The Sensitivity of Light Modulation of Enzyme Activity to Arsenite and Sulphite and of Photosynthetic Induction toArsenite is Determined by a Cytoplasmic Gene

Muschinek, G., Alscher, R. and Anderson, L. E. 1987. The sensitivityof light modulation of enzyme activity to arsenite and sulphiteand of photosynthetic induction to arsenite is determined bya cytoplasmic gene—J. exp. Bot. 38: 1069–1075. The membrane component of the light modulation system was moresensitive to arsenite and to sulphite in the Pisum cultivar‘Nugget’ than in the cultivar ‘Progress No.9’. Likewise, the induction phase of CO₂ fixation wasmore arsenite sensitive in chloroplasts isolated from ‘Nugget’plants. Sensitivity was controlled by a cytoplasmic gene. Key words: Induction, light modulation, arsenite sensitivity     

An architectural analysis of Archaeopteris9 a fossil tree with pseudomonopodial and opportunistic adventitious growth

Currently recognized hierarchies of lateral organs in Archaeopteris are presented and phenomena that mediate organography and organotaxis in the taxon are discussed. It is demonstrated that Archaeopteris is totally lacking extant architectural analogues, and the methodology employed in the architectural analysis of such fossil plants is introduced. Proposed growth categories or phases for the Archaeopteris plant are presented and tested against evidence from a large silicified log of Callixylon, the trunk of Archaeopteris. An architectural model is put forward that encompasses such growth phaseS. Finally, the occurrence of reiterative, opportunistic growth in Archaeopteris is discussed.     

Micronuclear DNA from Paramecium tetraurelia: Serotype 51 A Gene Has Internally Eliminated Sequences

A method for the isolation of micronuclear DNA from Paramecium tetraurelia has been developed. After cell lysis, a low speed centrifugation at 1,000 g is used to remove all of the unbroken cells and macronuclei and approximately two thirds of the macronuclear fragments. Next a higher speed centrifugation of 9,000 g sediments the micronuclei and frees them from small particulates and soluble constituents. Advantage is then taken of the fact that micronuclei have a lower density than do macronuclear fragments in 45%–60% Percoll. Micronuclei float to the top during centrifugation at 24,000 g , while macronuclear fragments sediment. After several cycles of centrifugation in Percoll, the micronuclei, although heavily contaminated with cytoplasmic components, are essentially free of macronuclei and macronuclear fragments. Micronuclear DNA can then be extracted from the suspension. The whole procedure is very rapid and in about an hour micronuclear and macronuclear DNA can be separated. About 2 μ g of micronuclear DNA can be obtained from 6 times 10⁷ paramecia. We find that there are internal sequences in the micronuclear A gene DNA in wild type cells which are eliminated when the micronuclei develop into macronuclei. They yield unique restriction fragments for micronuclei and macronuclei. Therefore the purity of the preparations is easily monitored by probing Southern blots of restriction enzyme-digested DNA with the cloned A gene. No differences have been found between the micronuclear A gene in wild type and the d48 mutant.     

Results of Intracecal Inoculation of Germfree and Conventional Guinea Pigs and Germfree Rats with Axenically Cultivated Entamoeba histolytica

SYNOPSIS. Germfree and conventional guinea pigs and germfree rats were inoculated with large numbers of axenically cultivated Entamoeba histolytica. Amebic lesions were not found in any of the animals, and there was no indication that the ameba had established lumen infections in any instance. The axenic amebae appeared to have lost their pathogenicity. This loss was believed to depend, in part at least, upon the fact that they did not encyst and thus did not complete their life cycle in axenic culture.     

