VO」UME 34 JUNE。2012 NUIVIBER : 2 1SSN NO, 0126" 0537
易ABLE OF CONTENTS
He「itability of F田it QuaIity in the P「ogenies of Day‑Neut「ai and Short Day Hyb「id St「awbe「ry CuItiva「s
Genetic Diversities in the Sixth ‑ Gene「ation of Selection (S。) of Some lnb「ed Lines of Maize based on the Phenotypic Cha「acte「s and SSR
Sago Baruk PaIm (Arenga microca仰ha Becc) as a Supe「io「 Locai Food Sou「ce and Soii Conservation
Plant at Sangihe lsiand Regency
Phytochemicai Anaiysis of Water Hyacinth (E/chhomia claSS佃es〉 of Ag「icuitu「ai Waste as Biosensitize「
fo「 Fe面Photo「eduction
Joh小yAlfrods R°rong, SudiaISO, Bud/ Prasefya, Jeany Po肌Mandang and Ed/ Su1岬nto... .. 152
ident胴cation of M4 Gamma i「「adiated Maize Mutant Based on RAPD Ma「ke「s
Rus鍬aw∈鴫EやS叩巧OnO, Atra Rome肘a, CaturHe庵On and Sudono H・ Su的l直… .. 161
ParticuIate O「ganic Matte「 as a SoiI Quaiity indicato「 of Suga「cane Piantations in East Java
星図
Nu肋idaya朽E/7dang A高eoes伯nhgs肌Didik S叩rayogo, and Kumfatun Haihah ……‥ . 1 75
Cha「acte「ization of F調it on SeveraI Saiak Varieties and Their Hyb「ids
Distinctness Assessment on Ya「dIong Bean (∨臼na sesqu毎)eda〃s (L.) F「uhw,) Varieties (Case Study fo「
Five Ya「diong Bean Va「ieties in PVP RightAppii∞tion〉
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Intemational Edito「iai Boa「d
Prof. Hunsa Pumapayak
(MicrobioIogy ‑ Universfty of ChuIaIongkom Thaiiand)
B. Mohan Kuma「, Ph.D, FNASc, FNAAS, FNiE (Agroforestry ‑ Unive「S韓y of Agricuitu「ai Keraia india)
P「of. Ryo Akashi
(BiotechnoIogy‑ Unive「sity of Miyazak口apan)
Dr. Chris Ande「son
(Bio‑mining Remediation ‑ University of Massey New Zeaiand)
Sivananda Ti「umaia「皐ju, Ph.D.
(Plant Genetic and Plant B「eeding ‑ Unive「Sity of South Dakota State, United State of America)
D「. Je「oen C.J, G「oot
〈Organlc Fa「ming ‑University of Wageningen The Nethe「iands)
Xjnbin Feng, Ph.D
(Bio‑mining Remediatjon ‑1nstitute of Geochemistry Chjnese Academy of Sciences China〉
P「Of, Bambang Gu「itno
(Ag「icuituraI EcoIogy, Cassava, Muitipiec「OPPing ‑ Unive「sity of B「aw桓ya lndonesia)
P「of. Wani Hadi Utomo
(」and Management ‑ Unive「Sity of B「aw胆ya indonesia)
Prof. Kurniatun Hai「iah
(Soil Bioiogy ‑ Unive「Sity of B「aw時ya lndonesia)
Prof.Eko Handayanto
(Soii o「ganic management ‑ Unive「sity of B「aw時ya indonesia)
P「Of. ika Rochdjat… Sast「ahidayat
(EpidemioIogy ‑ University of B「aw時ya Indonesia)
P「Of. Tsuyoshi imaj
(Bioiogicai Wastewate「 Treatment, BioiogicaI T「eatment of Organic SoIid Waste,
Composthg of Organic So=d Waste, Wate「 Envi「Onment Conservation‑Unive「sity of Yamaguchi Japan〉
Editoriai Board wouId like to thank to pee○ ○eviewer who has been invited by Agrivita JournaI of AgricuIturaI Science VoIume 34 numbe「 2, 2O12
Ass. Prof. Nutthe Potapohn
(BiotechnoIogy, T「OPicai FIowe「 ‑ Chiang Mai UniVersity ThaiIand)
Sivananda Ti「umaia「aju, Ph.D.
