In this study, we examined whether and to what extent oxidative stress is induced in seedlings of two winter triticale (Triticosecale Wittm.) varieties (susceptible Tornado and resistant Witon) in response to infestation by the cereal grain aphid (Sitobion avenae L.) and bird-cherry-oat aphid (Rhopalosiphum padi L.). We compared the level of hydrogen peroxide (H2O2) and lipid peroxidation products as well as markers of protein damage (protein-bound thiol and carbonyl groups). The studied parameters were measured at 6, 24, 48 and 96 h post-initial aphid infestation compared to the non-infested control seedlings. Our studies indicated that the cereal aphid feeding evoked oxidative stress in the triticale seedlings. Cereal aphid feeding increased the H2O2 level in triticale tissues, with maximum levels observed at 24 and 48 h post-infestation. Triticale infestation with aphids also increased lipid peroxidation products in triticale seedlings, with the maximal levels at 48 or 96 h post-infestation. Further, there was a reduction in protein thiol content and an increase in protein carbonyl content in the triticale seedlings after infestation with female aphids. Stronger triticale macromolecule damages were evoked by the oligophagous aphid R. padi. There was a more substantial protein thiol content reduction in the resistant Witon cultivar and higher accumulation of protein-bound carbonyls in the tissues of the susceptible Tornado cultivar. The changes were proportional to the aphid population and the time of aphid attack. These findings indicate that the defensive strategies against cereal aphid (S. avenae and R. padi) infestation were stimulated in triticale Tornado and Witon seedlings. Our results explain some aspects and broaden the current knowledge of regulatory mechanisms in plant-aphid interactions.

We studied the effect of qualitative and quantitative variation of saponin content in foliar tissues of four European alfalfa (Medicago sativa L.) cultivars (Radius, Sapko, Sitel, Radius line 1) on pea aphid (Acyrthosiphon pisum Harris) development, and the effect of aphid infestation on alfalfa saponin content. Aphids (adult apterae, larvae, and adult alatae) were counted on 3-, 6- and 9-month-old plants (before the first, second and third cutting). Thin-layer chromatography was used to detect and estimate the quantity of the following saponins: 3GlcA, 28AraRhaXyl medicagenic acid; 3Glc, 23Ara, 28AraRhaXylApi zanhic acid (zanhic acid tridesmoside); and 3RhaGalGlcA soyasapogenol B (soyasaponin I). Radius, Sapko, and Sitel contained all three saponins but Radius line 1 did not contain zanhic acid tridesmoside or medicagenic acid glycoside. Saponin content was highest in Radius and lowest in Radius line 1. Regardless of the cultivar, saponin content was higher in aphid-infested than uninfested plants. For all sampling dates, aphid numbers were highest on Radius line 1 and lowest on Radius; that is, aphid numbers were inversely related to saponin content. Alfalfa has a herbivoreinduced defense. Saponin levels increase in the foliage of infested alfalfa. Attempts of plant breeders to reduce saponin content in order to increase alfalfa digestibility for livestock might make the plants more susceptible to aphids and other pests.