Phloem Transport

Ten years ago, at the International Botanical Congress in Edinburgh, a group of us from various countries discussed the difficulty of pursuing academic problems in depth at such meetings. In particular, we were discouraged at the poverty of time for phloem transport. From long association, we were conscious of the extraordinary breadth of the problem, from developmental through anatomical, to biophysical and physiological. Only by a reasonable understanding of all these components could one hope to come to some kind of understanding. We decided to establish common plant material so that data would have a common source. Similarly, we resolved to exchange information by circulating pre-publication manuscripts. For awhile, after the meeting was a pleasant memory, the plan seemed to be working; but, as is so often the case, human infirmities and foibles played early and, subsequently, predominant roles. Some became administrators (a punishment for good behaviour); others concentrated on alternative rings in their academic circuses. The next Congress (in Seattle) proved similar to its predecessor in its neglect and, consequently, succor was sought elsewhere. A little known, but remarkably understanding group becoming visible was the Science Committee and the Division of Scientific Affairs of N. A. T. O. Its sponsorship of Advanced Study Institutes including phytochemistry and phytophysics, was unusual both in the generosity of its funding and in the requirements for academic quality.

Contenu

I: Anatomy.- 1. Phloem Tissue in Angiosperms and Gymnosperms.- Cell Types: Their Spatial Distribution, Longevity of Sieve Elements, Aging of Phloem.- Discussion.- 2. Structure and Differentiation of Sieve Elements in Angiosperms and Gymnosperms.- Living Sieve Elements, Cytological and Nuclear Changes During Differentiation; Preparatory Artefacts.- Discussion.- Includes discussion paper: "The Distribution of Filaments in Sieve Tubes in Freeze-Etched, Rapidly-Frozen, Intact Translocating Vascular Bundles".- 3. P-Proteins.- Isolation, Chemistry, Morphology, Formation, Dispersal, Conformational Changes, Enzyme Activity and Functions.- Discussion.- Includes discussion paper: "Biochemistry of Phloem Proteins,".- 4. Sieve Element Cell Walls.- "Nacre" wall, "Secondary" wall. Structure and Chemical Composition, Development and Final Structure of Sieve Areas Plates.- Discussion.- 5. Companion Cells and Transfer Cells.- Structure, Function, Development of Transfer Cell.- Discussion.- Includes discussion paper: "Development of Transfer Cells in Higher Parasitic Plants".- 6. Phloem Tissue and Sieve Elements in Algae, Mosses and Ferns.- Discussion.- Includes discussion paper: "The Phloem (Leptome) of Bryophytes,".- 7. Sieve Element Structure in Relation to Function.- Overview of Fine Structural Differentiation, P-Protein Formation and Biochemical Characterization of Sieve Element Contents.- Discussion.- II: Physiology Of Translocation.- 1. Phloem Loading and Associated Processes.- Definition, Demonstration, Role in Translocation.- Discussion.- Includes discussion paper: "Phloem Loading,".- 2. Physiological and Structural Ontogeny of the Source Leaf.- Import-Export Transition, Carbon Balance and Sugar Synthesis; Ultrastructure of Minor Veins.- Discussion.- 3. Translocation Kinetics and Photosynthates.- Factors Affecting Tracer Kinetics; Translocation Profiles (Kinetic and Spatial); Autoradiography, Anatomy and Tracer Kinetics.- Discussion.- 4. The Effect of Externally Applied Factors on the Translocation of Sugars in the Phloem.- Water Stress, "Hormone-directed" Transport, Anaerobic Conditions and Metabolic Inhibitors, Temperature, Adaptation to Cold.- Discussion.- 5. Bidirectional Transport.- Historical Survey, Anatomical Aspects and Mechanism.- Discussion.- 6. The Use of Phloem Exudates from Several Representatives of the Agavaceae and Palmaein the Study of Translocation of Assimilates.- Phloem Origin of Exudates, Origin of Water and Sucrose in Exudate and Bleeding Mechanism.- Discussion.- Includes discussion paper: "Exudation from Cuts and Aphid Stylets,".- III: Biophysics Of Phloem Transport.- 1. Basic Biophysics of Transport.- Passive Permeation of Membranes, Water Transport, Irreversible Thermodynamics, Active Transport.- 2. Horwitz-Type Models of Tracer Distribution during Unidirectional Translocation.- Irreversible Lateral Loss, Loss by Enzyme Kinetics and Reversible Lateral Loss.- 3. Kinetics of Tracer Efflux from Leaves.- Discussion.- 4. Steady State Models of Münch Pressure Flow.- Discussion.- Includes discussion paper: "Time-Dependent Behaviour of Munch Translocation in Sugar Beet and Trees: Theory vs. Experiment,".- 5. Some Aspects of the Münch Hypothesis.- Discussion.- 6. The Electro-Osmotic Theory.- Presuppositionf History, Physical Model and Evaluation.- 7. Activated Mass Flow: Surface Flow.- 8. Mechanisms: Comparative Behaviour.- Munch Hypothesis, Ionic Relations, Role of P-Protein.- Discussion.- Includes discussion paper: "Discussion of Electro-Osmotic Theories of Phloem Transport,".- 9. Summary of the Conference.- Participants.