Effect of Trifluralin Growth, Morphology, and Nucleic Acid ... · Plant Physiol. (1968), 43....

Plant Physiol. (1968), 43. 265-273

Effect of Trifluralin on Growth, Morphology, andNucleic Acid Synthesis1

Donald P. Schultz,2 H. H. Funderburk, Jr., and N. S. NegiDepartment of Botany and Plant Pathology, Auburn University, Auburn, Alabama

Received Aigust 28, 1967.

Abstract. Roots and shoots of corn seedlings (Zea inays L. var. Dixie 18) germinated intrifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropvl-p-toluidine) solutions are characterizedby radial enlargement of the cortical cells and by multinucleate cells in the meristematicregions. Trifluralin inhibits elongation of A vena coleoptile sections at concentrations of0.1 gM to 10 tM. Synthesis of DNA. RNA, and protein is suppressed in the root tips whileno significant effect is noticeable in the shoots of corn germinated in trifluralin. A 32ptime-course study of 48, 72, and 96 hours utilizing phenol extraction and MAK column separationof corn root and shoot nucleic acids showed suppression of 32p incorporation in the treatedroots; however, the 72 and 96 hour treated shoots incorporated a much greater amount thanthe control with most of the increased incorporation found in the sRNA and DNA fractions.The increased activity in the DNA may be due to a high G-C type DNA. No selectivesuppression or enhancement of any particular RNA species was noticed in the treated plants.

Certain growth regulating chemicals such as

'Tordon (4-amino-3,5,6-trichlo.ropi'colinic acid) and2,4-D prommote radlial enlargement of iplant segmentsand also affect nucleic acid metabolism (11, 12,17).The carbamates also promote radial enlargement ofroot tissue and are believed to disrupt spindle for-miation in cell division (7). Standifer et al. (28)and Talbert (29) found 'that swelling of the rootterminalts was the iobvious morphological effectcaused by the herbicide trifluralin (a, a, a-tri-fluoro-2, 6-dini.tro-N, N-dipropyl-p-tolluidine). Tal-ber't (29) alIso reporlted that histological stuidiesindicated that ce1l division was affected in sovbeanroot tips. Amato et al. (1) reported similar re-

sponses in corn and cotton. Mann et al. (19)found th,at trifluralin did not significantly affectproitein synthesis in barley coleoptiles or Sesbaniahypocotyls.

These studies xvere initiated to investigate thesttunting and radial enlargemenit of roots and shootstreated wiith trifluralin and to determine whetherthe herbicide promotes the synthesis of a particullarnucleic acid fraction.

' Thi. investigation wxas supported in part by anlNDEA Fellowship to the seniior author and in part bya grant fronii the Department of the Interior, FederalWater Pollution Conitrol Administration (WP 00636-04).This mnaterial represents a portion of a thesis presented

the senior author to tile Graduate School of AuburnU;niversity in partial fulfillment of the requiiremiient forthe Ph.D. degree.

2 Present Address: Department oef Plant Pathology,University of Missouri, Columbia, Missouri 6520)1.

Materials and Methods

Histological Stutdlics. Corn seeds (Zcat maysL. var. Dixie 18) were germinated in 0.1 mM CaCl.,,w-ith and without 'trifluralin (5 mg/I), for 3.5 daysin the (lark at 270. Three 5 mm segments of theprinmar- root beginning at the tifp and three 5 mmsegments of 'the shoot from the base of the firstinternode were sampled and embedded in paraffinutilizing standiard killing, dehydration and infiltra-tion techniques. Transverse and longitudinal sec-tionls 10 i in thickness were cut with a rotarymicrotome, and the sections were stained by thetannoc acid-ferric chloride method.

