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Abstract reacti.on•’the res1lJ.t8obte.1n8d cQU1.dbe s zedin 10118foU.O’Wi,ng :,_ ~ ••WIlberof fUllgaJ. iBol.e.t••••showed e. ,,14. epect~ ofvirul-encelevelS. It waSnot possi.~· to d•••1•&11&’·such iSolates ••••dUferent races bSCalJlleof the l.-lEof differentiaJ. lin ••••with known geneUc compaeiUS. 2- CCOIlPIlX’W resiSt””,t and sU8cepti~e cotton vsri.e1il” in both the ”hesl;tb;J” and ”diSeaSed” C(Dd1ti.OIllI111.respect to lIlidn0 acl4 compollition indj.c.ted that Ie.) At early at,.gee ot plant grOWth. :zoot canteD’ll oflIIIlinoacids willialJDOIItidenticaJ. in both r881B\- and susceptibl.8 healthy p~an:tsl then clecrea8e4’With age and to a greater extent in the 8U8~roots. As a. reeul t of infection, higher levelS of free amino acids were experienced with 1’OOt8 ofthe susceptible variety and continued to increaeein rel.atio~ to healtb1 tiSsues as the disea.ee p~ogressed.Although some degree of reduction i.n ejhinoacids occurred in the roots of infeoted resistan~variety at early stages, their !evel maintained a60 % lllcrease over the healthy tiSsues at l.ater stag •• •The most consistent change was ’the increwa8 in theooncentration of cystine in the resistant varietywhich ’WIIS reported to affect the production of~aric acid. Someother amino a.cids changed in concentration as a result of in:fection; however,theJ.r ro:le 1.a\mel-ear exc~pt for tryptophan whichcou1d have some bearing on III synthesiSb- J1,2aOet .iaiJ,.a;r reaul.ts. witll some di:ffe:renQes, were observed for the aminoaoid contents of stems· Total aI3 well. as certain amino acids increased as a result of infection. The degree of variation was :lesspronounced for leaf tiS sues. Few aJDino acidsincreaeed in leaves of infected suso.epti~8 variety, whereas aU. but tryptophan decrea.aed in the resiStantTariety.It appears difficuJ.t to rel.ate the type of p~ant reaction to any given aJDi,no acid in the heal-thYtissues • ~e ohange in certain aJIlino acids triggered by in:fection o.o111.dbe one of the key detet’!l1inante of the outcome of hoet-P8%’aS1te interaction. In other words, resistance mq not be a preformed but rather an induced state. ,_ With respect to sugars t different organs ot differentvarieties exhib1 ted both Q.ualitative and quantitative differences in BUBarcontent. Sucrose, gaLactoee andglucose were pr08ent in aU. organs of both susceptibleand resistant varieties, whereas maltose was only f0UD4J~ -~----_.~.- .. ’in stem tissue,.( c:n the other hand, fructos e was onl.7 found in different organs of the susceptible variety • .Asa result,.’ of 1n:fection, sugar contenta deer.as ed Iin roots of both v~i.et1est with galactose + glucose remaini ng at almost the SaJIle concentration in the suscept1b~e variety; however, they inereseed in the resistant one. On the other hand, sucrose decreased in the susceptible and increased in the resistantvariety when comparedwith the respective contltols. fluch change8 in sU«ar levels could have aOlfe hea~ on the nutri tiou of the invading fungus either dir.c~ on indirectly and indicate certain metabolie changes in carbohydrate metabolism due to infect1c.n. Other p~ant organs responded somewhat diftereatly from roots wJ:tl:l respeot to certain sugars. As to the stems, sucrose allowed a.much more increase in the resi.stant variety than in the suscept1b~e one. On the cantrary, galactose + gJ.UOOS8 increased first and th8i1 decrea#3edupon infection of the ausceptib1e variety, whereas they were always Leas in the resistant variety subjected to ~ect:lon whencomparedwith the respective healthy oontrols. As to leaf tissue, no change occurred in the level of sucrose 1n the resistant variety, whereas it increased in the ausoeptib.1.e one. On the contrary, a marked decrease in the level of gaJ-actose + gJ.ucose followed the infection of the suscep’tibl.e variety and the appoait8 was true for the resistant variety. 