Light interception efficiency explained by two simple variables: a test using a diversity of small- to medium-sized woody plants.

• Plant light interception efficiency is a crucial determinant of carbon uptake by individual plants and by vegetation. Our aim was to identify whole-plant variables that summarize complex crown architecture, which can be used to predict light interception efficiency. • We gathered the largest database of digitized plants to date (1831 plants of 124 species), and estimated a measure of light interception efficiency with a detailed three-dimensional model. Light interception efficiency was defined as the ratio of the hemispherically averaged displayed to total leaf area. A simple model was developed that uses only two variables, crown density (the ratio of leaf area to total crown surface area) and leaf dispersion (a measure of the degree of aggregation of leaves). • The model explained 85% of variation in the observed light interception efficiency across the digitized plants. Both whole-plant variables varied across species, with differences in leaf dispersion related to leaf size. Within species, light interception efficiency decreased with total leaf number. This was a result of changes in leaf dispersion, while crown density remained constant. • These results provide the basis for a more general understanding of the role of plant architecture in determining the efficiency of light harvesting.

Photosynthetic adaptation to high temperatures: a field study in death valley, california.

The photosynthesis of Tidestromia oblongifolia (Amranthaceae) is remarkably well adapted to operate at the very high summer temperatures of the native habitat on the floor of Death Valley. The photosynthetic rate was very high and reached its daily maximum when the light intensity reached its noon maximum at the high leaf temperatures of 460 degrees to 50 degrees C which occurred at this time. At the intensity of noon sunlight the rate decreased markedly when the leaf temperature was experimentally reduced to below 44 degrees C. The optimum rate occurred at 47 degrees C. At this temperature the photosynthetic rate was essentially directly proportional to light intensity up to full sunlight.

Proxy assessment of quality of life in patients with prostate cancer: how accurate are partners and urologists?

OBJECTIVES: To assess the ability of partners and clinicians to make proxy judgements on behalf of patients with prostate cancer relating to selection of life priorities and quality of life (QoL). DESIGN: 47 consecutive patients with histologically proven adenocarcinoma, and their partners, were recruited. The partners were asked to assess, by proxy, the QoL of the patient by completion of a series of interview-led questionnaires assessing global QoL (SEIQoL-DW), health-related QoL (FACT-P) and overall QoL (visual analogue score [VAS]). The patients' clinicians were asked to complete the SEIQoL-DW and VAS by proxy as soon as possible after a consultation with the patient. SETTING: Patients with histologically proven adenocarcinoma, their partners and their clinicians. MAIN OUTCOME MEASURES: Proxy scores for SEIQoL-DW, FACT-P and VAS, as provided by partners and clinicians. RESULTS: 25 partners made a proxy assessment of the patients. The results showed that partners were able to select similar QoL cues to those of the patients (Spearman-Rank correlation 0.89). Comparison of the QoL scores obtained from patients and partners in proxy using the questionnaires showed no statistically significant difference (paired t-test). Urologists were poor predictors of areas of life (cues) that were important to their patients. The doctors overemphasized the importance of survival, postoperative complications, urinary symptoms, sexual ability, activities of daily living and finance, but underestimated the importance of wife, family, home and religion. Comparison of the QoL scores obtained from patients and urologists by proxy showed a significantly lower score when assessed by urologists using the SEIQoL-DW questionnaire. CONCLUSIONS: Partners are able to accurately assess, by proxy, the areas of life that are of importance to patients. Clinicians, however, who are charged with making decisions on behalf of patients, are very poor judges of their patients' life priorities and QoL. This illustrates that conventional views held by most doctors regarding the priorities patients set themselves when planning treatment should be called into question and consequently suggests that the way in which doctors and patients arrive at treatment decisions must be reviewed.

Concurrent Measurements of Oxygen and Carbon Dioxide Exchange during Lightflecks in Maize (Zea mays L.).