(Plant Genetic and Plant B「eeding ‑ Unive「sity of South Dakota State, United State of Ame「ica)
D「. He「u Kuswantoro
(PIant Breeding and PIant Genetic ‑ 1ndonesian Legumes and Tube予Crops Researoh institute)
P「of. Kuswanto
(Plant B「eeding ‑ Unive「sity of B「awiiaya Ind6nesia)
Ku「niawan Budiarto, M.Sc
(PIant Breeding and Plant Genetic ‑ indonesian OmamentaI Crops Resea「Ch Inst餌te)
P「of. Sumamo
(Piant Breeding and Piant Genetic ‑ 1ndonesian Agency fo「 Agricultural Resea「ch and Deve10Pment)
P「of. Hartono
(Remote Sensing ‑ Unive「sity of Gadjah Mada Indonesia)
D「. Bagyo Yanuwiadi
(Bioiogicai Control ‑ Unive「sfty of B「aw時ya lndonesia)
Prof. Eko Handayanto
(Soil Scjence‑ University of B「aw時ya indonesia〉
D「, Rurini Retnowati
(Organic Chemist「y‑ University of B「aw桓ya lndonesia)
D「, Muhammad Azrai
(PIant B「eedihg ‑ Indonesian Ce「eals Resea「ch lnstitute)
Prof. Meine Van Noordw呼
(Ag「Oferestry‑ inte「nationai Center fo「 Resea「ch in Agroforest「y〉
Yuzammi, M,Sc,
(PIant Breeding ‑ Bogor BotanicaI Ga「den Indonesian institute of Science)
SOME WEED SPECiES AFFECTING SOYBEAN NODUしATiON AND NODULE FUNCTION
i「awati Chaniagol書〉, Ac「am Taij2〉. pauI K「istiansen3), and Robin Jessop3)
1) FacuIty of Ag「icu'tu「e Unive「sity of A=daIas
Kampus Limau Manis, Pauh, West Sumat「a Padang 25163 1ndonesia
2)Directo「 intemationa‑ G「aduate Research, Queens‑and University of Technoiogy.Brisbane, Aus圃a 3) schoo1 0f Envi「onmental and Ru「al Science, Unive「sity of New Angla=d, Amida‑e, Australia
) corresponding autho「 Phone: +62‑751‑71 181 , 71302 E‑ma帖[email protected]
Received: February 8, 2O12I Accepted: July 24, 2012
ABSTRACT
Exp料ments aimed at examining the effect of
aqueous extracts of three weed species on
noduiation and noduIe function of soybean cv.Mel「OSe have been ca巾ed out at the Laborato「y of
PIant Physioiogy and BiotechnoIogy, Department
Of Ag「onomy and SoiI Science, University of New EngIand, Austraiia. Aqueous ext「acts of fresh Weed mate「iaI (Amaran紡us powe妨 Qpe仙S rofundus and Paspa/um d atatum) at the COnCentration of lO% (W/v〉 we「e added to a mi…S‑nitrogen Hoagiand s nutrient solution in which the SOybea[ Plants we「e grown with 14 hours day Iength, day and night tempe「atures of 28 and 20。C, reSPectively, Iight intensity of 790 LlmOl/m2/s, and the 「eiative humidity of 65%. The pIants were kept fo「 th「ee weeks prior to the measu「ement of
activity of nitrogenase enzyme and ammonium COntent Of the root nodules. AII weed extracts
tested 「esulted in impaiment of soybeannoduIatidn and noduIe function as indicated by
reduced activity of nit「ogenase enzyme activity
禦需霊慧i器S謹言舘岩操
nit「ogenase enzyme activity, it was less inhibito「y than nutg「ass ext「act in 「educing the totai ammonium content of the soybean 「oot nodules.
