IndustriesLtd., 1000 Kamisida-cho, Midori-ku, Yokohama, 227 Japan. (Received September 29, 1986; Accepted January 22, 1987)     

Malate Decarboxylation by Mitochondria of the Inducible Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum

Mitochondria isolated from leaves of Mesembryanthemum crystallinumoxidized malate by both NAD malic enzyme and NAD malate dehydrogenase.Rates of malate oxidation were higher in mitochondria from plantsgrown at 400 mil NaCl in the rooting medium and performing Crassulaceanacid metabolism (CAM) than in mitochondria from plants grownat 20 mM NaCl and exhibiting C₃-photosynthetic CO₂ fixation.The mitochondria isolated from plants both in the CAM and C₃modes were tightly coupled and gave high respiratory control.At optimum pH for malate oxidation (pH 7.0), pyruvate was themajor product in mitochondria from CAM-M. crystallinum, whereasmitochondria from C₃-M. crystallinum produced predominantlyoxaloacetate. Both the extracted NAD malic enzyme in the presenceof CoA and the oxidation of malate to pyruvate by the mitochondriafrom plants in the CAM mode had a pH optimum around 7.0 withactivity declining markedly above this pH. The activity of NAD-malicenzyme, expressed on a cytochrome c oxidase activity basis,was much higher in mitochondria from the CAM mode than the C₃mode. The results indicate that mitochondria of this speciesare adapted to decarboxylate malate at high rates during CAM. ¹Current address: Lehrstuhl für Botanik II, UniversitätWurzburg, Mittlerer Dallenbergweg 64, 8700 Würzburg, WestGermany. ²Current address: KD 120, Chemical Research Division, OntarioHydro, 800 Kipling Avenue, Toronto, Ontario M8Z5S4, Canada. ³Current address: Department of Botany, Washington State University,Pullman, Washington 99164-4230, U.S.A. (Received March 13, 1986; Accepted September 18, 1986)     

Effect of the age of tobacco leaves on photosynthesis and photorespiration

Relationships among the activities of enzymes related to photosynthesisand photorespiration, and ¹⁴CO₂ photosynthetic products wereinvestigated with individual tobacco leaves attached to thestalk from the bottom to the top. P-glycolate phosphatase ofthe chloroplasts and glycolate oxidase of the peroxisomes hadtheir maximum activities in the 25th leaf from the dicotyledons.Maximum photorespiration was similarly distributed. The highestratio of serine-¹⁴C to glycine-¹⁴C in the photosynthesates andmaximum glycolate formation were also observed in the 25th leaf.Glutamateglyoxylate aminotransferase, serine hydroxymethyltransferaseand glycine decarboxylase were more active in the upper leaves.RuDP carboxylase had nearly constant activity in all leaves,except for the youngest in which activity decreased. MaximumCO₂ photosynthesis and enzyme activity for the C₄ dicarboxylicacid cycle occurred in the upper, youngest leaf. Distributionof photosynthetic CO² fixation among the leaves did not coincidewith RuDP carboxylase activity. The photosynthetic capacityappeared to be better related to the distribution pattern forenzymes of the C₄ dicarboxylic acid pathway, i.e. PEP carboxylase,pyruvate Pi dikinase and 3-PGA phosphatase in the upper leaves.The results suggest that the C₄ dicarboxylic acid pathway participates,to some extent, in photosynthesis in young leaves of tobacco,a dicotyledonous plant. ¹This work was reported at the Annual Meeting (1970) of theJapanese Plant Physiologists in Kobe. ²The Central Research Institute, Japan Monopoly Corporation1-28-3, Nishishinagawa, Shinagawaku, Tokyo, 141 Japan. (Received November 2, 1972; )     

PHOTOSYNTHESIS OF GLYCINE AND SERINE IN GREEN PLANTS

1. The effects of "carbonyl" reagents on the photosyntheticin-corporation of ¹⁴CO₂ into the assimilation products of tobaccoand spinach leaves were studied. The presence of "carbonyl"reagents causes an increase in the ratio of ¹⁴CO₂ incorporatedin glycine and a decrease in serine. The incorporation of ¹⁴Cfrom glycolate-1-¹⁴C and glycolaldehyde-2-¹⁴C into glycine andserine was also affected by "carbonyl" reagents, as in the caseof ¹⁴CO₂-experiment. 2. The feeding experiments of glycine-1-¹⁴C and serine-1-¹⁴Cin the presence and in the absence of "carbonyl" reagents revealedthat these reagents inhibit the conversion of glycine to serine. 3. The results obtained above, together with the effects ofthiols on ¹⁴CO₂ incorporation presented in this paper, supportthe assumption that glycine and serine are formed via glycolateand glyoxylate during photosynthesis in green plants. 4. Comparison of ¹⁴C incorporation in malate from ¹⁴CO₂, glycolate-1-¹⁴C,glycine-1-¹⁴C and serine-1-¹⁴C in the presence and in the absenceof "carbonyl" reagents suggested the occurrence of the pathwayof the malate formation via glycolate and glyoxylate, not passingthrough glycine and serine, during photosynthesis. ¹ A part of this paper was presented at the Symposium on "Nitrogenand Plant" by the Japanese Society of Plant Physiologists, inOctober, 1963 ² Present address: Radiation Center of Osaka Prefecture, Sakai,Osaka     

