The synergistic tumoricidal activity of anticancer drugs and oxidative burst-triggered macrophages

Summary The anticancer drugs adriamycin (ADR) and actinomycin D (AMD) were tested for their effect on the oxidative burst (OB) of mouse peritoneal macrophages (MPM) and on the killing of tumor cells by OB-stimulated MPM. The oxidative burst of MPM determined by hydrogen peroxide (H₂O₂) production was severely impaired by ADR (10 g/ml) and AMD (40 g/ml) after a 1 h treatment and by lower concentrations of the drugs following a 24 h treatment. The toxicity of the drugs against MPM was comparable to their effect on EL4 cells. Pretreatment of EL4 and TLX-9 tumor cells with sublethal amounts of ADR for 4 h rendered the cells sensitive to the cytotoxic effect of OB-stimulated MPM which were otherwise unable to kill these cells. It seems that anticancer drugs and OB-stimulated macrophages can cooperate in the destruction of tumor cells in vitro.     

Induction of Near-vessellessness in Ephedra campylopoda C. A. Mey.

Near-vessellessness was induced in the secondary xylem of Ephedracampylopoda C. A. Mey. by mechanical bark blocking or by wounding.Both treatments resulted in regions of near-vesselless xylem.Xylem formed after the mechanical bark blocking also had regionsin which the orientation of the axial components was changedfrom axial to lateral. Since either mechanical arrest of phloemand cambial transport or wounding of the cambium almost stoppeddifferentiation into vessels, and instead induced differentiationinto tracheids, it seems that the developmental signal for tracheiddifferentiation is not the same as that for vessels. The possibleregulation of near-vessellessness in Ephedra is discussed.Copyright1994, 1999 Academic Press Differentiation, Ephedra campylopoda, near-vessellessness, wood formation, xylem     

The Potential Anti-Herbivory Role of Microorganisms on Plant Thorns

Thorns, spines and prickles are some of the anti-herbivore defenses that plants have evolved. They were recently found to be commonly aposematic (warning coloration). However, the physical anti-herbivore defense executed by these sharp structures seems to be only the tip of the iceberg. We show that thorns of various plant species commonly harbor an array of aerobic and anaerobic pathogenic bacteria including Clostridium perfringens the causative agent of the life-threatening gas gangrene, Bacillus anthracis, and Pantoea agglomerans. Septic inflammation caused by plant thorn injury can result not only from bacteria. Medical literature indicates that thorns, spines or prickles also introduce pathogenic fungi into animals or humans. Dermatophytes that cause subcutaneous mycoses are unable to penetrate the skin and must be introduced into the subcutaneous tissue by a puncture wound. The common microorganism-thorn combinations seem to have been an important contributor to the fact that so many plant thorns are aposematically colored, as a case of convergent evolution of aposematism in these organisms.Key Words: aposematism, herbivory, pathogen, spine, thorn, bacillus anthracis, clostridium perfringens, sporotrichosis, Mycetoma, subcutaneous mycotic disease     

Plant coloration undermines herbivorous insect camouflage

The main point of our hypothesis "coloration undermines camouflage" is that many color patterns in plants undermine the camouflage of invertebrate herbivores, especially insects, thus exposing them to predation and causing them to avoid plant organs with unsuitable coloration, to the benefit of the plants. This is a common case of "the enemy of my enemy is my friend" and a visual parallel of the chemical signals that plants emit to call wasps when attacked by caterpillars. Moreover, this is also a common natural version of the well-known case of industrial melanism, which illustrates the great importance of plant-based camouflage for herbivorous insects and can serve as an independent test for our hypothesis. We claim that the enormous variations in coloration of leaves, petioles and stems as well as of flowers and fruits undermine the camouflage of invertebrate herbivores, especially insects. We assume that the same principle might operate in certain animal-parasite interactions. Our hypothesis, however, does not contrast or exclude other previous or future explanations of specific types of plant coloration. Traits such as coloration that have more than one type of benefit may be selected for by several agents and evolve more rapidly than ones with a single type of advantage.     

The Distance to Which Wound Effects Influence the Structure of Secondary Xylem of Decapitated Pinus pinea

Decapitation of stems of annuals and trees for the study of vascular and fiber differentiation with or without hormonal application is a common procedure. There is controversy about whether wound effects play a role in such experiments, and to what distance from the point of decapitation. To examine this question, the distance from the point of decapitation at which apparent wound effects are obvious developmentally, was studied in decapitated 4-year-old Pinus pinea plants. The wound effects just below the cut included differentiation of many traumatic resin ducts, a parenchyma band instead of tracheids, more tracheid files, and a higher proportion of late wood. The increase in the number of resin ducts was still considerable and statistically significant 10 cm below the point of decapitation compared with the nondecapitated control. These results indicate that in pines, wound effects in the first 5 cm below the decapitation point (a common point for tissue examination) cannot be ignored in experiments on the regulation of vascular differentiation.     

Plant biological warfare: thorns inject pathogenic bacteria into herbivores

Thorns, spines and prickles are among the rich arsenal of antiherbivore defence mechanisms that plants have evolved. Many of these thorns are aposematic, that is, marked by various types of warning coloration. This coloration was recently proposed to deter large herbivores. Yet, the mechanical defence provided by thorns against large herbivores might be only the tip of the iceberg in a much more complicated story. Here we present evidence that thorns harbour an array of pathogenic bacteria that are much more dangerous to herbivores than the painful mechanical wounding by the thorns. Pathogenic bacteria like Clostridium perfringens, the causative agent of the life-threatening gas gangrene, and others, were isolated and identified from date palm (with green-yellow-black aposematic spines) and common hawthorn (with red aposematic thorns). These thorn-inhabiting bacteria have a considerable potential role in antiherbivory, and may have uniquely contributed to the common evolution of aposematism (warning coloration) in thorny plants.