Keywo「ds: aiIeIopathy, SOybean, nOduiation, nutg「ass, ama「anth, PaSPaium
INTRODUCTION
SimiIa「 to othe「 CrOPS, Weed interfe「en∞ in
SOybean cuItivation is common and causes
Se「ious probiems. Coble et a/. (1981〉 「eported that weeds competed di「ectly with soybean fo「iight, nut「ients, and moisture, and might inte「fe「e
Accredited SK No.: 81IDIKTIIKep/201 1
indirectIy through the p「oduction and reIease of aiielochemicals that inhibited c「op g「owih.
A=eiochemicais refer to seconda「y metaboiites P「Oduced by pIants, mic「oo「ganisms, Vi「uses and f…gi that in仙ence the g「owth and deveiopment Of agricultu「aI and bioIogicai systems (excluding animaIs〉 (NarwaI, 1 999). in addition, Weeds often Serve aS hosts for insects and piant pathogens that attack soybean, and the physicai p「esence of Weeds in the crop may interfe「e with othe「 pest COnt「Ol. These constraints make weeds more S日gnificant than diseases and insects to soybean famers (Eyhe「abide, 2002),
Some stress conditions decreased noduIe
activfty in soybeans such as tempe「atu「e and lighト dark period (Schweitzer and Harpe「, 198O), Salt St「eSS (Se岬j et a/., 1998), Wate「 st「eSS (M酬e「 et a/., 1996), and heavy metaIs (Balest「asse et a/., 2003). Aiielochemicais, cauSing abiotic st「ess, may affect leguminous nit「Ogen fixation through different mechanisms such as interfe「ence with Iegume hosts, the mic「OSymbionts, and the noduiation process. Fo「 exampIe, 10% (W/v) aqueous ext「acts of phaiaris (ma/a疎e aqua鍬oa)「educed 60% noduie fo「mation in subcIove「
(7崩o〃um subte胴neum) and lotus (Lotus pedmcu伯tus) (HaIsaII et a/., 1 995). Howeve「, the autho「s argued that 「educed noduiation was a SeCOnda「y e範頼Of the aIIeIochemicals foiiowing the reduced growth in 「oots that 「etarded 「oot hai「
deveiopment. Simila「ly, red「OOt Pigweed extract at 20 mg/mL o「 Iowe「 SeVe「eiy inhibited g「OWth, and
COmPietely suppressed noduIation in soybean
(Ma=ik and Watson, 1998), demonst「ating theCOnSistent effect of a=elochemicals on noduIation
even at iow concentrations. 1t was specuiated that
these resuIts were an indication of water solubility
Of the aIieiochemicaIs in the weed 「esidues,Zimdahi (1980) reported that a lO% Ioss of
ag「icuitu「al production couid be a軸buted to the COmPetitive effects of weeds言n spite of intensive Weed cont「OI in most ag「icuitu「ai systems.
Soybean yieId losses of 50 to 90% are common
fo「 SOybean g「own in naturai weed popuiations (Coble et aI., 1981〉, and this yield ioss has become se「ious due to the sIow g「owth of the C「OP at ea「Iy stages (And「ade, 1995〉, hig輔ghting the sign航cance of weed‑f「ee competition in SOybean.
・しittle is known about nutg「ass (C)pe仰s
rowhdus) alIeIopathy on soybean nodulation and
nit「ogenase enzyme activities. Simiia「ly, effects of Powe= s ama「anth (Amaranmus powe/仰 and PaSPaium (Paspaんm diIafa他m) ext「acts on SOybean noduIation 「emain uncIea「. The「efo「e, the「e is a need to study the aIlelopathic effects of ama「anth, nutg「aSS and paspa看um ext「acts on SOybean nodulation to bette「 unde「stand the
Weed extracts mode of action on soybean growth
「eduction. Resea「Ch reported he「e was aimed at Studying the effect of those weed aqueous ext「act On nOduIation and noduIe function of soybean cv, Mel「ose.
