Photodynamic Effects of Rose Bengal on Senescent Flax Cotyledons

Senescent cotyledons, excised intact from 6-d-old Flax (Linumusitatissium) seedlings, were treated with Rose Bengal, a photo-sensitizingagent. In continuous light, chlorophyll breakdown was increasedfrom 44% in untreated cotyledons to 73% in Rose Bengal-treatedcotyledons. Depletion of carotenoid and linolenic acid was enhancedby 25% and 39% respectively over the same period. After 48 hthe decline in uncoupled photosynthetic electron transport wasincreased from 58% to 82% in isolated chloroplasts. Over thesame period CO₂ exchange was greatly inhibited in treated cotyledons.Rose Bengal had little effect on dark incubated cotyledons,suggesting that singlet oxygen generated by photo-sensitizedreactions was responsible for the enhanced deterioration ofstructure and function of senescent cotyledons and the primesite of action was the photosynthesis apparatus. These photodynamiceffects are discussed in relation to the possible involvementof toxic oxygen species in the senescence of leaf tissue. Key words: Senescence, Photodynamic damage, Rose Bengal, Singlet oxygen     

Fruit Softening I. Changes in Cell Wall Composition and endo-Polygalacturonase in Ripening Pears

Softening of pome fruits during ripening is characterized bythe solubilization of pectin. The activity of endo-polygalacturonase(endo-PG, EC 3.2.1.15 [EC] ) was determined in pears (Pyrus communisL.) ripened at 18 °C, after storage at –1°C. Theenzyme was assayed, using viscometry, in the presence of pectinesterase(EC 3.1.1.11 [EC] ) with citrus pectin as substrate. Endo-PG activitywas not detected in fruit assayed immediately from store at–1 °C but the enzyme was present after 2 d at 18 °Cwhen the fruit had started to soften and degradation of solublepectin was apparent.     

The Communal Way of Life in the Splendid Wren,Malurus splendens

Splendid Wrens were studied over 7 breeding seasons in Western Australia. A colourbanded population (54 adults and 160 nestlings) of these small dimorphic passerines occupied a saturated habitat and dispersed little. Annual mortality of ♀♀ was 57% compared to ♂♂ at 29%; this high rate of turnover of ♀♀ reduces the chances of inbreeding. 2/3 of the territorial groups contained one or more helpers; groups with helpers did not produce more young than those without, but the helping role ensured priority of opportunity to inherit their own group-territory or to succeed to a neighbouring one, wheresoever breeding vacancies occurred. Helpers reduced the stress on breeding ♀♀ in many ways.     

Arbuscular mycorrhizal fungi: genetics of multigenomic, clonal networks and its ecological consequences

Arbuscular mycorrhizal fungi are thought to have remained asexual for 400 million years, although recent studies have suggested that considerable genetic and phenotypic variation could potentially exist in populations. A brief discussion of these multigenomic organisms is presented.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 59–60.     

Ordovician conodont biogeography – reconsidered

Review of the traditional separation of global Ordovician conodont distribution into the North American Midcontinent Province (NAMP) and North Atlantic Province (NAP) reveals a confusing variety of concepts and definitions that hinder biogeographic analysis. Use of this twofold scheme and its subsequent variants should be­discontinued in favour of the more detailed divisions proposed here. Major biogeographical entities of the Shallow-Sea and Open-Sea Realms, separated by the shelf-slope break, are both further subdivisible into Tropical, Temperate and Cold Domains. In the Cold domains, faunal differences between the two Realms and their subdivisions are not easily discernible, since biofacies zones and different habitats were highly condensed. Faunal differences are amplified in the tropical regions, where the North American Midcontinent Province and North Atlantic Province were originally defined. Recognition of endemic taxa is essential for finer classification within domains of the Shallow-Sea Realm (SSR). Our preliminary analysis of Early Ordovician conodont distribution identifies the Laurentian Province (in the Tropical Domain), Australian­(Tropical Domain), North China (Tropical Domain), South China (Temperate Domain), Argentine Precordillera (Temperate Domain) and Balto-Scandian Province (in the Cold Domain). The Open-Sea Realm (OSR) is dominated by cosmopolitan and widespread taxa, and formal subdivision at provincial level is yet to be achieved. The North Atlantic Province encompasses both the Open-Sea Realm and the Temperate and Cold Domains of the Shallow-Sea Realm. The North American Midcontinent Province sensu stricto is more or less equivalent to the Laurentian Province, representing shallow-water regions fringing Laurentia; in a broader sense the North American Midcontinent Province includes all provinces of the Tropical Domain within the Shallow-Sea Realm.     

