Abstract:The mistletoes, stem hemiparasites of Asia and Europe, have been used as medicinal herbs for many years and possess sophisticated systems to obtain nutrients from their host plants. Although knowledge about ethnomedicinal uses of mistletoes is prevalent in Asia, systematic scientific study of these plants is still lacking, unlike its European counterparts. This review aims to evaluate the literature on Scurrula and Viscum mistletoes. Both mistletoes were found to have anticancer, antimicrobial, antioxidant and antihypertensive properties. Plants from the genus Scurrula were found to inhibit cancer growth due to presence of phytoconstituents such as quercetin and fatty acid chains. Similar to plants from the genus Viscum, Scurrula also possesses TNFα activity to strengthen the immune system to combat cancer. In line with its anticancer activity, both mistletoes are rich in antioxidants that confer protection against cancer as well as neurodegeneration. Extracts from plants of both genera showed evidence of vasodilation and thus, antihypertensive effects. Other therapeutic effects such as weight loss, postpartum and gastrointestinal healing from different plants of the genus Scurrula are documented. As the therapeutic effects of plants from Scurrula are still in exploration stage, there is currently no known clinical trial on these plants. However, there are few on-going clinical trials for Viscum album that demonstrate the functionalities of these mistletoes. Future work required for exploring the benefits of these plants and ways to develop both parasitic plants as a source of pharmacological drug are explained in this article.

Cuscuta species (dodders) are widespread stem holoparasites that depend on host plants for their entire mineral and water and most carbohydrate requirements. Dodders negatively affect host photosynthesis but precise information on their impact on hosts in the presence of environmental stress factors (i.e. drought) is little known. In a pot experiment, the leaf traits, gas exchange and chlorophyll a fluorescence of the invasive climber, Mikania micrantha, parasitized by Cuscuta australis, were investigated in order to study variations of host photosynthesis in response to parasitism and drought. The results showed that the concomitant presence of C. australis infection and drought significantly impacted the leaf traits (i.e. increased leaf dry mass content), gas exchange (i.e. decreased stomatal conductance and transpiration rates and increased water-use efficiency) and quantum yield of chlorophyll a fluorescence of M. micrantha. The presence of a single stress factor (C. australis infection or drought), however, only significantly affected the leaf traits and gas exchange of M. micrantha. These results suggested that the combined additive effects of C. australis parasitism and drought significantly suppressed the photosynthesis of M. micrantha in relation to both stomatal and non-stomatal limitation of host photosynthesis. This study provides insights into Cuscuta-host interactions under drought conditions in the tropics.

Most mistletoe -host ecophysiological studies have paid attention to the infl uence of parasites on host performance. Th is paper explored the impact of varying hosts on the photosynthesis of a single mistletoe species. Here, we studied an obligate xylem-tapping tropical mistletoe ( Dendrophthoe curvata (Blume) Miquel) parasitizing four diff erent hosts ( Acacia auriculiformis A. Cunn. Ex Benth, Andira inermis (W. Wright) DC., Mangifera indica L. and Vitex pinnata L.) in a homogeneous tropical heath forest patch in Brunei Darussalam. We compared photosynthetic capacity and photosynthesis-related characteristics of the mistletoe on four diff erent hosts to evaluate the overall impact of hosts on the parasite. Results showed that the mistletoe -host patterns of CO 2 assimilation rates, transpiration rates and water use effi ciency varied signifi cantly based on the host. In the D. curvata -Vitex pinnata association, the mistletoe exhibited signifi cantly lower CO 2 assimilation rates but showed no signifi cant variations in transpiration rates and water use effi ciency when compared to the host. In D. curvata -Andira inermis and D. curvata -Mangifera indica associations, the mistletoe showed signifi cantly higher photosynthetic rates than the hosts, whereas in the D. curvata -Acacia auriculiformis association, there was no signifi cant diff erence in photosynthetic rates between the counterparts. Host specifi city also signifi cantly infl uenced some mistletoe photosynthetic parameters such as light saturated photosynthesis, specifi c leaf area, leaf chlorophyll content, CO 2 assimilation rates, stomatal conductance, transpiration rates and water use effi ciency. Diff erent tree hosts intrinsically off er diff erent resources to their obligate mistletoe parasites based on their physiology and environmental parameters. We argue that hostspecifi c responses have driven these intra-specifi c variations in mistletoe physiology. Th is study provides background for future investigation on potential host-regulated mechanisms that drive functional changes in host-dependent mistletoes.