Van der Heijden, M.G.A. and Sanders, I.R. (eds) Microrhizal ecology

In his foreword to the volume, Philip Grime says: ‘Themost significant challenge for ecologists at the present timeis to continue to exploit the many current opportunities forpenetration into detailed mechanisms but simultaneously to activelypromote integration . . . within ecological research.Mycorrhizal ecology is uniquely positioned . . . toprovide a lead.’ The volume, edited by van der Heijdenand Sanders, thus aims to meet the twin needs of scaling up,from detailed molecular science to the ecosystem, and demonstratingthat the plant, as found in nature, is itself a community oforganisms that interact with other such     

Partial purification of hatching activity for Globodera rostochiensis from potato root diffusate

The potential of several chromatographic methods for isolating hatching factors for potato cyst nematodes from potato root diffusate was investigated using a bioassay based on emergence of juveniles from cysts. Gel filtration provided an overall estimate of molecular weight of 437 Da for the hatching activity and ion exchange chromatography indicated that at least 60% of the recovered activity was anionic in nature. Material less polar than the hatching activity could be removed by passing potato root diffusate through a reversed-phase Sep-Pak C₁₈ cartridge and the elutant showed 83.3 ± 4.4% (mean of 32 cysts) of the initial hatching activity. High performance liquid chromatography (HPLC) with a reversed phase, C₁₈ column and gradient elution (0–80% CH₃OH in water) confirmed that much of the hatching activity was polar and that it was not retained by this method of separation. A weak anion exchange resin achieved slight retention of much of the hatching activity and an ion pairing reagent lowered the polarity sufficiently to allow some retention in subsequent reversed phase HPLC on a C_IS column. Both ion exchange and ion pairing HPLC suggested that hatching activity was not chromatographed as a single compound and indicated that fractions able to influence the nucleolus of the nucleus within the dorsal pharyngeal gland cell did not always show hatching activity.     

Cytotaxonomic observations in tropical Vaccinieae (Ericaceae)

Chromosome numbers are reported for 36 accessions representing 31 species from nine genera of the tribe Vaccinieae, family Ericaceae. The plants are tropical and come from Southeast Asia and Central and South America. The taxonomy of the tribe is outlined in these regions. Genera are often poorly defined and taxa were chosen to reflect the range of variation of the Vaccinieae. Most Southeast Asian Vaccinium species were diploid (2n= 24) as were those of Agapetes subgenus Agapetes (apart from the Himalayan A. flava), Agapetes scortechinii and Costera endertii. All other accessions were found to be polyploid. The correlation between polyploidy, geographical distribution and the possession of an ‘anatomical complex’ of the leaf and stem in Vaccinieae of New Guinea and the neotropics is discussed.     

Changes in Stomatal Conductance in Intact Ageing Wheat Leaves in Response to Abscisic Acid

The characteristics of ABA-induced changes in the fluxes ofCO₂ and water vapour from whole leaves of spring wheat (Triticumaestivum cv. Wembley) were examined. Aqueous solutions of ABAwere supplied via the transpiration stream to intact leavesof different ages mounted within a gas exchange cuvette. ABA caused a reduction in stomatal conductance (g) that wasproportional to the concentration in the solution fed to theleaf. For the maintenance of a reduction in g there was a requirementfor a continual supply of ABA. At concentrations greater than10^–2 mol m^–3 ABA reduced g by at least 50% of thecontrol value, while 1.0 mol m^–3 closed stomata within2 h. Concentrations as low as 10^–3 mol m^–3 produceda 20% reduction in g. As leaves aged they became less responsiveto applied ABA. The possibility that the stomatal response may change aftera leaf has previously experienced a pulse of ABA was exploredby repeating the exposure of a leaf to 10^–2 mol m^–3ABA. The first pulse of ABA produced a greater reduction ing than a subsequent exposure the following day. This declinein response of g to ABA on repeated exposure was maintainedwith leaves of different ages. The characteristics of the stomatal response to ABA are discussedin the context of what is known about the location of receptorsfor the hormone. It seems likely that a failure to respond toABA that has previously accumulated in the guard cells shouldbe viewed by means of maximizing the sensitivity to the currentsupply of ABA. It is suggested that the smaller response ofthe stomata of older leaves to ABA makes them more susceptibleto water stress, so that they can act as sensors for decliningwater potentials to give early protection to younger, metabolicallyactive leaves. Key words: Abscisic acid, leaf age, stomatal conductance, Triticum aestivum     

Modification of Stomatal Conductance by Sulphur Dioxide

The mechanism of SO₂-induced changes in stomatal conductance(g) of alder was examined to determine if SO₂ affects guardcell function directly or indirectly through the SO₂-inducedchanges in photosynthesis. During experimental fumigations at SO₂ concentrations of 3–3µmol m^–3 (0.08 µl l^–1), stomatal closurepreceded declines in net photosynthetic rate (A), indicatingthat SO₂ can directly affect guard cells. From these and otherstudies it appears that the sequence of A and g responses maybe influenced by SO₂ concentration as well as by species. Fumigation with SO₂ did not cause increases in g, even whenthe intercellular substomatal CO₂ concentration (c_i) was reducedby 50 µmol mol^–1. Increases in g are not attributableto SO₂ effects on the CO₂-based stomatal control system. Key words: Air pollution, Alnus serrulata, gas exchange, stomata, sulphur dioxide