No abstract

Summary. A 2-step, 1-d:,mens-ional thn-layer chromatograph-c proceduire fnr isolating indoleacetic ac:d (IAA) was developed and util:zed in inve,t at:ons of the biosynthesis of JAA from tryl)to,)han-_4C in cell-fre'-extracts of ipea (Pi.sun sativitmn L.) shoot tips. Identfcat;on of a 14C-prodnict as IAA was bv (a) co-chromatograT)hv of atitheiiitc IAA and '4C-pro(duict on th.:n-layer chromatography, and (b) gas-liqu-;d and thin-laver chromategraphy of authentic and presumptive IAA methyl esters. Dalysis of enzyme extracts and addt;on of a-keto-li1tqr`c ac d anl pvr:doxal phosphate to reactioni m;xtl'res re,ulited in ap)prox:mately 2-to 3-f-ld increases in net y;elds of IAA over yields in non-d:alyzed react-on m:xtres wW:ch d:d not conta;n ad,d:tives esqent:al to a translaminace reaction of trvptophan. Add`t:on of thiam:ne pyro0hoonbh,,te to reacton m;xtl,req fiurther enhanced npt b;h,vnth-s-s of I'A. It is conclhlded that the format;on of indolepyrtiv:c ac;d and its silhbenlent decarboxvlat:on prohablv are seeventtal react:onis in the maior pathway of IAA bocvnfhsis from trvntonhan in cell-free extracts of Pisutnt short t:pS. ComDar;-on of max:mtlm n't-IAA biosynthes;s in extracts of shoot t:ps of etiolated anid leht-grown dwvarf and tall pea !dluui;nzs reveal-id. aln order, on a uin:t T)rofe:n N ba:, of: 1`lo-4-rown tall > Pght-zrown dwarf > etiolated tall _ etolated dwarf. It is conclrxded that the d:fferent rates of stpm elonzation among et;el"ted and l:ght-pr-wrn dwarf and tal!l pea seedl:ngs are correlated, in general, with differences in net TAA biosynthesis aild setisiitivity of the tissules to IAA.Ex'olan.utions for the (Ifferer(nces in stemi elomioatioIl betweeil dwarf and(l tall varne;es of a snecies e.g. Pisumin sativ'mi, and betweon et;olatod atnd tlc-ht-grown l)lants of the sam-var;ety have he-n sought repeatedly throu"gh inve-t;zat:ons of pols):bVe (orrelat;ve difference,s in endogen-onls aulx;n an1d ib,berell;n relationships. The maiori'ty of these investigations have been either: (a) studies of comparat:ve resp)onses of intact see(linzs or excised stem sectioins to exogenotus hormones: or (b) extraction and bWoassay of enidozeniouis hormones. Another kin(d of exoer:mmntal avnroach which is tusefult in attempts to elu1cidate comparative g,rowth hormone relationships is invest:gation of hormone bWosvntheses tsi;ng cell-free enzymne prepatrations. Tn 1958, Gor(lon (12) f:rqt 'describe-d an enzyme system from shoot ti'ps of Phascoluts autreus seedlings w,hich catalvzed the coniversion of trvntophan to indole-3-acetic ac&d (IAA). Wghtman ;ind Cohen (39) recently described in detail the intermediary steps in the enzymic conlversion of trvptophan to TA.A in cell-free preparation;s from 1 This investigation was supported in part by Grauit GBI-4613 from the National Science Founidation. mntg be-an (Ph1 rscolls (1a1 remis) seedlPl;ngs. So)me propert e-of an TAA-syntheq;z;ng syvtem isol-te-d from ani:ces of Avona. coleoptiles and otllel-W'ant mrn-er:akc were de-cr'be,l by Lant.can and Mui:r (17). WhIle cel...