Interactions between growth, Cl− and Na+ uptake, and water relations of plants in saline environments. I. Slightly vacuolated cells

Abstract. Slightly vacuolated cells, i.e. microalgae and meristematic cells of vascular plants, maintain low Cl^? and Na⁺ concentrations even when exposed to a highly saline environment. The factors regulating the internal ion concentration are the relative rate of volume expansion, the membrane permeability to ions, the electrical potential, and the active ion fluxes. For ion species which are not actively transported, a formula is developed which relates the internal concentration to the rate of expansion of cell volume, the permeability of membranes to that ion, and the electrical potential. For example, when the external concentration of Cl^? is high, and Cl^? influx is probably mainly passive, the formula predicts that rapid growth keeps the internal Cl^? concentration lower than that in a non-growing cell with the same electrical potential; this effect is substantial if the plasmalemma has a low permeability to Cl^?. For ion species which are actively transported, the rate of pumping must be considered. For instance Na⁺ concentrations are kept low mainly by an efficient Na⁺ extrusion pump which works against the electric field across the membrane. The requirement for Na⁺ extrusion is related to the external Na⁺ concentration, the rate of expansion of cell volume, the membrane permeability, and the electrical potential. It is possible that microalgae have a more positive electrical potential than many other plant cells; if so, requirements for high rates of active Na⁺ extrusion will be lower. The required rates of Na⁺ extrusion are lower during rapid growth, provided that the permeability of the plasmalemma to Na⁺ is low. The energy required for the regulation of Cl^? and Na⁺ concentrations is low, especially in rapidly expanding cells where Na⁺ extrusion requires only 1–2% of the energy normally produced in respiration. The exclusion of these ions, however, must be accompanied by the synthesis of enough organic compounds to provide adequate osmotic solutes for the increases in volume accompanying growth. This process reduces the substrates available for respiration and synthesis of cell constituents, but the reduction is not prohibitively large—even for cells growing in 750 mol m^?3 NaCl, the carbohydrate accumulated as osmotic solute is only 10% of that consumed in respiration.     

Stored xylem sap from wheat and barley in drying soil contains a transpiration inhibitor with a large molecular size

Xylem sap was collected from wheat and barley growing in a drying soil, and the effect of the sap on transpiration was detected by a bioassay with detached wheat leaves. The inhibitory activity of fresh sap was small, and could be largely accounted for by the abscisic acid content (about 2×10^-5mol m^-3). When fresh sap was stored at -20°C for several days, the activity increased. Maximum activity developed after a week. This increase in activity was due to a compound that increased in size with storage at -20°C. When fresh sap was fractionated with filters of different molecular size exclusion characteristics, and the separated fractions stored at -20°C for a week, activity developed only in the fraction containing compounds smaller than 0·3 kDa. However, when sap already stored at -20°C was fractionated, activity was only in fractions containing compounds larger than 0·3 kDa. The increase in activity and in size did not occur with storage in liquid nitrogen (-196°C) or at -80°C. These results suggest that storage at -20°C causes the aggregation or polymerization of a small compound with low activity to form a large compound with high activity. This change is not catalysed by an enzyme because it can occur in a fraction from which molecules larger than 0·3 kDa are removed. It is probably promoted by high solute concentrations when ice crystals form. Sap collected from plants in soils of high water potential had little or no activity after storage at -20°C.     

Physiological processes limiting plant growth in saline soils: some dogmas and hypotheses

Recent progress in improving the salt tolerance of cultivated plants has been slow. Physiologists have been unable to define single genes or even specific metabolic processes that molecular biologists could target, or pinpoint the part of the plant in which such genes for salt tolerance might be expressed. While the physiological might be expressed. While the physiological processes are undoubtedly complex, faster progress on unraveling mechanisms of salt tolerance might be made if there were more effort to test hypotheses rather than to accumulate data, and to integrate cellular and whole plant responses. This article argues that salts taken up by the plant do not directly control plant growth by affecting turgor, photosynthesis or the activity of any one enzyme. Rather, the build-up of salt in old leaves hasten their death, and the loss of these leaves affects the supply of assimilates or hormones to the growing regions and thereby affects growth.     

A comparative study: conventional preparation and ThinPrep® 2000 in respiratory cytology

In order to compare and contrast conventional preparation (CP) with ThinPrep 2000 (TP) in respiratory cytology, 207 samples were divided equally and processed by the two different preparation methods, generating three CP and one TP slide per sample. No lesion identified by CP was missed by TP and there were no significant differences between TP and CP in the diagnostic categories. However, two cases of squamous cell carcinoma were detected on TP which had been classified as unsatisfactory and moderate squamous dyskaryosis, respectively, on CP. ThinPrep was found to be superior to CP in many respects as it provided standardized preparations in a greater proportion of cases and problems such as cell overlapping and background debris were markedly reduced. In several instances the diagnostic accuracy in CP was compromised by smears that were either too thick, too thin, or too scanty. Cell preservation was also better on TP when compared with CP, facilitating more accurate diagnosis and significantly reducing the primary screening and reporting time, especially of sputum samples. A major advantage of TP methodology is the fact that it facilitates optimal use of skilled cytotechnologists and streamlines the workflow in the laboratory.     