MATERIALS AND METHODS
丁he expe「iments we「e conducted at the Labo「ato「y of PIant PhysioIogy and Bio‑
technoiogy, Department of Agronomy and SoiI
Science, Unive「sity of New Engiand, Aust「aIia f「om Janua「y to Ap「ii 2004. A compIeteIy
randomised block design with 5 repIicates was
used to study the effects of weed ext「act on SOybean g「OWth and noduIation, The 4 expe「imentaI t「eatments inciuded lO% (V/v of SOiution) of ama「anth, nutg「aSS O「 PaSPalum ext「acts, and the control g「OuP COntaining no Weed ext「act, Soybean cv. Mei「OSe Seeds were Surface ste「iIised using NaOCl and ethanoI SOIution befo「e 「insed with ste周e disti=ed wate○○The seeds were then inoculated with Nitroge「in lOO, (No. CB 1809) at a 「ate ofO.3 g of inocuIant Pe「 100 soybean seeds fo「 30 minutes at room temperatu「e. The seeds we「e ge「minated in SteriIe sand, and we「e kept for 7 days in a gIasshouse with an ave「age temperature 「ange of 25 and 32OC unde「 the ambient light 「egime.
One seven‑day‑OId soybean seedIing was
t「ansfer「ed into an individuaI I L ja「刷ed with modified, minus‑nit「ogen Hoagland s nut「ient SOlution (Schweitze「 and Ha「Pe「, 1980), Cotton
WOOI was w「apped around the hypocotyl before insertion into the cent「e of the jar lid to hoid the Seediing in place, To p「event the effect of Iight to the 「oots, the jar was w「apped with aIuminium foiしThe soIution was aerated with a continuous flow of air bubbles using a fish‑tank pump. F「esh nut「ient solution pIus the weed ext「acts, acco「ding to t「eatments, WaS added to the jars as needed, and was renewed eve「y week during the Study pe「iod to ensu「e that su怖cient ions and unoxidised i「OnS Were aVailabie. The plants we「e
kept in a growth cabinet (ThermoIine Piant
G「OWth CabinetTM) which was set fo「 a day lengthOf 14 hours, and day and night temperatures
蒜諾:誓書。撚Ct藍h言書経
humidity was 65%,
Three weeks a償e「 t「ansfe「 to the nutrient SOIution, the acetyiene 「edudion assay (ARA) was Ca面ed out to measure nit「ogenase enzyme activfty (Hardy et aI., 1973). PIants were 「emoved from the nutrient soIution and noduIated 「oots we「e bIotted dry w肌pape「 towei fdiIowed by detaching the roots什om shoots at the cotyiedonary node, The roots from each plant we「e then quickIy encIosed in a l L jar fd州owed by an injection of lO% acetyiene th「Ough a 田bber septum assembIed on the lid. P「io「 to acetylene i巾ection, 10% of the ai「 voiume was 「emoved f「om the ja「
and repIaced by the same amount of acetyIene.
The 「OOtS We「e incubated at 「OOm temPeratu「e fo「
30 minutes. The ja「 WaS gently shaken intem請entiy every lO minutes to aiiow good COntact between the root noduIes and the acetyIene, After incubation, 500いL samples of gas We「e Withd「awn f「om each ja「 using a hypodemic Sy血ge and were 叶yected into a gas Chromatog「aphy (GC〉 to measure the amount of ethyiene 「eieased by the 「oot noduies. A gas Chromatog「aphy with a hydrogen ¶ame‑ionization detecto「, uSing Heiium as ca巾er gas, WaS uSed in
this assay. The GC coIumn was 30 m long and
320 um wide. The column tempe「ature was 500C.