Avena Straight-Growth Test. The procedure ofNitsch and Nitsch (22) was used wiith severalmodifications. Avenat satiza seeds (var. Torch,hul,less: olbtained from H. W. Tomlin, Encino,Calif.) were presoaked in runnring tap water for2 hours before planting in sterilized verm,iculite.Growth of the first internode was retarded byillumination from a Kodak BD Safety Lamp.After germinating for 72 hours, unliform coleop-tiles were excised, the apical 4 mm .removed and thenlext 10 mm section placed in a solution of 1 mgAMnS04-7HW,O1/liter for 3 hours. One hundredgrouips o-f 5 sections each were then selected atrandom and placed in test tubes containing 4 ml oftest soluitions. To prevent cutrvatture of the sections,the test tulbes were placed in an upright drum re-volving at 1 rpm. Alil procedures after initialplanting w-ere performed under a safety lamp.After 20 hours in the test solutions, the sections

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I'LANT' PHYSIOLOGY

vere *reiiioved andmtieasuiredI to the nearest 0.1 mmiinder a binocular dissecting miticroscope.

Nutcleic Acids and P-otein. Corn seeds (Zeamal(lys L. var. Dixie 18) were germinated embryoside down for 3 days at 280 in darkness on 2 'layersabsorbent paper placed in a 22 X 32 cm gllassbaking (Fji!sh saturated with 0.1 m.m CaGl_. The(lishes were covered Nvilth thin plastic which hadbeen perforated for aerationi. Crystalline trif'lu-ralin di'ssolved in methaniol Nvas added 'to the CaCl2soltution in sufficienit aquantity to give a finali con-centraition of 14.9 ,M (5 mg/l). Apical sections(10 mm) from primary anid seminal roots andcntire shoots were excised inito iceid Petri dishes,blottted and weighed. The Smil'lie-Krotkov (27)procedure for extraction of DNA and RNA wasused. Two to 3 grams (fr wt) of tissue was

homogenized for 5 minutes in 10 ml of ice-coldmethaniol in an ice jacketeld g,la,ss homogenizer fittedwilth a power-driven Teflon pestle. The slurry was

centrifuged (O0, 10 miil, 7000 X g) and the super-nate di'scarded. The residule was extracted withmethano,l, trichloroacetic acid, ethain.ol, etthanol:etherandl ether. The remaining ether was removed byaspiration and 'the residtue air-dried, powdered andweighed (etther-dry wt). RNA in the residue wasthen hydrolyzed with 0.3 N KOH (16 hr, 30°).The RNA hydrolysate was adsorbed on a columnof Do,wex-1 iou-exchange resin (chloride fornm,200-400 mesh), ithe nucleotides wvere eluted (flowvrate, 0.5 ml/min) with 30 nIl of HCl-N'aCl. solutioll(27) and RNA determiined by the orcinol reacetioi.DNA 'ini the iresidue was hydrolyzed with 10 ml of0.5 N HC104 (40 mins, 700) and (letermilied by thedipheniylamiine reaction. 'I'The method of Lowry.t al. (16) was used to determiine proteini in theresidtue.

32PO4 Incorporationt. Corn seedlings were

geZrminated in CaCL solution for 48, 72, or 96 hours.Tihe excess CaCl9 soltition was drained from thedish 8 hours before harvesting the 'seedlings and

repla,ced wiith 1 mc H332PO4 (carrier-free, inaqueous solution, source-New England Nucleair)dilluited with 30 iml di,stilled water. The emtractionprocedure of Ingle et al. (10) for RNA and DNAwas uised with certain modifica'tions. Roots (5-10g) and shoots (2-5 g) were excised and homog-enized for 2 minutes at mediLm speed fo,llowed bystirring for 3 minutes at slow speed in a Virtis"45" homogenizer. All extractions were carriedouit at 0 to 40 'unless otherwise stated. Root tissue(10 g) was homogenized in 15 ml tiis-satturatedphenol, 2.7 ml bentonite (50 mg/mIl), 2 ml tris(pH 7.4) and 0.3 ml sodium lauryl sulfate (SLS).Shoots were homogenized 'in 'similar fashion withproportioned amounits of each evtradtant. T(hehomogenaites were centrifuged (10 mins, 7000 X g),the aqueou's iphalse was removed 'and 'st'ored in thecoild, the phenol residue was re-extraoted and thecombined aqueous phases were idepro,teinized by two2-mini'fte extraetion-s with e(pual volumes of Itris-

