The Effect of N-nutrients on the Acceptor Pool of PS I and Thylakoid Energization as Measured by Chlorophyll Fluorescence of Dunaliella salina

Changes of PS II chlorophyll fluorescence of Dunaliella salinawere used to study the effect of micromolar concentrations ofN-nutrients (nitrate, nitrite and ammonia) on photosyntheticelectron flow. The responses were evoked by changes in lightintensity which were controlled by a special protocol. Thisenabled the splitting of the overall response into individualcomponents by curve fitting and the assignment of these componentsto particular reactions of the photosynthetic apparatus. Byvirtue of a comparison with simultaneously measured changesin transmission at 532 ran, the identification could be madeof the component which is related to redox changes of the acceptorpool of PS I. The time-constant related to this acceptor pool was found toincrease by a factor of up to 5 after the addition of N-nutrients.The results indicate that the addition of N-nutrients increasesthe acceptor pool of PS I. The relationship between nutrientconcentration and effect is not consistent. In contrast to theelectron flow to the Calvin cycle, the electron flow to nitrogenassimilation is not related to a strong consumption of ATP.Thus, it gives rise to an increase in the transthylakoid pHgradient. The expected increase in the kinetic component ofchlorophyll fluorescence related to thylakoid energization isobserved after the addition of nitrate. Key words: Chlorophyll fluorescence, noise, N-nutrient metabolism, time-constants, thylakoid energization     

Correlations Between Electrolyte Leakage and Degree of Saturation of Polar Lipids from Aged Potato (Solanum tuberosum L) Tuber Tissue

Age-dependent changes in the concn (nmol g d. wt^–1) andrelative proportion of polar lipid fatty acids in potato tubertissue were characterized over a 32-month storage period. Astubers advanced in age from 2 to 14 months, a decrease (approximately22%) in concn of both saturated (16:0, 18:0) and unsaturated(18:2, 18:3) fatty acids was evident. This decrease was followedby an exponential increase through 32 months. Electrolyte leakagestudies with excised tissue revealed age-dependent differencesin membrane permeability. The relationship between maximum electrolyteleakage (% total) and tissue age was described by a cubic polynomial.Leakage declined approximately 4% as tissues aged from 2 to7 months; however, from 7 to 24 months, leakage increased 21%.These trends were followed by partial restoration of membranefunction in 24 to 32-month-old tissues, as indicated by attenuatedleakage. Similarly, the trend in double bond index (DBI) withage was defined by a cubic polynomial; however, the minima andmaxima were the opposite of those for electrolyte leakage vs.age. The regression of DBI upon leakage was inverse and linear(r = –0·97, P < 0.01). Furthermore, the effectof decreasing temperature from 5 to –2 °C on tissuepermeability (after equilibration with the bathing medium) wasalso dependent upon DBI. The higher the DBI, the greater theresistance of the tissue to increased electrolyte leakage inducedby chilling temperatures (r = 0·99, P < 0·05).Although the evidence is largely correlative, it appears thatchanges in the degree of saturation of membrane lipids are relatedto age-dependent fluctuations in membrane integrity and maybe important in dictating chilling sensitivity in potato Potato (Solanum tuberosum L.), tuber age, electrolyte leakage, membrane fatty acids     

Changing Patterns of Gene Regulation in the Evolution of Arthropod Morphology

SYNOPSIS. What can the comparative study of gene expressionpatterns during development contribute to the study of phytogeny?I discuss the basic properties of gene networks that functionin development, using information gleaned from developmentalmodel systems. Using examples from the analysis of anteroposterior,dorsoventral and proximodistal axis formation, I outline howthe gene networks that pattern these three axes of developmentare linked in evolution. Finally, I discuss the types of analysesnecessary to further our understanding of how gene networksfunction in regulating the evolution of morphology     

Selection for enemy‐free space: eggs placed away from the host plant increase survival of a neotropical ithomiine butterfly

1. The selection of an oviposition site by a phytophagous insect can depend on many factors, including the risk of predation. Many species avoid predators by laying eggs where enemies searching host plants are unlikely to find them. 2. Females of the Peruvian butterfly, Oleria onega Hewitson (Lepidoptera: Nymphalidae: Danainae: Ithomiini) lay most of their eggs (76 ± 9%) off the host plant, Solanum mite Ruiz & Pav. These off‐host eggs may be laid up to 0.5 m from the nearest host‐plant individual, on twigs or leaf litter, as well as on living plants of species unsuitable for larval food. 3. Disappearance of eggs on and off the host plant was recorded by transferring eggs laid in captivity to known locations in the wild and recording rates of disappearance before the larvae emerged. After 2 days, eggs on the host were significantly more likely to have disappeared compared to eggs laid elsewhere. 4. We conclude that a high risk of predation is a likely trigger that caused O. onega to evolve a behaviour of laying eggs off its host plant.     

Developmental plasticity in a meristic character: the number of tentacles in the lophophore of a bryozoan species

There is increasing interest among evolutionary biologists in developmental plasticity. Previously ignored by many as being irrelevant to evolution because a plastic response to an environmental change is not inherited, the current, more positive, view of plasticity focuses on the fact that, although any individual plastic response is nonheritable, the overall pattern of developmental response to environmental variation (i.e. the developmental reaction norm) is heritable and may vary among genotypes within a population. Characters subject to plastic variation, like those that are entirely genetically determined, may vary in continuous, meristic or discrete ways. Of these, the least work has been carried out on meristic variation. In the present study, we contribute to the rectification of this imbalance by examining the plastic response of the number of tentacles in the lophophore of a species of bryozoan, Membranipora membranacea, to three environmental variables: temperature, salinity and food concentration. Because the approach taken was an experimental one, unlike the majority of studies of bryozoan tentacles to date, we are able to make statements about the causality of variation in tentacle number. The main conclusions of the present study are: (1) that plastic responses occur to all three environmental variables; (2) that these are part of a more generalized plastic response in the overall development of the zooids rather than being lophophore‐specific; and (3) that the issue of whether the relevant developmental reaction norms are adaptive or not is an open (and interesting) question. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 541–551.     

Comparison of the 24 kDa Flagellar Calcium-Binding Protein cDNA of Two Strains of Trypanosoma cruzi

ABSTRACT. DNA sequences encoding the 24 kDa flagellar calcium binding protein (FCaBP) of two strains of Trypanosoma cruzi were found to differ at fourteen positions, six of which result in amino acid differences. Four of the amino acid differences are located within the calcium-binding domains of FCaBP; however, none is predicted to affect the calcium-binding ability of the protein. Chromosomes harboring the FCaBP gene clusters differ in size among T. cruzi strains.