INTRA- AND INTERSPECIFIC VARIATIONS IN CALCIUM CONTENT OF FRESHWATER MOLLUSCA IN RELATION TO CALCIUM CONTENT OF THE WATER

Analyses of calcium content of molluscs collected from 53 freshwaterhabitats on a naturally occurring calcium gradient between theCanadian Shield and limestone formations in southern Ontarioshowed both intraspecific and interspecific variations in relationto pH, total alkalinity, total hardness and calcium hardnessof the water. The calcium content of individuals is relatedto the calcium concentration of the water for only about halfof the species analysed. Two species (Sphaerium rhomboideumand Sphaerium simile) showed negative correlations, while six(Cincinnatia cincinnatiensis, Pisidium casertanum, Pisidiumcompressum, Sphaerium striatinum, Anodonta grandis grandis,and Elliptio complanata showed positive correlations beteencalcium content of individuals and environmental calcium content.In general, species associated with the sediments (e.g. bivalves)showed better calcium concentrations than did species associatedwith macrophytes (e.g. gastropods). (Received 12 July 1982;     

MESOCOTYL ROOT FORMATION IN ECHINOCHLOA PHYLLOPOGON (POACEAE) IN RELATION TO ROOT ZONE AERATION

Echinochloa phyllopogon was grown hydroponically under four root zone gassing treatments to determine aeration effects on the growth and development of the plant root system. Although mesocotyl growth and the number of nodal roots were unaffected by the treatments, other aspects of plant growth were altered. Shoot growth was reduced by hypoxic (5 kPa partial pressure O₂ in nitrogen gas) and anoxic conditions (O₂ free nitrogen gas), but not by ethylene (0.1 ppm in air). Seminal root growth was unaffected by hypoxia or ethylene treatments, but was reduced under anoxia. Hypoxic environments stimulated the emergence of roots along the length of the mesocotyl when compared to aerobic controls; anoxic and ethylene treatments had no significant effects. Mesocotyl roots elongated from primordia that were produced de novo in response to the hypoxic treatment. Under hypoxic conditions, aerenchyma was present in the cortex of nodal roots and to a lesser extent in seminal roots, but mesocotyl roots were devoid of aerenchyma under these conditions. The results are compared with the literature concerning flooding and aeration effects on growth and development in other species.     

CARDIOLIPIN CONTENT OF WILD TYPE AND MUTANT YEASTS IN RELATION TO MITOCHONDRIAL FUNCTION AND DEVELOPMENT

The phospholipid composition of various strains of the yeast, Saccharomyces cerevisiae, and several of their derived mitochondrial mutants grown under conditions designed to induce variations in the complement of mitochondrial membranes has been examined. Wild type and petite (cytoplasmic respiratory deficient) yeasts were fractionated into various subcellular fractions, which were monitored by electron microscopy and analyzed for cytochrome oxidase (in wild type) and phospholipid composition. 90% or more of the phospholipid, cardiolipin was found in the mitochondrial membranes of wild type and petite yeast. Cardiolipin content differed markedly under various growth conditions. Stationary yeast grown in glucose had better developed mitochondria and more cardiolipin than repressed log phase yeast. Aerobic yeast contained more cardiolipin than anaerobic yeast. Respiration-deficient cytoplasmic mitochondrial mutants, both suppressive and neutral, contained less cardiolipin than corresponding wild types. A chromosomal mutant lacking respiratory function had normal cardiolipin content. Log phase cells grown in galactose and lactate, which do not readily repress the development of mitochondrial membranes, contained as much cardiolipin as stationary phase cells grown in glucose. Cytoplasmic mitochondrial mutants respond to changes in the glucose concentration of the growth medium by variations in their cardiolipin content in the same way as wild type yeast does under similar growth conditions. It is concluded that cardiolipin content of yeast is correlated with, and is a good indicator of, the state of development of mitochondrial membrane.     

水生维管束植物对水体铅污染的反应、抗性和净化作用

重金属铅污染环境的一个主要方面是对水体的污染。主要的污染源是某些矿山(如铅锌矿等)、有色金属冶炼厂、铅制品加工厂等的废水和废气以及汽车尾气等。按金属的生物效应来分类,铅为有毒金属。大量的铅直接或者通过食物链的富集进入人体会造成严重的危害。目前,国内外对于铅污染的环境对陆生植物的影响以及陆生植物对铅污染的反应开展了一些     

荔枝胚珠中多胺含量变化与胚胎发育的关系

荔枝胚胎发育与胚珠中３种多胺（ＰＡｓ）含量及其比例变化关系密切。试验结果表明：正常发育的胚珠中腐胺（Ｐｕｔ）、亚精胺（Ｓｐｄ）和精胺（Ｓｐｍ）的含量在胚胎发育的各个阶段均高于败育胚珠,并在花后７ｄ即达到最高值,其中Ｐｕｔ的含量最高,随后都呈下降趋势。但正常胚珠中Ｓｐｍ含量在花后２２至３１ｄ（球形胚至心形胚发育阶段）均有所回升,而败育胚珠无此现象。败育胚珠中的Ｓｐｄ和Ｓｐｍ在胚胎败育期的下降速度显著     

CHANGES IN WATER ECONOMY IN RELATION TO ANATOMICAL AND MORPHOLOGICAL CHARACTERISTICS DURING THALLUS DEVELOPMENT INPARMELIA ACETABULUM

The influence on uptake and water loss of the structural changes experienced by Parmelia acetabulum during thallus development were investigated. Small specimens were characterized by flat lobes and a thin thallus and cortex. Large specimens appeared strongly rugose, imbricate and irregularly folded, and had a significantly thicker cortex and medulla than small thalli. Maximum water storage capacity did not differ between large and small thalli, although water retention was much higher in large thalli, presumably due to the interaction of structural characteristics and a higher boundary layer resistance. This translated into a longer duration of the period of thallus hydration in large thalli compared to small thalli. Incubation of thalli in water-vapour-saturated atmospheres induced full recovery of photosynthetic electron transport to the values before desiccation in small thalli but only induced a partial recovery in large thalli. The close correlation between photosynthetic electron transport and net photosynthesis during desiccation found in this species suggested that carbon-fixation activity could be regained to a larger extent by incubation of thalli in water vapour in small compared to large thalli. The higher ability for water vapour uptake of small thalli might allow them to efficiently use small amounts of intermittently available water or periods of high relative humidity. The significance of this differential ability to utilize water is discussed with regard to the known ecological preferences of the species.