Permeability of Apricot Leaf Cuticle

Altlhoughl cutimize(d tissue in some forlmi is the first harrier to the entrv of chemicals into plants, dlirect measurements of the permeability properties of cuticular membranes are limited aandl qualitative (1, 5 ).Froml clirect miieasuremleints oin isolated cuiti- cle Skoss (9 ) has reported that Eniglish ivy leaf cuticle is relativelv illmpermleable to w ater, aandl that lemloni leaf cuticle is impermeable to the sodiunm salt of 2,4-dichlorophenoxyacetic acid, to the ammiioolniunm salt of dIinitro-o-sec-but lplleinol.andl to silver and chloriOle ionls.Similarly Orgell (7 ) hlas reported little, if any, penetration of isolated apricot leaf cuticle bv "polar solutes in a(queous solutioni, e.g.acids, bases, salts, (IN-es, and miniscellanieouis otlher conllpoullis.Adding to these hiis oWln o)servation that oils (lo not penetrate the upper cuticle of apricot leaves (11), van Overbeek (12) conclucledl that penetration of leaf cuticle by clhelmiicals is unlikely.MIitchell, Snmale, and \IMetcalf (5), hlov-ev-er, accepting that cuticle in some forml covers the enitire aboveground surface of the plant.concludledl that hydrated cuticle is permneable to a (legree to water an(l to (lissolveel compounds associatedl -with tlis water, and is highly permleable to nolnpolar compoundis.The objectives of this x-ork xvere to (luaintita- tivelv niieasure penetration througlh stomata-free iso- lated leaf cuticle andl attempt to assess the imlportanice of this entry pathwx av in intact plants-to imieasure the effect of substitueint variation oni penetration 1w the nmodlel conmpouncl a-clhloroacetanmide (ClCH.,-CONH.,'; aiad to seek a correlation betxveen peine-tratiotIand chloroform-water plartitioning that imlighlt allowx a prediction of leaf penetration rates of other Coml l)ounds.Methods & Materials Reayeits.The a-clhloroacetaimiides xwere svnthe- size(l froml carboxy I C' 4-labeledl chloroacetic acid having a specific activity of 1 imc 'mmlllole, purchasedl froml tlle New Englacndl Nuclear Corp.The dlerivatives wx ere madcle undlel-the superv-isioni .fXV.H. Yaniko at our Dayton, Ohio laboratory by converting the label-d clii wroacetic aci(d to chloroace'tvl chlori(le ani(l reactiig tlis x ith the app)ropriate ainiiie.The labeled products xvere separatedl by fractional (listil- lattiCn ciand the p)redlicted specific activ-ities c-onfirmed.