Studies on the Physiology of Host-parasite Relationship in Orobanche. III. Carbohydrate and Nitrogen Metabolism of Host and Parasite

Determination of different carbohydrate and nitrogen fractions was made in tomato (Lycopersicum esculentum Mill.) and mustard (Brassica campestris L.) serving as hosts for Orobanche cernua and O. aegyptiaca respectively. Shoots of Orobanche were also subjected to such analyses. Infection raised the level of total reducing and total sugar in the host with a simultaneous decrease in the level of acid-hydrolyzable and total carbohydrates in the constituent organs of infected hosts. This has been explained to be due to predominance of hydrolytic activity in the infected host. Infection also brought about a depression in the proportion of sucrose to the pool of total sugar in the host. This was also possibly due to predominance of hydrolytic processes and retardation in the synthetic processes. Higher concentration of acid-hydrolyzable and total carbohydrates in Orobanche than in the host indicated a high demand for sugars by the parasite. The insignificant differences between the relative proportions of different nitrogen fractions to the pool of total nitrogen in healthy and infected hosts indicated that nitrogen metabolism was not deranged in any way due to infection. Orobanche always had a lower concentration of total soluble and total nitrogen than the host root.     

Studies on the Physiology of Host-parasite Relationship in Orobanche. II. Growth and Mineral Nutrition of Host and Parasite

The effects of Orobanche infection on the growth and mineral compostition of the host were studied. Parallel observations were made in host and parasite. Orobanche infection reduces the height of main shoot, the length of root, the number of branches, and the number and total area leaves per plant. Consequently the fresh and dry weight of the host is also decreased. Infection affects NAR and LAR only slightly but reduces RGR and RLGR at a later period of infection. The retardation in the growth of host seems to be due mainly to a continuous extraction of metabolites and inorganic nutrients. Infection increases the nitrogen, calcium and magnesium content in the host, especially in the leaves. This fact is connected with the retarded growth in the host. The process of absorption is probably not changed. The phosphorus and potassium contents diminish in the infected host, a fact related to the higher translocation to the parasite. The Orobanche plants grow faster during early stages and accumulate 88 % of total dry matter before flowering, The growth stages of Orobanche do not coincide with those of the host suggesting that the parasite is capable of synthesizing its own growth substances. Studies with ₃₂P show that the flow of minerals is mainly in the direction from host to parasite. The major part of the requirement of the parasite is met by the host. Orobanche maintains a higher phosphorus and potassium content in its tissues than the host, while the nitrogen, calcium and magnesium content is lower.     

Cytamoeba bacterifera Labbé, 1894. I. Morphology and Host Incidence of the Parasite in California.

SVXOPSIS. Parasites belonging to the genus Cytamoeba have been found in amphibians from central and northern California. The infected animals and their numbers were (URODELA) Aneides flavipunctatus (2), A. lugubris (29), Batrachoseps a. atttnuatus (81). Dicamptodon ensatus (2), and (SALIENTIA) Rana b. boyli (1). The rates of infection varied between 0.6% and 29.3%, and the number of parasites per infected cell ranged from one to seven.
Preparations stained with haematoxylin and Romanowsky dyes indicated several types of parasite: some were homogeneous, others possessed several dark staining granules and some possessed large, dark staining central bodies or peripheral dark staining rims. Parasites were seen in the erythrocytes, the plasma and, occasionally, in endothelial cells and monocytes. They were found in the peripheral and heart blood and in the blood of the liver, spleen, kidneys and lungs. Cell division was common in erythrocytes, and yielded daughter cells of identical size. In some cases, chains of 3 to 5 individuals were seen and, rarely, three bodies, in a cloverleaf configuration, were produced as the result of a single division. Following acid hydrolysis, methylene blue-stained parasites showed a peripheral ring of granules, and, in some, a few stained centrally located bodies.     

