The large-scale organization of metabolic networks

A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

Microbes play key geoactive roles in the biosphere, particularly in the areas of element biotransformations and biogeochemical cycling, metal and mineral transformations, decomposition, bioweathering, and soil and sediment formation. All kinds of microbes, including prokaryotes and eukaryotes and their symbiotic associations with each other and 'higher organisms', can contribute actively to geological phenomena, and central to many such geomicrobial processes are transformations of metals and minerals. Microbes have a variety of properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Such mechanisms are important components of natural biogeochemical cycles for metals as well as associated elements in biomass, soil, rocks and minerals, e.g. sulfur and phosphorus, and metalloids, actinides and metal radionuclides. Apart from being important in natural biosphere processes, metal and mineral transformations can have beneficial or detrimental consequences in a human context. Bioremediation is the application of biological systems to the clean-up of organic and inorganic pollution, with bacteria and fungi being the most important organisms for reclamation, immobilization or detoxification of metallic and radionuclide pollutants. Some biominerals or metallic elements deposited by microbes have catalytic and other properties in nanoparticle, crystalline or colloidal forms, and these are relevant to the development of novel biomaterials for technological and antimicrobial purposes. On the negative side, metal and mineral transformations by microbes may result in spoilage and destruction of natural and synthetic materials, rock and mineral-based building materials (e.g. concrete), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment, all with immense social and economic consequences. The ubiquity and importance of microbes in biosphere processes make geomicrobiology one of the most important concepts within microbiology, and one requiring an interdisciplinary approach to define environmental and applied significance and underpin exploitation in biotechnology.

http://dzumenvis.nic.in/Physiology/pdf/Metals,%20minerals%20and%20microbes.pdf

Metals, minerals and microbes: geomicrobiology and bioremediation

As the result of intensive research and breeding efforts over the last 20 years, the yield potential and yield quality of cereals have been greatly improved. Nowadays, yield safety has gained more importance because of the forecasted climatic changes. Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. Yield safety can only be improved if future breeding attempts will be based on the valuable new knowledge acquired on the processes determining plant development and its responses to stress. Plant stress responses are very complex. Interactions between plant structure, function and the environment need to be investigated at various phases of plant development at the organismal, cellular as well as molecular levels in order to obtain a full picture. The results achieved so far in this field indicate that various plant organs, in a definite hierarchy and in interaction with each other, are involved in determining crop yield under stress. Here we attempt to summarize the currently available information on cereal reproduction under drought and heat stress and to give an outlook towards potential strategies to improve yield safety in cereals.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2007.01727.x

The effect of drought and heat stress on reproductive processes in cereals.

1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom: CONVOLVULACEÆ

It appears that the tapetum is universally present in land plants, even though it is sometimes difficult to recognize, because it serves mostly as a tissue for meiocyte/spore nutrition. In addition to this main function, the tapetum has other functions, namely the production of the locular fluid, the production and release of callase, the conveying of P.A.S. positive material towards the loculus, the formation of exine precursors, viscin threads and orbicules (= Ubisch bodies), the production of sporophytic proteins and enzymes, and of pollenkitt/tryphine. Not all these functions are present in all land plants:Embryophyta. Two main tapetal types are usually distinguished in theSpermatophyta: the secretory or parietal type and the amoeboid or periplasmodial type; in lower groups, however, other types may be recognized, with greater or lesser differences. A hypothetical phylogenesis of the tapetum is proposed on the basis of its morphological appearance and of the nutritional relations with meiocytes/spores. The evolutionary trends of the tapeta tend towards a more and more intimate and increasingly greater contact with the spores/pollen grains. Three evolutionary trends can be recognized: 1) an intrusion of the tapetal cells between the spores, 2) a loss of tapetal cell walls, and 3) increasing nutrition through direct contact in narrow anthers.

