Attack on all fronts: functional relationships between aerial and root parasitic plants and their woody hosts and consequences for ecosystems

Abstract

This review discusses how understanding of functional relationships between parasitic plants and their woody hosts have benefited from a range of approaches to their study. Gross comparisons of nutrient content between infected and uninfected hosts, or parts of hosts, have been widely used to infer basic differences or similarities between hosts and parasites. Coupling of nutrient information with additional evidence of key processes such as transpiration, respiration and photosynthesis has helped elucidate host-parasite relationships and, in some cases, the anatomical nature of their connection and even the physiology of plants in general. For example, detailed analysis of xylem sap from hosts and parasites has increased our understanding of the spatial and temporal movement of solutes within plants. Tracer experiments using natural abundance or enriched application of stable isotopes ((15)N, (13)C, (18)O) have helped us to understand the extent and form of heterotrophy, including the effect of the parasite on growth and functioning of the host (and its converse) as well as environmental effects on the parasite. Nutritional studies of woody hosts and parasites have provided clues to the distribution of parasitic plants and their roles in ecosystems. This review also provides assessment of several corollaries to the host-parasite association.

Why do mixotrophic plants stay green? A comparison between green and achlorophyllous orchid individuals in situ

“…This may also apply far beyond mycoheterotrophy, in the numerous other mixotrophic lineages. Among the so-called ''hemiparasitic'' plants, i.e., green parasitic plants that tap into the sap of other plants, mixotrophy turns out to be the rule (Teˇšitel et al 2010, Bell et al 2011). Yet, the evolution into pure heterotrophy (''holoparasitism'') occurred in a limited number of lineages only (Westwood et al 2010).…”

“…Yet, the evolution into pure heterotrophy (''holoparasitism'') occurred in a limited number of lineages only (Westwood et al 2010). Although the adaptations required for holoparasitism differ somewhat from those in MH plants, they are complex, too (Westwood et al 2010, Bell et al 2011. Mixotrophic nutrition may be evolutionarily stable in hemiparasitic plants because, in this framework, simple loss of function cannot achieve successful transition to heterotrophy.…”

Host specificity and experimental assessment of the early establishment of the mistletoe Phoradendron crassifolium (Pohl ex DC.) Eichler (Santalaceae) in a fragment of Atlantic Forest in southeast Brazil

“…These plants grow on twigs and branches of host plants (usually trees) using a specialized system of roots, called haustoria, that penetrate into the vascular tissue of the host and extract essential minerals and water (Kuijt 2003). Mistletoes may alter host growth, reproduction and physiology, decreasing its fitness (Mourão et al 2009;Bell & Adams 2011). Thin twigs (< 1 cm in diameter) often die when infected by mistletoes (Sargent 1995), as can highly infected hosts (Teodoro et al 2013).…”

Changes in Antioxidant Enzyme Activities of European Mistletoe (Viscum album L. subsp. Album) Leaves as a Response to Environmental Stress Caused by Pollution of the Atmosphere by Nitrogen Dioxide

“…It is known that the mistletoe parasite has a huge impact on the transport of primary metabolites in a host plant and has a decisive infl uence on its growth [33]. During plant-pathogen interactions the deposition of β-1,3-glucan, triggered by reactive oxygen species [34], leads to callose accumulation in the form of a structural scaffold for toxic molecules [35] and refl ects its participation in host self-defence mechanisms.…”