The Regulation of the Water Potential Gradient in the Host and Parasite Relationship betweenSorghum bicolorandStriga hermonthica

A glasshouse experiment was carried out to investigate the factorscontrolling the abstraction of xylem fluid from its host bythe parasiteStriga hermonthica(Scrophulariaceae).Strigahad amean daily transpiration rate far exceeding that of its hostsorghum (Sorghum bicolor), with infestation byStrigaalso shownto lower the transpiration rate of the host. Stopping the host'stranspiration was shown to decrease the transpiration rate ofthe parasite. Stopping the parasite's transpiration only gavean initial increase in the host's transpiration rate which wasnot sustained. The parasite had a lower water potential thanits host, values being -0.42 MPa and -0.23 MPa, respectively,and an accompanying higher osmotic pressure of 0.68 MPa against0.51 MPa for sorghum. Modifying the water potential gradientby bagging both partners together showed that the differentialin osmotic pressure and water potential was largely maintainedby the parasite's higher rate of transpiration. A favourablewater potential gradient towards the parasite still existedfollowing the cessation of transpiration, this being generatedby the haustorial resistance to hydraulic conductivity whichwas found to be some 1.5–4.5 times greater than that offeredby the parasite shoot. Both the high rate of transpiration andthe increased resistance across the haustoria would appear tobe necessary means to facilitate the diversion of host resourcesto the parasite.Copyright 1997 Annals of Botany Company Striga hermonthica; sorghum; water relations; haustorium; root parasite     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues2

Feeding strawberry and poplar leaves with iodoacetate, arsenite,or fluoride decreased the contents of sucrose and ascorbate.The content of hexose increased in high concentrations of iodoacetatebut decreased in moderate strengths. Iodo-acetate increasedthe rate of CO₂ output and caused a large decrease in phospholipidwith increase of inorganic phosphate. When iodoacetate was fedin nitrogen, CO₂ output did not increase. An explanation of the results is that the sucrose and ascorbateof the cell are mainly confined to the vacuole and that theabove poisons accelerate the leakage of these compounds fromthe vacuole so that they are metabolized more rapidly in thecytoplasm. An additional possibility is that iodoacetate ‘uncouples’oxidative phosphorylation, thereby stimulating respiration andmore rapid metabolism of both sucrose and ascorbate.     

Studies on Orobanche hederae Physiology: Pigments and CO2 Fixation

In order to investigate some aspects of Orobanche hederae physiology in relation to its parasitism, the pigment composition and the ¹⁴CO₂ incorporation, both in light and in dark, were studied. By means of various chromatographic techniques, it was shown that chlorophyll is probably quite absent and that the carotenoids are very largely distrihuted and consist almost exclusively of xanthophylls. Flavochrome, flavoxanthin, and a pigment resembling neoxanthin were found to be the major components; lutein-5,6-epoxide, taraxanthin, and traces of β-carotene and α-carotene-5,6-epoxide were also present. CO₂ incorporation is completely of heterotrophic type, being in no way stimulated by the light; the major radioactivity was detected in the fractions containing amino acids and organic acids.     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues1

Oxygen at pressures of 2 and 3 atmospheres caused an initialincrease in CO₂ output of strawberry leaves followed by a decrease.In oxygen at 2 atmospheres, but not in oxygen at 3 atmospheres,the increase in CO₂ output could be attributed to an increasein glucose-6-phosphate and in fructose diphosphate; in oxygenat 3 atmospheres the increase may be due to an increased accessibilityof substrates and enzymes or to other causes. The decline inCO₂ output in oxygen at both 2 and 3 atmospheres was associatedwith large decreases in glucose-6-phosphate and 3-phosphoglycerate,probably due to a large decrease in adenosine triphosphate relatedto a ‘block’ of the tricarboxylic acid cycle.     

Studies on the Respiratory Physiology of Euglena gracilis Cultured on Acetate or Glucose

SYNOPSIS. The glyoxylate cycle operates at a high level in Euglena gracilis when acetate is the only carbon source, and at a low level when glucose is the only carbon source, as indicated by activities of malate synthase. Altho glucose causes a moderate repression of some of the enzymes of the glyoxylate cycle, it neither represses nor inhibits malate synthase. The specific activity of the malic enzyme was about 5-fold greater in acetate-grown Euglena than in glucose-grown cells, but the absolute rate of CO₂ fixation was about twice as great in cells grown on glucose. The respiratory quotient was unity regardless of substrate.     

