The contribution of setal blades to effective swimming in the aquatic mite Limnochares americana (Acari: Prostigmata: Limnocharidae)

Two rows (anterior and posterior) of long fine setae inserted on the 3rd, 4th and 5th segments of the last two pairs of legs of L. americana form functional swimming blades. Each swimming setal is mounted in a mobile basal socket, and the structure of the setal base and socket configuration ensure that the blades will be passively erected during the leg's power stroke to provide increased thrust and collapsed during the recovery stroke to reduce water resistance. The erect swimming blades increase the effective area for thrust by approximately 500%, making it possible for the mite to lift itself off the bottom. The IVth legs contribute the greater proportion of the thrust developed during paddling, and the 4th segment (genu) bears the largest swimming blades on both legs.     

The Axenic Culture of Strains of the Various Syngens of Paramecium aurelia*

SYNOPSIS Strains of the various syngens of Paramecium aurelia respond differently to the culture media developed for Strain 299 of syngen 8. Not only is there a variety of response between the syngens, but strains belonging to the same syngen respond differently to the 3 growth media.     

Neurohormonal control of ecdysone production: Comparison of insects and crustaceans

Summary

Ecdysteroid synthesis is regulated in insects by prothoracicotropic hormone (PTTH) and in crustaceans by molt-inhibiting hormone (MIH). These neurohormones exert opposite effects on their respective target tissues, PTTH stimulating the prothoracic glands and MIH inhibiting the Y-organs. The present work reviews recent progress in the neurohormonal regulation of prothoracic gland and Y-organ function. The steroid products of these glands are briefly discussed, as is current information on the structures of PTTH and MIH. Focus is placed on the mechanism of action of these hormones at the cellular level, as well as developmental changes in cellular sensitivity to PTTH. Though exerting different effects on ecdysteroid secretion, both PTTH and MIH increase cyclic nucleotide second messengers, are influenced by alterations in cellular calcium, and are likely to activate protein kinases. The contrasting steroidogenic effects of PTTH and MIH probably arise from differences in the cellular kinase substrates. In insects, such substrates enhance ecdysteroid secretion, possibly by increasing the translation of glandular proteins. In crustaceans, MIH-stimulated changes lead to the inhibition of both protein synthesis and steroidogenesis.     

Appraisal of contaminants in sediments of the Inner Bristol Channel and Severn Estuary

In the inner Bristol Channel and Severn Estuary, most contaminated stations were in muddy, depositional areas of the estuary, particularly along the Welsh coast between the Rivers Taff and Usk, and also on the English coast between Avonmouth and Severn Beach. Some deeper areas, dominated by sand and mixed sediments, also showed contaminant concentrations in excess of those predicted from sediment texture, organic matter, and aluminium or iron concentrations.
Concentrations of lead, copper, chromium, nickel and zinc have decreased in the muddy sediments since the 1970s, but only lead has decreased in sand. With the exception of zinc, which is high in the Severn, trace element concentrations were comparable to those from other British estuaries.
Landward of the proposed barrage, contaminants are associated with the sub-estuaries and muddy areas at their confluence with the main estuary. Post-barrage effects on contaminants will be focused in these muddy areas. However, fine sediment deposition on what are now sandy areas would increase their contaminant burden unless calcium build-up from the resulting molluscan fauna has the antagonistic effect of contaminant dilution in the sediment.     

Energy Metabolism and Pyridine Nucleotide Levels during Xenopus Oocyte Maturation*, 1

The rate of oxygen consumption increased in maturing Xenopus oocytes within 2 hr after progesterone addition, well before GVBD. This suggested an early requirement for energy metabolism during maturation, similar to the situation in sea urchin eggs during fertilization. Yet, the absence of similar increases in glucose-6-phosphate levels, glucose-6-phosphate dehydrogenase activity, glucose conversion to CO₂, and the conversion of NAD(H) to NADP(H), indicated that carbohydrate metabolism was not being stimulated in Xenopus oocytes during maturation. The oxidation of other energy yielding substrates is discussed which might account for the finding that, within 5 min of progesterone addition, both reduced forms of the pyridine nucleotides increased 20% over control levels. This was later followed by a drop in NADH levels and a rise in NAD relative to controls. The significance of these changes in pyridine nucleotide levels and their relationship to a number of maturation events are discussed.     

The reflectance properties of plant internodes modify elongation responses to lateral far-red radiation

The quality and quantity of light reflected from Nicotinia tabacum L. internodes was monitored as the angle of incidence was varied. Reflectance of incident light, which was either normal or longitudinal to the internode axis, was investigated. Increasing the angle of incidence caused a greater proportion of incident light to be reflected. Light striking N. tabacum internodes was always modified prior to reflection, and smaller incident angles produced greater modification of the reflected light quality. At larger angles, interactions with the internode were reduced. As a parallel investigation, the extension growth rate of light-grown Sinapis alba L. seedlings was monitored continuously using sensitive linear displacement transducers. When the angle of illumination by fibre-optic probes, presenting far-red light to the growing internode, was changed from 0° to 45°, an increase was observed in stem extension rate. There is a possibility that this rate increase was the result of a fall in the red:far-red ratio (R:FR) present inside the plant internode as the angle of incidence was altered. However, it is more likely that it was due to the larger surface area of stem being illuminated. The consequences of these observations are discussed in relation to the potential influence of such modified reflections on canopy light environments and resultant shade responses which may occur when light of known R:FR impinges on plant internodes at angles other than 0°. The possibility is discussed that plants may perceive the quality of reflected radiation from neighbouring plants to be substantially different dependent upon the angle at which it is reflected.