phenol. 'T'lle finial aquieotus phase was made 0.15 Mlwitlh rCsl)cCt to potassiuim aceita,te. Ethanol wasadded to a final concentration of 70 % and thesoluition placel in a deep-freeze for 3 to 5 houtrs,centri fuiged (20 mins, 7000 X g) and 'the pelletcon-taining nucleic acids dissolved in 5 mnl 0.05 M1NaH.,PO, (pH 6.7). The dissolved pel/let wvasdialyzed for 12 houirs at 4° aga,inst a changingflow of K aceitate (pH 5.2). The OD..,, was deter-mine(l and equivalent OD units from treated anidcontrol tissuie were ads'orbed onl met-hylatted-albumsinkieselgu'hr colunmns prepared according to Mandellanld Herslhey (18). A 2-stage linear gradienit ofNaC'l-PO1 was puimped th,rough the columns (9).The first stage consisted oif 0.35 Mi NaCl-PO4(170 ml) to 0.8 Mi NaCl-PO4 (170 ml) anld thesecon(d of 0.8 mr NaCl-PO4 (275 ml) to 1.20 AiNaCI-PO1 (275 ml). A pressure of 1.5 psi -wasaippllied to the system with purified nitrogen and(I aflo,w rate of aboult 1 mIl/minuite mainta)ine(l with aperistaltic pump (LKB, Model 4912 A). TheOD2n, of eachl 7-nil fraction was (letermined and0.1 to 0.5 ml alliquots from each fraction werepipette(l inito 10 ml aclqueouis scintililation flutiid forradioassay in a Beckman liquid scintillkation spec-'trometer. Molarity of the elulanit was (leterminedby measuring the conductance of aliquots fromevery fifth fraction. Conductance valuies were coIn-verted to molar,rity by uise oof a standla,rd cuirve.

Results

Histological Study. The radial enlargement ofthe root tipl) and first initernode was dtie to swollenicortical cells (fig 2). The epidermis in both theroots and shoots of 'the trea-tedl seedlings wt a's oithcrdi,sorga,nized or Inot present. M\Iultinutcleate cellswere noticed in bo-th the root tips and first inter-node regions (fig 3, 4). Nuclei, in some cases4 to 5, wiere generally aggregated and were oftendifferent in size. The frequency of m&iltinuicleatecells was greatest in the meristematic regions of theroot and shoot. There was no significant changein the number of cells per tunit of length 'betweenthe treated and control itissue.

Aveina Straighlt-Grozuth Test. Figutre 5 showsthlie resullts of va,rious concentrations of triflturalilon the elongation of Avenia( coleoptile sections.Inhibition of elongation may be seen at concentra-tions of 0.1 to 10 pei 'trifluralin even in the !presenceof IAA. Without IAA, 10-6 M tnifluralin 1inhrihbittedelongation more than 50 % that of the control.Repeated experiments ulsing 10-6 :M 'trifluralin wiithantd without IAA showed nearly a 50 % decrease inelongation of the sec'tions, al,though the exogenousatixin did reduce t'he degree of inhibition.

Total Nuiclcic Acids and Protein. Root tips ofcorn seedlings ge,rmin'ated in trifluraIlin (1.49 pu,5 mg/Il) 'showed a significianit decrease -in totalRNA, DNA, a(l prcoteiinwhenc 'tlnpalreld tbOle cm-

26)6-

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SCHULTZ ET AL.-EFFECTS OF TRIFLURALIN

_, , t..1_.I4-

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f

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- ,,. 1

Ok 'tat0-4 4

A-*9'

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p

*A i/~~~~~~~U!,

..A.

*F~F..Ot.t ...

FIG. 1. (top)) PhotlmicI-r''graph of cross section of corni roots 3 imm froml the til) germinated 3.0 (lays in water.Magnified 120X.