The injecto「 and detecto「 temperatu「es were 220 and 300OC, 「eSPeCtiveIy. The nit「ogenase activfty is exp「essed as叫mOles C2H4 Produced/pianVhou「,
At the end of the nitrogenase assay, the nodules
We「e detached什Om roOtS and we「e d「ied in an aiト fo「ced oven at 70oC for 48 hou「s.
Fo「 measuring the noduIe function through measu「ing ammonium content, the fo=owing ProCedu「es were implemented. Root noduies were
陣gu「e 4, Roots of soybean CV, Mei「ose grown in modified HoagIand s soIution with l O%
(W/v) nutg「ass extract.
(Ruie「js lO cm)
Figu「e 5. Roots of soybean CV. Melrose g「own modified HoagIand s soIution lacking
the weed extracts
(Ru看e「 is lO cm)
Figu「e 6, A cIose「 Iook at the
「OOtS Of soybean cv. Mei「OSe
grown in modified
Hoagland‑s soiution (Note
the smalle「 noduies aIong the roots systems that we「e not observed in the other
Figure 4 shows the adve「se effects of nutg「ass extract on soybean 「oot g「owth. Roots 什Om this g「oup we「e Iess deveIoped and had a Very SmalI propo巾On Of root hairs, SuggeSting root
growth inhibition was accompanied by changes in
root appearance, ln cont「ast, SOybean 「oots f「om the cont「oI g「oup deveioped weIl (Figure 5) and盤許諾喜捨譜蕊誓霊需
groups (Figu「e 6).
Weed extracts ma「kediy inc「eased total
ammonium in the root noduies of soybean cv,
Mel「OSe (P<0.001 ), and nutgrass ext「act 「esuited in the greatest inc「ease (P<0.001) in totai ammonium (Figure 7). Ama「anth and paspaium extracts inc「eased totaI ammonium but the inc「ease was not highiy significant compa「ed tothe control group (P=0.02 and O.04, reSPectiveIy), indicating that interference in ammonium accumuIation in root noduies is one of the aIieIopathic mechanisms of the weed extracts in SOybean nodulation.
The present experiment confimed that a=
Weed ext「acts reduced both noduie function (nit「ogenase activity, ARA) (Figu「e l) and nodulation (Figu「e 2 and Figure 3). Howeve「, the
mechanism th「Ough which the weed ext「acts inhibited soybean nitrogen fixation 「emains uncIea「. The nitrogenase enzyme system consists Of two ∞mPOnent P「Oteins, the i「on (Fe‑) p「otein and the moIybdenum‑i「on (MoFe一) protein. Both a「e 「esponsibIe fo「 the A丁P dependent 「eduction Of N2 f「om the atmosphe「e (Van Kammen, 1995), Since the reduction of N2 requires la「ge amounts of
energy which is generated by oxidative
Phospho「yIation, there is a high demand fo「 O2 innoduies, Respiration invoives the oxidation of NADH, COuPled to the phosphorylation of ADP
Which then generates ATP. The「efo「e, the「e is a StrOng link between 「espi「ation and nitrogenase
enzyme activity. The overaIl reaction of bioIogicai
nit「ogen fixation (Van Kammen, 1995) f「om which We Can See that nitrogenase enzyme activjty「equi「es Ia「ge amounts of energy (ATP) is
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Sou「ce: Van Kammen (1995)
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Figu「e 7" Totai ammonium (% of noduie d「y matte「) f「om 「oot nodules of soybean CV. Mel「ose at d附e「ent aqueous Weed ext「acts with concentration of
lO% (WIv〉,
AileIochemicai effects on 「espi「ato「y activfty
have been reported in com (Koeppe, 1972;
Abrahim et a左2000; Abrahjm et aI., 2003a),
SOybean (PenueIas et al., 1996; Jose and
Gi=espie, 1998; Sert et a/., 1998; Ab「ahim et al., 2003b), Onion 「oct tips (KupidIowska et al., 1994), mycorrhizal fungi (Boufalis and Pe冊ssier, 1994), and yeast mitochond「ia (Einhe=jg, 1995 and PaPers therein). Chaniago (2004) demonst「ated that amaranth, nutg「aSS O「 PaSPaium ext「acts redu∞d 「espiratory activity of germinating SOybean. Reduced 「espi「ation 「e¶ected growth reduction due to Iess 「espi「atio=‑generated ene「gy, Which may indirectly lead to 「educed nit「OgenaSe enZyme aCtivity.Minchin et aI・ (1981) proposed that N2 fixation and its conve「sion to o「ganic N COmPOunds is an ene「gy intensive process which may requi「e as much as 25% o=egume,s net
Photosynthate. An adequate suppIy of energy by
Photosynthesis is 「equi「ed fo「 efficient noduIe initiation and deveIopment (F「ansisco J「 and Ha「pe「, 1995; Schuitze and Kondorosi, 1998).
