Luis J. Corcuera

Role of hydroxamic acids in the resistance of cereals to aphids.

Abstract Hydroxamic acid concentration in Gramineae, both natural and incorporated, correlates with resistance to the aphid Metopolophium dirhodum . 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one, a hydroxamic acid isolated from corn extracts, is deleterious to aphids fed on artificial diets. It is proposed that hydroxamic acids act as naturally-occurring protective factors against M. dirhodum .

Effect of content and distribution of hydroxamic acids in wheat on infestation by the aphid Schizaphis graminum

Abstract The content of hydroxamic acids in wheat plants shows substantial variations between different species and cultivars (1.0–6.3 mmol/kg fr. wt). It also varies with the age of the plant and the organ assayed. The maximum concentration is reached by the fourth day in epicotyls and roots. The amount in leaves at different plant ages is always higher in the younger leaves. Based on feeding and infestation experiments, it is proposed that the distribution of aphids on leaves of different ages is regulated by the hydroxamic acid content.

TOXICITY AND FEEDING DETERRENCY OF HYDROXAMIC ACIDS FROM GRAMINEAE IN SYNTHETIC DIETS AGAINST THE GREENBUG, SCHIZAPHIS GRAMINUM

2,4‐Dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one (DIMBOA), the main hydroxamic acid isolated from maize extracts, increased the mortality of Schizaphis graminum when fed in artificial diets. Electrically‐monitored feeding assays showed that DIMBOA acted as a feeding deterrent at concentrations as low as 1 mM. On 12 mM DIMBOA diets, feeding by aphids was completely inhibited. Additional feeding experiments showed that when DIMBOA was ingested there was an increase in aphid mortality relative to that of aphids which did not ingest the compound. Thus, the deleterious effects of DIMBOA on aphids are due to feeding deterrency and toxicity. The 2‐ß‐0 glucoside of DIMBOA (DIMBOA‐Glc), the form in which DIMBOA naturally occurs in Gramineae, had a slight effect on lowering aphid survival and an appreciable feeding‐deterrent effect on diet‐fed aphids. The relevance of the effects of DIMBOA and DIMBOA‐Glc on aphids to resistance of certain graminaceous crops against aphids is discussed.

Hydroxamic acid content in wild and cultivated gramineae

Abstract The content of two hydroxamic acids, 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), in cultivated and wild species of Gramineae was determined. Zea mays and Triticum durum contained both DIBOA and DIMBOA, the latter being in greater concentrations. Secale cereale and Arundo donax contained only DIBOA, while Elymus gayanus and Chusquea cumingii contained only DIMBOA. Poa annua, Bromus unioloides, Dactylis glomerate, Phalaris canariense, Lolium perenne, Hordeum species, Setaria verticilata, Cynodon dactylon and a Sorghum hybrid lacked these hydroxamic acids. The maximum concentration of hydroxamic acid in A. donax was found at the end of summer, and the minimum at the beginning of winter. In annual plants, such as wheat, while neither acid was found in the fruits, their concentrations in coleoptiles and leaves increased rapidly reaching a maximum 4 days after germination and decreasing gradually afterwards. DIBOA and DIMBOA had toxic and feeding deterrent effects on the greenbug Schizaphis graminum at concentrations similar to those found in both cultivated and wild Gramineae.

Inhibition of ATPase from chloroplasts by a hydroxamic acid from the gramineae

Abstract -DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), a hydroxamic acid from the Gramineae involved in the resistance of cereals to aphids, inhibits

Role of an indole alkaloid in the resistance of barley seedlings to aphids

Abstract The content of the simple indole alkaloid gramine in barley leaves decreased with age. Conversely, susceptibility to aphids increased in older plants. Population growth rate of the greenbug Schizaphis graminum correlated with gramine content of leaves of several barley cultivars. Gramine decreased rate of feeding, survival and reproductive index of aphids feeding on artificial diets at concentrations similar to those found in plant leaves. Thus, it is suggested that gramine plays a role in the resistance of barley seedlings to S. graminum. Benzyl alcohol, a previously reported insect resistance factor from barley, was absent from all barley cultivars analysed.

Effect of gramine in the resistance of barley seedlings to the aphid Rhopalosiphum padi

Gramine (N,N‐Dimethyl‐3‐aminomethylindole) content in various barley cultivars varied from 0 to 2.6 mmoles/kg fresh weight. Those cultivars which were lacking gramine were the most susceptible to the aphid Rhopalosiphum padi (L.). The population growth rate of R. padi negatively correlated with gramine content in leaves of barley seedlings. In addition, gramine incorporated in artificial diets decreased survival, amount of diet ingested and reproduction of aphids at concentrations similar to those found in plant leaves. Thus, it is suggested that gramine may be one of the factors responsible for the resistance of barley seedlings to R. padi.

Effects of indole alkaloids from gramineae on aphids

Abstract The indole bases N ∞ -methyltryptamine, 5-methoxy- N, N -dimethyltryptamine, 3- N,N -dimethylaminomethylindole (gramine) and 5-methoxytryptamine decreased survival of nymphs of Rhopalosiphum maidis with LD 50 of 3.8, 3.5, 2.9 and 2.3 mM, respectively, after 48 hr of feeding with a synthetic diet. Gramine also decreased survival of Schizaphis graminum with an LD 50 of 0.7 mM after 48 hr of feeding. The four compounds tested showed feeding deterrent activity on the aphids at concentrations as low as 0.5 mM. In addition, gramine showed toxic effects on S. graminum . Since the deleterious effects of gramine and related compounds in synthetic diets are observed at concentrations similar to those found in plants, it is possible that these molecules may have a role in protecting the plant against aphids

Distribution of gramine and hydroxamic acids in barley and wheat leaves

Abstract The first leaf of 12-day-old barley seedlings, contained 1.3 μmol/g fr. wt gramine while the concentrations were 2.2, 2.0 and 3.1 μmol/g fr. wt in lower and upper epidermis and mesophyll parenchyma, respectively. Gramine was not detected in the vascular bundles, nor in xylem exudates or guttation drops. Thus, about 70% of total gramine in the leaf was found in the mesophyll parenchyma and 30% in epidermal tissue. The content of hydroxamic acids was 3.0 μmol/g fr. wt in the first leaf of 12-day-old wheat plants, while the concentrations were 6.8 and 4.1 μmol/g fresh wt in the vascular bundle and mesophyll parenchyma, respectively. These compounds were not detected in epidermis, xylem exudates and guttation drops. About 50% of total hydroxamic acids were found in the vascular bundles. The significance of these results in plant protection against aphids is discussed.

Effect of gramine on the feeding behavior of the aphids Schizaphis graminum and Rhopalosiphum padi

The effects of the indole alkaloid gramine on the behavior of the aphids Schizaphis graminum and Rhopalosiphum padi feeding on barley seedlings and on artificial diets were studied. On barley cv. F. Union, which lacks gramine, S. graminum ingested from phloem tissue for 30–80 min and non‐phloem for 20–40 min, over a period of 3 h. In cultivar Datil ‘S’, gramine was found only in the epidermis and parenchyma mesophyll cells. On this cultivar, the non‐phloem wave form of S. graminum was not observed. On F. Union, R. padi ingested non‐phloem with short periods of ingestion from phloem. On cv. Datil ‘S’, this aphid did not show the non‐phloem wave form. In experiments performed with cv. F. Union seedlings that contained exogenous gramine S. graminum did not ingest from phloem. Exogenous gramine was found only in the vascular bundles. It is suggested that gramine content and location may affect the feeding behavior of aphids in barley.