Conserving weedy natives: Two Tasmanian endangered herbs in the Brassicaceae

Abstract Two species of endangered Brassicaceae, Barbarea australis and Lepidium hyssopifolium, occur in a few small populations in Tasmania. The former species is associated with streams where it occurs in vegetation with numerous exotics. The latter species is usually found in the root zone of exotic large trees, usually on roadsides, and often in the absence of many other native species. Populations of both species have disappeared since European settlement, some in the last two decades. Both species are rapid and prolific producers of easily germinated seed. Both species are absent from places grazed moderately or intensively by sheep or cattle. The establishment of new individuals of Lepidium occurs only on relatively bare ground. The species is tolerant of root competition and intolerant of above ground competition. It will also establish from soil-stored seed after mechanical disturbance. Its future is linked to the survival of grazing-free locations where above ground competition from herbs and grasses is subdued. Barbarea is a ruderal that requires freedom from stock grazing for its persistence in Tasmanian riparian habitats. These results reinforce the importance of some degraded ecosystems for biodiversity conservation, and the critical role of disturbance regimes in influencing the survival or extinction of a subset of native plant species. In the fragmented and variegated landscapes of today, weedy natives cannot necessarily be expected to survive in non-weedy environments.     

Prediction of the coefficient of variation of carrot embryo length from a germination test

The value of the International Seed Testing Association (ISTA) germination test in estimating levels of variation in embryo length between carrot seed lots was examined. For the two groups of seed lots used, the coefficient of variation (c.v.) of embryo length ranged from 16 to 50%. The c.v. of embryo length was negatively correlated with the numbers of normal seedlings counted after 7 days of germination at 20°C, r_s= - 0·72 D.F. 12 and - 0·82, D.F. 15 for the two groups of seed lots used. Provided the relationship between these two characters is established for each laboratory, it is likely to be useful in identifying seed lots of potentially low c.v. of embryo length.     

Alpha, an Infectious Macronuclear Symbiont of Paramecium aurelia

SYNOPSIS. A spiral, rod- or crescent-shaped symbiont here designated alpha, is present in the macronucleus of killer stock 562, syngen 2 of Paramecium aurelia. This stock has a cytoplasmic symbiont, kappa, as well as alpha. Lines were obtained which had only alpha, others which had only kappa, and some which had neither. It was possible to purify and separate both kinds of symbiont from homogenates of stock 562 using an ECTEOLA column. The killing action of this stock is due to kappa, not alpha. Observations on the structure of alpha with the electron microscope indicate that alpha, like the cytoplasmic symbionts in this species, is a bacterium. Alpha is never seen in the micronucleus, is rarely found in the cytoplasm, but abounds in the macronucleus. If paramecia are allowed to grow slowly after autogamy, alpha passes from the old macronuclear fragments, infects the new macronucleus, and all animals retain alpha. In exautogamous paramecia growing at maximum fission rate, however, alpha often does not infect the new macronucleus and is lost from many lines when the old macronuclear fragments disappear. In mixed cultures containing alpha-bearing and alphafree paramecia, it has been found that alpha readily invades the macronucleus of paramecia of susceptible stocks. Homogenates of alpha-bearing cultures are also infective. Infection is highly specific, occurring in only 6 of the 44 stocks of P. aurelia in which infection was attempted, and these 6 are all syngen 2. It is suggested that the short rod or crescent form of alpha is the reproductive form, while the elongated spiral form is probably the invasive motile form.     

Studies on the Origin of the Methyl Groups of Choline in Ochromonas malhamensis*

SYNOPSIS. Five- to 6-day-old resting cells of Ochromonas malhamensis were incubated at pH 6.5 with glucose and appropriate C¹⁴ precursors of the methyl groups of phospholipid-choline. Under the experimental conditions L-methionine-C¹⁴H₃ was the most efficient source of choline-methyl groups, followed by formate-C¹⁴, formaldehyde-C¹⁴ and DL-serine-3-C¹⁴, respectively. Glycine-2-C¹⁴ was not incorporated into choline. Both L-methionine-C¹⁴H₃ and formate-C¹⁴ served as precursors for the methyl groups of monomethylethanolamine, dimethylethanolamine and choline. Addition of non-radio-active L-methionine depressed the incorporation of formate-C¹⁴ into choline-methyl groups by 50%. The results support the hypothesis that methionine can be the source of all 3 methyl groups of choline, and that formate is probably converted to the methyl group of methionine before transmethylation to choline. However, an alternate pathway from single-carbon sources cannot be excluded.