Effects of external NaCl on the growth of Atriplex amnicola and the ion relations and carbohydrate status of the leaves

Abstract Atriplex amnicola, was grown in nutrient solution cultures with concentrations of NaCl up to 750 mol m^?3. The growth optimum was at 25–50 mol m^?3 NaCl and growth was 10–15% of that value at 750 mol m^?3 NaCl. Sodium chloride at 200 mol m^?3 and higher reduced the rate of leaf extension and increased the time taken for a leaf to reach its maximal length. Concentrations of Na⁺, K⁺ and Mg²⁺ in leaves of different ages were investigated for plants grown at 25, 200 and 400 mol m^?3 NaCl. Although leaves of plants grown at 200 and 400 mol m^?3 NaCl had high Na⁺ concentrations at young developmental stages, much of this Na⁺ was located in the salt bladders. Leaves excluding bladders had low Na⁺ concentrations when young, but very high in Na⁺ when old. In contrast to Na⁺, K⁺ concentrations were similar in bladders and leaves excluding bladders. Concentrations of K⁺ were higher in the rapidly expanding than in the old leaves. At 400 mol m^?3 NaCl, the K⁺:Na⁺ ratios of the leaves excluding bladders were 0.4–0.6 and 0.1 for rapidly expanding and oldest leaves, respectively. The Na⁺ content in moles per leaf, excluding bladders, increased linearly with the age of the leaves; concurrent increases in succulence were closely correlated with the Na ⁺ concentration in the leaves excluding the bladders. Soluble sugars and starch in leaves, stems and buds were determined at dusk and dawn. There was a pronounced diurnal fluctation in concentrations of carbohydrates. During the night, most plant parts showed large decreases in starch and sugar. Concentrations of carbohydrates in most plant organs were similar for plants grown at 25 and 400 mol m^?3 NaCl. One notable exception was buds at dusk, where sugar and starch concentrations were 30–35% less in plants grown at 400 mol m^?3 NaCl than in plants grown at 25 mol m^?3 NaCl. The data indicate that the growth of A. amnicola at 400 mol m^?3 NaCl is not limited by the availability of photosynthate in the plant as a whole. However, there could have been a growth limitation due to inadequate organic solutes for osmotic regulation.     

Cereal production,crop protection and plant breeding*

Trends in British agriculture which have led to the eclipse of rotations, to the concentration of cereal production on wheat and barley, and to a changeover to winter cereals, have increased the vulnerability of cereal crops to disease. Epidemics have been prevented by the deployment of effective resistances and, more recently, of a wide range of crop protection chemicals. Ecological protection by means of variety mixtures and field diversification has now added a new and effective element for the defence of cereals. The problem of durability of resistances and of the continuing effectiveness of chemicals remains, and new problems of susceptibility of crop varieties to herbicides have arisen. It is possible through the combined use of genetical, chemical and ecological defence mechanisms, to maximise the period of effectiveness of resistance genes and of fungicides and insecticides. The experience of the past half-century has shown that dependence on a single protective mechanism provides only a transient solution to controlling disease.     

The Rate of Morphogenesis of Embryos and Seeds in Four Species of Grain Legumes

Comparative embryo development has been studied histologicallyin Lupinus albus, Lupinus mutabilis, Vicia faba, Pisum sativumand Latkyrus latifolius. The detailed histology of the stagesof embryo formation up to the early differentiation of tissuesof the seed is reported. The rate of embryogenesis has beentimed through 15 stages of development from anthesis and comparativerates of tissue formation established between the species. Themain observation was the slow rate of morphogenesis of embryosand seeds in Lupinus albus in comparison with the very rapidrate observed in Pisum sativum. A long period at the globularembryo stage, when embryo morphogenesis was inactive contributedto the extended development time of embryos and seeds in Lupinusalbus. Slow differentiation of reproductive tissues in L. albusdetermines late maturity in seeds and pods. Lupinus albus, white lupin, L. mutabilis, tarwi, Vicia faba, faba bean, Pisum sativum, pea, Lathyrus latifolius, everlasting pea, embryo development     

Effects of Anoxia on Wheat Seedlings: I. INTERACTION BETWEEN ANOXIA AND OTHER ENVIRONMENTAL FACTORS

Anoxia was imposed on 4–6-d-old, intact wheat seedlings,after the roots had first been exposed for 1 d to O₂ concentrationsbetween 0·016 and 0·06 mol m^–3. Apices ofthe main axis of the seminal roots were considered to have toleratedanoxia if elongation occurred after return from anoxia to air,hereafter called ‘retention of elongation potential’.During anoxia, elongation potential was retained longer in rootsof intact seedlings than in 0–5 mm excised root tips suppliedwith 50 mol m^–3 glucose. In intact seedlings, elongation potential was retained longerat 15°C than at 25°C, and at pH 50 and 60 than at pH40. These differences between treatments were maintained inthe presence of exogenous glucose, and glucose supply prolongedthe retention of elongation potential in all anoxic treatments. Elongation potential was retained much longer at very low 02concentrations (0006 to 00l mol m^–3) than under anoxia;this was established at pH 40. Anoxia inhibited the transport of sugars from the shoots and/orendosperm to the root by 79-97%, as assessed from experimentswith roots of intact plants exposed to anoxia at pH 60 and 15°C. Overall, the results demonstrate: (i) that the occurrence ofadverse effects of anoxia during waterlogging in the field mayinteract with other environmental factors and (ii) that thereare pronounced difficulties integrating data on tolerance toanoxia obtained in different laboratories. Key words: Anoxia, wheat seedlings, pH, temperature     

Effects of external NaCI, and of changes in turgor pressure and volume, on K+ concentrations in Chlorella emersonii

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.     

Root Development and Aerenchyma Formation in Two Wheat Cultivars and One Triticale Cultivar Grown in Stagnant Agar and Aerated Nutrient Solution

Stagnant nutrient solution containing 0.1% agar and with anextremely low oxygen level (‘stagnant agar solution’)was used to simulate the gaseous composition and slow gas diffusionof waterlogged soils. Comparisons were made between the growthof two wheat cultivars(Triticum aestivum,cvs. Gamenya and Kite)and one triticale cultivar(Triticosecale,cv. Muir) grown instagnant relative to aerated solution. For all genotypes tested,immersion of roots in stagnant agar solution resulted in thedeath of the entire seminal root system and led to profuse branchingof the laterals of the nodal roots. In the stagnant agar solutionaerenchyma, as a percentage of the total cross sectional areaof nodal roots, was 18% for Muir, 14% for Kite and 12% for Gamenya;the roots of species with more aerenchyma also attained a longermaximum root length as predicted by the model of Armstrong (in:Woolhouse HW, ed.Advances in botanical research, vol. 7. London:Academic Press, 1979). Muir also had a nodal root/shoot freshweight ratio of 0.5 compared with 0.2–0.3 in Kite andGamenya. The greater number and length of nodal roots of Muirdid not lead to better shoot growth than in the other genotypes;one possible reason for this lack of improvement is a low efficiencyof aerenchymatous roots in wheat.Copyright 1998 Annals of BotanyCompany Root development; aerenchyma; stagnant agar;Triticum aestivumcv. Gamenya;Triticum aestivumcv. Kite;Triticosecalecv. Muir.     

INVESTIGATIONS ON RESISTANCE TO DISEASE AMONG SPECIES OF THE GENUS AVENA

Fifty-three samples representing species of the genus Arena were tested for resistance to infection by Ustilago avenae and U. kolleri following artificial inoculation. Among the diploid and tetraploid species tested, eleven out of thirty-seven samples of Arena strigosa subsp. strigosa showed complete resistance to all the cultures with which they were inoculated. Avena strigosa subsp. barbata (three samples), and Avena strigosa subsp. abyssinica (one sample), also proved to be resistant to all the available races.
Variation in morphological and physiological characteristics within species and samples (varieties?) of the lower chromosome groups of Avena were observed and its consequences in breeding and race identification discussed.
Race identification was carried out on the eight Ustilago cultures and the existence of at least six races established. The tester varieties used in the present study proved inadequate for the complete separation of the smut races.