The「efore 「educed soybean biomass may Iead to iess photosynthate suppIy to the nodしIes (WaIsh, 1995). Ama「anth and nutg「ass ext「acts
SignificantIy lowered the net assimiIation rate
(NAR) of soybean (Chaniago, 2004), 「eflecting the dec「eased capacity of shoots to suppIy Photosynthate to the nodules. Therefore,韓is SuggeSted that weed ext「act effects on nit「ogenase enzyme is a seconda「y effect.Weed ext「acts may enhance the mechanism th「ough which soybean noduIe numbe「 is 「egulated. One of the mechanishs is known as autoreguiation or feedback inhibition (Fransisco J「 and Ha「pe「, 1995) th「ough which the inhibition of furthe「 noduIe fomatio= is 「egulated by existjng o「 developing noduIes. This is in accordance with Figu「e 3 that shows nodule number in the co=t「OI g「oup was significantly highe「 than that of the weed‑eXt「act‑t「eated groups. Soybean什om the ∞ntrOI group had言in add圃on to the la「ge noduies at the c「own region of the 「oot, Ia「ge amount of medium and smaIi size noduies (≦ 3 mm in diamete「) in the iate「al roots (Figu「e 6). These noduies did not appea「 to be
「egulated by the feedback inhibition mechanism.
The auto「eguIation controliing 「oot noduie numbe「s acts systematica=y and the autoregulatory signals o「iginate什om the shoot (Kosslak and Bohlool, 1984). However言n addition to autoregulation, reduced noduIe numbe「 was Pe「haps a combined effect between alieIochemicals and soybean prefe「en∞ tO fom
the N‑fixing symbiosis.
Reduced 「OOt g「OWth and noduIation may result f「om the indi「ect effect of weed ext「acts th「Ough changes in pIant intemaI nutrient status, Which resulted什Om mOd師ed growth envi「onment.
Soybeans we「e g「own in nut「ient soIution SuPPlemented with weed ext「acts. Roots that we「e exposed to the nutgrass extract we「e poorly deveioped and had fewer Iate「ai roots w軸 Sigr価cantly fewer 「oot hairs (Figu「e 4), it is POSSibie that noduIation inhibition was a re¶ection
Of thjs effect. This finding agrees with work
「eported by Halsa= et a/. (1995), that 「esidue ext「acts of phaiaris 「eta「ded 「oot hai「 deveiopment in subtema=ean Ciove「 as weII as root length and numbers. AIleIochemicals may interfe「e with 「oot meristematic p「ocesses and 「esuIt in impai「ed ceii division Naughan and O「d, 1990), Which may reduce root growth.
