Megaspore germination, embryo development and maintenance of the symbiotic association in Azolla filiculoides Lam.

Megaspore germination and embryo development in Azolla filiculoides was examined using SEM and thin–sectioning. Within the released megaspore apparatus, resting cells of the endosymbiont Anabaena azollae Stras. arc located distally to the outside of the mcgasporangial wall and adhering to the inside of the megasporocarp wall. Growth of the female gametophyte displaces the floats pushing this part of the wall (the indusial cap) upwards, so providing access to the archegonia for the multifiagellalc spermalozoids. Embryo development and its inoculation with Anabaena involves a subtly–timed sequence of events resulting in the perpetuation of the symbiosis. Growth of the lunnel–shaped cotyledon leaf ruptures the mcgasporangial wall to provide access and a channelled route between the Anabaena and embryo shoot apex; subsequent leaf development severely restricts such access. During this process, the Anabaena is dislodged by the cotyledon leaf and growth of the first leaf traps the now actively–dividing Anabaena colonv; this becomes established around subapical trichomes from where filaments become incorporated into the cavities of developing leaves. The voung sporophyte rises vertically to the water surface as a result of gas accumulation in intercellular spaces; at no stage do floats endow buoyancy.     

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.     

The Aeration of Catharanthus roseus L. G. Don Suspension Cultures in Airlift Bioreactors: The Inhibitory Effect at High Aeration Rates on Culture Growth

An investigation was carried out to examine the effect of aerationon the growth of Catharanthus roseus suspension cultures inairlift bioreactors. A high aeration rate (0·86 v.v.m.)was found to inhibit the growth of cultures. Venting culturesat a high rate with low oxygen content gas mixtures was equallyinhibitory to culture growth, showing that high aeration wasnot inhibitory as a result of oxygen toxicity. The dissolvedcarbon dioxide tension was found to be lower in cultures operatedat high aeration than those operated at low aeration. Supplyingexogenous CO₂ to cultures at high aeration restored the CO₂tension to values normally encountered at a low aeration rate,and was found to alleviate the inhibitory effects at high aeration.However, further increasing the CO₂ supply to cultures was foundto be severely inhibitory to growth. Therefore, the growth ofC. roseus cultures is very sensitive to dissolved CO₂ concentration,growth being inhibited at values either higher or lower thanan optimum. Key words: Aeration, carbon dioxide, Catharanthus roseus suspension culture     

Terrestrial carbon storage resulting from CO2 and nitrogen fertilization in temperate grasslands

Abstract. A temperate grassland model has been used to simulate carbon sequestration under various environmental conditions. The results suggest that the CO₂ and nitrogen fertilization that has occurred may contribute appreciably to the so-called missing carbon sink, which it has been suggested must exist to balance the global carbon budget.