D. W. Griffiths

Effects of environment on the composition of epicuticular wax esters from kale and swede

Abstract The composition of intact leaf epicuticular wax esters of two individual genotypes each of kale and swede grown indoors (I) and outdoors (O) at SCRI, Scotland, and outdoors at Wadenswil in Switzerland (S), were determined by GC-mass spectrometry. For all genotypes (I, O, S) esters were found to consist of unbranched ( n- ) and branched anteiso - ( a- ) and iso - ( i- ) components in the a : a , a : i , i : a , a : n , n : a , n : n and i / n : n / i acid-alcohol combinations. Esterification was non-random, n : n and doubly branched br -/ br - combinations were favoured over mixed n -/ br - combinations. Combinations with extremes of acid and alcohol chain-length were generally uncommon, although longer-chain alcohols were more predominant in some swede esters. There were considerable compositional differences between indoor-grown plants (I) and those grown outdoors (O and S). In general, i : n / n : i , i : a and a : i esters were relatively more abundant in (O and S) and n : n and n : a esters were more abundant in (I), whereas a : n and a : a esters were of similar abundance in all (I, O and S). Generally, (I)-grown plants were found to have proportionally more esters of longer chain-length and (O, S)-grown plants proportionally more esters of shorter chain-length. For kale a : a , n : n , a : n and n : a esters, this was particularly related to variation in alcohol chain-length. There were also major compositional differences between kale and swede esters, long-acid-short-alcohol combinations were more prominent in the former, while short-acid-long-alcohol combinations dominated in the latter.

Changes in the chemical composition of volatiles released by the flowers and fruits of the red raspberry (Rubus idaeus) cultivar glen prosen

Volatiles at various stages of inflorescence development, bud formation, flowering, fruit formation and ripening of a red raspberry, were entrained on the porous polymer Tenax TA and analysed by thermal desorption-gas chromatography-mass spectrometry. Major classes of compound identified included aliphatic and aromatic hydrocarbons, aldehydes, ketones, alcohols and esters, monoterpenes and sesquiterpenes. As the inflorescences matured, levels of green leaf volatiles such as trans-β-ocimene and cis-3-hexenyl acetate declined and the monoterpenes, α-pinene, camphene, β-myrcene and limonene increased. During fruit ripening several additional compounds appeared including α- and β-ionone, α- and β-phellandrene and hexanoic acid ethylester. Ethyl acetate at 12–18% was the major detectable volatile product of the ripe fruit.

Oviposition and chemosensory stimulation of the root flies Delia radicum and D. floralis in response to plants and leaf surface extracts from resistant and susceptible Brassica genotypes

In Brassica crops differences in susceptibility to root fly attack can be largely attributed to antixenotic resistance. Plants of four genotypes (two swedes and two kales) with widely differing resistance in field trials, were compared in laboratory choice assays for their susceptibility to oviposition by the root flies Delia radicum (L.) and D. floralis (Fallen) (Diptera, Anthomyiidae). For both species the preference among the genotypes corresponded to the susceptibility of the genotypes in the field. The preference ranking in response to surrogate leaves treated with methanolic surface extracts of the four genotypes was identical to the preference among potted plants, demonstrating that chemical factors on the leaf surface mediate host preference for oviposition in these species.

Influence of Increasing Herbivore Pressure on Modification of Glucosinolate Content of Swedes (Brassica napus spp. rapifera)

The effect of increasing herbivore pressure, in the form of larval feeding damage by the turnip root fly, Delia floralis, on the glucosinolate content of swede roots (Brassica napus ssp. rapifera) was investigated. Only one of the 14 root glucosinolates detected, 3-indolyl methyl glucosinolate, rose significantly with increasing levels of insect attack. Although other root glucosinolate concentrations altered following damage, the induced changes were no greater from inoculation with 20 eggs/root than with 5 eggs/root. Swedes roots that had been damaged by D. floralis contained approximately three times the concentration of total indolyl glucosinolates of control roots. This change was strongly influenced by a fourfold increase in the concentration of 1-methoxy-3-indolyl methyl glucosinolate. The total glucosinolate concentration found in swede roots remained unchanged overall as a result of a fall in the concentration of five of the aliphatic glucosinolates, which balanced the rise in aromatic glucosinolates. The relevance of these results to studies of crucifer–insect interactions are discussed.