Synthesis and Characterization of Nicotiana-Solanum Graft Chimeras

Intergeneric Nicotiana tabacum L./Solanum laciniatum Ait. graftchimeras were produced from decapitated grafts made betweenthese two graft compatible species. Graft unions were treatedwith or without either the auxin, p-chlorophenoxyacetic acid(p-CPA) or the cytokinin, benzylaminopurine (BAP). While BAPwas inhibitory to shoot formation, p-CPA increased the numberof adventitious shoots and raised the frequencies of shoot-forminggrafts obtained. Approximately 9% (14/151) of the shoots producedat p-CPA-treated graft unions were intergeneric chimeras. Theauxin application significantly increased levels of chimeralshoot recovery numbers thus indicating a direct auxin effecton chimeral shoot production. The types and numbers of chimerasproduced were independent of the scion/stock graft combinationemployed. All chimeras appeared to arise initially as mericlinalor sectorial chimeras, with a proportion of the former ones(5/14) stabilizing into periclinal chimeras. The morphologicalcharacteristics of these latter chimeras were compared withthose of the two parental species. The LII layer of speciesdetermined the characteristics of the vegetative and floralcomponents. However, the LI layer modified the qualitative traitsof both components. The LIII layer on the other hand alteredthe quantitative traits of the vegetative organs and the flower.This layer also determined the growth type, breeding behaviourand inflorescence type of synthesized chimeras. These organizationalfunctions of the LIII layer have not been reported previously. Chimeras, intergeneric chimera synthesis, grafting, graft chimeras, Nicotiana tabacum, Solanum aviculare, p-chlorophenoxyacetic acid, peroxidase isoenzymes     

Ion Concentration and Carbohydrate Status of the Elongating Leaf Tissue 4Hordeum vulgare Growing at High External NaCl: II. CAUSE OF THE GROWTH REDUCTION

The cause for the growth reduction of a salt-tolerant varietyof barley (cv. ‘Beecher’) was investigated in plantsgrowth for 5 d at 120 mM and 180 mM NaCl. The NaCl treatmentsincreased the concentrations of soluble carbohydrate in theelongating tissues of the growing leaf, while starch did notchange. This shows that photosynthesis was not limiting growth,and indicates that the cause for the growth reduction was locatedin the growing leaves, specifically in the elongating tissue. Leaf elongation increased rapidly after transfer of plants from120 to 60 mM NaCl. The rate elongation during the first hourafter transfer was already equal to that of plants grown at60 mM NaCl, despite the persistence of high Cl^– and (Na⁺+ K⁺) concentrations in elongating as well as fully elongatedtissues. This indicates that the growing tissues suffered fromwater deficit rather than from adverse effects of ions on metabolism.     

Water Potential, Growth, and Polyribosome Content of the Stressed Wheat Apex

The effect of drought on the growth, ribosomal content, andwater potential of the immature floral apex of wheat plantswas studied under controlled environment conditions. Duringdrought the water potential of the apex (measured with a thermocouplepsychrometer) decreased at approximately the same rate as thatof expanded leaves. Elongation and differen tiation of the floralapex ceased at approximately –12 x 10⁵ Pa and the polyribosomalcontent decreased from 50% of the total ribosomal populationto less than 10%. At this water potential also, elongation ofexpanding leaves was severely inhibited. With continued drought the water potential of the apex continueddecreasing. The exposed leaves died at a water potential ofabout –35 x 10⁵ Pa but the apex was still alive at a waterpotential of –60 x 10⁵ Pa and after rewatering it eventuallyresumed growth.     

Water Loss via the Glandular Trichomes of Chickpea (Cicer arietinum L.)

During late vegetative growth chickpea leaves and stems canbe covered with aqueous glandular droplets. If these dropletspersist at low humidities there may be substantial water lossvia the glandular trichomes Four solution culture experimentsin growth chambers tested for glandular water loss at differenthumidities. In the daytime, exudate persisted between relativehumidities of 55% and 95%, and the exudate water potential variedbetween - 2.0 M Pa and - 8.0 M Pa. Even by night, chickpea leaves,like wetted alfalfa leaves, were cooler than non-wetted alfalfaleaves or the ambient air. Daytime leaf temperatures were significantlyhigher in a mutant that produced fewer droplets than in itsnormal parent. It was concluded that water loss via the glandulartrichomes can be enough to lower leaf temperature by severaldegrees C within a wide range of atmospheric conditions. The exudate solutes, analysed to confirm the osmotic potentialmeasurements, were primarily malic, hydrochloric and oxalicacid. Without the strong acids a chickpea leaf, wet even ondry days, would be ripe for parasitic attack. Key words: Add exudate, leaf hairs, transpiration, leaf temperature