The tapetum: its form, function and possible phylogeny in Embryophyta

Contributing Authors. Preface. 1. Introduction E. Pacini, S.W. Nicolson. 1.1 Evolutionary origins. 1.2 Secretions analogous to nectar. 1.3 Floral and extrafloral nectarines. 1.4 Nectar components. 1.5 Organization of this volume. 2. A Systematic Survey of Floral Nectaries G. Bernardello. 2.1 Introduction. 2.2 Nectaries in gymnosperms. 2.3 Nectaries in angiosperms. 2.3.1 Diversity. 2.3.1.1 Nectar presentation. 2.3.1.2 Structure. 2.3.1.3 Fate. 2.3.1.4 Symmetry. 2.3.1.5 Number. 2.3.1.6 Colour. 2.3.2 Factors influencing nectary diversity. 2.3.3 Basic types of floral nectarines. 2.3.4 Nectariferous spurs. 2.3.5 Patterns of variability in nectarines. 2.3.5.1 Asteraceae. 2.3.5.2 Brassicaceae. 2.3.5.3 Cucurbitaceae. 2.3.5.4 Euphorbiaceae. 2.3.5.5 Ranunculaceae. 2.3.5.6 Solanaceae. 2.3.6 Nectaries and deceit pollination. 2.3.6.1 Apocynaceae. 2.3.6.2 Bignoniaceae. 2.3.6.3 Orchidaceae. 2.3.7 Relictual nectarines in anemophilous species. 2.3.8 Distribution of nectary types. 2.3.8.1 Early-branching lineages. 2.3.8.2 Magnoliids. 2.3.8.3 Early-branching monocots. 2.3.8.4 Monocots. 2.3.8.5 Commelinids. 2.3.8.6 Ceratophyllales. 2.3.8.7 Eudicots. 2.3.8.8 Core Eudicots. 2.3.8.9 Rosids. 2.3.8.10 Eurosids I. 2.3.8.11 Eurosids II. 2.3.8.12 Asterids. 2.3.8.13 Euasterids I. 2.3.8.14 Euasterids II. 2.3.9 Evolutionary trends. 3. Nectary Structure and Ultrastructure M. Nepi. 3.1 Introduction. 3.2 Nectary structure and ultrastructure. 3.2.1 Epidermis. 3.2.1.1 Secretory trichomes. 3.2.1.2 Nectary-modified stomata. 3.2.2 Nectary parenchyma. 3.2.2.1 Patterns of plastid development in nectary parenchyma cells. 3.2.3 Subnectary parenchyma. 3.2.4 Nectary vasculature. 3.3 Gynopleural (septal) nectarines. 3.4 Extrafloral nectarines. 3.5 Nectary histochemistry. 4. Nectar Production and Presentation E. Pacini, M. Nepi. 4.1 Introduction. 4.2 Nectar secretion mechanism and models of nectary function. 4.3 Dynamics of nectar components. 4.3.1 Nectar reabsortion: resource recovery and homeostasis. 4.3.2 Nectar standing crop. 4.4 The source of nectar components. 4.5 Ecophysiological significance of parenchyma plastids. 4.6 Nectar presentation. 4.6.1 Floral nectarines. 4.6.2 Extrafloral nectarines. 4.7 Fate of nectar and nectarines. 4.8 Variability of nectar characteristics. 4.8.1 Environmental variables. 4.8.2 Intraspecies variability. 4.8.3 Interpopulation differences. 4.8.4 Variability and experimental design. 5. Nectar Chemistry S.W. Nicolson, R.W. Thornburg. 5.1 Introduction. 5.2 Water. 5.2.1 Nectar concentration. 5.2.2 Chemical and microclimatic influences on nectar concentration. 5.2.3 Viscosity and feeding rates. 5.3 Sugars. 5.3.1 Constancy of sugar composition within species. 5.3.2 The use of sugar ratios can be misleading. 5.3.3 Is sugar composition determined by floral visitors or common ancestry? 5.4 Inorganic ions. 5.5 Amino acids. 5.5.1 Non-protein amino acids. 5.5.2 Nectar amino acids are under the control of environmental factors. 5.5.3 Contribution of amino acids to the taste of nectar. 5.6 Proteins. 5.6.1 Proteins in leek nectar. 5.6.2 Nectar redox cycle. 5.7 Other nectar constituents. 5.7.1 Lipids. 5.7.2 Organic acids. 5.7.3 Phenolics. 5.7.4 Alkaloids. 5.7.5 Terpenoids. 5.8 Conclusion. 6. Molecular Biology of the Nicotiana Floral Nectary R.W. Thornburg. 6.1 Introduction. 6.2 The ornamental tobacco nectary. 6.3 Developmental processes. 6.3.1 Origin of the floral nectary. 6.3.2 Conversion of chloroplasts into chromoplasts. 6.3.3 Filling of the nectary. 6.4 Protection of the gynoecium. 6.5 Gene expression. 6.5.1 Macroarray analysis indentifies defence genes. 6.5.1.1 Role of hydrogen peroxide in plant stress and defence. 6.5.1.2 Role of ascorbate in plant stress and defence. 6.5.2 EST analysis. 6.5.3 Nectary-specific gene expression. 6.6 Nectary molecular biology in other species. 6.6.1 Other n