FIG. 2. (bottom) Photomicrograph of cross section of corni roots 3 mm froml tie lip gerniimated 3.0 dayss in5 tug/liter trifluralin showing typical swelling of cortical cells. Alagnified 120X.

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PLANT PHYSIOLOGY

2Ijp V

=...A

.

r._Silp -:i

*/,,

FIG. 3. (top) Photomicrograph of loingitudinal section of corn root tip, germinated for 3.0 days in 5 mg/litertrifluralin. Magnified 620X.

FIG. 4. (bottom) Photomicrograph of longitudinal section of first interniodal region of corn shoot germinatedfor 3.0 days ill 5 ilg/liter trifluiralin. Multinucleate celIls found predominantly iii the meristematic region. Mag-ni'fied 620X.

268

*:4tsi

no'.




10-4 M IAA

Buffer only

106 M trifluralin

10 4 M IAA + 10 5 M trifluralin

10 M IAA + 10 6 M trifluralin

10 M IAA + 10 7M trifluralin

-410 IAA + 10 il methaolol

1 2 3 4 5 6 7 8 9 10

MILLIMETER INCREMENTS ABOVE 10

FIG. 5. Growth increments of 10 mm Avenia coleop-tile sections grown for 20 hr in 0.1 to 10 /AM trifluralinsolutions. All solutions contained buffer.

trol (table I). 'Phe greatest decrease was in theDNA fractioni (31 ). 'rhe root ti,ps of treatedseedl,ing,ts were stunted and swollen (fig 7). Shootssho-wed similar morphological effewts, butt the swell-.ng was most pronounced in the lnodal region (fig7): helnce, these studies were extendedl to the shoottissule. There wvas no significant change in RNA,DNA, or protein content in the shooits of treatedanid control plants ( table I) .

H 32P04 Incorporation. Figuire 8 illustrates a

tyl)ical l)lot of the OD2,,,, versuis fraction numberfor nuicleic acids of root tissue resolved on MAKcolumns. Peaks I and II have been categorized as

soluble RNA (sRNA) (4). The radioactivity doesnot coinc:(le well with the individual peaks but isspread over both peaks. This presumably resultsfrom the heterogene,ity of the 2 sRNA firactions.

Peak III is primarily DNA but probably also

contains a rapidlv metabolized DNA (24) and some

RNA (3). It may be seen that the radioactivity

peaked 1 fraetion. before the optical density. Ingleet al. (10) found a similar situiation in excisedsoybean hypocotyls and postula-tedl that this earlypeaking is dtue to the metabolically-lahile DNA inthis fracotion.

Peaks IV and V have been identified as lightand heavy ribosomal RNA (lrRNA and hrRNA,respectively) (4). The radioactivi'ty coincides wellwith the OD,60 of these fractions. Peak VI hasbeen found thuts far only in monnocotyledenoutsplants (5) and may be due to aggregation ofrRNA (8).

Table I. RNA, DNA, and Protein Content of the 10mm Apical Segmient of Corn Roots and of 'holeShoots Germinated in 5 mg/l Trifluralin or in

Control Solution for 3 Days

,mg RNA/Treatment mg dry- wt

ControlTrifluralin

p2=

ConitrolTrifluralin

p2=

55.2145.1<0.00

37.937.1N.S.

,tg DNA/ ,ug Protein/iig dry wt mg dry wvt

Root Tips

5 <

Shoo0ts

6.494.460.005

7.098.25N.S.

1 Valuies are meanis of 3 experimentsof 2 replicates.

2 Probabilitv values were (deterluilledanalysis of v-ariance.

87.664.1<0.01

96.7113.3N.S.

e:ich cotnsistinlg

hv ulse of thl

When total OD.,,, per peak is exl)ressed as a

percenitage of the total OD26, from the MAKcolumns of corn roots and sho-ots (table II), thereare no major differences in the RN'A fractionsbetween trealted and contro.l tissue. Thuis, there isno preferential RNA syn.thesis ias in the case of2,4-D or Tordon treatment (11, 12, 17).

