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

Plant cells encase themselves within a complex polysaccharide wall, which constitutes the raw material that is used to manufacture textiles, paper, lumber, films, thickeners and other products. The plant cell wall is also the primary source of cellulose, the most abundant and useful biopolymer on the Earth. The cell wall not only strengthens the plant body, but also has key roles in plant growth, cell differentiation, intercellular communication, water movement and defence. Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.

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Growth of the plant cell wall

The ways in which plant growth promoting rhizobacteria facilitate the growth of plants are considered and discussed. Both indirect and direct mechanisms of plant growth promotion are dealt with. Th...

The enhancement of plant growth by free-living bacteria

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

Soil bacteria are very important in biogeochemical cycles and have been used for crop production for decades. Plant–bacterial interactions in the rhizosphere are the determinants of plant health and soil fertility. Free-living soil bacteria beneficial to plant growth, usually referred to as plant growth promoting rhizobacteria (PGPR), are capable of promoting plant growth by colonizing the plant root. PGPR are also termed plant health promoting rhizobacteria (PHPR) or nodule promoting rhizobacteria (NPR). These are associated with the rhizosphere, which is an important soil ecological environment for plant–microbe interactions. Symbiotic nitrogen-fixing bacteria include the cyanobacteria of the genera Rhizobium, Bradyrhizobium, Azorhizobium, Allorhizobium, Sinorhizobium and Mesorhizobium. Free-living nitrogen-fixing bacteria or associative nitrogen fixers, for example bacteria belonging to the species Azospirillum, Enterobacter, Klebsiella and Pseudomonas, have been shown to attach to the root and efficiently colonize root surfaces. PGPR have the potential to contribute to sustainable plant growth promotion. Generally, PGPR function in three different ways: synthesizing particular compounds for the plants, facilitating the uptake of certain nutrients from the soil, and lessening or preventing the plants from diseases. Plant growth promotion and development can be facilitated both directly and indirectly. Indirect plant growth promotion includes the prevention of the deleterious effects of phytopathogenic organisms. This can be achieved by the production of siderophores, i.e. small metal-binding molecules. Biological control of soil-borne plant pathogens and the synthesis of antibiotics have also been reported in several bacterial species. Another mechanism by which PGPR can inhibit phytopathogens is the production of hydrogen cyanide (HCN) and/or fungal cell wall degrading enzymes, e.g., chitinase and s-1,3-glucanase. Direct plant growth promotion includes symbiotic and non-symbiotic PGPR which function through production of plant hormones such as auxins, cytokinins, gibberellins, ethylene and abscisic acid. Production of indole-3-ethanol or indole-3-acetic acid (IAA), the compounds belonging to auxins, have been reported for several bacterial genera. Some PGPR function as a sink for 1-aminocyclopropane-1-carboxylate (ACC), the immediate precursor of ethylene in higher plants, by hydrolyzing it into α-ketobutyrate and ammonia, and in this way promote root growth by lowering indigenous ethylene levels in the micro-rhizo environment. PGPR also help in solubilization of mineral phosphates and other nutrients, enhance resistance to stress, stabilize soil aggregates, and improve soil structure and organic matter content. PGPR retain more soil organic N, and other nutrients in the plant–soil system, thus reducing the need for fertilizer N and P and enhancing release of the nutrients.

Soil beneficial bacteria and their role in plant growth promotion: a review

The ability of low pH and CO(2) to induce rapid cell elongation and wall loosening in the Avena coleoptile has been examined with the use of a continuous growth-recording technique and an Instron extensometer, respectively. In particular, the properties of the response to hydrogen ions have been examined in detail and have been compared with the responses initiated by CO(2) and auxin. The optimal pH for growth is about 3.0, and both the maximal growth rate and wall extensibility are similar to that produced by optimal auxin. The timing (initiated in less than 1 minute) and duration (up to 2 hours) of the response to hydrogen ions, as well as certain other aspects of the growth and wall-loosening responses, are described. It is shown that the pH response can be clearly separated from the CO(2) response. Possible mechanisms for the initiation of the growth response to low pH are briefly discussed.

Enhancement of Wall Loosening and Elongation by Acid Solutions

Publisher Summary This chapter discusses the evidence that in Avena coleoptiles and pea stem tissues the hormone auxin induces cell enlargement, by activating proton extrusion, and that the resulting acidification of the wall leads to enzymic cell wall loosening and thus cell enlargement. It emphasizes the point that auxin itself does not act directly on the wall but acts at the cell surface or within the cytoplasm. When a plant cell enlarges, most of the increase in volume is due to the uptake of water into an expanding–centrally located vacuole. The direction of the cell expansion depends on the molecular architecture of the wall and can be primarily in one direction or equally in all directions. Cell enlargement can be initiated in one of the two ways: by an increase in the osmotic concentration of the cell or by an increase in cell wall extensibility (cell wall loosening). In most systems, cell enlargement is initiated by wall loosening. If a section is removed from the elongation zone of a pea stem and placed in water, the cells enlarge, but only at a slow rate. Rapid enlargement can be induced by only four agents: the group of hormones called auxins, hydrogen ions, CO, and the phytotoxin fusicoccin. If hydrogen ions are excreted from auxin-treated Avena coleoptile cells, and if the pH of the wall region falls below 5.8, the walls would undergo cell wall loosening and growth would occur.

Control of plant cell enlargement by hydrogen ions.

BURSTOM1 recently criticized the generally held view that plant cell enlargement involves physical yielding of the cell wall driven by turgor forces, saying, “turgor does not cause expansion and is not the driving force … The driving force of any expansion is a difference in water potentials (because) expansion is due to water uptake … The literature on plant cell growth would certainly improve if the notion of turgor expanding the cell was abandoned and replaced by accepted equations for water balance of fluxes”.

Role of Turgor in Plant Cell Growth

One of the most dramatic and rapid hormone responses in plants is the induction by auxin of rapid cell elongation in isolated stem and coleoptile sections. The response begins within 10 minutes after the addition of auxin, results in a 5-10 fold increase in the growth rate, and persists for hours or even days (22). It is hardly surprising that this may be the most studied hormonal response in plants.

Robert E. Cleland

Papers

Enhancement of Wall Loosening and Elongation by Acid Solutions

Control of plant cell enlargement by hydrogen ions.

Role of Turgor in Plant Cell Growth

Auxin and Cell Elongation

Is plant development regulated by changes in the concentration of growth substances or by changes in the sensitivity to growth substances