Photosynthetic electron transport in relation to thylakoid membrane composition and organization

Abstract. A review is given of the organization and properties of thylakoid membrane proteins and lipids as a basis for understanding the factors which regulate the light reactions of photosynthesis. Particular emphasis is placed on the lateral organization of the major intrinsic multipeptide complexes and on the importance of diffusional processes in controlling the kinetics of electron transport and the distribution of light energy between photosystems 1 and 2.     

Seasonal variation of sieving efficiency in a lotic habitat*

Sieving efficiency, defined as the percent increase in yield of numbers or biomass of organisms, obtained by use of a sieve with 0-25-mm mesh openings instead of a 0-50-mm meshed sieve, was investigated in a lotic habitat over a 12-month period. Greatest elficiencies obtained were 300 to 600% for mayflies, chironomids, simuliids, ‘other dipterans,’ water mites and plecopterans and 90 and 190% for trichopterans and coleopterans, respectively. For the fauna as a whole, efficiency varied from 95 to 325% over the study period. Efficiency in estimating biomass was not as great as that with numbers and generally was below 10% for trichopterans. mayflies, ‘other dipterans’, coleopterans and the fauna taken as a whole. For chironomids, simuliids and water mites efficiencies generally were higher than 10% and reached as high as 174%, 60% and 80%, respectively. In all groups efficiency varies throughout the year with lowest occurring during winter months. The findings are compared with data found in the literature and discussed in relation to structural, behavioural, and life history characters.     

The Effect of Micro-organisms on the Absorption of Inorganic Nutrients by Intact Plants: I. APPARATUS AND CULTURE TECHNIQUE

A technique is described for growing barley and wheat plantsin nutrient culture under completely sterile conditions. Theapparatus required is simple and cheap and therefore allowsrelatively large numbers of plants to be produced. Germinationand subsequent growth of plants are little affected by the methodof seed sterilization employed and a high degree of sterilityis obtained.     

A molecular phylogeny of Eumorpha (Lepidoptera: Sphingidae) and the evolution of anti‐predator larval eyespots

Many insects possess conspicuous external circular ring markings that resemble the eye of a vertebrate. These ‘eyespots’ typically function to startle or otherwise deter predators, but few studies have examined how eyespots have evolved. We study the evolution of the posterior larval eyespot in the charismatic New World hawkmoth genus Eumorpha. While Eumorpha has a range of posterior larval eyespot shapes and sizes, little is known of how this trait has evolved because phylogenetic relationships of Eumorpha remain largely unknown. In this study, we included 62 individuals from 23 of 26 described Eumorpha species, and sequenced four genes (CAD, EF‐1α, Wingless and COI), totaling 3773 base pairs. Maximum likelihood and Bayesian phylogenetic methods produced largely congruent trees with well‐supported relationships. Our analyses reveal that Eumorpha probably had an ancestor with a posterior larval eyespot and that the eyespot was subsequently lost in at least three lineages. Eumorpha appears to have originated in Central and South America and expanded its distribution to North America.     

The Relationship between Metabolism and the 'Exchangeability' of Ions in Plant Tissues2

The uptake of the rubidium ion by well-washed disks of carrotparenchyma has been determined at 0·2° C and 25°C., in the presence and absence of 10^–4M. dinitrophenol,from solutions of rubidium chloride containing 0·5 and5·0 meq./l. Readily-exchangeable and non-exchangeablefractions were separately indentified. The lowering of temperature and application of DNP reduced themagnitude of both ion fractions at each of the two concentrationsof rubidium chloride. Despite the fact that the uptake of ionsinto an exchangeable form at 5·0 meq./l. was about 3times greater, the combined effect of low temperature and thepresence of DNP reduced this fraction by a relatively constantabsolute amount. Under the same conditions the uptake of ionsinto a non-exchangeable form from each concentration was reducedby approximately the same percentage. Over a 6-hour period the rate of uptake of rubidium into a non-exchangeableform at 25° C. was relatively constant, whereas at 0·2°C. there was an initial rapid uptake lasting for about 60 minutesfollowed by a slow steady uptake. The Q₁₀ of this latter processmeasured after 360 minutes was 2·3. It is concluded that an appreciable part of the capacity ofthe tissue to hold ions by exchange is dependent on concurrentmetabolism. The significance of measurements of exchangeability in the interpretationof mechanisms of ion uptake is discussed.