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Notes: Summary The coupling of ion transport to energy sources in the light and in the dark in green cells ofAtriplex spongiosa leaves was investigated using light of different qualities, an inhibitor of electron transport (dichlorophenyl dimethyl urea), and an uncoupler (p-CF3O-carbonyl cyanide phenylhydrazone). Two different mechanisms of ion uptake were, distinguished. (1) A light-dependent Cl− pump which is linked to light-dependent K+ uptake. The energy for this pump is probably derived from photosynthetic electron transport or from nicotinamide adenine dinucleotide phosphate, reduced form. This mechanism is dichlorophenyl dimethyl urea-sensitive and enhanced by uncouplers. (2) A mechanism independent of light, which operates at the same rate in the light and in the dark. This mechanism is sensitive to uncouplers. It is probably aK−Na exchange mechanism since K+ and Cl− uptake and a small net uptake of H+ are balanced by Na+ loss.

Notes: Summary Poly-L-lysine concentrations (10−6 m) which cause slight leakage of pigment from beet cells completely disrupt the kinetics of*K (labeled) absorption at 25°C in the range 0.01 to 50mm KCl. Lower concentrations of polylysine (10−7 to 10−9 m) interfere with potassium fluxes at both cell membranes, initially increasing efflux across the plasma membrane and decreasing the capacity of the cytoplasm to retain ions during flux experiments at 2°C. At 25°C, these concentrations of polylysine increase*K (labeled) absorption from 0.2mm KCl, but not from 10mm KCl. These responses are discussed in relation to ion transport via the three-compartment in-series model proposed for plant cells. Particular emphasis is placed on the role of the plasma membrane in K transport from solutions of low concentration.

Notes: Objective To examine how maternal diet in pregnancy and parental body size and birthweight influence an infant's thinness at birth measured by a low ponderal index.Design An observational study of newborn infants and their parents.Setting Southampton, England.Population Five hundred and thirty-eight infants born at term.Main outcome measure Ponderal index at birth.Results Women who had a high intake of carbohydrate in early pregnancy and a low intake of dairy protein in late pregnancy tended to have infants that were thin at birth (P= 0.01 and P= 0.03, respectively, in a simultaneous analysis). Women who themselves had a low birthweight also tended to have thin infants, ponderal index falling from 28.3 kg/m3 to 26.2 kg/m3 as the women's birthweights decreased from more than 4.0 kg to 2.5 kg or less (P 〈 0.0001). Tall fathers had thin infants, but ponderal index was not related to the women's heights or the fathers’ birthweights.Conclusion These associations may reflect constraints on placental development imposed by a woman's nutrition in pregnancy and during her own intrauterine life. Effects of the father's height may be mediated through genetic influences on skeletal growth.

Notes: Fingerprint whorl patterns are formed during fetal life. In a group of 180 term infants, those with more fingerprint whorls tended to have a small abdominal circumference (P= 0.09) and high ratio of head to abdominal circumference (P= 0.008). These associations were independent of the relation between the whorl counts of the mothers and their infants. We also found an independent correlation between the babies’ whorl count and the combination of increasing subscapular (P= 0.03) and decreasing triceps (P= 0.02) skinfold thicknesses of the mothers. Whorl patterns are associated with adult hypertension; maternal nutritional status may influence their common origin during fetal development.

Notes: Objective To investigate whether low maternal haemoglobin and ferritin levels are associated with increased placental volume by mid-pregnancy.Design Prospective study of women attending hospital for shared antenatal care.Setting A teaching hospital in the south of England.Subjects Five hundred and sixty-eight women booking for delivery in the hospital.Main outcome measures Placental volume measured by ultrasound at 18 weeks gestation.Results At 14 weeks gestation 9% of women had haemoglobin levels ≤ 11 g/dl and 26% had ferritin levels 〈 13 μg/1. Placental volume at 18 weeks was inversely related to the maternal haemoglobin and ferritin levels. The influence of haemoglobin and ferritin concentrations was independent of maternal social class, parity, smoking, and weight. Larger placentae were found in taller women, those who had previously been pregnant, and in those who were smoking more than 15 cigarettes daily at the time of their last menstrual period.Conclusion These data suggest that placental development is influenced from early in pregnancy by the intrauterine environment provided by the mother. In conjunction with other studies they support the proposal that, as a result of these changes, programming of adult blood pressure may be initiated in early pregnancy.

Notes: 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.

