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Over the last decade, considerable advances have occurred in understanding the molecular biology and biophysics of water permeation across plant membranes and tissues. Spurred on by the rapid advances in cloning and functional characterization of a super-family of major intrinsic proteins, some of which function as aquaporins, the biophysics of transport of water and small non-electrolytes across plant membranes is being re-examined based on the proposed function of these membrane-integral proteins in their native membranes. This review focuses on a number of issues that are central to an understanding of aquaporin function: (1) the need to be able to test for water-channel activity in native membranes; (2) the implications of the observed solute/water selectivity of aquaporins; (3) the putative functional roles of aquaporins at the cell, tissue and organ levels in plants; and (4) information that can be obtained from studies of the abundance, diversity and expression patterns of aquaporins. It is clear that to answer many of the critical questions that remain concerning aquaporin function, combined studies using appropriate molecular and biophysical techniques will be required.

Great strides have been made in the last 15 years in our understanding of phloem mobility of xenobiotics. The subject has been transformed from a poorly understood phenomenon to a process that can be accurately described by the physicochemical properties of the xenobiotic and the nature of the vascular system through which it moves. The basic tenet of the unified mathematical model is that the combination of the permeability and the acid dissociation constant (pKa) determines phloem mobility, and this has been largely validated for many compounds in many plant systems. More precise testing of the model is, however, difficult due to the lack of requisite knowledge on the membrane composition of the sieve tube, permeation characteristics and sieve-cell biochemistry. Furthermore, attempts to relate quantitatively a compound's intrinsic mobility to its whole-plant mobility are often confounded by competing loss mechanisms. On the practical side, there is the challenge of coming up with efficacious phloem-mobile pesticides. Considerations are forwarded to explain why so far there are numerous phloem-mobile herbicides and yet precious few such insecticides and fungicides, and why the situation might be difficult to change. The knowledge of phloem mobility is robust enough to allow specific structural prescriptions to impart such mobility to existing pesticides. However, such structural changes often lead to a reduction of pesticidal activity. Recently, it has been demonstrated that this problem can be circumvented by combining oxamyl glucuronide (a phloem-mobile pro-nematicide) with a transgenic tobacco plant harboring a root-specific β-glucuronidase gene to release oxamyl for root-knot nematode control. This propesticide and in situ activation strategy is one way to use the existing body of knowledge for practical purposes. The same principle should be generally applicable to other plant-xenobiotic technologies.

Dans le but de selectionner des individus resistant a la salinite, l'effet de NaCl sur la croissance d'embryons somatiques de Sapindus trifoliatus a ete etudie. L'analyse des modifications de concentrations en lipides et en elements mineraux en reponse au stress salin a ete realisee dans le but de mieux comprendre les mecanismes de tolerance au sel des embryons somatiques

Mesure des concentrations et flux de NO 3 − et NH 4 + dans les cellules corticales de segments racinaires excises et plonges dans des solutions nutritives completes ou NO 3 − et/ou NH 4 + sont les seules sources d'azote. Recherche d'activites nitrate reductase et glutamine synthetase. Interactions entre NO 3 − et NH 4 + pour leur incorporation et leur transport. Mise en evidence de phenomenes de transport actif. Comparaison des resultats avec ceux de travaux analogues anterieurs

In this paper we report further in vivo observations of the movement of recently fixed photoassimilate through a surgically modified pea ovule which support the view that phloem unloading is symplastic

We report a study in which we estimate by means of non-equilibrium processes the value of an effective partition coefficient, a parameter that we use to take into account the non ideal behaviour of the electrolyte of the external medium in the cell wall space. To that purpose, concentration potentiel in NaCl, LiCl and CuCl 2 solutions was measured across an isolated cell wall of Nitella flexilis at different PH

Premier signalement d'une liberation rapide de H + des racines d'une halophyte S.m. en milieu nutritif complet, en presence de lumiere

Drakeford, D. R., Mukherjee, I. and Reid, D. M. 1985. Some early responses of Helianthus annuus L. to flooding. I. The effects of flooding on the uptake and leakage of'non-electrolytes' by roots.—J. exp. Bot. 36: 1705-1715. The object of this work was to examine some of the early effects of flooding on roots. A hydroponic system was developed that gave good control over watering, degree of oxygenation of the bathing medium and allowed measurement of short term changes in the composition of the bathing medium. Excised roots, flooded for 24 h, were shown to take up less [3H) ^-alanine than non-flooded roots and also leaked more [3H] ^-alanine into a distilled water bathing medium. Further, flooded excised roots lost more protein to the bathing medium, with 'young' (5-7 d) roots showing greater losses than 'old' (11-14 d) roots. However, young roots had more protein in the tissue even after greater loss. Young roots remained healthier and lost less fresh weight than old roots. Abscisic acid was shown to have a small role in protecting 'young' roots from the effects of flooding. Key words—ABA, abscisic acid, anaerobic, flooding, leakage, roots, uptake, waterlogging. Correspondence to: Plant Physiology Research Group, Department of Biology, University of Calgary, Calgary, Alberta, Canada T2N 1N4.

Ahmad, N, Wyn Jones, R. G. and Jeschke, W. D. 1987. Effect of exogenous glycinebetaine on Na+ transport in barley roots.—J. exp. Bot. 38: 913-921. A comparison has been made of the kinetics of 22Na+ uptake into excised barley roots and roots pre-loaded with glycinebetaine. The elevated intracellular glycinebetaine or a metabolic consequence thereof increased the Na+ influx, and the effect was related to the level of internal glycinebetaine and/or Na+ [CI-]. The quasi-steady-state Na+ influx at the tonoplast rather than the plasmalemma influx was apparently influenced by glycinebetaine loading. The tonoplast fluxes and vacuolar Na + content were consistently higher in glycinebetaine-loaded roots than unloaded roots. A membrane modifying role of glycinebetaine in relation to ion compartmentation is discussed. Key words—Excised roots, glycinebetaine, Na+, ion fluxes, barley. Correspondence to: Department of Biochemistry and Soil Science, University College of North Wales, Bangor, Gwynedd, Wales, U.K.

Ginzburg, M. and Richman, L. 1985. Permeability of whole Dunaliella cells to glucose.—J. exp. Bot. 36: 1959-1968. When glucose was dissolved in medium in which Dunaliella cells were suspended, the amount recovered from pellets of centrifuged cells was greater than that expected if the glucose had been restricted to intercellular space, as measured with Blue Dextran. Glucose is not metabolized by whole Dunaliella cells. The glucose additional to that in the intercellular space must be either adsorbed in the coating outside the cells or must penetrate the cell through the cell membrane. Grounds are given for suggesting that the latter hypothesis is correct and that the glucose comes to equilibrium with a space within the cell (the glucose-space) equivalent to 20-40% of the cell-water. It is suggested that most of the cell Na+ is restricted to the glucose-space. Key words—Dunaliella, glucose, permeability. Correspondence to: Laboratory of Plant Biophysics, Botany Department, Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel.