ALBERT

Notes: Abstract The effect of salinity on the growth and ion concentrations in a number of tobacco cultivars is described. Sodium chloride, at a concentration of 200 mol m−3, hardly affected the fresh weight, but significantly reduced the dry weight. The difference in the response of fresh and dry weights to salt was due to a change in succulence (water per unit leaf area); the latter increased with increasing leaf Na+ and Cl− concentration. Under saline conditions, increasing the external Na+: Ca− ratio by decreasing the Ca2+ concentration increased the accumulation of Na+ and Cl− into the leaf tissue.

Notes: 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.

Notes: Abstract The present paper describes the effects of growth of roots of wheat (Triticum aestivum cv. Gamenya) in hypoxic nutrient solutions on acrenchyma formation and O2 movement from shoots to roots. Two types of roots were investigated: (1) seminal roots of 4–7-d-old seedlings, and (2) seminal and nodal roots of 10–28-d-old plants. Gas-filled porosity of seminal and nodal roots increased from 3 to 12% and from 5–7 to 11–15%, respectively, when the roots emerged in stagnant or N2-flushed solutions (0.003 mol m −3 O2) compared with growth in continuously acrated solutions (0.26 mol m −3 O2). However, neither root type increased in porosity when they were longer than 100–200 mm at the start of the exposure to these stagnant or N2-flushed treatments. A vernier microscope and cylindrical platinum-electrode were used to examine the relationship between root extension and transport of O2 from shoots to roots via the gas spaces. Measurements were made when the roots were in an anoxic medium and were dependent solely on O2 supplied from the shoots. For seminal roots of 5–7-d-old seedlings raised in stagnant solutions (90–100 mm), internal O2 transport was sufficient to support a rate of root elongation in the O2-free medium of between 0.03 and 0.17 mm h−1. When the O2 pressure around the shoots was increased from 20 to 100 kPa O2, the O2 concentrations at the walls of the expanding zone (2–7 mm from the tip) of these roots increased from 0.006 mol m−3 to between 0.04 and 0.26 mol m−3, and the rate of root extension increased five-fold. Oxygen transport to roots grown continuously in acrated solutions was considerably less than for roots raised in stagnant solutions; this difference was greater for seminal than for nodal roots. When the acrated seminal roots were longer than 100 mm and transferred to an O2-free root medium, O2 concentration became zero at the root tip causing elongation to cease. After 24 h of anoxia, none of these roots were able to resume elongation following a return to acrated solutions.

Notes: Abstract. In a highly saline environment high rates of ion uptake are required to generate sufficient osmotic pressure to maintain the turgor that is needed for the continued growth of plants. We estimate the rates of net uptake of Cl− and Na+ required by growing cells to sustain cell expansion at an external NaCl concentration of 500 mol m−3. We also estimate the ion fluxes required to regulate turgor of expanding and fully expanded cells during diurnal changes in transpiration. Passive fluxes could contribute significantly to osmotic regulation, but active fluxes are still essential and would consume a substantial amount of energy. We discuss whether a limitation to growth at high salinity would arise from lack of energy, or from insufficient capacity for ion uptake. There is insufficient evidence to choose between these possibilities.

Notes: Abstract. A method is described here for isolating protoplasts and vacuoles from leaves of the halophyte Suacda maritima. Integrity of the protoplasts and vacuoles was tested by staining and shown to be more than 75%, while use of biochemical markers, staining and light microscopy suggested a high degree of purity of the vacuoles. Phosphatase and NADH cytochrome-c-reductase were associated with vacuoles; phosphatase showed an eight-fold enrichment and NADH cytochrome-c-reductase a 3.5-fold enrichment relative to protoplasts. The vacuoles contained only 15% of the protein in protoplasts.

