1. Plant Nutrients. 2. The Soil as a Plant Nutrient Medium. 3. Nutrient Uptake and Assimilation. 4. Plant Water Relationships. 5. Plant Growth and Crop Production. 6. Fertilizer Application. 7. Nitrogen. 8. Sulphur. 9. Phosphorus. 10. Potassium. 11. Calcium. 12. Magnesium. 13. Iron. 14. Manganese. 15. Zinc. 16. Copper. 17. Molybdenum. 18. Boron. 19. Further Elements of Importance. 20. Elements with More Toxic Effects. General Readings. References. Index.

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Principles of plant nutrition

Agricultural productivity worldwide is subject to increasing environmental constraints, particularly to drought and salinity due to their high magnitude of impact and wide distribution. Traditional breeding programs trying to improve abiotic stress tolerance have had some success, but are limited by the multigenic nature of the trait. Tolerant plants such as Craterostigma plantagenium, Mesembryanthemum crystallinum, Thellungiella halophila and other hardy plants could be valuable tools to dissect the extreme tolerance nature. In the last decade, Arabidopsis thaliana, a genetic model plant, has been extensively used for unravelling the molecular basis of stress tolerance. Arabidopsis also proved to be extremely important for assessing functions for individual stress-associated genes due to the availability of knock-out mutants and its amenability for genetic transformation. In this review, the responses of plants to salt and water stress are described, the regulatory circuits which allow plants to cope wit...

Drought and Salt Tolerance in Plants

The level of abscisic acid (ABAabscisic acid) in any particular tissue in a plant is determined by the rate of biosynthesis and catabolism of the hormone. Therefore, identifying all the genes involved in the metabolism is essential for a complete understanding of how this hormone directs plant growth and development. To date, almost all the biosynthetic genes have been identified through the isolation of auxotrophic mutants. On the other hand, among several ABA catabolic pathways, current genomic approaches revealed that Arabidopsis CYP707A genes encode ABA 8′-hydroxylases, which catalyze the first committed step in the predominant ABA catabolic pathway. Identification of ABA metabolic genes has revealed that multiple metabolic steps are differentially regulated to fine-tune the ABA level at both transcriptional and post-transcriptional levels. Furthermore, recent ongoing studies have given new insights into the regulation and site of ABA metabolism in relation to its physiological roles.

/pdf/abscisic-acid-biosynthesis-and-catabolism-4l6t1g3h13.pdf

Abscisic acid biosynthesis and catabolism

INTRODUCTION 440 TECHNIQUES 440 Quantification of ABA . ...... . . ...... . 440 Separation of Sand R-Abscisic Acid 441 Stable Isotopes and Mass Spectrometry 442 Extraction and Quantification of Xanthoxin 442 METABOLISM 443 Biosynthesis in Fungi 443 Biosynthesis in Higher Plants 444 Catabolism . . . . . . . . . .. . .... . . . . . . . . . . . . . . .. . . ..... . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ..... . . . . . . . 453 Compartmentation 454 EFFECTS OF ABSCISIC ACID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456 Physiological Responses 456 Biochemical Responses..... . ...... . 461 CONCLUDING REMARKS 463

Metabolism and physiology of abscisic acid

The plant hormone abscisic acid (ABA) plays a major role in seed maturation and germination, as well as in adaptation to abiotic environmental stresses. ABA promotes stomatal closure by rapidly altering ion fluxes in guard cells. Other ABA actions involve modifications of gene expression, and the analysis of ABA-responsive promoters has revealed a diversity of potential cis-acting regulatory elements. The nature of the ABA receptor(s) remains unknown. In contrast, combined biophysical, genetic, and molecular approaches have led to considerable progress in the characterization of more downstream signaling elements. In particular, substantial evidence points to the importance of reversible protein phosphorylation and modifications of cytosolic calcium levels and pH as intermediates in ABA signal transduction. Exciting advances are being made in reassembling individual components into minimal ABA signaling cascades at the single-cell level.

Abscisic acid signal transduction

The involvement of abscisic acid (ABA) in many physiological processes has been suggested [1, 36], but in most cases the role of ABA has not been established unequivocally. The main reason for this uncertainty is that it is not possible at present to grow plants devoid of ABA, since no ABA-less mutants are available and no specific inhibitors of ABA biosynthesis have been found. Nevertheless, it is clear that ABA plays a role in mediating responses to water stress. For example, application of ABA to turgid leaves causes rapid closure of stomata, and levels of ABA in leaves of mesophytic plants increase many times under conditions of water stress. In ABA-deficient mutants (wilty or droopy) applied ABA causes stomatal closure, but the ABA content of these mutants is not increased by water stress. Another phenomenon involving ABA is seed maturation. Observations made on ABA-deficient mutants of various species indicate that precocious germination of developing embryos (vivipary) is prevented by ABA [16, 18].

R. A. Creelman

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Metabolism and physiology of abscisic acid

Metabolism of Abscisic Acid