Nectaries and nectar

Pollenkitt – its composition, forms and functions

Nectaries differ in many aspects but a common feature is some kind of advantage for the plant conferred by foraging of consumers which may defend the plant from predators in the case of extrafloral nectaries, or be agents of pollination in the case of floral nectaries. This minireview is concerned mainly with floral nectaries and examines the following characteristics: position in flower; nectary structure; origin of carbohydrates, aminoacids and proteins; manner of exposure of nectar; site of nectar presentation; volume and production of nectar in time; sexual expression of flower and nectary morphology; nectar composition and floral sexual expression; variability of nectar composition; fate of nectar; energy cost of nectar production. The species of certain large families, such as Brassicaceae, Lamiaceae and Asteraceae, resemble each other in nectary organisation; other families, such as Cucurbitaceae and Ranunculaceae, have various types of organisation. A scheme is presented to illustrate factors influencing nectary and nectar biodiversity.

Nectar biodiversity: a short review

Genomic DNA base composition (GC content) is predicted to significantly affect genome functioning and species ecology. Although several hypotheses have been put forward to address the biological impact of GC content variation in microbial and vertebrate organisms, the biological significance of GC content diversity in plants remains unclear because of a lack of sufficiently robust genomic data. Using flow cytometry, we report genomic GC contents for 239 species representing 70 of 78 monocot families and compare them with genomic characters, a suite of life history traits and climatic niche data using phylogeny-based statistics. GC content of monocots varied between 33.6% and 48.9%, with several groups exceeding the GC content known for any other vascular plant group, highlighting their unusual genome architecture and organization. GC content showed a quadratic relationship with genome size, with the decreases in GC content in larger genomes possibly being a consequence of the higher biochemical costs of GC base synthesis. Dramatic decreases in GC content were observed in species with holocentric chromosomes, whereas increased GC content was documented in species able to grow in seasonally cold and/or dry climates, possibly indicating an advantage of GC-rich DNA during cell freezing and desiccation. We also show that genomic adaptations associated with changing GC content might have played a significant role in the evolution of the Earth’s contemporary biota, such as the rise of grass-dominated biomes during the mid-Tertiary. One of the major selective advantages of GC-rich DNA is hypothesized to be facilitating more complex gene regulation.

https://www.pnas.org/content/pnas/111/39/E4096.full.pdf

Ettore Pacini

Papers

The tapetum: its form, function and possible phylogeny in Embryophyta

Nectaries and nectar

Pollenkitt – its composition, forms and functions

Nectar biodiversity: a short review

Ecological and evolutionary significance of genomic GC content diversity in monocots.