The negative alielopathic effects of weed
extracts, eSPeCiaりy amaranth and nutg「ass, We「emore pronounced in root biomass. Roots and the
「hizosphe「e is the primary site where
a=eIochemicais can continuousiy be supplied by
donor piant 「oots, Where c軸Ciai chemicaI and bioIogical conve「sion take place, and where alIelochemicals enter the ta「get p看ant (Tang et a/.,1989)" Although the system used in this study
d胴ered to field condition, SOybean 「oots we「e
directIy in contact with weed ext「acts and therefo「e di「ectIy absorbed the ext「acts.
Weed extracts affected soybean noduIation
through reduced nit「OgenaSe aCtivity and ammonium assimilation. Ama「anth ext「act 「esulted
in the Iowest nitrogenase activity, aIthough its effect on ammonium was less pronounced than
that of nutg「ass ext「act, 「eflecting the compIexmechanisms involved in nitrogen fixation.
Ammonium is toxic to celis and must be 「apidIy
assimiIated. This is achieved by the concerted action otwo highIy reguiated pathways, gIutamine Synthetase (GS) and glutamate synthase (GOGAT). Both pathways result in the synthesis of
gIutamine which is the dono「 for the biosynthesis Of m争jor nitrogen‑COntaining compounds incIuding amino acids, nuCleotides, and chIo「OPhyils
(Louiakakis et a/., 1994; Coruzzi and Last, 2000;
しancien et al., 2OOO; and Nkoa et aI., 2003〉.
Therefo「e, any interfe「ence in the metabo=c Pathways of ammonium assimifation may interfe「e with othe「 physioiogicai p「OCeSSeS. Reduced
ChIorophy= content and piant biomass reflected the
indi「ect effects of weed ext「acts on photosynthesis th「ough chio「ophyII synthesis reduction, due POSSibiy to a decrease in gIutamine assim航ated f「om ammonium.High ammonium conten=n 「OOt nOduIes re¶ected the imbalance of inorganic nitrogen.
Fixation and assimiiation of inorganic nit「Ogen, in the fomi of ammonia言nto carbon skeletons to P「Oduce amino acids is one of the most important biochemicaI processes in piants (Lancien el al・, 2000 and BaIestrasse et a/., 2003). For the
GSIGOGAT cycIe to work, N metaboIism must interact with C metaboIism, Since GS activity
「equires energy in the form of ATP, and the GOGAT uses C skeietons and 「eductant in the form of 2‑OXOgIuta「ate and 「educed fe「「edoxin or
NADH, reSPeCtiveIy (Lancien et a/,, 2000).
However, how weed ext「acts inhibited
ammonium assimilation was not studied further in
this resea「ch, lnterference in ammoniumassimiiation may be expIained by analysing
enzymes invoived in the p「OCeSS SuCh asgiutamate dehydrogenase, giutamine synthetase,
and aspa巾ate aminot「ansferase. An increase in noduie totaI ammonium f「om the weed‑eXt「act‑t「eated g「oups may be one of the a=eIopathic
mechanisms of the weed extracts on soybean
noduiation.CONCLUSiONS AND SUGG訂IONS
Ama「anth, nutg「aSS, and paspaIum ext「acts reduced the nodulation and nitrogenase activities (ARA) of soybean cv. Melrose. Ama「anth was most inhibito「y to nit「ogenase enzyme activity.
However, ama「anth ext「act was less inhibito「y than …tg「aSS eXt「aCt in total ammonium" Since N2
fixation is a compIex mechanism invoIving many
enzymes, futu「e work 「equi「es the study of weed ext「act influence on GS/GOGAT cycle and theenzymes invoIved in the cycIe.
ACKNOW」EDGEMENTS
丁his study is part of the first autho「 s PhD PrQject carried out a=he Unive「Sity of New Engiand, Armidale ‑ Austra=a. The autho「 WOuld iike to since「ely thank ali peopIe and parties that have cont「ibuted in every way fo「 the compIetion Of this deg「ee"
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