Well‐lighted plants may contain considerable amounts of ascorbic acid (AA) particularly in their chloroplasts. AA is known to be a strong reductant which fulfils several functions in photosynthesis. AA may also influence detoxification of polluted plants, e.g. by reducing SO2. AA contents of forest tree species were distinctly decreased by shading, particularly in light demanding species. Continued SO2 fumigation depressed AA contents long before visible symptoms of injury appeared. AA thus deserves more attention in physiological air pollution research.
The detection of hidden F‐injury of forest trees by a simple colorimetric determination of peroxidase actívity. The paper describes a simple routine method for determining colorimetrically peroxidase activity (p. a.) in foliage of forest tree species, including conifers. The effect of factors such as foliage age, F Content, external F dust, necrosis etc. on p. a. is investigated. Analyses of plants exposed at different distances to F exhalates of an aluminum plant show that with decreasing distance F content and p. a. increase. P. a. thus is an indicator of air pollution effects on tree physiology even in the range where no visible symptoms of injury occur.
The detection of winter SO2 pollution effects on young spruce. A comparison of three methods. The suitability, sensitivity and tediousness of three methods (turbidity-test, peroxidase activity, buffering capacity) were compared for detecting the effect of SO2 pollution in winter on spruce seedlings. Buffering capacity failed to detect a difference between controls and fumigated trees. Turbidity test and peroxidase activity yielded statistically significant differences. The turbidity test is less tedious but also less sensitive than peroxidase activity and its use is restricted to conifers.
Two insecticides, acephate or azadirachtin, were added to tissue culture media to determine their effectiveness in controlling onion thrips (Thrips tabaci Lindeman.) and to determine if these insecticides could damage the plant shoot cultures. To test for insecticide phytotoxicity, microshoots from European birch (Betula pendula), American elm (Ulmus americana), `Pink Arola' chrysanthemum (Dendranthema grandiflora), `America' rhododendron (Rhododendron catawbiense), `Golden Emblem' rose (Rosa hybrida), and `Gala' apple (Malus domestica) were placed in 130-ml baby food jars containing 25 ml of medium supplemented with 6.5, 13, or 26 mg/l Orthene® (contained acephate) or 0.55, 1.1, or 2.2 ml/l Azatin® (contained azadirachtin). Control jars lacked insecticide. To test for thrips control, 13 mg/l Orthene® or 0.55 ml/l Azatin® was added to Murashige and Skoog medium, and 10 thrips were placed on `Gala' apple microshoots in each jar. Jars were sealed with plastic wrap. In both studies, microshoot dry weight and heights were determined. In the second study, the total number of thrips per jar was also determined 3 weeks after inoculation. Microshoots on Orthene®-treated media lacked phytotoxicity symptoms, regardless of the concentration used. In contrast, Azatin® hindered plant growth, decreasing shoot height or dry weight by up to 85% depending on the species. Both insecticides prevented thrips populations from increasing, since less than 10 thrips were found in jars with insecticide-treated medium. Control jars, however, contained an average of almost 70 thrips per jar. This study demonstrated that both Orthene® and Azatin® were effective for eradicating thrips from plant tissue cultures, but Orthene® should probably be used because Azatin® was phytotoxic to all species tested.
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