INFLUENCE OF ZINC ON PERIPHYTIC COMMUNITIES

The glass-slide technique was used in a 14-week study to show the effects of 4 concentrations of zinc on periphytic communities in 4 outdoor canals supplied with running pond water containing its natural biota. No species was found that could be considered an indicator of zinc. The effect of adding 1 mg/liter or more of zinc was to reduce the number of dominant species. A geometric regression of the average number of dominant algal species was found beginning with the control, with no added zinc, and proceeding from that to the largest concentration of zinc. A relatively large concentration of zinc resulted in comparatively low biotic diversity. Fungi and slime-forming bacteria produced a large standing crop in the largest zinc concentration, apparently by digesting the killed incoming phytoplankters that were used as their food.     

INFLUENCE OF IRRADIANCE ON THE FATTY ACID COMPOSITION OF PHYTOPLANKTON1

Eight species of marine phytoplankton commonly used in aquaculture were grown under a range of photon flux densities (PEDs) and analyzed for their fatty acid (FA) composition. Fatty and composition changed considerably at different PFDs although no consistent correlation between the relative proportion of a single FA and μ or chl a · cell^?1 was apparent. Within an individual species the percentage of certain fatty acids covaried with PFDs, growth rate and/or chl a · cell^?1. The light conditions which produced the greatest proportion of the essential fatty acids was species specific. Eicosapentaenoic acid. 20:5ω3 increased from 6.1% to 15.5% of the total fatty acids of Chaetoceros simplex Ostenfield grown at PFDs which decreased from 225 μE · m^?2· s^?1 to 6 μE · m^?2· s^?1, respectively. Most species had their greatest proportion of 20: 5ω3 at low levels of irradiance. Conversely, docosahexaenoic acid, 22:6ω3, decreased from 9.7% to 3.6% of the total fatty acids in Pavlova lutheri Droop as PFD decreased. The percentage of 22:6ω3 generally decreased with decreasing irradiances. In all diatoms the percentage of 16:0 was significantly correlated with PFD, and in three of five diatoms, with growth rate (μ). Results suggest that fatty acid composition is a highly dynamic component of cellular physiology, which responds significantly to variation in PFD.     

THE INFLUENCE OF PRECURSOR POOL SIZE ON MITOCHONDRIAL COMPOSITION IN NEUROSPORA CRASSA

The chemical composition of mitochondria obtained from exponentially growing Neurospora can be varied by addition of choline or amino acids to the culture medium. The variation affects the phospholipid to protein ratio, and the density of mitochondria as determined by isopycnic centrifugation in sucrose gradients. These variations have been observed in biochemical mutant strains as well as wild type cultures. In a choline-requiring strain, two levels of choline supplementation to the medium have been defined: a low choline concentration just adequate to support maximal logarithmic growth, and a high choline concentration which permits maximal incorporation of radioactive choline into cellular lipids. Mitochondria isolated from cultures growing at the low choline concentration have one-half the phospholipid to protein ratio of those from high choline cultures, and their density is significantly higher. Artificial mixtures of the two types of mitochondria can be resolved into two populations by isopycnic centrifugation. The concentration of cytochromes (measured by mitochondrial difference spectra) and of malate and succinate dehydrogenases (measured by enzyme activity) were the same in both types of mitochondria, on a protein basis. The results suggest that during growth of the mitochondrial mass, the incorporation of phospholipid and protein components can vary independently. Direct kinetic measurements did indeed show that choline, added to a culture growing at low choline concentration, was incorporated into mitochondrial lipids at a rate faster than the incorporation of protein. The mitochondrial phospholipid to protein ratio can also be influenced by the level of leucine supplementation to a leucine-requiring mutant, so that with leucine concentrations above those required for maximal exponential growth, mitochondria of increasing density and decreasing phospholipid to protein ratio are produced. Additions of choline or amino acids to the minimal medium of wild type cultures influence mitochondrial composition in a manner directly comparable to that observed in biochemical mutant strains. The results suggest that mitochondrial composition, in general, is determined by rates of incorporation of the two major components, phospholipid and protein; that these rates can vary independently in response to precursor concentration in the culture medium; and that they normally operate at a precursor (substrate) concentration below saturation level.     

斑管巢蛛对柑桔害虫的捕食作用研究

在系统观察桔园蜘蛛优势种斑管巢蛛与主要柑桔害虫自然种群数量季节消长相关关系的基础上,采用血清学方法检测了蜘蛛对柑桔害虫的自然控制作用。在不同实验条件下测定了斑管巢蛛对柑桔害虫的捕食量、功能反应,以及相互干扰、温度对蜘蛛捕食作用的影响,建立了模拟模型。     

利它素对中华通草蛉不同龄期幼虫捕食行为的影响

本文测定了棉蚜及棉花嫩梢不同溶剂提取液对中华通草蛉捕食行为的影响,结果表明,棉花受害嫩梢及未受害嫩梢提取液对中华通草蛉幼虫捕食行为无明显影响;棉蚜虫体浆液、棉蚜水提液,均含有很强的利它素活性物质,而棉蚜无水乙醇提取液利它素活性物质含量甚微,中华通草蛉各龄幼虫对棉蚜水提液均表现有明显的滞留和调转行为.     

THE INFLUENCE OF X-RAYS ON THE PROPERTIES OF BLOOD

When rabbits are exposed to x-radiation as described, there results a definite change in the See PDF for Equation ratio of their plasma. This change is evidently one which defines a state of uncompensated alkali excess. The time required for a maximum change in the chemical reaction is the same as that required for a maximum change in the decrease of leucocytes. Sodium bicarbonate injected into the peritoneal cavity is followed by results identical with those observed following exposure to x-rays. The maximum changes occur in a shorter time following bicarbonate injection, but the relation between chemical and morphological changes are the same. We consider this analogy to be an important one in that it is suggestive of a relationship between the effect of salt and the effect of x-rays.