Notes: The effects of introduced chloroplast gene mutations affecting D1 synthesis, turnover and function on photosynthesis, growth and competitive ability were examined in autotrophic cultures of Chlamydomonas reinhardtii (Chlorophyta) adapted to low or high irradiance. Few discernible effects were evident when the mutants were grown in low light (LL, 70 μmol m−2 s−1). The herbicide-resistant psbA mutation Ser264→ Ala (dr) slowed electron transfer and accelerated D1 degradation in cells grown under high light (HL, 600 μmol m−2 s−1). The maximum rate of light-and CO2-saturated photosynthesis, cell growth rate and competitive ability in the dr mutant were reduced compared to wild type under HL. However, the wild-type rate of D1 synthesis in dr was adequate to compensate for accelerated D1 degradation. 16S rRNA mutations conferring resistance to streptomycin and spectinomycin (spr/sr) that altered chloroplast ribosome structure and assembly were used to inhibit chloroplast protein synthesis. In spr/sr cells grown under HL, D1 synthesis was reduced by 40–60% compared to wild type and D1 degradation was accelerated, leading to a 4-fold reduction in D1 pool size. The reduced D1 levels were accompanied by an elevation of Fo and a decline in Fv/Fm, quantum yield and maximum rate of CO2-saturated photosynthesis. Chemostat experiments showed that the growth rate and competitive ability of spr/sr were reduced against both wild type and dr.

Notes: Prior work demonstrated that Heuchera americana, an evergreen herb inhabiting the deciduous forest understory in the southeastern United States, has a 3-4-fold greater photosynthetic capacity under the low-temperature, strong-light, open canopies of winter compared to the high-temperature, weak-light, closed canopies of summer. Moreover, despite the reductions in soil nitrogen, the chilling temperatures, and the increased quantum flux associated with winter, chronic photoinhibition was not observed in this species at this time of the year. We were interested in the photosynthetic acclimation and photoinhibition characteristics of this species when grown under contrasting light and nitrogen regimes. Newly expanded shade-acclimated leaves of forest-grown plants exposed to strong light varying in intensity and duration at 25°C showed a reduction in Fv/Fm (the ratio of variable to maximum room temperature chlorophyll fluorescence measured after dark adaptation), which was correlated with a decline in øa (the intrinsic quantum yield of CO2-saturated O2 evolution on an absorbed light basis). Plants grown in the glasshouse under contrasting light (high and low light; HL and LL, respectively) and nitrogen supply (high and low nitrogen; HN and LN, respectively) regimes showed that photosynthetic acclimation to HL was impaired in LN regimes. The HL-LN plants also had the lowest values of Fv/Fm and of ø on both incident and absorbed light bases and had 50% less chlorophyll (per unit area) compared to plants from other growth regimes. Controlled exposure to bright light at low temperatures (2-3°C) for 3 h resulted in a sharp decrease in Fv/Fm (and rise in Fo, the minimum fluorescence yield) in all plants. Shade-grown plants from both N regimes were highly susceptible to chronic photoinhibition, as indicated by a greater reduction in Fv/Fm and incomplete recovery after 18 h in weak light at 25°C. The HL-HN plants were the least susceptible to chronic photoinhibition, having the smallest decrease in Fv/Fm with near full recovery within 6 h. The decline in Fv/Fm in HL-LN plants was comparable to that of shade-acclimated plants, but recovered fully within 6 h. Low-N plants from both light regimes displayed greater increases in Fo which did not return to pretreatment levels after 18 h of recovery. These studies indicate that HL-LN plants were sensitive to chronic photoinhibition and, at the same time, had a high capacity for dynamic photoinhibition. Experimental garden studies showed that H. americana grown in an open field in summer were photoinhibited and did not fully recover overnight or during extended periods of weak light. These results are discussed in relation to the photosynthetic acclimation of H. americana under natural conditions.

Notes: The consequences of biotic stress have been poorly understood, partly because its application is difficult to control and partly because its physiological consequences are highly variable. Many plant viruses are recognised on the basis of leaf symptoms that depend on localised changes to chloroplast structure and function. This paper reviews recent progress in understanding early interactions between plant viruses and the photosynthetic apparatus, using chlorophyll fluorescence analysis of novel, defined algal-virus systems and using high resolution imaging of chlorophyll fluorescence and other photosynthetic processes in higher plant systems. We then consider the consequences of viral effects on photosynthetic functioning for whole plants and populations with an emphasis on the potential interactions with other environmental factors. Early responses indicated by increase in both non-photochemical quenching of fluorescence and increased reduction state of the primary electron transport acceptor QA suggest that, not surprisingly, both photoprotective and photoinhibitory processes contribute to the accelerated local demise of the photosynthetic apparatus and symptom development. In other cases, localised accumulations of carbohydrate and source-sink imbalance following infection may inhibit gene expression, leading to altered levels of chloroplast protein complexes and enzymes of photosynthetic metabolism coincident with symptom development. Recent experiments suggest that much of the variability in plant responses to biotic stress may result from interactions with other environmental factors, such as light intensity and nutrition. Experiments suggest that virus infections may have greater effects on fitness and competitive ability in low N, high light environments than in shaded, high nutrient conditions. Some ecological implications of these observations are discussed.