Ecological biochemistryEffects of environment on the composition of epicuticular wax from kale and swede

The composition of leaf epicuticular waxes of two genotypes each of kale and swede were determined by gas chromatography-mass spectrometry. Plants were grown indoors (I) and outdoors (O) at SCRI, Scotland, and outdoors at Wadenswil in Switzerland (S). Epicuticular waxes from outdoor-grown plants (O and S) were found to have higher proportions of n-alkanes, octacosanoic acid, primary alcohols and long-chain esters but lower proportions of aldehydes, ketones, ketols and secondary alcohols than waxes from (I)-grown plants. Outdoor-grown plants were also found to have proportionally more shorter chain length compounds and indoor-grown plants proportionally more compounds of longer chain length. Variations in wax composition between genotypes of a species and between species were also observed. Differences in leaf surface wax ultrastructure, between species, and between different growth conditions were detected using scanning electron microscopy. The possible role of leaf wax chemicals in the antixenotic resistance to the turnip root fly, Delia floralis, of certain genotypes was also considered.

The effect of cultivar, maturity and storage on photo-induced changes in the total glycoalkaloid and chlorophyll contents of potatoes (Solanum tuberosum)

Abstract The tubers of 20 potato genotypes were exposed to light, equivalent to a radiant flux density of 140 μmol−1 s−1 m−2, approximating to dull daylight conditions, for a continous period of 48 h. Tubers were exposed when immature, mature and also after a period of storage. There were significant differences between the genotypes in their rates of increase of both glycoalkaloid and chlorophyll contents. Notably, potato genotypes responded differently to light in their rates of glycoalkaloid and chlorophyll synthesis, this being dependent on the physiological state of the tubers as well as their inherent characteristics.

LEAF SURFACE COMPOUNDS AND OVIPOSITION PREFERENCE OF TURNIP ROOT FLY Delia floralis: THE ROLE OF GLUCOSINOLATE AND NONGLUCOSINOLATE COMPOUNDS

The role of leaf surface compounds influencing the oviposition of the turnip root fly, Delia floralis, was investigated using bioassays and fractionation of leaf surface extracts from four Brassica genotypes. Polar leaf surface extracts contained between 65 and 175 nM/g leaf equivalent of glucosinolates. However, following fractionation it was found that nonglucosinolates were the major stimuli for D. floralis oviposition. Electrophysiological studies of leaf surface extracts and their fractions were performed by using D. radicum, the cabbage root fly, as an analytical tool. The most behaviorally active fractions contained stimulatory compound(s) that had an activity profile identical to that previously described for recently discovered nonglucosinolate compounds. The role of leaf surface chemicals in influencing antixenotic resistance to D. floralis is discussed.

The identification of potential aeroallergen/irritant(s) from oilseed rape (Brassica napus spp. oleifera): volatile organic compounds emitted during flowering progression

Volatile organic compounds emitted by growing intact oilseed rape plants have been detected using an entrainment apparatus enabling volatile headspace analysis by thermal desorption coupled to capillary gas chromatography‐mass spectrometry. In total, 22 volatile compounds were identified as being emitted during the flowering period. The main constituents were α‐farnesene (a sesquiterpene); β‐myrcene (a monoterpene); linalool (a monoterpene alcohol) and the ‘green leaf’ volatile (E)‐3‐hexen‐1‐ol acetate. These compounds constituted between 50 and 87% (mean 68%) of the total volatiles emitted in all of the entrainments carried out with flowering oilseed rape plants. The remaining constituents consisted of a range of compounds including other terpenoids, the characteristic ‘green leaf’ volatile (E)‐3‐hexen‐1‐ol, short chain alcohols and ketones, organic sulphides and nitrogen‐containing compounds. These were generally present as minor constituents but some plant entrainments revealed that higher relative amounts could be emitted. This was particularly apparent for dimethyl disulphide, 3‐methyl‐2‐pentanone, 3‐hydroxy‐2‐butanone, sabinene, isomyrcenol and (E)‐3‐hexen‐1‐ol. The possible role of the 22 compounds in respiratory mucosa and conjunctiva irritation associated with airborne releases from oilseed rape is discussed.