Tab)le II. Total 0D.6,) U7its per ANuiclcil Acid Peak Exprcssed as Percenit of Total OD.,0 U-nits fromi 7treated anidControl Corni Root (ad Shoot Nucleic Acids Resolved on MAK Columns

% Of total OD.,6,0 uinits1Total Peak nulmiber

Time OD units' I II III IV Vl VI

hrRoot-control

Root-treated

Shoot-control

Shoot-treated

48

72?

7296487296

487296

63.154.357.759.851.950.675.886.553.768.484.253.4

14.114.617.215.217.218.814.816.012.815.113.716.2

4.04.7

4.33.94.85.0

4.24.7

6.54.44.15.2

10.37.3

10.310.5

8.311.712.112.510.010.710.413.2

13.515.113.013.714.212.414.312.515.414.613.414.5

13.112.112.0'13.114.013.712.612.014.013.215.214.2

45.046.043.443.841.638.441.842.141.342.142.936.7

I Each value is the mean of 2 replicates.

269



PLANT PHYSIOLOGY

H

TRIF.

PPM

1 6;.(t( plp) C(,ori sc(clin1gs germiiitiatcd for 3.0 (lays in w.-Iler showing iiOrinial elonigatioIn of shioot and( roots.FIG. 7. (bottoIll) Corn seedlinigs germinated for 3 days in 5 ug/liter riflir11i11n solutionl lhowi;, 1 adial c 11

largement -an1d stuIting of shoots and roots.

270




e

b.G

J45E,1c

l.0

0.9

0.8

0.7

0.6

0.5

0.6

0.3

0.2

0.1

I 111I

:i~lV V Vl 5080

-1

," . 9 M 3-2000

-.8m

*.1-.17 M

.6

10 20 30 40 50 60 70 80 90 100 110F8ACrION NUMIER

1600

FIG. 8. Typical elution profile of corn root nucleicacids resolved on MAK columns. One mC 32p wasplaced in flats 8 hours before harvesting the plants.Nucleic acids were extracted with cold phenol (seeMethods). Ultraviolet absorbancy (260 m,u) (--),nadioactivity (control root . . ., treated root ---), andmolarity of eluant (- -) from consecutive 7 mlfractions. Right ordinate= CPM/fraction X 10-3.

If the vailtues for the sRNA l)eaks (I and I1)are combined and also those of the rRNA (IV,V, VI), )there ,is an increase in the sRNA fractionsand a decrea,se in the 'rRNA fraction from 48 to 96houirs in the control and treated roots. DNA(peak III) shows no change beltween treated andcontrol roots from 48 to 96 hours, wh,ile tthe controlshoots have a decreased amounit ait 96 hours andthe treated shoots an increased amoSunit.

The relative specific aotivities of the individualpeaks are given in tables III and IV. Iit is evident('table III) ithat there was suppression of nuicleiicacid synthegi's in the treaited roots at each timeperiod and 'in ,all fractions. This suppression paral-lel's the earlier results ('table I) where total RNA,DNA and protein of root tips were reduced by thepresence of truifluralin.

The relative specific acitiv!ities of the treatedand control shoot's are anomalous when the varioustime periods are observed (table IV). At 48 hoursthe treated shoots ,showed only abt)u't half of thespecific activity of the control, btuit th,ere was alarge increase in activity alt 72 and 96 hourts. Thelower specific activity at 48 houtrs in tihe treate(d

Table III. Relative Specific Activity of Individual Nucleic Acid Peaks Expressed as Total cbpmi/Tot(al OD200 fromiiCornit Root Nutcleic Acids Resolzved otn AMAK Columnns

The data are the means of 2 experiments.

l'otal CPMN1/total ODlIPeak number

11 lit IV

ControlTrifluralin (5 iug/l)% Control

ControlTrifluralin% Control

ControlTrifluralin% Control

hr48 62148 458

7272 143872 864

6496 138096 859

63

67451075

161098668

26531560

61

1 33682562

25831769

7239593239

84

505

36871

1258

66155

1606108270

499

39678

1258666553

140084860

472361

114860054

114060452

I Numbers in these colum-ns are 10-3 of actual means.

