Transport in Plants I

When WILHELM RUHLAND developed his plan for an Encyclopedia of Plant Physiol­ ogy more than three decades ago, biology could still be conveniently subdivided into classical areas. Even within plant physiology, subdivisions were not too difficult to make, and general principles could be covered sufficiently in the two introductory volumes of the Encyclopedia on the physical and chemical basis of cell biology. But the situation changed rapidly even during the 12-year publication period of the Encyclopedia (1955-1967). The new molecular direction of genetics and structural research on biopolymers had an integrating effect on all other biological fields, including plant physiology, and it became increasingly difficult to keep previously distinct areas separated. RUHLAND'S overall plan included 18 volumes and about 22,000 pages. It covered the entire field of plant physiology, in most cases from the very beginning. But, as each volume appeared, it was clear that its content would soon be outdated.

Contenu

I. Structural Considerations in Phloem Transport.- 1. Sieve-Element Structure.- A. Introduction.- B. Terminology, Sieve-Element Size and Shape.- C. Structure of Sieve Elements.- Angiosperms.- Gymnosperms.- Vascular Cryptogams.- D. Longevity of Sieve Elements.- E. Structure of Sieve Elements and Translocation.- Undifferentiated S.E..- S.E. Structure and Possible Mechanisms of Transport.- F. Conclusion.- References.- 2. Sealing Systems in Phloem.- A. Introduction.- B. Callose.- Identification and Distribution.- Structure and Properties.- Changes of Callose Content.- Sieve-Tube Callose in Relation to Transport.- Conclusions.- C. Sieve-Tube Slime.- General Considerations.- Distribution and Origin.- Position of Filaments.- Conclusions.- References.- II. Nature of Substances in Phloem.- 3. Nature of Transported Substances.- A. Introduction.- B. Methods for the Analysis of the Transported Substances.- C. Different Groups of Transported Substances.- Water.- Carbohydrates.- Nitrogenous Substances.- Lipids.- Organic Acids.- Constituents and ATP.- Growth Substances and Inhibitors.- Vitamins.- Other Organic Substances.- Inorganic Substances.- Viruses and Flagellates.- Physical Properties of S.T. Exudate.- D. Concluding Remarks.- References.- 4. Biochemistry of Phloem Constituents.- A. Introduction.- B. Enzymic Activities in Sieve Tubes.- Sources of S.T. Exudates.- Enzymes in S.T..- C. Maintenance of the Living State of Sieve Tubes.- Respiration.- Enzymes of Glycolysis and Gluconeogenesis.- D. Origin of Enzymes in Sieve Tubes.- E. Biochemical Reactions in Sieve Tubes in Relation to Function.- Enzymes Normally Present.- Metabolism of Sucrose and Derivatives.- Nucleic Acids.- Synthesis and Breakdown of Callose.- P-Protein and Plastids.- F. Conclusions.- References.- III. Phloem Transport: Assessment of Evidence.- 5. Mass Transfer.- A. Introduction.- B. Methods of Measuring Mass Transfer.- Gain by Fruit Sinks.- Loss from Leaf Sources.- Transfer through Tree Trunks.- Special Systems: Palm Inflorescence.- Aphid Stylet.- Results of the Measurements.- C. Factors Related to Mass Transfer.- Concentration Gradient.- Path Distance.- Morphology and Patterns of Movement.- Flow Models.- Speed Components.- D. Summary.- References.- 6. Aphids and Translocation.- A. Introduction.- B. Distribution of Aphids on Plants and Its Bearing on Translocation.- C. Aphid Honeydew as a Source of Information on Substances Translocated in Phloem Elements.- Sterols.- Phenols.- Minerals.- Plant Hormones.- D. Growth Efficiency of Aphids.- E. Damage Done to Plants by Aphids.- Galling.- Premature Senescence and Death of Plant Tissue.- Speed of Response of Plants to Aphid Infestation.- Hormonal Changes Induced.- F. Aphids as "Sinks".- G. Aphid Stylets and Phloem Transport.- H. Summary.- References.- 7. Investigations with Aphid Stylets into the Physiology of the Sieve Tube.- A. Introduction.- B. The Aphid Technique as a Method of Obtaining Samples of Sieve-Tube Sap.