Glucose and Pyruvate Metabolism in Daucus carota Cells: The Effect of the Ammonium Ion

In Daucus carota cells cultivated in vitro, the ammonium ionstimulates the incorporation of radioactivity from labelledglucose and labelled pyruvate into CO₂ and into the residueinsoluble in 60 per cent (v/v) ethanol. There is a higher ¹⁴CO₂production from [6-¹⁴C₂] glucose than from [6-¹⁴C] glucose.These results suggest a possible stimulation of glycolysis bythe ammonium ion.     

Metabolism of [14C]GA20 in a Cell-Free System from Developing Seeds of Phaseolus vulgaris L.

The metabolism of [¹⁴C]GA₂₀ during seed maturation of Phaseolusvulgaris was studied using cell-free systems from embryos rangingin age from 10 DAF (day after flowering) to 24 DAF. Enzyme preparationsfrom very immature seeds actively converted GA₂₀ to GA¹, GA₅and GA₆. The ratio of incubation products suggested the biosyntheticpathway of GA₂₀—GA₅—GA₆. Fluctuation in the levelsof endogenous C₁₉-GAs, namely GA₁, GA₄, GA₅, GA₆, GA₈, GA₉ andGA₂₀ was analyzed by GC-SIM using internal standards to compareenzyme activity with the levels of endogenous GAs. AlthoughGA₁, GA₄ and GA₆ showed maximum levels on 20 DAF, enzyme activitydecreased during seed maturation and showed weak activity on20 DAF. ¹Graduate student of the University of Tokyo, Department ofAgricultural Chemistry, Bunkyo-ku, Tokyo 113, Japan. ³Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., Takarazuka, Hyogo655, Japan. (Received December 17, 1987; Accepted March 30, 1988)     

14C2H4: Distribution of 14C-labeled tissue metabolites in pea seedlings

The ¹⁴C-metabolite distribution pattern following ¹⁴C₂H₄ metabolismin intact pea seedlings (Pisum sativum L.) was determined undervarious conditions. After a 24 hr exposure to ¹⁴C₂H₄, the majorityof ¹⁴C-metabolites were water-soluble (60–70%) with lesseramounts in the protein (10–15%), lipid (1%), and insoluble(1–2%) fractions. Ion exchange chromatography of the water-solublecomponents into basic, neutral, and acidic fractions revealeda 50 : 40 : 10 distribution, respectively. Chromatography ofthe neutral fraction revealed two regions of radioactivity (Rf=0.38)and 0.63 which did not cochromatograph with twenty-two knownsugars or neutral metabolites. Chromatograms of the basic fractioncontained 3 regions of radioactivity. Similar distribution patternswere noted when ¹⁴C₂H₄ exposure was followed by a 6 hr air chaseor when 5% CO₂, an antagonist of ethylene action, was presentduring the exposure. Marked differences in the ¹⁴C-metabolite distribution patternswere obtained when ¹⁴CO₂ was substituted for ¹⁴C₂H₄. These resultsindicate that the metabolic pathway involved in ethylene metabolismis different from that involved in intermediary carbon metabolism. ¹ Contribution No. 2338 from Central Research and DevelopmentDepartment, Experimental Station, E. I. du Pont de Nemours andCompany, Wilmington, Delaware. (Received June 28, 1976; )     

Distribution of enzymes related to C3 and C4 pathway of photosynthesis between mesophyll and bundle sheath cells of Panicum hians and Panicum milioides

Enzymes of the C₄, C₃ pathway and photorespiration have beenanalyzed for P. hians and P. milioides, which have chlorenchymatousbundle sheath cells in the leaves. On whole leaf extracts thelevels of PEP carboxylase are relatively low compared to C₄species, RuDP carboxylase is typical of C₃ species, and enzymesof photorespiratory metabolism appear somewhat intermediatebetween C₃ and C₄. Substantial levels of PEP carboxylase, RuDPcarboxylase, and photorespiratory enzymes were found in bothmesophyll and bundle sheath cells. Low levels of C₄-acid decarboxylatingenzymes may limit the capacity for C₄ photosynthesis in P. hiansand P. milioides. The results on enzyme activity and distributionbetween mesophyll and bundle sheath cells are consistent withCO₂ fixation via C₃ pathway in these two species. ¹ This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and bythe University of Wisconsin Research Committee with funds fromthe Wisconsin Alumni Research Foundation; and by the NationalScience Foundation Grant BMS 74-09611. (Received September 16, 1975; )     

Coupling of malate decarboxylation to CO2 fixation and the reduction of 3-phosphoglyceric acid in corn bundle sheath cells,2

1. In the presence of NADP⁺ and Mg⁺⁺, the bundle sheath strandsisolated from corn (Zea mays) leaves by cellulase treatmentsdecarboxylated malate in the light at an initial rate (200 µmoles/mgchl.hr), which was sufficient to account for photosyntheticCO₂ fixation in intact leaves. This rate gradually slowed downand then stopped. The final level of the malate decarboxylatedwas approximately equal to the amount of NADP⁺ added.
2. Rapidand continued decarboxylation of malate was observed whenNADP⁺,3-phosphoglyceric acid and ATP (and Mg⁺⁺) were addedtogether.The addition of ADP instead of ATP showed a similareffect.Light did not show any effect on the malate decarboxylationin the presence of ATP or ADP.
3. When malate was added to thebundle sheath strands in the presenceof exogenous NADP⁺ NADP⁺was rapidly reduced. The reductionstopped after 2 min when,73% of the added NADP⁺ was reduced.The further addition of3-phosphoglyceric acid and ATP broughtabout a decrease in theNADPH-level, which rose again to attaina new steady level.
4. The transfer of radioactivity from (1-¹⁴C-3-phosphoglycericacid to dihydroxyacetone phosphate in the bundle sheath strandsin the presence of ATP and NADP⁺ was greatly enhanced by theaddition of malate.
5. In the presence of ribose 5-phosphateand ATP, the rate of ¹⁴C-transferfrom (4-¹⁴C)-malate to theintermediates of the reductive pentosephosphate cycle was equalto that of ¹⁴CO₂ fixation in the light.

All these results support the current view that in the bundlesheath cells of C₄ plants belonging to the NADP-malic enzyme-group,the decarboxylation of malate is coupled to the fixation ofthe released CO₂ and the reduction of 3-phosphoglyceric acidformed as a result of CO₂ fixation. ¹ Part of this research was reported at the 40th Annual Meetingof the Botanical Society of Japan Osaka, December, 1975. ³ Present address: Laboratory of Chemistry, Faculty of Medicine,Teikyo University, 359 Otsuka, Hachioji-City, Tokyo 173, Japan. (Received April 30, 1977; )     

Ethylene Evolution from Bracts and Leaves of Poinsettia, Euphorbia pulcherrima Willd

Woodrow, L. and Grodzinski, B. 1987. Ethylene evolution trombracts and leaves ol Poinsettia, Euphorbia pulcherrima Willd.—J.exp. Bot. 38: 2024–2032. Ethylene release from fully expanded, red and white bracts andleaves of poinsettia, Euphorbia pulcherrima Willd., was compared.On a laminar (area) basis leaves contained about 50 times morechlorophyll and demonstrated 10 times the photosynthetic rateof the bracts. Both tissues contained starch, however, solublecarbohydrate in the bracts consisted primarily of reducing hexoseswhile the leaves contained mainly sucrose for translocation.The total free alpha-amino nitrogen content of the bract tissuewas twice that of the leaf tissue. The leaves contained moreACC (1-aminocyclopropane-1-carboxylic acid) and produced proportionallymore endogenous C²H⁴ than either the red or white bracts. ACC-stimulated₂H₄ release was also greatest from the green tissue indicatingthat the EFE (ethylene forming enzyme) was most active in theleaves. The specific activity of the ¹⁴C₂H₄/¹²C₂H₄ releasedfrom [2,3-¹⁴C]ACC confirmed ACC as the primary precursor ofC₂H₄ in this tissue. Ethylene release from the non-photosynthetic,bract tissue was not markedly affected by alterations in CO₂or light conditions. In green leaf tissue endogeneous ethylenerelease increased from 1·5 to 6·0 pmol C₂H₄ cm^–2h^–1 while ACC-stimulated ethylene release increased from10 to 35 pmol C₂H₄ cm^2– h^1– as the CO₂ partial pressureincreased from 100 to 1 200 µbar. Key words: Poinsettia, ethylene, bracts     

Photosynthesis in Cell Suspension Culture of a C4 Plant, Gisekia pharnaceoides L.