Table IV. Relative Specific Activity of Individual Nucleic Acid Peaks Expressed as 7otal CPM/Total OD,260fr-otm Corn Shoot Nucleic Acids Resolved on1 MAK Columins

The data are the means of 2 experiments.

Total CPM/total OD 1Peak number

Treatment Time I II III IV V VI

hrControl 48 441Trifluralin 48 234% Control 53

Control 72 658Trifluralin 72 820% Control 125

Control 96 332Trifluralin 96 547% Control 162

Numbers in these column's are 10-2 of actual nmeanls.

43722952

643993154443764182

70028741

72115710215784

1604204

34617250

488568

1,18315440137

34819957

487544

1,12302427140

32818456

521532102262335128

'T'reatmenut Tinie 1 Z \7 I

271



PLANT PHYSIOLOGY

shoots may have been caused by a lack of transportof the 32P from the treated roots, or (more prob-ably), the newly emerged shoots may be verysusceptible to the herbicide.

Discussion

Tlri,ftluralrin has no effect UpoIn germination butinhibits elongation o,f roots and shoots of susceptiblespecies by 50 % at 0.1 mg/liter (25). From thesefacts, in conjunction with the Avena te,st (fig 5),one may infer that trifluralin has a direct or in-(lirect inhi'bitory effect oin the processes necessaryfor cell elongaltion sulch as protein or RNA syn-

thes,is (20,23). It has also been reported (21)that elongation in certa,in plant tissue is dependenton DNA synthesi s. Exogenous IAA overcomes

soime of ithe inhibitory effects of trifluralin (fig 5).'I'huis, if IAA acts by enhancing the synthesis ofsome compound(s) suich as mRNA or sRNA(6,12, 20), any adverse effect upon IAA wouldrestilt in reduced tissuie growth.

Triflur.lini has an inhi,bitor\ effeict on RNA,DNA and p)rote,in of corn root "tip's (table I).Hlowever, the shoots of corn seedlings are alsos'tlinte(l by- triflutralin (fi,g 5, 6) and )there was no

significatm change in the RNA, DNA, or proteiicontent of t,he treate(l sho(ots wvhen compared to theconutrols (table I). Ini fact, it appears that there\\ as aln increased aniouint of DNA anld protein in

the trelated shoots. Also, the mnltinluicleate condi-tioii Nwas nioted in the shoo,ts as xwell as the roots(fig 3, 4); hence it is probable that no simpleexplanatiol such as in,hibition of TAA synthesis o,r

actioin can explain tihe results.\Ve have also fouind (uinpulblished data) that

the vapors of trifluralin are as effective as contactw ith the trifluralin solution in prodticing the mor-

phologicial symptoms in corn seedlings; therefore,tranislocation olf the herbicide \\-otuld probably notb)e a factor in the (lifferences note(l between theroot and shoot.

The supp,ressioni of ticleic acidl synthesis in thetreated roots based on relative specific activity(table III) xwas nIot surprising after the gross

mncleic acid analysis. The greatest stuippression was

fotind in jthe sRNA aind rRNA fractions at 72hours. The ratios betweeni the treated and controlsl)ecific a,ctivities decirease(d at 96 hours in the DNAand rRNA fractions. 'I'his is probably due to theroots overcoming the effect oif the initial concen-

trabion of herbicide and beginning new growth.The large increase in tspecific activity of the

treated shoot at 72 and 96 hotirs may be dtle toherbicide-indduced prodtiction of a high G-C fractionof DNA. The radioactivity associated with thiishigh G-C DNA has been reported by other workers(9, 17) to eltlte just iprior to the OD,60 peak. This

early eluttion was fotind in both the roots andshoots of control and treated corn seedilings. Insoybean, the maturing regions of the roots and

excised hypocotyls have beein shown to producelarge quantities of the high G-C DNA (9, 10).S4ince elongation of the trifluralin-treated cornseedllings virtually ceased at 72 hours (figs 6,7)and m,ature vasculair elements were present, thetreated plants may have produced the high G-CDNA instead of the normal A-T DNA. The fuinc-tioiI an(d origin (nucleolar?) of the high G-C DNAhas not been clariftied at present.

