Plant Epicuticular Lipids: Alteration by Herbicidal Carbamates

Abstract

The effect of several carbamates and trichloroacetic acid on the biosynthesis of epicuticular lipids from leaves of pea (Pisum satirum) was tested by chemical and visual methods. The carbamates tested included S-(2,3-dichloroallyl)diisopropylthiocarbamate (diallate), N-(3-chlorophenyl)isopropylcarbamate (chloropropham), S-ethyl dipropylthiocarbamate, and 2-chloroallyl diethyldithiocarbamate. Diallate reduced epicuticular lipids by 50% when the plants were root-treated and by 80% when vapor-treated. These results were supported by scanning electron microscopy and carbon replica techniques with transmission electron microscopy. The ratio of wax lipid components in the diallate-treated plants remained unchanged, with the exception of the primary alcohols, which were reduced. Diallate appears to interfere with the biosynthesis of a precursor to the elongation-decarboxylation pathway of lipid synthesis. N-(3-Chlorophenyl)isopropylcarbamate had no significant effect on total amounts of extractable epicuticular lipids, nor did it alter the structure of the wax formation on the leaves. The scanning electron microscopy micrographs indicated that S-ethvl dipropylthiocarbamate significantly reduced wax formation on pea leaves. 2-Chloroallyl diethyldithiocarbamate altered the structure of the wax formations, but not the total amount of wax (scanning electron microscopy). Trichloroacetic acid had little effect on wax deposition compared to diallate or S-ethyl dipropylthiocarbamate (scanning electron microscopy). The implication of the effect of the carbamates on epicuticular lipids and penetration of subsequent topically applied chemicals is discussed.Surface lipids (or waxes) are the first plant barrier encountered by any material applied to the foliage. For a compound to penetrate into the plant it must spread over the surface of the leaf, stem, or fruit, and then pass through the surface lipid, the cuticle, the cell wall, and into the cytoplasm of the epidermal cells. Stomatal penetration may also be a method of entry into the plant, but so far there has been no satisfactory proof that this (3,11,12). Electron microscopy has revealed that these patterns appear to be consistent for each plant species, with differences found between species. Attempts are being made to utilize surface lipid components for taxonomic classification (2, 3, 9). Some of the components of surface lipids are hydrocarbons, wax esters (long chain alcohol esters of long chain acids), primary and secondary alcohols, ketones and fatty acids. As a rule, the hydrocarbons are nparaffins (10-50% in plants) containing 21 to 35 carbon atoms in chains with odd number of carbons predominating (3).Trichloroacetic acid (1,11,15) and EPTC3 (6, 7) have been shown to reduce epicuticular wax. EPTC had no effect on the composition of lipids from sicklepod petioles, although the thickness of the petiolar cuticle was reduced by 35%r, at the strongest concentration tested (23). Several other pesticides have been screened for their abilities to inhibit or stimula...

Sicklepod Surface Wax Response to Photoperiod and S-(2,3-Dichloroallyl)diisopropylthiocarbamate (Diallate)

“…Hydrocarbons tended to be increased at 0.28 kg/ha diallate under all photoperiods examined (Table I) as compared with other rates of application. However, in all photo periods except 10-hr, the concentration of hydrocarbons was less in treated samples than in the untreated controls (Table I) The influence of several thiocarbamate compounds on fatty acid synthesis was corroborated by Harwood and Stumpf (5) and Still et al (15). The data presented herein corroborate the reduction by diallate of the epicuticular lipid content described by Still et al (15).…”

“…They reported diallate to inhibit wax synthesis quantitatively but did not qualitatively influence epicuticular lipids except for the primary alcohols. However, Still et al (15) utilized the entire shoot for extractions of surface lipids and extensive differences in the hydrocarbon and fatty acid contents of various morphological units in sicklepod have been observed in this laboratory (16,17).…”

Inhibition of Cuticular Lipid Biosynthesis in Pisum sativum by Thiocarbamates

“…Treatment of slices of young pea leaves (Pisum sativum) with gM solutions of a-chloralyl diethyldithiocarbamate, dichloroalHyl diisopropylthiocarbamate, or S-ethyldipropylthiocarbamate resulted in inhibition of incorporation of [1-V4C] Certain thiocarbamates were reported to be inhibitory to wax production on foliage (4,5,12). Experimental evidence thus far available shows that fatty acid elongation is a key process involved in cuticular wax synthesis (2, 10).…”

Cycloate, an inhibitor of fatty acid elongase, modulates the metabolism of very‐long‐side‐chain alkylresorcinols in rye seedlings

“…Thiocarbamates may exert different effects on plants and plant lipids. These chemicals may alter the quality and/or the quantity of lipidic constituents of their cuticular layers 10, 11. When used at concentrations exceeding 25 µ M , this class of herbicides inhibits the synthesis of C 20 and C 24 fatty acids in germinating pea seeds12 or the synthesis of VLCFAs in barley and wilt oat shoots 13.…”