4- With respect to phenol.ic compounds, three major groups i.e. mono-, d1- and poly-pheno~s were found in both varieties. The di-and pol.yphenol.s were present in comparable concentrations in the healthY org~ of both resistant 8lld susceptibl.e var1e’t1t1Js. Uponinfection, these two groups of phenolS increased in orgaJl8 of the sUBcept1bl.e variety, whereas the opposite vas true, in most cases, With the resistant one. .Aa to the memo...• phenoJ.a, the two varieties exhibited comparable concentrations in roots and 1eaves at early stages and in st8J18 at relatively later stag.. Following infection, the susceptible variety alwa;ya exhibited a DROP in the monophenoJ. ~evel compared with the healthy tissues, whereas the opposite was mostly the case for the ~reaiatant variety - Such interconve1.”8iona of phenolic SUbstances couJ.d be accomplished by the eneymes ot the pathogen and/ or the host in . response to infection. and the 1I:ype of phenolic compotmdsthspredominate: could play a roJ.e in determining the type of host reaction as these compOt1nds differ in their toxicity. 5- With respect to certain hydrolytic en~eaJ 1_.1.:. pectic and celluJ.o1ytic enzymes, comparative studies shoved that: a) Healthy tissues of both 8usoeptible ana. resistant varieties containe4 some activity of PMB’but none of the pectin degrading ~,m.ee. Upon infection, 80me increase in PU activity occurred; however, to greater extent in the susoeptible than in the resistant variety. On the other hand, the pectin degrading enzymes were not found except in the infected susoeptible tissues_ b) Very low activity of cell~ases vas found :in the healthy t1eeue8 ot both rea’istant and SUBcepti.bJ.e -varieties. In:fection was usu.a1].y followed by some inorease in acti.v1ty i however, to a greater extent ion the susceptible variety. The magnitude of increase was relatively low to warrant major role ot these enzymes in pathogenesis. 6- Oertain oxidative enz.ymes,i...!- po~yphenol oxidase, peroxidase, catalaSe, and ascorbic acid oxidase were studied in various host-parasite ccabinations• ResUl-ts obtained coul.d be sYDJrnar1zed as followS :- a) With respect to PFO, comparab1.eactivi.ty was found, in most casee, in the healthY susceptible and resistant varieties. As a reauJ.t of inf action, the enzYDl9activity increa.8ed in root tiSsues of both varieties; however, to a greater extent in the 8uscept1bl.e one. At later stages, the activity in the two varieties w~ not too muohdifferent. In .1I.om -tiSsues, siJDilar situation was found, except that the acti.vity in the resiStant variety maintained a somewhathigher levu than ”the control at laterstages- The Emhancedactivity of PPOin the roots of infected susceptible variety could account for the oxidation of phenoliCS to non-toxic polymeric substanoes ~ead;ng to the production of the brownish p1£sD81lts characteriStic of vascular diScoloration. On the other hand. the J.:!Jnj.ted1.ncreelie 1.nPFO fC)Ulld1.nresistant tiSSUes IIl8Y result 1.n a ~ow Qld.dation products such 8IJ \I.”unotUIS”,bich are highlY reactive end more toxic. SUChproducts could a1Jlo ,nbibit the enzym•••••thus pertiaUY accountiD.!l for the lOWactivity level. obServed· ~herefore. 