Rosemary A. Cole

Isothiocyanates, nitriles and thiocyanates as products of autolysis of glucosinolates in Cruciferae

Abstract Glucosinolates from seventy-nine 8-week-old plant species were hydrolysed and the volatile products identified by GC-MS and related to previous published findings. Known compounds, identified in new plant sources, were 4-methylthiobutyl thiocyanate in Alyssum , 4-methylthiobutyl isothiocyanate in Diplotaxis and Eruca and isopropyl isothiocyanate and 5-vinyl-2-oxazolidinethione in Plantago .

The relative importance of glucosinolates and amino acids to the development of two aphid pests Brevicoryne brassicae and Myzus persicae on wild and cultivated brassica species

This paper describes an experiment to investigate the relative importance of glucosinolates and the availability of free amino acids in the phloem to the feeding behaviour and development of the specialist brassica aphid, Brevicoryne brassicae (L) (cabbage aphid) and the generalist, Myzus persicae, (Sultzer) (peach potato aphid). Aphid development was determined on brassica species and cultivated brassica varieties. Analysis of individual glucosinolates in the wild brassica species identified significant differences in their profiles and in their concentrations present in freeze dried leaves. Multiple regression analysis showed a significant correlation (r = 0.83) between the intrinsic rate of increase of B. brassicae and glucosinolate concentrations; four glucosinolates, 2‐OH‐3‐butenyl, and 2‐propenylglucosinolate, 3‐methoxyindolyl and 4‐pentenylglucosinolates accounted for 79% of the variation. The intrinsic rate of increase of M. persicae was less correlated, though still significant (r = 0.5); 3‐indolyglucosinolate and 3‐butenylglucosinolate accounted for 47% of the variation. Regression analysis also showed a correlation between phloem amino acid concentrations and the intrinsic rate of increase of B. brassicae (r = 0.48) but not of M. persicae. The concentration of the important amino acids tyrosine, alanine, leucine and glutamic acid, accounted for 43% of the variation in intrinsic rate of increase. Leaf water potential of the Brassica species showed no relationship with the intrinsic rate of increase of either B. brassicae or M. persicae.

Locating a resistance mechanism to the cabbage aphid in two wild Brassicas

Feeding behaviour of the cabbage aphid, Brevicoryne brassicae, was monitored electronically on two resistant Brassica species, B. fruticulosa and B. spinescens, and compared with a susceptible control B. oleracea var. capitata cv. Offenham Compacta. Aphids, monitored for 10 h on the under side of leaves, performed recognizable feeding behaviour on all species. Electrical Penetration Graphs (EPGs) of aphids on resistant and susceptible plants showed no difference in behaviour for aphids on resistant Brassica species compared to susceptible until stylets penetrated the phloem sieve elements when a large reduction in the duration of passive phloem uptake (E2 pattern) on B. fruticulosa was indicated. Although feeding behaviour on 6 week‐old plants of B. spinescens was similar to the susceptible controls, behaviour on 10 week‐old plants was similar to that recorded for B. fruticulosa. The mechanism of resistance is thought to be located in the sieve element as the normal sieve element salivation (E1 signal was either quickly terminated by withdrawal of the stylets from the sieve element or continued as a disrupted E2 pattern. Analysis of secondary plant compounds in the three Brassica species only identified significant differences in the glucosinolate profile. No reproducible differences were detected in the concentration of phenolics or anthocyanins. The major glucosinolate component of B. fruticulosa and B. spinescens was gluconapin rather than glucobrassicin and glucoiberin as found in the susceptible host plant. However, both pure glucosinolates and glucosinolate extracts from all three species did not reduce aphid survival on chemically‐defined artificial diets. These results suggest that the mechanism of resistance may be a mechanical blocking of the sieve element or stylets rather than a difference in the secondary plant chemistry of glucosinolates and phenolics.

Low aromatic amino acid concentrations in leaf proteins determine resistance to Frankliniella occidentalis in four vegetable crops

Analysis of total aromatic amino acid (free and bound) in some cucumber accessions selected previously for resistance to western flower thrips, Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], indicated that low concentrations of these essential nutrients, relative to total leaf protein, were correlated with a reduction in damage by the insect. Further analysis of samples of four important horticultural crops (lettuce, tomato, pepper and cucumber) with unknown levels of resistance to thrips showed a significant genotypic variation in the concentrations of total aromatic amino acids relative to the total leaf protein. Accessions from each crop with low or high concentrations of aromatic amino acids in proteins were exposed to thrips larvae. Regression analysis showed a highly significant positive correlation between aromatic amino acid concentration in leaf protein and thrips damage, regardless of crop species. It is concluded that higher concentrations of aromatic amino acids in plant proteins are important for successful thrips development. These results provide plant breeders with a promising tool for indirect selection without using undesirable insect bioassays.

