Role of lndole‐3‐acetic Acid in the Interaction of the Phanerogamic Parasite Cuscuta and Host Plants

Abstract

Abstract: During infection with the phanerogamic parasite Cuscuta reflexa the incompatible host plant Lycopersicon esculentum shows characteristic anatomical tissue modifications at the infection sites that are exclusively provoked following contact with Cuscuta ‐ striking cell elongation is observed in the hypo‐dermis and collenchyma of the host plant. Due to the influence of auxins on the process of cell elongation in plants, the role of indole‐3‐acetic acid (IAA) in the interaction of Cuscuta and Lycopersicon was studied using a highly specific enzyme‐linked im‐munosorbent assay for hormone measurement. It was shown that the tissue modifications in the host plant as well as cell elongation in the parasite tissue leading to the formation of an adhesive‐secretory epithelium are correlated with increasing IAA levels in the respective tissues. Both anatomical modifications can also be induced artificially by injection of IAA into control tissue. Based on the obtained data, it can be hypothesized that during the parasitic attack IAA is accumulated in the haus‐toria‐bearing regions of Cuscuta and exuded from the epithelial cells. Due to the close contact between host and parasite, the hormone probably enters the host plant tissue causing the observed anatomical reactions.