Root herbivory in vitro: Interactions between roots and aphids grown in aseptic coculture

Abstract

An in vitro coculture system has been established to study interactions between roots and aphids. Eight aphid species (Aphis spiraecola P., Trama rara M., Macrosiphum euphorbiae S., Rhopalosiphum padi L., Sitobion avenae E, Rhopalosiphum maidis E, Metopolophium dirhodum W., and Pemphigus populivenae E) were reared on six species of hairy root cultures, Carthamus tinctorius L. cv N10, Tagetes patula L., Trichosanthes cucumerina L. var anguina, Hyoscyamus muticus L., Nicotiana tabacum L., and Beta vulgaris L. subsp, vulgaris. All species of aphids survived on root cultures for at least 2 d. Three cocuhures have been maintained aseptically for periods ranging from 2 too. to over 2 yr. The coculture ofR. padi on C. tinctorius cv N10 (N10-Rp) was used to study morphological and biochemical responses of roots under aphid herbivory.Aphid he,'bivory caused browning of cultures, reduced root vegetative growth, and increased production of polyacetylenes in C. tinctorius cv NIO roots. Our results suggest that this coculture system may improve our understanding of interactions between aphids and plant roots.

Root Exudation and Rhizosphere Biology

“…In addition to their fluorescent nature, these alkaloids exhibit strong phototoxicity against a polyphagous feeder, Trichoplusia ni, suggesting their insecticidal activity may be linked to photoactivation (Larson et al, 1988). The Andean highlands, where O. tuberosa is primarily cultivated, are subjected to a high incidence of UV radiation, and it was observed that the strongest fluorescence intensity occurred with oca varieties that showed resistance to the larvae of Mycrotrypes spp., the Andean tuber weevil (Flores et al, 1999). These data suggest that UV light penetrating soil layers could photoactivate fluorescent ␤-carboline alkaloids secreted by oca roots to create an insecticidal defense response.…”

“…Although the studies are not yet conclusive, these compounds may also be responsible for vesicular-arbuscular mycorrhiza colonization (Becard et al, 1992(Becard et al, , 1995Trieu et al, 1997). In contrast, survival of the delicate and physically unprotected root cells under continual attack by pathogenic microorganisms depends on a continuous "underground chemical warfare" mediated by secretion of phytoalexins, defense proteins, and other as yet unknown chemicals (Flores et al, 1999).…”

“…However, root herbivory by pests such as aphids can cause significant decreases in yield and quality of important crops including sugar beet (Beta vulgaris), potato (Solanum tuberosum), and legumes (Hutchison and Campbell, 1994). One attempt to study root-insect communication was developed by Wu et al (1999) using an in vitro coculture system with hairy roots and aphids. In this study, it was observed that aphid herbivory reduced vegetative growth and increased the production of polyacetylenes, which have been reported to be part of the phytoalexin response (Flores et al, 1988).…”

“…Our understanding of the biology, biochemistry, and genetic development of roots has considerably improved during the last decade (Smith and Fedoroff, 1995;Flores et al, 1999;Benfey and Scheres, 2000). In contrast, the processes mediated by roots in the rhizosphere such as the secretion of root border cells and root exudates are not yet well understood (Hawes et al, 2000).…”

“…In contrast, the processes mediated by roots in the rhizosphere such as the secretion of root border cells and root exudates are not yet well understood (Hawes et al, 2000). In addition to the classical roles of providing mechanical support and allowing water/nutrient uptake, roots also perform certain specialized roles, including the ability to synthesize, accumulate, and secrete a diverse array of compounds (Flores et al, 1999). Given the complexity and biodiversity of the underground world, roots are clearly not passive targets for soil organisms.…”