Epithiospecifier protein in turnip and changes in products of autolysis during ontogeny

Abstract An epithiospecifier protein present in turnip tissue gives rise to 1-cyano-epithioalkanes during autolysis. Volatile hydrolysis products are produced from glucosinolates during autolysis of seeds, seedlings and plant tissue more than 6 weeks after sowing.

Comparison of feeding behaviour of two Brassica pests Brevicoryne brassicae and Myzus persicae on wild and cultivated brassica species

Feeding behaviour of the specialist Brassicae aphid, Brevicoryne brassicae (L) (cabbage aphid) and the generalist, Myzus persicae, (Sulzer) (peach potato aphid) was monitored electronically on the susceptible cauliflower, Brassica oleracea var. botrytis cv Newton Seale, and a range of 17 Brassica species, B. carinata, B. juncea, B. nigra, B. macrocarpa, and B. villosa var. drepanensis and cultivated brassica varieties, B. oleracea, B. campestris and B. napus. Aphids, monitored for 10 h on the underside of leaves, performed recognisable feeding behaviour on all brassica species. The main differences in feeding behaviour, between M. persicae and B. brassicae, on the susceptible cauliflower Newton Seale, were fewer probes, shorter times to initially reach the phloem but longer times to establish sustained phloem ingestion and the longer times spent, by M. persicae, in xylem ingestion.

Isolation of a chitin-binding lectin, with insecticidal activity in chemically-defined synthetic diets, from two wild brassica species with resistance to cabbage aphid Brevicoryne brassicae

A lectin, with a chitin‐binding domain and chitinase activity, is present in significant quantities in the wild brassica species B. fruticulosa and B. spinescens but at low levels in cultivated cabbage cv. Offenham Compacta. The lectin, purified > 1000 fold after binding to chitin, migrated on SDS ‐ PAGE gels as a single band with a Mr of 14.500. The amino acid composition of the lectin from B. spinescens indicated high concentrations of asparagine/aspartic acid, glycine, leucine and serine in common with other chitin‐binding lectins with insecticidal and antifungal activities. Brassica lectin and the closely related agglutinin from wheatgerm and nettle show significant insecticidal activity when presented to Brevicoryne brassicae in chemically‐defined synthetic diets.

1-cyanoepithioalkanes: Major products of alkenylglucosinolate hydrolysis in certain cruciferae

Abstract Autolysis of glucosinolates in several crucifers produced 1-cyano-2,3-epithio-propane and 1-cyano-3,4-epithiopentane, in addition to the previously described 1-cyano-3,4-epithiobutane.

Abiotic induction of changes to glucosinolate profiles in Brassica species and increased resistance to the specialist aphid Brevicoryne brassicae

Brevicoryne brassicae is highly host-specific, feeding almost exclusively on the phloem sap of Brassica or other closely related plant species. Despite the evolution of specific feeding apparatus and the protection afforded by the stylet sheath, aphids may be exposed to sufficient amounts of secondary plant compounds transported by the phloem to reflect the suitability of potential species as host plants. Glucosinolates are the characteristic secondary plant compounds of brassica crops, responsible for the odour and flavour and are major determinants in the feeding response of the Brassica specialist B. brassicae. When glucosinolate profiles of some partially-resistant cauliflower varieties were analyzed, increased concentrations of 2phenylethylglucosinolate were detected (Kazantzidou et al., 1994). The glucosinolate content of brassica crops can be altered as a systemic response to plant signalling molecules such as salicylic acid (Kiddie et al., 1994). 2-Phenylethylglucosinolate showed the greatest increase in concentration in oilseed rape within days of treatment with 10 mM root drench of the abiotic elicitor salicylic acid.

Electronically monitored feeding behaviour of the lettuce root aphid (Pemphigus bursarius) on resistant and susceptible lettuce varieties

Feeding behaviour of the lettuce root aphid Pemphigus bursarius was monitored electronically on six lettuce varieties. Aphids, monitored for a minimum of 5 h on lettuce roots, performed recognizable feeding behaviour on the susceptible varieties, Webbs Wonderful and Borough Wonder including non probing, pattern A start of new penetration, C (stylet pathway activities) sometimes including clear B‐waves (salivary sheath secretions), potential drops (intracellular penetrations), intracellular E (phloem ingestion) distinguishing E1 and E2 (Tjallingii, 1990) and occasionally xylem ingestion. Although aphid probing was recorded on the resistant varieties Lakeland and Grand Rapids continued penetration to the phloem elements was deterred and the time spent ingesting phloem was short. Aphids rarely probed the resistant varieties Avoncrisp and Avondefiance and all attempted penetrations quickly terminated.