Glandular trichomes of Solanum berthaultii leaves contain two unique forms of polyphenoloxidase (α- and β-PPO) and a separate peroxidase. The β-PPO appeared to be a polymer of α-PPO and exhibited a similar Km but an apparently higher specific activity with chlorogenic acid and caffeic acid. These data are directly related to studies on the insect defensive properties of the trichomes.

AbstractExudate from glandular trichomes of the wild potato species, Solanum berthaultii Hawkes, and the cultivated potato, S. tuberosum L., contained volatile substances including sesquiterpenes when examined with gas chromatography/mass spectrometry procedures. Sesquiterpenes were the major volatile constituents of Type A trichome exudate but were a minor constituent of Type B exudate. Sesquiterpene mixtures of the two potato species differed qualitatively and quantitatively. β‐Caryophyllene and E‐β‐Farnesene were major components identified in Type A trichome exudate of the cultivated potato. Sesquiterpene mixtures of both potato species were repellent to the green peach aphid, Myzus persicae (Sulzer). The role of trichome sesquiterpenes as a determinant of aphid behavior on the two potato species and in the expression of host resistance is discussed.RésuméSesquiterpènes des trichômes glandulaires de Solanum berthaultii et S. tuberosum, répulsifs de puceronsL'examen en chromatographie gazeuse et en spectométrie de masse a révélà la présence de substances volatiles contenant des sesquiterpènes dans l'exsudat des trichômes glandulaires des pommes de terre sauvage (Solanum berthaultii) et cultivée (S. tuberosum). Les sesquiterpènes étaient le principal composé volatile de l'exsudat de type A, tandis qu'ils n'étaient que faiblement représentés dans l'exsudat de type B. Les mélanges de sesquiterpènes des deux espèces différaient qualitativement et quantitativement. Le β‐Caryophyllène et le E‐β‐Farnesène constituaient les principaux composés identifiés dans l'exsudat de trichôme de type A de S. tuberosum. Les mélanges sesquiterpéniques des deux espèces ont repousée Myzus persicae Sulzer. La discussion a porté sur l'influence des sesquiterpènes des trichômes dans la définition du comportement des pucerons sur ces deux plantes et sur la manifestation de la résistance de l'hôte.

Insect-resistant cultivars offer a realistic and practical foundation upon which to build an economical and environmentally sound crop protection system. Insect resistance of a wild Bolivian potato species is conditioned by the presence of glandular trichomes on its foliage. Resistance is expressed both mechanically and behaviorally. Mechanical resistance involves release of a viscous exudate from the trichome gland upon contact by an insect. The trichome secretions accumulate initially on tarsi, first impeding movement and later entrapping the insect. In addition to immobilization, entrapment and resultant mortality, glandular trichomes dramatically alter normal insect behaviors, particularly those involving host acceptance and feeding. Pest species adversely affected by glandular trichomes include the Colorado potato beetle, green peach aphid, potato leafhopper, potato flea beetle, and spider mites. The mechanical and behavioral defensive properties of glandular trichomes are conditioned by the presence of specialized chemistry in trichome exudate. The Cornell University potato breeding program has introgressed the genetic information for expression of glandular trichomes into germplasm of the cultivated potato. Commercially acceptable levels of resistance have been maintained in 8 successive breeding cycles under development for horticultural adaptation. Elite hybrids can experience greater than 85% reduction in populations of insect pests, compared to those on susceptible commercial cultivars. Insecticide use on resistant hybrids can be reduced by at least 40% of that presently needed on susceptible cultivars.

Journal Article Mitochondrial Interaction with Helminthosporium maydis Race T Toxin: Blocking by Dicyclohexylcarbodiimide Get access PIERRE-Y. BOUTHYETTE, PIERRE-Y. BOUTHYETTE Department of Plant Breeding and Biometry, Cornell UniversityIthaca, New York 14853, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar VITALY SPITSBERG, VITALY SPITSBERG Department of Plant Breeding and Biometry, Cornell UniversityIthaca, New York 14853, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar PETER GREGORY PETER GREGORY Department of Plant Breeding and Biometry, Cornell UniversityIthaca, New York 14853, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Experimental Botany, Volume 36, Issue 3, March 1985, Pages 511–528, https://doi.org/10.1093/jxb/36.3.511 Published: 01 March 1985 Article history Received: 15 October 1984 Published: 01 March 1985

Glycoalkaloids are important potato quality factors. Tuber-bearingSolanum species exhibit wide quantitative and qualitative diversity in glycoalkaloid contents. Some species, of interest to breeders, contain extremely high total glycoalkaloid (TGA) levels and/or unusual types of glycoalkaloids of ill-defined or unknown toxic and teratogenic properties. Characterisation of glycoalkaloid content is a dynamic and, in some cases, controversial subject. Problems associated with analytical methodology and, to a lesser extent, with environmental effects and intraspecific heterogeneity have probably been the major causes of disagreements in the literature. Recent methodological developments have facilitated more accurate and sensitive measurements of TGA levels and of individual glycoalkaloid compositions. Such measurements should be used to analyze parental material and selected hybrid progeny in breeding programs. This is particularly important when certain wildSolanum species are being exploited as undesirable levels and types of glycoalkaloid can be genetically transmitted from the wild species to hybrid progeny. Absence of glycoalkaloid assessment from a breeding program can result in wasted effort, time and money.

Polyphenoloxidase (PPO) activity in the glandular trichomes of 32Solanum tuberosum ×S. berthaultii F3 hybrid clones differentially resistant to the green peach aphid,Myzus persicae (Sulzer) was determined. Within this population of segregating clones, aphid infestation levels varied 8-fold, while a 5-fold difference in glandular trichome PPO activity was observed.

