Characteristics of Hydroxamic Acid Induction in Wheat Triggered by Aphid Infestation

Abstract

Abstract-Hydroxamic acids (Hx) are natural products of Gramineae that are associated with cereal resistance to pests. We aimed at characterizing the induction of Hx accumulation in seedlings of wheat, Triticum aestivum, by short-term infestation of the cereal aphid, Rhopalosiphum padi. A load of 25 aphids increased significantly the Hx levels in the infested primary leaf in comparison with control levels. Lower loads did not increase Hx concentration. Aphid infestation lasting 16 hr did not elicit induction of Hx, even after a time-lag of 32 hr to allow the expression of any induced response. Fortyeight hours was the minimum duration of aphid infestation required to trigger Hx induction. The age of the infested tissue (the primary leaf) did not affect induction. Similar increases of Hx were found in unfolding, expanding, and totally expanded primary leaves. It was determined that the regime of nutrient supply (N-intensive nutritive solutions at low and high concentration) to wheat seedlings had no effect on the magnitude of the aphid-induced Hx (N-based secondary metabolites). Results obtained are discussed in the framework of general theories of plant defense allocation.

Allocation of herbivory-induced hydroxamic acids in the wild wheat Triticum uniaristatum

“…Seedlings of T. uniaristatum with heavier loads of aphids than that those in the basic experiment (20 aphids/clip-cage) did not show higher levels of Hx induction. Interestingly, 10 aphids per clip-cage were sufficient to elicit Hx induction; a result different from that obtained for cultivated wheat (Gianoli & Niemeyer, 1997b). The phenomenon of Hx induction in this wild wheat appears to possess a discrete nature.…”

Induced twining in Ipomoea purpurea (L.) Roth.: response threshold and induction by volatiles and snail damage

“…Previous studies have compared the twining rate of undamaged vs. damaged plants; it is less known, however, about the damage threshold that needs to be reached for the induced twining to be triggered. Damage threshold has been described for other induced responses to herbivory (Gianoli & Niemeyer 1997, Underwood 2000, but it is usually associated to the cost of such responses rather than the necessary thresholds (Agrawal 2005).…”

Estudo semi-empírico de ácidos hidroxâmicos: ácido formoidroxâmico e derivados do aleloquímico dimboa

“…As plantas produzem metabólitos secundários, chamados substâncias alelopáticas ou aleloquímicos, que atuam na sua defesa contra herbívoros, patógenos ou mesmo contra plantas competidoras 1 . Estudos têm demonstrado que ácidos hidroxâmicos (Hx) cíclicos do tipo 4-hidróxi-1,4-benzoxazin-3-onas (benzoxazinóides), presentes em cereais na forma de 2-β-O-D-glicosídeos, atuam sobre insetos, fungos e bactérias [2][3][4][5] . Os glicosídeos são biologicamente inativos, mas a ruptura das células vegetais libera β-glicosidases que degradam os glicosídeos enzimaticamente, liberando as agliconas tóxicas 6 .…”

“…Em solução aquosa, 1 está em equilíbrio com a forma aldólica 2 (Figura 1) 7 . A participação desse Hx na defesa do trigo contra insetos é sugerida pelo aumento de seus níveis na planta após infestação por afídios 3,5 e pelo seu efeito anti-alimentar em insetos alimentados com dietas artificiais contendo 1 8 . Existem várias indicações quanto aos possíveis sítios bioquímicos de ação dos áci-dos hidroxâmicos.…”