The rhodopsin system of the squid

Squid rhodopsin (λ_max 493 mµ)—like vertebrate rhodopsins—contains a retinene chromophore linked to a protein, opsin. Light transforms rhodopsin to lumi- and metarhodopsin. However, whereas vertebrate metarhodopsin at physiological temperatures decomposes into retinene and opsin, squid metarhodopsin is stable. Light also converts squid metarhodopsin to rhodopsin. Rhodopsin is therefore regenerated from metarhodopsin in the light. Irradiation of rhodopsin or metarhodopsin produces a steady state by promoting the reactions, See PDF for Equation Squid rhodopsin contains neo-b (11-cis) retinene; metarhodopsin all-trans retinene. The interconversion of rhodopsin and metarhodopsin involves only the stereoisomerization of their chromophores. Squid metarhodopsin is a pH indicator, red (λ_max 500 mµ) near neutrality, yellow (λ_max 380 mµ) in alkaline solution. The two forms—acid and alkaline metarhodopsin—are interconverted according to the equation, Alkaline metarhodopsin + H⁺ acid metarhodopsin, with pK 7.7. In both forms, retinene is attached to opsin at the same site as in rhodopsin. However, metarhodopsin decomposes more readily than rhodopsin into retinene and opsin. The opsins apparently fit the shape of the neo-b chromophore. When light isomerizes the chromophore to the all-trans configuration, squid opsin accepts the all-trans chromophore, while vertebrate opsins do not and hence release all-trans retinene. Light triggers vision by affecting directly the shape of the retinene chromophore. This changes its relationship with opsin, so initiating a train of chemical reactions.     

Ovule Development and Determination of Seed Number Per Pod in Oilseed Rape (Brassica napus L.)

Seed number per pod at maturity over the terminal raceme ofsingle plants of oilseed rape is closely correlated to the percentageof ovules with complete embryo sacs (ovule fertility) at floweropening. Approximately one-third of the ovules did not containan embryo sac and sterility, due to the absence of embryo sac,accounted for most of the difference between the numbers ofovules and seeds. Within the terminal raceme, both a decreasedproportion of fertile ovules and a lower number of ovules perovary in apical flowers contributed to the lower number of seedsper pod in the mature apical pods compared to the basal ones.A study of ovule development before flower opening showed thatdifferences in the differentiation of the embryo sacs arosebefore the buds were 40 mm long and probably involved the stagesof meiosis II and/or differentiation of the chalazal megaspore. Key words: Oilseed rape, ovule development, seed number per pod     

Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike

Abstract.

• 1 The control of ovine myiasis by suppression of populations of the blowfly Lucifia sericata was investigated experimentally on three farms in the south-west of England in 1992 and 1993.
• 2 In blind trials, sheep on one farm (control) were given two doses of placebo, on a second two doses of the larvicide cyromazine (Vetrazin®, CibaGeigy), and on a third cyromazine and a subsequent dose of placebo.
• 3 The first treatment was given shortly before the predicted spring emergence of L.sericata and the second shortly before the predicted emergence of the second generation. Previous simulation analysis had identified strategic early-season treatment as the optimum for blowfly population suppression.
• 4 On both treatment farms significantly smaller L.sericata populations were recorded throughout 1992 and the incidence of strike was significantly lower than on the control farm. The results show that appropriate early-season timing of sheep treatment can suppress populations of L.sericata and could be used by farmers to reduce the incidence of blowfly strike.
• 5 The results suggest, however, that the effectiveness of population suppression and strike incidence may have been influenced by immigration into the control areas and by adverse weather, the latter changing the susceptibility of sheep to strike and resulting in rising strike incidence even when L.sericata population densities were low. In practice, therefore, blowfly population suppression should be employed as a component of an integrated strike management programme.

     

Time course of photosynthetic temperature acclimation in Carex eleocharis Bailey

Abstract Photosynthetic temperature acclimation in Carex eleocharis has been demonstrated in a previous study in which warm grown (35/15°C) plants were shown to have photosynthetic temperature optima approximately 14°C higher than cool grown (20/15°C) plants (Monson, Littlejohn & Williams, 1983). The current study examined the time course of this acclimation by determining photo-synthetic temperature optima as a function of time, of cool grown plants moved to warm growing conditions. Leaves which had developed under cool conditions were capable of an upward adjustment of 6–8°C of their optimum photosynthetic temperature within a time span of 6–14 d. For greatest photosynthetic temperature acclimation it was necessary for leaves to form and develop entirely under warm conditions. These leaves exhibited a 14–15°C upward adjustment of their optimum temperature for photosynthesis within 20–31 d since moving plants from cool to warm growing conditions. Thus, the time course of this acclimation is of short enough duration to be significant during the growing season and presumably contributes toward the ability of this species to maintain active growth during the cool and warm portions of the growing season. It is also noted that the plant with its capacity to form new leaves, has a much wider acclimation capacity than any single leaf.     

Clinal variation, episodic evolution, and possible parapatric speciation: the trilobite Flexicalymene senaria along an Ordovician depth gradient

Pygidial segmentation in the trilobite Flexicalymene senaria changes with time (as measured in relation to bentonite beds) and with depth (as measured along downslopc transects along bentomtc beds and as measured by gradient analysis of fossil assemblages) along a 'fossil' depth gradient in the Middle Ordovician Trenton Group in central New York State. The pattern of strictly temporal change resembles a 'punctuation' between 'equilibria'. This evolutionary episode, a 10⁶ year interval of continuous change, may represent parapatric speciation. The clinal gradient is strongest during this episode and is weak or not apparent outside it. Strictly temporal change takes place by way of temporal change in the cline's shape. □ Evolution, geographic variation and dines, gradient analysis. Middle Ordovician, morphometry, speciation, Trilobita.     

Control of Botrytis cinerea on glasshouse tomato by high volume sprays

The new fungicides iprodione, vinclozolin and prochloraz, and also a mixture containing carbendazim and maneb, were compared with the established protectant fungicides dichlofluanid and chlorothalonil for effectiveness against grey mould ( Botrytis cinerea ) in an unheated tomato crop. Iprodione and vinclozolin gave the best control of lesions on leaves and stems but dichlofluanid was the most effective in controlling ghost-spotting of fruit. The carbendazim/maneb mixture was effective against a carbendazim-sensitive isolate but not against an insensitive isolate of B. cinerea . When applied 1 or 2 days after inoculation, all five protectant fungicides controlled the insensitive isolate better than the sensitive isolate.     

Environmental Effects on Transpiration and Leaf Water Potential in Avocado

A field study was conducted to determine how atmospheric and edaphic conditions influenced the water relations of avocado trees (Persea americana Mill. cv. Bacon). With high and low levels of incident photosynthetically active radiation (PAR, 400–700 nm wave length), and either wet or dry soil, leaf conductance decreased as the absolute humidity difference from leaf to air increased. For any water stress treatment, conductance was higher at high PAR than at low PAR. Both conductance and transpiration were higher in well-watered trees than in stressed trees, and in prestressed trees levels were intermediate to unstressed and stressed trees. A model for water flux through the soil-plant-atmosphere continuum was used to examine the relationship of leaf xylem pressure potential to transpiration in well-watered trees and in trees stressed by dry soil. There was a close linkage between leaf xylem pressure potential and transpiration in unstressed and previously stressed trees with high or low PAR, i.e. similar potentials occurred with equivalent transpiration regardless of previous treatment or time of day. In stressed trees, xylem pressure potential was lower than in unstressed trees both during the day and night, and at a given transpiration rate the potential was lower after 1400 h than before that time. The model indicated that in stressed trees xylem pressure potential was uncoupled from transpiration, presumably because of altered resistance in the soil-root portion of the transport system.     

The Effects of Heat and Cobalt-60 Gamma-Radiation on Excystation of the Rat Coccidium,Eimeria nieschulzi Dieben, 1924*

SYNOPSIS. Sporulated oocysts of Eimeria nieschulzi Dieben, a rat coccidium, were exposed for 1 hr to Cobalt-60 γ-radiation (15, 30. or 60 k-rads), to heat (35, 40, or 45 C). or to both concurrently (15, 30, or 60 k-rads at 35 C) to compare the excystation capabilities of treated vs nontreated parasites. Intact, treated oocysts appeared structurally unaltered when viewed with the light microscope. Excystation of sporozoites occurred in all treated groups when their sporocysts were exposed to a trypsin-sodium taurocholate (TST) fluid, but after 150 min in TST the excystation rate was significantly lower than in non-treated sporocysts. Sporozoites which excysted from treated sporocysts were abnormal both in the excystation process and in their form and movement once outside the sporocyst.     

Evolutionary biology of the Devonian Brachiopoda of New York State: no correlation with rate of change of sea-level?

McGhee, G. R., Jr. 1992 04 15: Evolutionary biology of the Devonian Brachiopoda of New York State: no correlation with rate of change of sea-level?Lethaia, Vol. 25, pp. 165–172. Oslo. ISSN 0024–1164. Previous study has revealed the surprising lack of a relationship between relative sea-level position and the evolutionary biology of the Brachiopoda during the Devonian. To further explore this seeming anomaly, the potential relationship between the rate of change of sea-level and the evolutionary biology of these sessile benthic organisms is analyzed here. Successive linear modeling reveals a lack of correlation between the rate of change of sea-level and either extinction rate, origination rate, or diversity of the Devonian brachiopods. *Sea-level, rate of sea-level change, extinction, origination, diversity, Brachiopoda.