Scanning Electron Microscope Observations on Some Life History Stages of Carchesium polypinum (Ciliata,Peritrichia)1

SYNOPSIS. Sessile zooids, and mobile telotrochs and microgamonts of Carchesium polypinum (Protozoa, Ciliata, Peritrichia), were examined by scanning electron microscopy. The results were compared to earlier light and electron microscope studies in order to investigate structural changes concerned with adaptation and differentiation. Telotrochs and microgamonts always had a contracted peristome and usually had a long phalange of cilia. Striae around the contracted buccal apparatus in all 3 stages were convoluted and often had thickened margins; those in telotrochs and microgamonts had oral-aboral ectoplasmic cross-connections. Nonbuccal striae of telotrochs and microgamonts varied in structure and height differences between epiplasmic peaks and alveoli surface membranes. The number of striae were constant in all 3 stages. Pellicular pore structure did not vary in any of the stages examined and resembled parasomal sacs located near buccal structures. Fully relaxed sessile zooids had ectoplasmic ridges coursing from polykinety kinetosomes and cilia to an area in front of the ciliated portion of the haplokinety; these ridges were interpreted to be the interkinetal fibers. Telotroch bands of sessile zooids consisted of 2 or 3 parallel ectoplasmic ridges which circled the aboral region and contained structures resembling pores. Telotroch bands in telotrochs and microgamonts had 2 enlarged, parallel ectoplasmic ridges circling the aboral region; telotroch band cilia were found between these ridges. In addition, a fold-like, ectoplasmic structure extended beyond the 2 ridges and was located between the telotroch band cilia and the aboral ridge. The epiplasmic shelf surrounding the stalk in sessile zooids was enlarged in telotrochs, and cilia were seen in the scopula depression. No scopula organelle was seen in any microgamont.     

A Further Study of {beta}-Galactosidase Activity in Apples Ripening in Store

Apples (Malus domestica Borkh.) were ripened in 2% O₂ at 3·3°C. The loss of galactose residues from the cortical cellwalls was initiated after 27 d although an increase in the ß-galactosidaseactivity of the tissue did not occur until after 50 d. ß-Galactosidase activity associated with the cellwall was determined using discs of cortical tissue. A substantiallevel of activity was observed prior to picking and subsequentlyduring ripening of the apples in air.     

Models of clines in sexual selection by female choice

Most models of sexual selection by female choice have considered discrete, homogenous populations. This paper studies the evolution of a female preference along a cline in the frequency of a preferred male trait. Single alleles control both the preference and preferred character.
Fisher's process initially causes the preference to spread to some 'maximum' frequency with a corresponding rise in character gene frequency. At this stage, the cline in preference does not necessarily mirror that of the trait. Then, however, preference frequency usually decreases, albeit very slowly, and the preference cline always comes to mirror that of the preferred character. Eventually, preference is completely lost from the cline and the character cline decays to that seen under random mating. This loss can only be prevented if the preference is initially frequent enough to push the character to fixation throughout the cline.
Consequently, a preference that arises after the preferred trait may increase very little in frequency itself and have a negligible effect on trait frequency before being lost from the population. Special conditions, such as cyclical natural selection, may be necessary to explain the spread of a preference in a cline from a low initial frequency to frequencies as high as those observed. A preference that predates the preferred trait can enter the population at a high frequency and radically alter a cline in the frequency of a preferred male trait, albeit often transiently.