Factors affecting the microdistribution of Gammarus pulex (Amphipoda): an experimental study

SUMMARY. 1. The tnierodistribution of Gammarus species is size assortative: larger animals are associated with larger substrate particles. Using an artificial stream with scrubbed substrate we investigate the hypothesis that the assortative mechanism is stimulated by current avoidance rather than food searching.
2. In uniformly mixed substrate, G. pulex tend to move upstream, but in patchy substrate they are found in a predictable substrate grade. There is no discrimination between patches by different size classes of G. pulex in static water. The size assortative field pattern can only be reproduced under flow conditions in the laboratory. It occurs in the absence of food and irrespective of the sequence or location of substrate patches.
3. As density increases, G. pulex are displaced from the optimal patches but move into the open stream rather than into the cover of alternative patch types.
4. We discuss the significance of these results and suggest that some earlier models explaining mechanisms for microdistribution patterns tnay have been unnecessarily complex. Contrasts between natural and simulated stream situations and their experimental advantages are noted.     

Starch Metabolism in Developing and Germinating Soya Bean Seeds is Independent of {beta}-Amylase Activity

Developing seeds of soya bean cultivars Chestnut and Altonahave only trace amounts of ß-amylase activity. Comparedto a standard variety, Wells, ß-amylase activitieswere 200–300 times lower in Chestnut and Altona. Nevertheless,Chestnut and Altona accumulate starch as a transient reservematerial which is utilized later in development. Seeds of Chestnutand Altona also produce starch early in germination which subsequentlydeclines after the 4th day of germination. Throughout germinationß-amylase levels in these cultivars are about 300-foldlower than that observed in Wells, which has a similar patternof starch metabolism. Widely varying levels of ß-amylasein both developing and germinating seeds appear to be unrelatedto starch metabolism which is very similar in all cultivarsstudied. Consequently, ß-amylase activity seems irrelevantto starch metabolism in the soya bean seed. starch, ß-amylase, Glycine max. (L.), Merr, soya bean     

Purification and some properties of oat golden stripe virus

Oat golden stripe virus (OGSV) was maintained in oats by mechanical inoculation and purified by extraction of leaves in borate buffer, two cycles of centrifugation through sucrose cushions and isopycnic centrifugation in CsCl. An antiserum with a titre of 1/1024 in precipitin tests was prepared. Particle length distribution was bimodal with median values, respectively, of 150 and 300 nm from dip preparations. Measurements from immunosorbent electron microscopy (ISEM) and purified preparations showed that the particles had partially degraded during these procedures. The virus sedimented as two components of 168 S and 218 S and had a buoyant density of 1321 g cm^-3. Four isolates of OGSV reacted with the antiserum. Antiserum to members and possible members of the furovirus group were tested in ISEM decoration tests and in ELISA. OGSV was related to soil-borne wheat mosaic virus but not to beet necrotic yellow vein virus, hypochoeris mosaic virus or potato mop-top virus.     

Rapid changes in xanthophyll cycle-dependent energy dissipation and photosystem II efficiency in two vines, Stephania japonica and Smilax australis, growing in the understory of an open Eucalyptus forest

Leaves of Stephania japonica and Smilax australis were characterized in situ on the coast of north-eastern New South Wales, Australia, where they were growing naturally in three different light environments: deep shade, in the understory of an open Eucalyptus forest where they received frequent sunflecks of high intensity, and in an exposed site receiving full sunlight. In deep shade the xanthophyll cycle remained epoxidized during the day and the vast majority of absorbed light was utilized for photosynthesis. In the exposed site both deepoxidation and epoxidation of the xanthophyll cycle and changes in the level of xanthophyll-dependent thermal energy dissipation largely tracked the diurnal changes in photon flux density (PFD). In the understory the xanthophyll cycle became largely deepoxidized to zeaxanthin and antheraxanthin upon exposure of the leaves to the first high intensity sunfleck and this high level of deepoxidation was maintained throughout the day both during and between subsequent sunflecks. In contrast, thermal energy dissipation activity, and the efficiency of photosystem II, fluctuated rapidly in response to the changes in incident PFD. These findings suggest a fine level of control over the engagement of zeaxanthin and antheraxanthin in energy dissipation activity, presumably through rapid changes in thylakoid acidification, such that they became rapidly engaged for photoprotection during the sunflecks and rapidly disengaged upon return to low light when continued engagement might limit carbon gain.