Synergistic effects of nutrients and light favor Nostocales over non-heterocystous cyanobacteria

Blooms of Nostocales (Cyanobacteria) are thought to be invading subtropical and temperate water bodies. According to nutrient stoichiometry and physiological differences between cyanobacterial groups, the replacement of non-heterocystous species by Nostocales is favored when dissolved inorganic nitrogen decreases. However, some studies have shown different trends. We used laboratory bioassays to evaluate the concomitant effects of light and nutrient enrichment on phytoplankton assemblages dominated by non-heterocystous filamentous cyanobacteria. Three nutrient conditions (no addition, addition of phosphate, and addition of nitrate and phosphate) and two light intensities (40 and 80 µmol photon m^?2 s^?1) were assayed. Nostocales replaced or co-dominated with non-heterocystous species in all treatments by the end of the study. The shift in community composition towards Nostocales dominance led to an increase in species richness, which suggests that species with different eco-physiological traits may have differential impacts on diversity. The highest saxitoxin concentrations were measured in no addition treatments, which could link production to nutritional stress. Nostocales featured high phenotypic plasticity in terms of changes in average trichome volume and growth rates. These results help to have a better understanding of the conditions under which Nostocales predominance can occur.     

Sugars in crop plants

We review current knowledge of the most abundant sugars, sucrose, maltose, glucose and fructose, in the world's major crop plants. The sucrose‐accumulating crops, sugar beet and sugar cane, are included, but the main focus of the review is potato and the major cereal crops. The production of sucrose in photosynthesis and the inter‐relationships of sucrose, glucose, fructose and other metabolites in primary carbon metabolism are described, as well as the synthesis of starch, fructan and cell wall polysaccharides and the breakdown of starch to produce maltose. The importance of sugars as hormone‐like signalling molecules is discussed, including the role of another sugar, trehalose, and the trehalose biosynthetic pathway. The Maillard reaction, which occurs between reducing sugars and amino acids during thermal processing, is described because of its importance for colour and flavour in cooked foods. This reaction also leads to the formation of potentially harmful compounds, such as acrylamide, and is attracting increasing attention as food producers and regulators seek to reduce the levels of acrylamide in cooked food. Genetic and environmental factors affecting sugar concentrations are described.     

Salt resistant crop plants

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The circadian clocks of plants and cyanobacteria

Classical research on the circadian rhythms of plants helped to demonstrate that all living organisms utilize circadian clocks to adapt their day–night cycles and that the clock is the basis for photoperiodic time measurements. Molecular models for the circadian oscillator have now been elucidated in Drosophila, Neurospora, mice and cyanobacteria. All share a similar feedback structure, but key proteins in each of the oscillators are different. A plant clock model has yet to be proposed, but clock mutants of Arabidopsis are expected to reveal key proteins in the mechanism. Here we discuss how a self-sustained oscillation is established in eukaryotic and prokaryotic models, and the polyphyletic evolution of these clock systems.     

Microbial inoculation of crop plants

Book Review

Microbial inoculation of crop plantsR. Campbell and R.M. MacDonald (Eds.), Special publication of the Society for General Microbiology, Volume 25. IRL Press, 1989. xi+118 pages. £40. ISBN 0-19-963016-X     

Glycerol concentrations in crop plants

A procedure has been developed for preparation of plant extracts for quantitation of their glycerol content using high performance liquid chromatography or enzymatic analysis. Fifteen crop plants grown under field conditions had leaf concentrations of glycerol between 10 and 39 μg/g wt weight of tissue. Approximately 12 h after relatively heavy rains leaves of maize, sugar beet, soybean, bean, pumpkin and alfalfa had several fold increases in concentrations of leaf glycerol. When barley plants were made anaerobic for 24 h, large increases in leaf glycerol concentrations were observed. It is proposed that part of the glycerol observed in anaerobic plants comes from glycerol synthesis in the root and transport to the leaves and part is produced in the leaves.     

Senescence and ageing in plants and cyanobacteria

This article is an introductory synopsis of the papers on senescence and ageing, presented in this issue of Physiologia Plantarum. The major results of the individual articles have been put into contiguity and are briefly reviewed in the light of the literature. Genetically controlled processes and stochastic reactions closely interact in the course of ageing of an individual. This holds for the cells and tissues of green plants as well as for the strongly specialized heterocysts of filamentous cyanobacteria.     

Marker assisted selection in crop plants

Genetic mapping of major genes and quantitative traits loci (QTLs) for many important agricultural traits is increasing the integration of biotechnology with the conventional breeding process. Exploitation of the information derived from the map position of traits with agronomical importance and of the linked molecular markers, can be achieved through marker assisted selection (MAS) of the traits during the breeding process. However, empirical applications of this procedure have shown that the success of MAS depends upon several factors, including the genetic base of the trait, the degree of the association between the molecular marker and the target gene, the number of individuals that can be analyzed and the genetic background in which the target gene has to be transferred. MAS for simply inherited traits is gaining increasing importance in breeding programs, allowing an acceleration of the breeding process. Traits related to disease resistance to pathogens and to the quality of some crop products are offering some important examples of a possible routinary application of MAS. For more complex traits, like yield and abiotic stress tolerance, a number of constraints have determined severe limitations on an efficient utilization of MAS in plant breeding, even if there are a few successful applications in improving quantitative traits. Recent advances in genotyping technologies together with comparative and functional genomic approaches are providing useful tools for the selection of genotypes with superior agronomical performancies.     

Anatomical anomalies in crop formation plants

Crop formations consist of geometrically organized regions ranging from 2 to 80 m diameter, in which the plants (primarily grain crops) are flattened in a horizontal position. Plants from crop formations display anatomical alterations which cannot be accounted for by assuming the formations are hoaxes. Near the soil surface the curved stems often form complex swirls with 'vortex' type patterns. In the present paper, evidence is presented which indicates that structural and cellular alterations take place in plants exposed within the confines of the 'circle' type formations, differences which were determined to be statistically significant when compared with control plants taken outside the formations. These transformations were manifested at the macroscopic-level as abnormal nodal swelling, gross malformations during embryogenesis. and charred epidermal tissue. Significant changes in seed germination and development were found, and at the microscopic level differences were observed in cell wall pit structures. Affected plants also have characteristics suggesting the involvement of transient high temperatures.