Epicuticular wax ester and triacylglycerol composition in relation to aphid infestation and resistance in red raspberry (Rubus idaeus L.)

Abstract Epicuticular waxes from two cultivars of red raspberry ( Rubus idaeus ) were collected from the newly emerging crown leaves, and also from the group of four more mature leaves immediately below the crown. One cultivar, Autumn Bliss, was identified as aphid-resistant, and the other, Malling Jewel, as aphid-susceptible following bioassay with the large raspberry aphid, Amphorophora idaei , just prior to collection of the wax. Biological activity was primarily associated with the more mature leaves. Epicuticular wax esters consisted predominantly of long-chain aliphatic compounds in which even-carbon-number acids were esterified to even-carbon-number alcohols. Lesser amounts of odd-carbon-number esters were also present. The acid : alcohol combinations of the major esters were C 38 : 14 : 24, 16 : 22, 20 : 18; C 40 : 14 : 26, 16 : 24, 18 : 22, 20 : 20; C 42 : 16 : 26, 20 : 22; 22 : 20, C 44 : 20 : 24, 22 : 22, 24 : 20; C 46 : 20 : 26, 22 : 24, 24 : 22; C 48 : 20 : 28, 22 : 26, 24 : 24, 26 : 22; C 50 : 20 : 30, 22 : 28, 24 : 26, 26 : 24, 28 : 22 and C 52 : 22 : 30, 24 : 28, 26 : 26. Terpenyl esters were also present and these consisted of α - and β -amyrin and cycloartenol esterified to C 16 , C 18 and C 20 acids. Compositional differences between the more mature leaves which may relate to resistance to A. idaei were higher levels of cycloartenyl esters and α -amyryl esters in wax from the resistant cultivar Bliss. There were also differences between the cultivars in the distribution of individual alkyl esters and their component acids and alcohols. Esters with longer acid : shorter alcohol combinations were more abundant in Jewel than Bliss. There were compositional differences between leaves at the different developmental stages. Alkyl esters were more abundant and cycloartenyl esters were not detected in wax from the immature leaves. Small amounts of an unusual class of triacylglycerol were found only on leaves of the aphid-susceptible cultivar, Jewel, which had been subject to bioassay with raspberry aphid. These compounds, which have a C 6 acid at C-2 of the glycerol backbone, were derived from the aphid, and are the major component in the insect’s cornicle secretions. The triacylglycerols probably arise from the presence on the leaf surface of shed aphid skins, or by incorporation of cornicle fluid into the leaf wax. The abundance of aphid triacylglycerols on the leaf surface may provide a measure of aphid-susceptibility.

A time-course study of chemical and physiological responses in Brassicas induced by turnip root fly (Delia floralis) larval feeding

Many pests and pathogens of Brassica crops (family Cruciferae) are influenced by a group of sulphur-containing secondary metabolites called glucosinolates. The effects of these chemicals on plant-pest interactions can differ greatly, depending on many complex factors: e.g. whether an insect is a ’generalise or Crucifer ‘specialist’ and on the concentrations in specific plant tissues at the time of insect attack. Recent studies at SCRI (Birch et al., 1990, 1992; Hopkins et al., 1992b, 1995) have shown that root fly attack induces multiple chemical changes (e.g. of glucosinolates, sugars, lignin, volatiles) in different Brassica host plant tissues following root damage. Root fly-induced effects on host plant metabolism can be localized and/or systemic (i.e. from root to leaf). These chemical changes in the host plant genotype, but cannit be mimick be artificial root damage (Griffiths et al. , 1994).