Polyphenol oxidase and peroxidase activities were detected in foliar glandular trichomes of the wild, insect-resistant potato species, Solanum berthaultii. These enzyme activities may provide the basis for conversion of clear, viscous trichome exudate into a hard, brown substance which is formed rapidly after insect attack.

The mechanism by which Helminthosporium maydis race T toxin inhibits respiration dependent on NAD(+)-linked substrates in T cytoplasm corn mitochondria was investigated. The toxin did not cause leakage of the soluble matrix enzyme malate dehydrogenase from the mitochondria or inhibit malate dehydrogenase or isocitrate dehydrogenase directly. The toxin did increase the permeability of the inner membranes of T cytoplasm, but not N cytoplasm, mitochondria to NAD(+). Added NAD(+) partially or fully restored toxin-inhibited electron transport in T cytoplasm mitochondria. Thiamin pyrophosphate had a similar effect when malate was the substrate. It was concluded that the inhibition of respiration of NAD(+)-linked substrates by the toxin is due to depletion of the intramitochondrial pool of NAD(+) and other coenzymes.

Evaluation of the only available method for comprehensive total glycoalkaloid determination was carried out. The method comprised bisolvent extraction of glycoalkaloids followed by purification and non-aqueous titration of the aglycones released from the glycoalkaloids by acid hydrolysis. Our data show that use of the bisolvent extraction procedure can result in poor and variable recovery of glycoalkaloid standard. The post-extraction part of the analysis yielded high and reproducible recoveries of glycoalkaloid standard.

Levels of total glycoalkaloids (TGA) in foliage of 10 wild, tuberbearingSolanum (Tourn.) L. species differentially resistant to infestation by the potato leafhopper,Empoasca fabae (Harris), were determined. Levels of TGA ranged from a high of 688 mg/100 g fresh wt. in a resistant species,S. polyadenium Greenm. to a low of 13 mg/100 g fresh wt. in a susceptible species,S. bulbocastanum Dun. Foliar concentration of TGA and nymphal infestation by the potato leafhopper were highly correlated (r = −0.75, p = 0.01). The significant correlation of TGA levels and potato leafhopper resistance suggests that foliar TGA may be a significant factor in the defense of wild potato species against this pest.

The study of southern corn leaf blight disease is of major economic and scientific value. The economic importance of this fungal disease was dramatically emphasized in 1970 when it reached nearly epidemic proportions in the U.S.A., resulting in severe losses for corn growers. Scientifically, research on the disease may result in novel and major gains in plant pathology, plant breeding and higher plant genetics. The main aims of this paper are to critically describe the present state of biochemical and ultrastructural knowledge about the mechanism of the disease, to highlight the most important gaps in our knowledge and to discuss some of the ways in which these gaps can be filled. General Characteristics of Southern Corn Leaf Blight Disease The causal organism of southern corn leaf blight disease is the fungus Helminthosporiummaydis Race T (HmT). This is one of several members of the genus Helminthosporium to produce host-specific toxins.

Zea mays inbred W64A in Texas (T, toxin sensitive) male sterile and non-male sterile (N, toxin resistant) cytoplasms were utilized. Roots of freshly germinated seeds were treated for 15 min of 2 hr with culture filtrate from liquid grown Helminthosporium maydis Race T, or with a chloroform extractable purified fraction from the culture filtrate. In the susceptible W64A T line, toxin treatment, both crude and purified, caused swelling and loss of matrix densiy in mitochondria of root cap and vacuolated cells in the region of elongation. One hour treatment with the chloroform extractable toxin fraction caused similar effects or mitochondria of isolated leaf protoplasts. This is the first report of such rapid in vivo effects of HmT toxin on mitochondria. Difficulty in obtaining consistent preservation of meristem mitochondria precluded drawing firm conclusions concerning that region of the root. In the resistant W64A N line, protoplast and root mitochondria were unaffected by the toxin.

Mitochondria were isolated from corn roots containing T or C (male-sterile) cytoplasms and from N (non male-sterile) cytoplasm. The mitochondrial preparations (T, C and N mitochondria respectively) were treated with various concentrations of digitonin and assayed for respiratory activity. The T mitochondria were markedly more digitonin-sensitive than C or N mitochondria, as shown by the inhibition of malate and succinate respiration and uncoupling of oxidative phosphorylation. There were also differences between C and N mitochondria with respect to digitonin-sensitivity. These data strongly suggest that T, C and N mitochondria differ from each other with respect to biochemical structure. The chemical, genetic and agricultural significance of these data is discussed.

Sensitivities of seven commonly used bioassays for Helminthosporium maydis race T-toxin were determined. The most easily quantified and highly sensitive bioassays were based either on dark CO2 fixation by green leaves or on respiration rates of isolated mitochondria. These bioassays were 5 to 10 times more sensitive than was the semiquantitative seedling root growth bioassay. Bioassays based on the production of visible lesions on leaves did not provide reliable dosage-response relationships and were estimated to be 20 to 100 times less sensitive to toxin than dark CO2 fixation or mitochondrial respiration. Choice of bioassay depends on the objective of the experiment in which it is used.

SUMMARY Gas liquid chromatography was used to investigate the influence of several T, S and unclassified cytoplasms on the fatty acid composition of oil from A632 and CrS4HLA maize seeds. The fatty acid compositions of the A632 and CrS4HLA seeds differed markedly from each other with respect to oleic and linoleic acids but were stable within each seed line with respect to all sixteen of the cytoplasms tested.