1’1’0could have a varied effsot 1.nthe host-parasiteoODlb>nationdependmg on the extent of <>xidatiCRl effected.b- AS to the peroxidas •••• , it was fC)Ulldthat their activity ”,as enhanced fol.l-owing:lJ1fection in roots of both susoeptibl.e and resistant varieties. Later. such activity DROPpedin the former bUt continuedto increase in the ~atter. SUChcontinued enhanced activity of peroxidas ••••in the resiStant variety could be one of the determinanta of such. r~\le; hOWever.it is dUficult to pinPoint the affectedprocesses sinoe peroxide/ites have quite a varied effect on different vi.taL processes. c) AS to catale/ites. it ”’e/itfound that infection resW.ted in an mereslle in their aotiv1.ty m both varieti”. with the magnitude of increase being h#gher in theres1Stan:’G variety. d- l!’or ascorbic ac1d ox1daIOe, the increase in a.ctivity in response to infection wall higher 1n roots of thesusoeptible variety, whereaf;l the rlifVerse was true for stems. ’rh1a enhanced activity in ”the stems of resistant tissues coUld exert a drainage effect on the concentration of ascorbic acid, thUS l.owering the reducing power and ~dering the phenoli.o compoundS maintain their oxidi.zed toxic form. Furthermore, such an en’!;Y’JDSeIld other ox1da.tive BIl’!;Y’JDmBs;y8p:J..ey a roJ.e in the reoxidation of NAID?Hproduced through the modified metaboJ..iSmariSing in response to infection. 7- Jbpl.oying the eJ.eotrophoretic techniQ.ues in polyacry- :l.am1degeJ..s, certain enzymeswere studied in extracts of healthy and diSeased plants aI3 well as in extracts of fw,gel iso).ates. ’rhe following results were obtained: a) NOdifference was obServed beiiween the healthy sUScept1bJ. e and resiStant varieties as to the peroxidase activ1ty or the isozyme patte:rn- AJ3 a result of infection, the l.evel. Of activity inereased ’e) as evidenced by band width and staining density. The magni-tude of increase was greater in the ausceptib~ e than in the resistant variety. Anactivity band corresponding to ”that found for the fungal peroxidae e appeared in the d1Seased extraots. The multiplicity of peroxidase iso~es was not evident with pyrogal.lol as the substrate, unless ’the activity was too low, thus preventing the coalescence of bands. b} With respect to esterases, ten healthy cotton varieties showeda high degree of similarity 1n their isozyme pattern. Stems were more active than roots. SimUarly J nine f’lmgal isolates were aimUar in their esterase pattern, regardless of their virulence. Whena susceptible and a resistant varie”ty subjected to ~ection vere oompared, it was found that healtbY roots of both varieties exhibited similar patterns; however, the level of acti.vity DROPped as the plants grew older. Oomparing diseased with healthy extraots, the former was alw8¥s poorer in activity as judged by the band staining density. AJ3 to the stem tissues, healthy extracts showed a high degree of simllar:1ty in both resistant and susceptible varieties; however, there was an indication of an additional band in the former. No consistent trend of change wasfound in reepons e to infection except that thediseased susoeptible tissues maintained theuo seteraae activity at later stages whlle the corresponding heal.tby tissues were almost devoid of such an activity. The role of esterase in disease physiology is unclear at present; however, it appears to have a val-us aI3 a diagnostic too~ in view of the high degree of s~arity in isozurme pattern amongciifferent cotton varieties and a,lso aJIlong different fungal isolatese 8- Certain groupS of growth regUlating substances were studied in both healthy and diseased susceptible cotton varietiese The results are summarized as follows :- a) With respect to auxin activity, as judged by the extent of root fOl.1llation in cowpea seedlingS, it was :found that infection resulted in a state of hyperaUXinJ’i however, to a greater degree in the suscept1bl.e variety part1eu1.arly at the early stages of disease deveJ.opment. b) With respect to gibberellinS, 1t was found that infection led to a reduction in the activity of th1s group of compounds;however, the magnitud6 of reduction waa greater in the infeoted susceptib~e variety than 1n the infected resistant onee This could Part1aJ.1Y.,tccount for the stunting Sympt~..---- __ oharaoteriziDB;the wllt disease. |