- Severed Stylets.- Whole Aphids.- Comparison of Stylet Technique with Incisions.- C. Evidence That Exudation from Stylets Involves Longitudinal Transport through the Sieve Tubes.- Experiments with Incisions and Radioactive Tracers.- D. The Pattern of Fluxes into and along the Sieve Tube in Relation to Stylet Puncture.- E. Severed Stylets and Aphids as Sinks.- Polarity Initiated by Stylets.- Velocity and Specific Mass Transfer of Sucrose in Pierced S.T..- F. The Control of Solute Loading into Sieve Elements.- Potential.- Specificity.- Metabolism and Loading.- G. The Nature of the Longitudinal Movement Produced in Response to Stylet Puncture.- Water Movement.- Hydrostatic Pressures in Sieve Tubes.- Effect of Hydrostatic Pressure Gradients in Xylem upon Stylet Exudation.- Simultaneous Bidirectional Movement.- Metabolism and Movement of Solutes.- H. Conclusions.- References.- 8. Phloem Exudation from Monocotyledonous Axes.- A. Introduction.- B. Exudation from Wounded Palms and Agaves.- Sugar-Rich Saps.- Use of Yucca flaccida.- Composition and Nature of Exudates.- C. Experimental Analyses of the Exudation Process.- Translocation to the Site of Bleeding.- Feeding Detached Inflorescence Axes.- Cooling Experiments with Yucca flaccida.- D. The Exudation Process and Its Relation to Phloem Transport.- Flow between Source and Artificial Sink.- Structure of the Sieve Plate.- Concluding Remarks.- References.- 9. Work with Isolated Phloem Strands.- A. Introduction.- B. Studies of Heat-Pulse Movement.- C. Electrical Studies.- D. Light Microscopy of Isolated Phloem Strands.- E. Micro-Injection of Tracers.- F. Feeding Sucrose Solution to Isolated Phloem Strands.- G. Electronmicroscopy of Isolated Strands.- H. Summary.- References.- 10. Bidirectional Transport.- A. Introduction.- Historical Survey.- Aims.- Anatomical Aspect.- B. Experiments.- Analysis of S.T. between Two Sources.- Bidirectional Spreading from a Single Source.- C. Bidirectional Transport in Relation to Vascular Differentiation.- Anatomy.- Differentiation and Transport 251,.- D. Conclusions.- References.- 11. Effects of Temperature, Anoxia and Other Metabolic Inhibitors on Translocation.- A. Introduction.- The Importance of Translocation Modification by Metabolic Inhibitors.- Possible Difficulties Encountered in Studying the Effect of Metabolic Inhibitors on Translocation.- B. Effects of Temperature, Anoxia and Metabolic Inhibitors on Translocation.- Whole-Plant Experiments.- Results of Path, Sink and Source Treatments.- C. Significance of Effects of Various Inhibitors.- Relation to Mechanism.- Effects on Growth and Productivity.- Future Work.- D. Summary.- References.- IV. Possible Mechanisms of Phloem Transport.- 12. Protoplasmic Streaming.- A. Introduction.- B. The Phenomenon of Streaming.- C. The Fine Structure of Streaming Protoplasm.- D. Chemical Basis of Protoplasmic Streaming.- E. Translocation Models Using the Streaming Properties of Protoplasm.- Rotation Streaming.- Transcellular Strands.- Peristalitic Pumping.- F. The Occurrence of Streaming in Sieve-Element Protoplasm.- G. Structural Components of Sieve Elements That Might be Related to Streaming.- H. Conclusion.- References.- 13. Electroosmotic Flow.- A. Presuppositions of the Potassium Theory.- B. Electroosmosis as a Phenomenon.- Anomalous Osmosis.- Design for an Electroosmotic Pump.- A Modified Design.- C. Statement of the Theory.- Further Comments.- Initiation of Transport.- Insertion of P-Protein into Pores.- Active Uptake of Potassium.- Membrane Expansion.- Limitation of Potassium Circulation.- Sieve-Element Length.- Function of Companion Cells.- D. Objections to the Potassium Theory.- E. Further Evidence for the Potassium Theory.- F. Comparison with Other Theories.- Münch Hypothesis.- Contractile Protein Theories.- G. Conclusion.- Addendum 1: Hydrodynamic Polarization of Sieve Plate.- Addendum 2: Donnan Equilibrium between Lumen and Pores.- Addendum 3.- References.- 14. Pressure Flow.- A. Introduction.- B. Press…