Host Density and Competency Determine the Effects of Host Diversity on Trematode Parasite Infection

Variation in host species composition can dramatically alter parasite transmission in natural communities. Whether diverse host communities dilute or amplify parasite transmission is thought to depend critically on species traits, particularly on how hosts affect each other’s densities, and their relative competency as hosts. Here we studied a community of potential hosts and/or decoys (i.e. non-competent hosts) for two trematode parasite species, Echinostoma trivolvis and Ribeiroia ondatrae, which commonly infect wildlife across North America. We manipulated the density of a focal host (green frog tadpoles, Rana clamitans), in concert with manipulating the diversity of alternative species, to simulate communities where alternative species either (1) replace the focal host species so that the total number of individuals remains constant (substitution) or (2) add to total host density (addition). For E. trivolvis, we found that total parasite transmission remained roughly equal (or perhaps decreased slightly) when alternative species replaced focal host individuals, but parasite transmission was higher when alternative species were added to a community without replacing focal host individuals. Given the alternative species were roughly equal in competency, these results are consistent with current theory. Remarkably, both total tadpole and per-capita tadpole infection intensity by E. trivolvis increased with increasing intraspecific host density. For R. ondatrae, alternative species did not function as effective decoys or hosts for parasite infective stages, and the diversity and density treatments did not produce clear changes in parasite transmission, although high tank to tank variation in R. ondatrae infection could have obscured patterns.     

The Relationship between Parasite Fitness and Host Condition in an Insect - Virus System

Research in host-parasite evolutionary ecology has demonstrated that environmental variation plays a large role in mediating the outcome of parasite infection. For example, crowding or low food availability can reduce host condition and make them more vulnerable to parasite infection. This observation that poor-condition hosts often suffer more from parasite infection compared to healthy hosts has led to the assumption that parasite productivity is higher in poor-condition hosts. However, the ubiquity of this negative relationship between host condition and parasite fitness is unknown. Moreover, examining the effect of environmental variation on parasite fitness has been largely overlooked in the host-parasite literature. Here we investigate the relationship between parasite fitness and host condition by using a laboratory experiment with the cabbage looper Trichoplusia ni and its viral pathogen, AcMNPV, and by surveying published host-parasite literature. Our experiments demonstrated that virus productivity was positively correlated with host food availability and the literature survey revealed both positive and negative relationships between host condition and parasite fitness. Together these data demonstrate that contrary to previous assumptions, parasite fitness can be positively or negatively correlated with host fitness. We discuss the significance of these findings for host-parasite population biology.     

Proteophosophoglycans Regurgitated by Leishmania-Infected Sand Flies Target the L-Arginine Metabolism of Host Macrophages to Promote Parasite Survival

All natural Leishmania infections start in the skin; however, little is known of the contribution made by the sand fly vector to the earliest events in mammalian infection, especially in inflamed skin that can rapidly kill invading parasites. During transmission sand flies regurgitate a proteophosphoglycan gel synthesized by the parasites inside the fly midgut, termed promastigote secretory gel (PSG). Regurgitated PSG can exacerbate cutaneous leishmaniasis. Here, we show that the amount of Leishmania mexicana PSG regurgitated by Lutzomyia longipalpis sand flies is proportional to the size of its original midgut infection and the number of parasites transmitted. Furthermore, PSG could exacerbate cutaneous L. mexicana infection for a wide range of doses (10–10,000 parasites) and enhance infection by as early as 48 hours in inflamed dermal air pouches. This early exacerbation was attributed to two fundamental properties of PSG: Firstly, PSG powerfully recruited macrophages to the dermal site of infection within 24 hours. Secondly, PSG enhanced alternative activation and arginase activity of host macrophages, thereby increasing L-arginine catabolism and the synthesis of polyamines essential for intracellular parasite growth. The increase in arginase activity promoted the intracellular growth of L. mexicana within classically activated macrophages, and inhibition of macrophage arginase completely ablated the early exacerbatory properties of PSG in vitro and in vivo. Thus, PSG is an essential component of the infectious sand fly bite for the early establishment of Leishmania in skin, which should be considered when designing and screening therapies against leishmaniasis.