A study of the epicuticular wax of Chionochloa

Abstract

Epicuticular wax from 18 New Zealand and one Australian species of Chionochloa was analysed to determine inter- and intra-specific differences. The majority of the wax was found on the adaxial surface of younger leaves consisting of rosette- and thorn-like structures.

The average lipid composition of the wax was 39% ester, 27% alkane, 16% aldehyde, 11% fatty alcohol and 6% fatty acid. Carbon chain lengths of 24, 28, 30 and 32 generally dominated the fatty acids, alcohols and aldehydes while C 29 and 31 were usually the major alkanes and the major wax esters ranged from C 40 - C 52. Each wax ester was composed of a mixture of different chain length fatty acids and alcohols and the differences in the chain lengths of the wax esters have been suggested to be determined by differences in the chain lengths of the alcohol components rather than the acids. Two unidentified minor homologous series were found in the fatty acid, alcohol and aldehyde fractions.

This lipid distribution resembled Cortaderia selloana (Cortaderieae, Arundinoideae) more closely than other members of the Gramineae, however the lipid composition showed some similarities with Echinochloa crusgalli (Paniceae, Panicoideae) and Sorghum vulgare (Andropogoneae, Panicoideae).

Computer analysis of the distribution of chain lengths in the five lipid fractions distinguished the species making taxonomic identification possible. It also confirmed biochemical races of some of these species. The clearest taxonomic identification was obtained when the samples were divided into groups using the chain lengths of the acid fraction and the resultant groups re-analysed utilizing the chain lengths of the other four lipid fractions. The samples were then divided among their respective areas and the lipid fractions which differentiated the samples in order of importance were acid, alkane, alcohol, aldehyde and ester. Such detailed chemotaxonomic identification of Chionochloa has not previously been demonstrated and was only possible through the advent of suitable high temperature gas-liquid chromatographic liquid phases that allowed the separation of the long-chained carbon components.

Intra-specific relationships among carbon chain lengths of the samples from C. flavescens, C. pallens and C. rubra indicated Nelson as a "source" of the species with branches to the North Island, the East Coast of the South Island and possibly the West Coast of the South Island.

A relationship was also found between the carbon chain lengths of the samples of all of the species and the range of soil fertility in the general area that the samples originated. This association suggests genetic adaptation of plants to ranges of soil fertility which in turn brings about the variation in chain lengths found in the plants. Biochemical races found by this method are discussed in relation to other methods.

The biosynthesis of C. rigida epicuticular wax was studied by incubating actively growing young tissue slices with [U-¹⁴C] acetate. The radioactivity incorporated into the lipid fractions was 33%,wax ester, 31% alcohol, 21% acid, 13% alkane and 4% aldehyde.

The time course of [U-¹⁴C] acetate incorporated into lipid fractions and the effect of inhibitors (DTE, CAR, TCA) on this incorporation suggest that the biosynthetic pathway of surface lipids in C. rigida is similar to the elongation-decarboxylation pathway proposed in other plants. The elongation system probably forms fatty acyls which are released as fatty acids, reduced to aldehydes and alcohols, decarboxylated to alkanes and esterified with alcohols to wax esters.