The chemical composition of plant galls: are levels of nutrients and secondary compounds controlled by the gall-former?

Abstract

The chemical composition of galled and ungalled plant tissue was compared in a series of experiments. Gall and adjacent plant tissue was analysed for 20 species of gall-former on 11 different plant species. There were clear differences between galled and ungalled tissue in levels of nutrients and secondary compounds. Gall tissue generally contained lower levels of nitrogen and higher levels of phenolic compounds than ungalled plant tissue. The gall tissue produced by the same plant in response to different species of gall-former differed in chemical composition, as did the gall-tissue from young and mature galls of the same species. The chemical differences between gall and plant tissues were studied in more detail in two field manipulations. Firstly, the seasonal changes in phenolic biosynthesis in Pontania proxima and P. pedunculi (Hymenoptera: Tenthredinidae) gall tissue were compared to those of their host plants, Salix alba and S. caprea. In both types of gall tissue, phenolic levels declined as the season progressed, but levels in the surrounding plant tissue increased. When the gall insects were killed with insecticide, phenolic levels in the galled tissue dropped to the same level as those in adjacent plant tissue. Secondly, the density of Cynips divisa (Hymenoptera: Cynipidae) galls on Quercus robur leaves was reduced by removing half the galls present, either those from the central region of the leaf or those from the edge. Decreasing gall density increased the size of the remaining galls and the weight of the insects, but these effects were most marked when the galls remaining were growing centrally on the leaf, i.e. when the galls from the edge had been removed. Decreasing gall density increased the nitrogen content of the remaining galls, again to a greater extent in galls growing centrally on the leaf. The results of these studies suggest that the levels of nutrients and secondary compounds in gall tissue are usually markedly different to those of surrounding plant tissue, and that gall-formers may produce species-specific and temporally variable changes in the chemical composition of gall tissue.

Reações de defesas químicas e estruturais de Lonchocarpus muehlbergianus Hassl. (Fabaceae) à ação do galhador Euphalerus ostreoides Crawf. (Hemiptera: Psyllidae)

“…Provavelmente, os mecanismos de ativação ou inibição do crescimento ocorreriam mediante aumento na biossíntese de fenóis, o qual inibiria as AIA-oxidases, aumentando assim a ação das auxinas, responsáveis pela hipertrofia celular (Fosket 1994) e pela conseqüente formação da galha. Os altos níveis de biossíntese de substâncias fenólicas nos tecidos das galhas são reflexo da juventude fisiológica da estrutura, na qual a atividade da PAL (fenilalaninaamonialiase) é alta (Hartley 1998), além de poderem atuar como uma barreira que protege o inseto indutor do ataque de outros herbívoros (Cornell 1983, Hartley 1998.…”

“…Muito embora a presença e a função dos derivados fenólicos nos tecidos das galhas tenha sido estudada por muitos autores (Cornell 1983, Taper & Case 1987, Schultz 1992, Hartley 1998, o papel dos flavonóides na sinalização entre insetos indutores de galhas e a suscetibilidade das espécies hospedeiras é praticamente desconhecida.…”

“…Estas alterações são acompanhadas por modificações bioquímicas, principalmente notadas em relação a metabólitos primários e secundários específicos (Hartley 1998). No primeiro grupo, merecem destaque substâncias com função nutricional, tais como carboidratos e lipídios.…”

Seasonal variation of phenolic content in galled and non-galled tissues of Calliandra brevipes Benth (Fabaceae: Mimosoidae)

“…Gall formation represents the most intimate and specialized form of plant-herbivore interaction, and causes anatomical and metabolic alterations in the host plant functions, which provides shelter and food for insects or their off spring (Edwards & Wratten 1980;Fernandes & Price 1988;Hartley 1998;Schönrogge et al 2000;Moura et al 2008;Formiga et al 2009). Th e most complex entomogenous galls are those induced by Cynipid wasps (Hymenoptera) (Schönrogge et al 2000), such as Tanaostigmodes spp.…”

“…Until now, phenolic compounds in non-galled tissues have been associated to a defensive plant mechanism against the gall inducers, but these herbivores may also benefi t from a secondary protection against the attack of their natural enemies (Abrahamson et al 1991;Hartley 1998;Nyman & Julkunen-Titto 2000;Pascual-Alvarado et al 2008;Formiga et al 2009). Interpretations of analyses of compounds in gall systems generally relate them to a chemical defense against natural enemies, but few studies discuss the primary reasons for their synthesis as well as the control performed by gall inducers, especially in the Neotropical region.…”