Intercellular Compartmentation of Ions in Barley Leaves in Relation to Potassium Nutrition and Salinity

X-ray microanalysis was used to determine the distributionsof several nutrient elements between vacuoles of epidermal andmesophyll cells in barley leaves and these distributions wererelated to shoot nutrient concentrations. Under the growth conditionsused, P was found only in mesophyll vacuoles, never in the epidermis.In contrast, Cl and Ca were located almost exclusively in theepidermis while K and Na were more evenly distributed betweenthe two cell types. The compartmentation of Ca and Cl in theepidermis was maintained over a wide range of tissue concentrationsof these ions. In particular, Cl was excluded from the mesophyllof salt-grown barley until the tissue concentration reachedabout 170 mol m^–3 and then it appeared in the vacuolesof these cells, but only at low concentrations. In contrast,Na was not excluded from the mesophyll of salt-grown or K-deficientbarley and there was evidence that this ion was preferentiallyaccumulated in the mesophyll. Nutrients were evenly distributedbetween the adaxial and abaxial epidermal layers, except K.which was at slightly higher concentrations in the adaxial epidermis.There was considerable variation in the concentrations of ionsin adjacent epidermal cells. The results indicate that intercellularcompartmentation of nutrients occurs in barley leaves and therole of this phenomenon in responses to nutrient deficienciesand salinity is discussed Key words: Compartmentation, barley, salinity, ions, potassium nutrition     

Differential effects of turgor on sucrose and potassium transport at the tonoplast and plasma membrane of sugar beet storage root tissue

When turgor was increased, by decreasing the concentration of mannitol bathing discs of sugar beet storage root tissue, the rates of sucrose and potassium uptake into the vacuole were decreased. At all external mannitol concentrations the rate of sucrose and potassium uptake across the plasma membrane was an order of magnitude greater than the rate of quasi-steady uptake into the vacuole, implying a very large efflux. Efflux of both sucrose and potassium was increased at high turgor. However, while increasing turgor decreased the rate of K⁺ uptake, the rate of sucrose uptake at the plasma membrane increased with time. Compartmental analysis of tracer exchange kinetics was used to determine unidirectional K⁺ fluxes. From these results, it was estimated that the increase in K⁺ efflux accompanying a 1.5 MPa increase in turgor could lead to a net increase of 140mol^?3h^?1 in the external potassium concentration. It is suggested that the turgor-imposed increase in solute efflux is a means of regulating intracellular osmotic pressure and/or turgor in sugar beet storage roots, but that sucrose is preferentially retrieved from the apoplast, even under conditions of excessively high turgor. However, much of this sucrose is probably lost from the cell, implying a ‘futile’ sucrose transport cycle at the plasma membrane. The turgor-stimulated leak of potassium could play a major role in the regulation of turgor pressure in sugar beet storage root tissue.     

The Effect of Nutrient Solution Composition on the Length of Root Hairs of Wheat (Triticum aestivum L.)

The length of root hairs of wheat (Triticum aestivum L.) growingin Long Ashton nitrate nutrient solution was affected mainlyby pH and the concentrations of calcium and nitrate. Root hairlength was decreased by high pH (> 7.0) and by low calciumconcentrations but was increased by nitrate. Buffering at pH6.5 was found to affect the relationship between nutrient solutionstrength and the length of root hairs. The interactions betweencalcium, nitrate and buffering were determined. Phosphate concentrationdid not affect the length of root hairs of wheat, although lowconcentrations have been reported to stimulate root hair growthin other plants. The mechanisms by which pH, calcium and nitratemay affect root hair length are discussed. Key words: Root hairs, Triticum aestivum, Wheat, Nutrient solutions     

Analyses of 22S Dynein Binding to Tetrahymena Axonemes Lacking Outer Dynein Arms

ABSTRACT. Tetrahymena thermophila mutants homozygous for the oad mutation become nonmotile when grown at the restrictive temperature of 39° C. Axonemes isolated from nonmotile oad mutants ( oad 39° C axonemes) lack approximately 90% of their outer dynein arms and are deficient in 22S dynein. Here we report that oad 39° C axonemes contain 40% of the 22S dynein heavy chains that wild-type axonemes contain and that oad axonemes do not undergo ATP-induced microtubule sliding in vitro. Wild-type 22S dynein will bind to the outer arm position in oad axonemes and restore ATP-induced microtubule sliding in those axonemes. Unlike wild-type 22S dynein, oad 22S dynein does not bind to the outer arm position in oad axonemes. These data indicate that the oad mutation affects some component of the outer arm dynein itself rather than the outer arm dynein binding site. These data also indicate that oad axonemes can be used to assay outer dynein arm function.     

Acoustically-orienting parasitoids in calling and silent males of the field cricket Teleogryllus oceanicus

Abstract.

• 1 On three Hawaiian Islands, the introduced Australasian field cricket Teleogryllus oceanicus Le Guillou (Orthoptera: Gryllidae) was found to be attacked by the phonotactic parasitoid tachinid fly, Ormia ochracea Bigot.
• 2 Noncalling males occurred with callers in all locations, but silent males were more heavily parasitized than callers.
• 3 Body size was unrelated to both calling status and the likelihood of harbouring parasitoid larvae.
• 4 An experiment examining the likelihood of calling in the laboratory by males collected as silent or calling individuals showed no difference between the two classes of males, after accounting for parasitoid levels; males harbouring larvae were less likely to call.

     

Extraction and analysis of sap from individual wheat leaf cells: the effect of sampling speed on the osmotic pressure of extracted sap

Abstract. A modification to the pressure probe is described which allows very rapid extraction of sap samples from single higher plant cells. The performance of this rapid-sampling probe was assessed and compared with the unmodified probe for cells of both wheat and Tradescantia. Under some conditions, the unmodified probe operated too slowly to avoid dilution of cell sap during the extraction process. This led to values for apparent sample osmotic pressures that were below the turgor pressures for the same cells. The problem was particularly acute in young wheatleaf epidermal cells which are small, elongate and have high turgor pressure. These exhibited rapid water influx when their turgor was depressed during the sampling of their contents (half-time for pressure recovery in wheat cells was less than 1 s while in Tradescantia cells it was 3–5 s). Dilution during sampling was apparently negligible when the rapid sampling probe was used. The study was complemented by a simple model of the way cells dilute during sampling. Quantitative predictions of the model were consistent with our observed findings. The model is used to assess the major factors which determine a cell's susceptibility to dilution during sampling.     

Growth and physiological responses of cotton (Gossypium hirsutum L.) to elevated carbon dioxide and ultraviolet-B radiation under controlled environmental conditions

Better understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO₂] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO₂] (360 and 720 µmol mol^?1) and three levels of 0 (control), 7.7 and 15.1 kJ m^?2 d^?1 biologically effective UV‐B radiations within each CO₂ level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO₂] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO₂]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO₂]. On the other hand, high UV‐B (15.1 kJ m^?2 d^?1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m^?2 d^?1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m^?2 d^?1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO₂] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress.