Synthesis of Isozymes of Superoxide Dismutase in Maize Leaves in Response to O3, SO2 and Elevated O2

Matters, G. L. and Scandalios, J. G. 1987. Synthesis of isozymesof superoxide dismutase in maize leaves in response to O₃ SO₂and elevated O₂.—J. exp. Bot 38: 842–852. The activities of the enzymes superoxide dismutase (SOD) andcatalase were determined in maize leaves treated with O₃or SO₂for8 h, or with elevated levels of oxygen for up to 96 h. NeitherO₃nor SO₂significantly increased the levels of superoxide dismutaseor catalase activity. However, after 72 h in an atmosphere containing90% oxygen, superoxide dismutase activity was increased, butnot the activities of catalase, ascorbate pcroxidase, and malatedehydrogenase. Immunological analysis showed that amounts ofthe cytosolic superoxide dismutase isozymes, SOD-2 and SOD-4,were increased by the elevated oxygen but not the chroloplast(SOD-1) or mitochondrial (SOD-3) isozymes. Immunoprecipitationof translation products of leaf polysomes indicated that thehigher levels of SOD-2 and SOD-4 were due to increased amountsof polysome-bound mRNA coding for these proteins. The specificresponse of SOD-2 and SOD-4 to 90% oxygen treatments contrastswith the increase in all SOD isozymes in maize leaves treatedwith the herbicide paraquat. Key words: Air pollutants, maize, oxidative stress, oxygen, superoxide dismutase     

Phosphorus availability and nitrogenase activity in aquatic blue-green algae

Metabolically active phosphorus-starved cultures of blue-green algae assimilate ³²P rapidly in the light and in the dark. The uptake of phosphorus results in a rapid (within 15 min) stimulation in acetylene reduction by Anabaena cylindrica, A. flosaquae, Anabacnopsis circuiaris and Chlorogloea fritschii, with a response being obtained to less than 5 μg/1 of phosphorus. Uptake of phosphorus also causes a rapid increase in respiration in the dark but not in photo respiration, and the size of the cellular ATP pool and the ¹⁴CO₂ fixation rate both increase more slowly. The metabolism of phosphorus-sufficient cells, which assimilate phosphorus more slowly, shows little response when phosphorus is provided. Excess phosphorus is stored in the vegetative cells of blue-green algae as polyphosphate bodies which may form within 60 min of adding phosphorus to phosphorusstarved cells and which serve as a source of phosphorus for the algae when exogenous phosphorus is limiting. Preliminary results from Scottish waters suggest that urban effluents are important sources of available-phosphorus for algal growth and that the levels entering fresh waters from agricultural land are, per unit volume, lower. In both types of water the levels of available-phosphorus are rather similar to the levels of orthophosphate-phosphorus present. Most detergents tested serve as a source of phosphorus for nitrogen-fixing blue-green algae and cause a rapid stimulation in reduction when added to phosphorus-starved cultures. Of the detergents assayed, the biological types were richest in available phosphorus. The addition of detergents may result in a rapid increase in number of polyphosphate bodies present in the algae. Detergents in general also contain an inhibitor of algal metabolism. Whether a stimu-lation or an inhibition occurs depends on the quantities of detergent added and on whether or not the alga is phosphorus-deficient.     

A Dynamic Growth Model of Vegetative Soya Bean Plants: Model Structure and Behaviour under Varying Root Temperature and Nitrogen Concentration

A differential equation model of vegetative growth of the soyabean plant (Glycine max (L.) Merrill cv. ‘Ransom’)was developed to account for plant growth in a phytotron systemunder variation of root temperature and nitrogen concentrationin nutrient solution. The model was tested by comparing modeloutputs with data from four different experiments. Model predictionsagreed fairly well with measured plant performance over a widerange of root temperatures and over a range of nitrogen concentrationsin nutrient solution between 0.5 and 10.0 mmol in the phytotron environment. Sensitivity analyses revealedthat the model was most sensitive to changes in parameters relatingto carbohydrate concentration in the plant and nitrogen uptakerate. Key words: Glycine max (L.) Merrill, dry matter, nitrogen uptake, partitioning, photosynthesis, respiration, sensitivity analysis     

Population Interactions and the Determinants of Population Size

Abstract The flux of individuals within populations is dependent upon six controlling processes: the intrinsic rate of increase of the plant, intraspecific competition for resources, interspecific competition, natural enemies, mutualisms and refuge effects such as the immigration of seeds from other populations. Although population interactions are generally believed to play a major role in determining the flux of individuals within populations, little attempt has been made to quantify the strength of these interactions and their role in the dynamics of populations. In this paper we examine the role of competition, herbivory and mutualistic interactions in determining the dynamics of a range of annual plant species. Firstly, it is shown that the dynamics of three weed species ( Bromus sterilis, Galium aparine, Papaver rhoeas ) in an experimental community in an arable cropping system of winter wheat are determined primarily by the rapid population growth of B. sterilis . Interactions between the species play a minor part in the dynamics of the system. Secondly, it is shown that current levels of grazing by overwintering populations of brent geese have a minor impact on the abundance of Salicornia europaea , but that increased grazing has the potential to reduce abundance and increase the instability of S. europaea populations. This is a consequence of the aggregative response of the geese, which results in an increasing proportion of the seeds of S. europaea being eaten as plant density increases. Thirdly, it is shown that there is a complex interaction between root pathogenic and arbuscular mycorrhizal fungi in natural field populations of Vulpia ciliata and that the benefit of mycorrhizal fungi to the plant is in providing protection against pathogens.