Photosynthesis, ionomics and metabolomics of the host-hemiparasite association Acacia gerrardii-Viscum schimperi.

Viscum schimperi is an evergreen hemiparasitic plant that can grow on stems and branches of several tree species. It penetrates the host tissues and forms a vascular bridge (haustorium) to withdraw the nutritive resources. Its relationships with hosts remain unknown. This study aimed to investigate the physiological and biochemical attributes of the host-hemiparasite association Acacia gerrardii -Viscum schimperi . The hemiparasite exhibited 2.4- and 3.0-fold lower photosynthetic activity and water use efficiency, and 1.2- and 4.1-fold higher transpiration rate and stomatal conductance. Equally, it displayed 4.9- and 2.6-fold greater water potential and osmotic potential, and in least 3.0times more accumulated 39 K, 85 Rb and 51 V, compared to the host. Nevertheless, it had no detrimental effect on photosynthetic activity, water status and multi-element accumulations in the host. Based on metabolome profiling, V. schimperi could use xanthurenic acid and propylparaben to acquire potassium from the host, and N -1-naphthylacetamide and N -Boc-hydroxylamine to weaken or kill the distal part of the infected branch and to receive the total xylem contents. In contrast, A. gerrardii could used N -acetylserotonin, arecoline, acetophenone and 6-methoxymellein to defend against V. schimperi infection.

Microenvironment in the canopy rivals the host tree water status in controlling sap flow of a mistletoe species.

Mistletoes absorb water from the vascular system of their hosts and thus the water use of mistletoes can be influenced by the water status of their hosts besides abiotic environmental conditions; however, there is a lack of studies on the dynamics of mistletoe water utilization in relation to both types of controlling factors. By building a canopy platform at 20 m above the ground, we monitored the dynamic changes of sap flow of Viscum coloratum (Kom.) Nakai (Loranthaceae) in combination with continuous measurements of microclimatic variables and volumetric water content (VWC) of its host tree branch xylem. We found that the host tree VWC exhibited substantial fluctuations during sunny days but lower VWC of the host did not negatively affect the sap flow of V. coloratum. Hourly and daily mean transpiration rates (Esap) of V. coloratum calculated from sap flow measurements showed strong positive correlations with photosynthetic photon flux density (PPFD) and vapor pressure deficit (VPD) measured in close vicinity to the point of mistletoe attachment. The mean Esap of V. coloratum was substantially higher than that of their host during clear days (4.55 ± 0.54 vs 2.01 ± 0.15 kg m-2 day-1). Moreover, the mistletoe-to-host transpiration ratio was not constant but became increasingly larger with the increase of PPFD or VPD on both hourly and daily bases, suggesting a weaker control of water loss in the mistletoe in comparison to its host species. The strong dependence of mistletoe Esap on micrometeorological variables and its decoupling from the host tree xylem water status suggests that the development of dense tree canopy functions as a potential mechanism for the host trees in reducing the competitive water use of mistletoes. These findings have important implications for the interactions between mistletoe species and their host trees in temperate forests.

Angiotensin-converting enzyme inhibitory activity of Viscum triflorum is host plant-dependent.

CONTEXT: Viscum triflorum DC. (Viscaceae) is a hemiparasitic plant used in traditional medicine on Réunion Island as a remedy to treat hypertension. OBJECTIVE: The in vitro angiotensin-converting enzyme (ACE) inhibitory activity of extracts of V. triflorum and the corresponding host plant species were examined to evaluate the use as a remedy against hypertension, and to investigate whether the host plants have an influence on the activity. MATERIALS AND METHODS: Aqueous, ethanol and acetone extracts of 24 leaf samples of V. triflorum and the corresponding host plants, representing 10 plant species, were prepared. The ACE inhibitory activities of the extracts were measured by HPLC using dansyltriglycine as substrate. RESULTS AND CONCLUSION: Water extracts of Viscum samples from only two of the 10 host plants, namely Acacia heterophylla Willd. (Fabaceae) and Sophora denudata Bory (Fabaceae), showed significant inhibitory activity, ≥ 50% inhibition in a concentration of 0.33 mg crude plant extract in 1 mL test solution. From the two mentioned host plant species activity was only detected in the water extract from one of the six samples of A. heterophylla. Three host species showed pronounced activity without any detection of activity in the samples of V. triflorum. The results support the traditional use provided that V. triflorum is collected from A. heterophylla or S. denudata.

Spatial and seasonal variation in amino compounds in the xylem sap of a mistletoe (Viscum album) and its hosts (Populus spp. and Abies alba).

In a field study, the composition and concentrations of amino compounds in the xylem sap of the mistletoe, Viscum album L., and in the xylem sap of two host species, an evergreen conifer (Abies alba Mill.) and a deciduous broad-leaved tree (Populus x euramericana), were analyzed. The xylem sap of both hosts and mistletoe contained large, but similar amounts of total organic nitrogen in low molecular weight amino compounds (TONLW). Nevertheless, individual amino compounds accumulated in the xylem sap of mistletoe relative to the host xylem sap, indicating selective uptake. In the xylem sap of Populus, major amino compounds (asparagine (Asn) and glutamine (Gln)) and the bulk parameters, TONLW and proteinogenic amino acids, showed significant seasonal variation. In Abies and in mistletoe on either host, variation of amino compounds in xylem sap was largely explained by inter-annual differences, not by seasonal variation. In both hosts, TONLW in the xylem sap was dominated by Gln. There was a steady decrease in relative abundance of Gln from the host xylem sap to the mistletoe xylem sap and to the stems and leaves of mistletoe. Simultaneously, the abundance of arginine (Arg) increased. Arginine was the predominant amino compound in the stems and leaves of mistletoe, occurring at concentrations previously observed only in leaves of trees exposed to excess nitrogen. We conclude that Gln (2 mol N mol(-1)) delivered by the host xylem sap is converted, in mistletoe, to Arg (4 mol N mol(-1)) and that the organic carbon liberated from Gln contributes significantly to the parasite's heterotrophic carbon gain. Statistical analyses of the data support this conclusion. Accumulation of Arg in mistletoe is an indication of excess N supply as a result of the uptake of amino compounds from the host xylem sap and a lack of phloem uploading.

Influence of the parasite Viscum cruciatum Sieber on the chemical constituents of Crataegus monogyna Jacq.

A phytochemical study of two plant species, Viscum cruciatum Sieber and Crataegus monogyna Jacq., was completed to investigate the influence of the parasite Viscum cruciatum on the host Crataegus monogyna. The study was carried out with two samples and consisted of hexane extracts of the Viscum cruciatum parasitizing on Crataegus monogyna and C monogyna. In these samples ursolic acid, beta-sitosterol and a triterpene fraction were found that contained mainly butyrospermol (3beta-lanost 8, 24-dien, 3-ol), 24-methylene-24-dihydrolanosterol (24-methylene-5alpha-lanost-8-en-3beta-ol), cycloartenol (9beta, 19-cyclo-5alpha, 9beta-lanost-24-en-3beta-ol), beta-amyrin (olean-12-en-3beta-ol) and several aliphatic alcohols identified as the C18 to C30 members of the 1-alkanol homologous series. beta-Amyrin acetate was only isolated from Viscum cruciatum and was not found in Crataegus monogyna.