Notes: Abstract Atriplex amnicola was grown at 25, 200 or 400 mol m3 NaCl. Root tissues at different stages of development were investigated for concentrations of K+, Na+ and Mg2+, and in some cases for Cl−. Sugar and starch concentrations were measured for plants grown at 25 or 400 mol m3 NaCl.In the ‘slightly vaeuolated’ root tips, Na+ was only 40 mol m−3 at an external concentration of 400 mol m−3 NaCl. The concentrations of K+ were not affected substantially by external NaCl between 25 mol m−3 and 400 mol m−3. The ‘highly vacuolated’ root tissues had substantially higher concentrations of K+, Na+ and Cl− in plants grown at 200 and 400 mol m 3 NaCl than in plants grown at 25 mol m−3 NaCl. Concentrations of Cr and of the sum of the cations in recently expanded tissue were similar to those in the bulk of the roots, consisting mainly of old cells. However, the K+: Na+ decreased with age; at 400 mol m−3 external NaCl with a K+: Na+ of 0.012, the K+: Na+ in recently expanded 12 mm root tips was as high as 1.6, compared with 0.7 for the bulk of the roots.These ion data were used to estimate cytoplasmic and vacuolar concentrations of K+ and Na +. Such calculations indicated that between 25 mol m3 and 400 mol m−3 external NaCl the concentration of the sum of (Na++K+) in the cytoplasm was maintained at about 180–200 mol m−3 (cell water basis). In contrast, the (Na++ K+) concentration in the vacuole was 170 mol m−3 for plants grown at 25 mol m−3 NaCl and 420 mol 400 mol m−3 NaCl.The expanding root (issues exhibited greatly decreased soluble sugars and starch between dusk and dawn. Ai both times, sugar and starch concentrations in these tissues were 2.5–4.0 times greater in plants grown at 400 mol m−3 NaCl compared with plants grown at 25 mol m−3 NaCl. In contrast, carbohydrate concentrations in expanded root tissues were very similar at 25 and 400 mol m−3 and showed little diurnal fluctuation.This paper considers the causes for the slower growth of A. amnicola at 400 than at 25 mol m”3 NaCl, using the data for the roots described here, and those for the shoots presented in the preceding paper (Aslam et al., 1986). There is no support for possible adverse effects by high internal ion concentrations. Instead, there may be deficiencies in supply of organic solutes for osmotic regulation; during part of the night a limited supply of such solutes may well restrict the rate of expansion of cells in plants growing at 400 mol m−3 NaCl. There is insufficient evidence to decide whether this limitation in the expanding tissues is particularly prominent for the roots or for the shoots.

Notes: Summary. Soluble potassium concentrations were determined for the slightly vacuolated, unicellular, walled alga Chlorella emersonii. Sap of cells grown in 1 mol m−3 NaCI contained 140 mol m−3 K+ and sap of cells grown in 125, 200, and 335 mol m−3 NaCI contained 160-180 mol m−3 K +.The possible regulation of K + concentrations by a system of lurgor and volume maintenance was investigated by supplying 3-0-methylglucose. This solute accumulates to 85-230 mol m−3 in C. emersonii, but is not metabolized. Accumulation of 3-0-methylglucose increased the volume of cells grown at both low and high NaCI by about 10%. Furthermore, accumulation of 3-0-methylglucose also increased turgor pressures of cells grown in 1 and 125 mol m−3 NaCI by 0.3 and 0.2 MPa, respectively. (Similar measurements were not attempted for cells grown in 200 and 335 mol m−3 NaCI, because of the insensitivity of available methods to measure turgor pressure of cells exposed to high external osmotic pressures.)At all NaCI concentrations, the K + concentrations of cells which had accumulated 3-0-methylglucose were only 10-20 mol m−3 lower than K+ in cells which had not been supplied with 3-0-methylglucose. In contrast, accumulation of 3-0-methylglucose greatly decreased concentrations of the endogenous osmotic solutes, proline and sucrose, which accumulated in cells grown in 125 mol m−3 and higher NaCI concentrations.It is concluded that K+ concentrations in Chlorella emersonii are not controlled by a system of turgor and volume maintenance.

