SOME EFFECTS OF HOST NUTRITION ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION BY CERTAIN VIRUSES

Fertilizer treatments that greatly influenced the growth of tobacco and potato plants in pots had little effect on the number that became infected with potato virus Y when the plants were colonized by equal numbers of infective aphids, though the number was slightly decreased by nitrogen and increased by phosphorus.
The number of local lesions produced on leaves of tobacco and Nicotiana glutinosa by tomato aucuba mosaic and tobacco mosaic viruses was increased by additions of both nitrogen and phosphorus, provided that these also increased growth. The predominant effect of both nutrients in increasing susceptibility was indirect by increasing plant size, but over certain critical ranges both elements also increased the numbers of lesions produced per unit leaf area. Conditions of maximum susceptibility approximated closely to those producing optimal growth, and susceptibility, whether measured by lesions per half-leaf or per unit area, was decreased by a deficiency or excess of either element. Sometimes the addition of nitrogen reduced susceptibility when still increasing plant growth.     

THE EFFECT OF DARKENING ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION WITH VIRUSES

The susceptibility of French bean plants to infection by the Rothamsted strain of tobacco necrosis virus as measured by the local-lesion method is increased by a rise in temperature and usually by darkening the plant before inoculation. If part only of a leaf is darkened, that part becomes more susceptible. Plants in full light also become more susceptible if carbon dioxide is removed from the air, whereas the susceptibility of plants in the dark is not altered.
Darkening leaves decreases their content of malic, fumaric, succinic and glycolic acids and increases the content of citric acid; the content of oxalic and malonic acids remains constant. These changes occurred in winter and summer and whether or not darkening increased susceptibility.
The effect on susceptibility of individual acids infiltrated into the leaf was measured in leaves kept in the light or in the dark before inoculation. None of the acids used produced any large change in susceptibility.     

SOME EFFECTS OF HIGH TEMPERATURE ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION WITH VIRUSES

When plants were kept at 36°C. for some time before inoculation, their susceptibility to infection by five mechanically transmissible viruses was greatly increased. When kept at 36° after inoculation, fewer local lesions were produced than at lower temperatures, but the effects of the post-inoculation treatment differed with different viruses. Tomato spotted wilt and tobacco mosaic viruses multiply in plants at 36°, and the post-inoculation treatment reduced the local lesions they caused to numbers that varied between 10 and 90% of the control; these two viruses also have large thermal coefficients of heat inactivation. By contrast, tobacco necrosis, tomato bushy stunt and cucumber mosaic viruses, were much affected by post-inoculation treatment, lesion formation being completely prevented by exposure to 36° for a day or more. These three viruses appear not to multiply in plants at 36°, and although they have high thermal inactivation points, they have small temperature coefficients of thermal inactivation.
The extent to which lesion formation was affected by pre- or post-inoculation exposure of plants to 36° depended not only on the length of the treatment, but also on the physiological condition of the plants.
The symptoms of infected plants changed considerably if kept at 36°. At 36° Nicotiana glutinosa , inoculated with tobacco mosaic virus, gave chlorotic local lesions instead of necrotic ones, and became systemically infected. When systemically infected plants were brought to ordinary glasshouse temperature, the infected tissues all collapsed and died in a day.     

THE IDENTIFICATION OF CERTAIN VIRUSES FOUND INFECTING LEGUMINOUS PLANTS IN GREAT BRITAIN

In a survey of the virus diseases of leguminous plants in Great Britain, it was not found possible to relate the virus of lettuce mosaic, which Ainsworth & Ogilvie (1939) found able to infect both culinary and sweet peas, to any other virus but, in the course of examining about seventy-five samples of material, a number of different viruses were identified. These, with possibly one exception, appear to have been described in other parts of the world, but the following notes include several new records for this country.     

LIGHT QUALITY AND PHOTOREACTIVATION OF PLANTS AND VIRUSES

Visible light of different spectral regions was tested for its ability to reverse three effects of ultra-violet radiation, namely, injury (glazing) of French bean leaves, increased resistance of French bean leaves to infection by the Rothamsted tobacco necrosis virus, and inactivation of potato virus X. The different spectral regions were obtained with colorimetric filters and the filtered and unfiltered light from fluorescent tubes; all three effects were reversed only by regions of wave-lengths shorter than 4700 Å. Thirty minutes of illumination at 300–380 f.c. gave substantial photo-reactivation, but irradiated potato virus X did not become affected by visible light until 30 min. after tobacco leaves were inoculated.     

INFLUENCE OF LIGHT OF VERY LOW INTENSITY ON PHOTOTROPIC REACTIONS OF ANIMALS

1. The negative phototropism of certain land isopods was investigated over a large range of intensities, especially low ones. The responses were determined quantitatively by measuring the angle through which an animal turned away from a line perpendicular to the rays of light. 2. In the absence of light the undirected movements set up by obscure stimuli were such as to compensate each other statistically, the average path being a movement in the direction in which the animal was headed. 3. Over a large range of intensities (0.0026 m.c. up) the average turning is maximal, about 55° (Oniscus). This maximal response is due to an anatomical peculiarity, in that the carapace cuts off the light on the eye after the animal has turned 50–60°. This peculiarity probably accounts for specific differences among land isopods. Any light, therefore, which is strong enough to turn an animal through this maximal angle in a radial distance of 10 cm. will give results whose mean will be maximal. 4. Below 0.0026 m.c. the amount of angular deflection becomes less and less, in proportion to the logarithm of the intensity, until at 0.00003 m.c. the movements are the same as in darkness. 5. This proportionality between amount of turning and the logarithm of the intensity indicates the photochemical nature of phototropism on the basis of Hecht''s work with Mya. As a result, Loeb''s theory of phototropism may then be stated in the mathematical form See PDF for Equation in which I ₁ and I ₂ are the two intensities, E ₁ and E ₂, their respective effects, and R, the muscular action set up by the difference in photochemical effect on the two sides.     

月光及光照对艾虎活动的影响

采用野外研究与室内研究相结合的方法研究了月光周期和光照对夜行性动物艾虎活动的影响。野外无线电遥测结果表明,艾虎的日活动时间不受月光周期的影响,雌雄艾虎在不同的季节及繁殖期和非繁殖期都有相对稳定的活动时间,其开始活动和结束活动的时间与月光周期和日出、日落都没有明显的相关性。室内模拟研究结果也表明,由于环境条件的变化,艾虎增加了白天的活动时间,但仍然以夜间活动为主,光照强弱对艾虎的活动格局和活动时间没有明显的影响。以上结果表明昼夜变换使艾虎形成了相对稳定的生物种节律,艾虎在取食过程中可能利用洞道等隐蔽场所降低明亮月光期的高捕食风险。     

STUDIES ON LUMINOUS BACTERIA : II. THE INFLUENCE OF TEMPERATURE ON THE INTENSITY OF THE LIGHT OF LUMINOUS BACTERIA.

1. A method has been described whereby the intensity of the light of luminous bacteria may be measured in a quantitative manner. 2. It is pointed out that the temperature coefficients for light intensity do not follow the van''t Hoff rule, but are higher and vary with each 10° temperature interval. 3. From a comparison with other data it is found that the process is not a simple one, but that the observed curve is the resultant of several reactions which proceed simultaneously. 4. The discrepancies in the temperature coefficients in the neighborhood of the "optimum temperature" may be due to a process of coagulation of the colloidal particles of the enzyme. This coagulation will tend to cause a deviation of the curve away from that normal for chemical reactions.