Photomixotrophic cell suspension culture was established fromthe leaf derived callus cells of Gisekia pharnaceoides L., aC₄ dicotyledonous weed. The late log phase cells possessed shade-typecharacters such as low chlorophyll a/b ratio, less pronouncedO₂ evolution and CO₂ fixation, saturation of photosyntheticCO₂ fixation at low intensity. The chloroplasts from these cellscontained granal stacking with high degree of a very few granawhich are characterized by their wide and high degree of stackings. The predominant labelling of 3-phosphoglyceric acid and sugarphosphates (40% of the total ¹⁴C incorporated) during 5 s exposureto ¹⁴CO₂ in light and subsequent decrease in percentage of ¹⁴Cin these compounds with increase in exposure time indicatedthe operation of the C₃ pathway in these cells. The simultaneoussynthesis of malate (23% of the total ¹⁴C incorporated) is relatedto the much pronounced glycolytic and tricarboxylic acid cycleactivities in these cells. The initial proliferation of callimainly from the zones of vascular supplies in the leaf, highstarch content of the cells, presence of large starch grainsin all the chloroplasts, activities of Calvin cycle enzymes,heavy labelling of C₃ type intermediates and less labellingof aspartate as early photosynthates and rapid accumulationof radioactivity into starch during ¹⁴CO₂ assimilation indicatedthat most of the cells in photomixotrophic culture were derivedfrom bundle sheath cells or the leaf cells of Gisekia changetheir function under culture conditions. ¹Present address: Tropical Botanic Garden and Research Institute,Navaranga Road, Trivandrum 695 011, India. (Received January 29, 1982; Accepted June 4, 1983)     

The mechanism supplying acetyl-CoA for terpene biosynthesis in sweet potato with black rot: Incorporation of acetate-2-14C, pyruvate-3-14C and citrate-2,4-14C into ipomeamarone

Silica gel thin layer chromatography showed that acetate-2-¹⁴C,pyruvate-3-¹⁴C and citrate-2,4-¹⁴C were incorporated into ipomeamaronein sweet potato root tissues infected by Ceratocystis fimbriata.Rates of incorporation of ¹⁴C, from these 3 substances, intothe CHCl³-CH₃OH-soluble lipid fraction and ipomeamarone wereof the followingder: acetate > pyruvate > citrate ¹This paper constitutes Part 82 of the Phytopathological Chemistryof Sweet Potato with Black Rot and Injury (Received December 11, 1969; )     

Panicum milioides, a Gramineae plant having Kranz leaf anatomy without C4-photosynthesis

Light and electron microscopic observations of the leaf tissueof Panicum milioides showed that the bundle sheath cells containeda substantial number of chloroplasts and other organelles. Theradial arrangement of chlorenchymatous bundle sheath cells,designated as Kranz leaf anatomy, has been considered to bespecific to C₄ plants. However, photosynthetic ¹⁴CO₂ fixationand ¹⁴CO₂ pulse-and-chase experiments revealed that the reductivepentosephosphate pathway was the main route operating in leavesof P. milioides. The interveinal distance of the leaves wasintermediate between C₃and C₄Gramineae species. These resultsindicate that P. milioides is a natural plant species havingchracteristics intermediate between C₃ and C₄ types. (Received March 6, 1975; )     

Kinetics of Endogenous Cytokinin, IAA and ABA Levels in Relation to the Growth and Morphology of Tobacco Crown Gall Tissue

The kinetics of endogenous cytokinin, IAA and ABA levels duringthe growth cycle of a wild-type tobacco crown gall (W₃₈-B₆S₃)were compared with that of a shoot-inducing (Shi^-) mutant. Inboth tumor types, high IAA and cytokinin (essentially ribosyl-trans-zeatinand its corresponding glucoside) levels were built up by theend of the linear growth phase and maintained during the greaterpart of the exponential growth period. The stationary phasewas preceded by a very drastic decrease in the endogenous levelof both hormones. Quantitatively, the wild-type tumour showed a higher IAA leveland a reduced cytokinin level compared with the Shi^- mutant.No significantly different endogenous ABA pattern was observed.The reduced cytokinin level might correspond to the ratio oftransformed/untransformed cells in the wild-type tumour whereasthe reduced IAA level in the Shi^- mutant may be correlated withthe deletion of gene 2 in the T-DNA of the pGV 2206 Ti plasmid. The elevated cytokinin/IAA ratio induced shooting mainly ofthe untransformed cells in the Shi^- mutant tissue whereas inthe wild-type, the shoot suppression was compatible with thereduced cytokinin/IAA ratio. ⁴Senior Research Associate Nationaal Fonds WetenschappelijkOnderzoek (N.F.W.O.). ⁵Research Associate N.F.W.O. ⁶Recipient of an Instituut voor Wetenschappelijk Onderzoek inNijverheid en Landbouw grant. (Received February 23, 1984; Accepted June 19, 1984)     

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)