Notes: Abstract. The type of endogenous osmotic solute accumulated by Chlorella emersonii grown at high external osmotic pressure (πext) depended on the light/dark conditions: proline accumulated to high concentrations in cells in the light, while sucrose accumulated to high concentrations in the dark. These findings were made during the alternating light dark cycles used to obtain synchronized cultures, i.e. cultures containing cells at only one stage of development at any one time. Similar decreases in proline and increases in sucrose in the dark were found for cells previously grown in continuous light to obtain non-synchronized cultures, i.e. cultures containing cells at all stages of development.In cultures synchronized at 200 mol m −3 NaCl (πext= 1.01 MPa), recently divided ‘daughter cells’ at the beginning of the light periods contained 60 mol m−3 proline and 100mol m−3 sucrose, while mature cells towards the end of light periods contained 130 mol m proline and 20 mol m−3 sucrose. The changes in proline and sucrose which occurred in synchronized cultures were due mainly to light/dark conditions and to a much lesser extent to different stages of cell development. The proportion of proline to sucrose in daughter cells collected from non-synchronized cultures in continuous light was not different from the proportion in heterogeneous populations of cells.Results are discussed in relation to the accumulations of two, rather than one, endogenous osmotic solute and to growth reductions of C. emersonii exposed to high external osmotic pressures.

Notes: Abstract. Environment and plant measurements were made to determine what factors may limit growth of deepwater and floating rice plants during partial or complete submergence. Field surveys included measurements of temperature, pH, light, O2 and CO2 in floodwater in Thailand. In addition, measurements were made of O2 and CO2 concentrations inside internodal lacunae of deepwater and floating rice growing at 0.5–2.0 m water depths.The bulk of measurements were taken during periods when the changes in water level were less than 50 mm d−1. In the 0–0.02 m surface layer of floodwater at any location there were large changes in oxygen concentrations over diurnal cycles: there were decreases during the night down to 0.02–0.18 mol m−3 O2 at 0600 h and increases during the day to 0.13–0.28 mol m−3 O2 at 1500 h (0.28 mol m−3 being 120% of the O2 concentration of air saturated water at 30°C). During the day oxygen concentrations decreased with increasing water depth; concentrations just above the soil surface were occasionally zero. Most of this gradient disappeared during the night, and at dawn the 0.6 m surface layer of water had uniform low O2 concentrations.O2 concentrations were also measured during flash floods in Thailand. In contrast to the conditions with only small increases in water level, the O2 concentrations in the water during flash floods were more uniform with depth and changed little over a diurnal cycle, the O2 ranging between 0.14–0.19 mol m−3.In most locations floodwater contained 0.2–1.9 mol m−3 CO2 and 0.7–1.6 mol m−3 bicarbonate; however, in a location with acid sulphate soil CO2 was only 0.05–0.2 mol m−3, and bicarbonate concentrations were several fold lower. Concentrations of CO2 in floodwater increased with increasing water depth.O2 and CO2 concentrations inside internodal lacunae of rice were determined in the field when water depth were 1–2 m. Concentrations of O2 in internodes at the water surface were 16–20%, and decreased to 10% and 5% at 0.8 and 1.8 m water depth respectively. There was no diurnal cycle in O2 concentrations inside internodes. In contrast, CO2 concentrations in the lacunae increased with water depth and ranged from 1–3% in internodes at the water surface to 5–10% in internodes at 1.8 m water depth. There was evidence for a diurnal cycle in CO2 concentrations in the basal internode near the soil surface, CO2 increased during the day and decreased during the night.The above data are used to show that there is little or no relationship between gas concentrations in floodwater and internodal lacunae of rice plants. Results are discussed in relation to O2 supply to submerged portions of rice and metabolism of these tissues at low O2 concentrations.