Recent work (15) has indicated that bacteri,alcontamiination may contrilbute to ,the 32p labelingof seedling nucleiic acids. The moist environmentin whic;h the seedliings were growin would be con-(lucive to bacterial growth. Such contaminationmight explain the differences in relative speciificactivity between the root and shooit ntucleic acids.However, the !roots, which were bathed in solui-tion,showed a net decline in specific activPity when com-pared to the shoot's. Most 32p labelfing of seedling,nucoleic acids has been short-term (15-60 mins)resul,ting in competition for the avlailable 32p be-tween bacteria and plants (2) whereas in theseexperiments the seedlings were exposed to thera,dionticlide for 8 houirs. If I)acterial contamina-tion wa,s of great importance in these experiments,one woultd expect a greater shift in the 32p peakfrom the OD,,,,, peak in the DNA anld rRNA peaks(15) whereas we founid the 321) in the DNA frac-tfion con'sistently peaked 1 fraction before theiOD.,60 while the 32p and OD2;, I)eaks in the rRNAfraction coincided consistently.

The specific activity of the nucleic acid peaks(itable IV) in ithe treated and control shoot tisslueparallel one another at 72 and 96 hours and thera,tio between treatedl and conltr-ol tissue is aboutthe !same at these 2 time periods. This is probablydtue to a restumption of normal growth of the shootas the herb)icide concentration is reduced throughv-olatilization.

It may be asked, what is the phytotoxic mecha-nism of trifluralin? Is it a 2-pronged attack onthe basic physiological processes of elongation andnuclei,c acid syn(thesis? Or are the 2 in,separableeffects of a different mech,anism? Is the histo-logical effect (mulItinucleate cells and radial en-largement) the primary causal agenit of death withthe effect onl elongation and nucleic aclid synthesismerely an indirect resutlt? Kihlman and Levan(14) report that the melthylaited oxypurines such ascaffeine, theophylline and theobromine, which sup-press cell formation, inhibit cell division withoutaffecting chromosome or nuclear division. Kihlman(13) also reports that the alkylated oxyppurineisproduce multinucleate cells and that the directionof the spindle axis frequently does not correspondwith the d-irection of the root axiis. Both o-f theseconditions may be seen in figure 3.

Although 'trifiluralin does not cauise preferentialsynthesis of rRNA as does 2,4-D and Tordon, itsstriiking effect on growth and nucleic acid synthesismark the chemical as a potent new growth inhibitor.

272




Acknowledgments

lilly

of trifluralin. also Mrs. Martha Bennett. and Mrs.Kathy Britt for teclinioal assistance.

Literature Cited

1. AMATO, V. A., R. R. HOVERSON, AND J. HACSKAYLO.1965. Microanatomical and morphological res-sponses of corn and cottonl to trifluralin. Proc.Assoc. Southern Agr. WVorkers Inc. 62: 234.

2. BARBER, D. A. 1966. Effect of micro-organismson nutrient absorption by plants. Nature 212:638.

3. CHERRY, J. H. 1964. Association of rapidly me-tabolized DNA and RNA. Science 146: 1066-69.

4. CHERRY, J. H., H. CHROBOCZEK, W. J. G. CARPEN-TER, AND A. RICHMOND. 1965. Nucleic acid me-

tabolism in peanut cotyledons. Plant Physiol. 40:

582-87.5. CHERRY, J. H. AND K. L. LESSMAN. 1967. Com-

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