Leaves of maize (Zea mays L.) were enclosed in a temperature-controlled cuvette under 35 Pa (350 [mu]bars) CO2 and 0.2 kPa (0.2%)O2 and exposed to short periods (1-30 s) of illumination (light-flecks). The rate and total amount of CO2 assimilated and O2 evolved were measured. The O2 evolution rate was taken as an indicator of the rate of photosynthetic noncyclic electron transport (NCET). In this C4 species, the response of electron transport during the lightflecks qualitatively mimicked that of C3 species previously tested, whereas the response of CO2 assimilation differed. Under short-duration lightflecks at high photon flux density (PFD), the mean rate of O2 evolution was greater than the steady-state rate of O2 evolution under the same PFD due to a burst of O2 evolution at the beginning of the lightfleck. This O2 burst was taken as indicating a high level of NCET involved in the buildup of assimilatory charge via ATP, NADPH, and reduced or phosphorylated metabolites. However, as lightfleck duration decreased, the amount of CO2 assimilated per unit time of the lightfleck (the mean rate of CO2 assimilation) decreased. There was also a burst of CO2 from the leaf at the beginning of low-PFD lightflecks that further reduced the assimilation during these lightflecks. The results are discussed in terms of the buildup of assimilatory charge through the synthesis of high-energy metabolites specific to C4 metabolism. It is speculated that the inefficiency of carbon uptake during brief light transients in the C4 species, relative to C3 species, is due to the futile synthesis of C4 cycle intermediates.

Regulation of Photosynthetic Induction State by the Magnitude and Duration of Low Light Exposure.

This study was undertaken to examine the dependence of the regulatory enzymes of photosynthetic induction on photon flux density (PFD) exposure in soybean (Glycine max L.). The induction state varies as a function of both the magnitude and duration of the PFD levels experienced prior to an increase in PFD. The photosynthetic induction state results from the combined activity of separate processes that each in turn depend on prior PFD environment in different ways. Direct measurement of enzyme activities coupled with determination of in situ metabolite pool sizes indicated that the fast-induction component was associated with the activation state of stromal fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11) and showed rapid deactivation in the dark and at low PFD. The fast-induction component was activated at low PFD levels, around 70 [mu]mol photons m-2 s-1. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 2.7.1.19) deactivated very slowly in the dark and required higher PFD for activation. Both enzymes saturated at lower PFD than did photosynthesis, around 400 [mu]mol photons m-2 s-1. Ribulose-5-phosphate kinase (EC 2.7.1.19) appeared never to be limiting to photosynthesis, and saturated at much lower PFD than either FBPase or Rubisco. Determination of photosynthetic metabolite pool sizes from leaves at different positions within a soybean canopy showed a limitation to carbon uptake at the stromal FBPase and possibly the sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) in shade leaves upon initial illumination at saturating PFD levels.

Regulation of Photosynthetic Induction State in High- and Low-Light-Grown Soybean and Alocasia macrorrhiza (L.) G. Don.

Alocasia (Alocasia macrorrhiza [L.] G. Don) and soybean (Glycine max [L.]) were grown under high or low photon flux density (PFD) conditions to achieve a range of photosynthetic capacities and light-adaptation modes. The CO2 assimilation rate and in vivo linear electron transport rate (Jf) were determined over a range of PFDs and under saturating 1-s-duration lightflecks applied at a range of frequencies. At the same mean PFD, the assimilation rate and the Jf were lower under the lightfleck regimes than under constant light. The activation state of two, key enzymes of the photosynthetic carbon reduction cycle pathway, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and fructose-1,6-bisphosphatase, and the photosynthetic induction states (ISs) were also found to be lower under flashing as compared to continuous PFD. Under all conditions, the IS measured 120 s after an increase in PFD to constant and saturating values was highly correlated with the Rubisco activation state and stomatal conductances established in the light regime before the increase. Both the fructose-1,6-bisphosphatase and Rubisco activities established in a particular light regime were highly correlated with the mean Jf in that regime. The relationships between enzyme activation state and Jf and between IS and enzyme activation state were similar in soybean and Alocasia and were not affected either by growth-light regime, and hence photosynthetic capacity, or by flashing versus constant PFD. The common relationship between the linear Jf and the activation state of key enzymes suggests that electron transport may be the determinant of the signal regulating IS, at least to the extent that the IS is controlled by the activation state of key stromal enzymes.

Xanthoma disseminatum: a case report and literature review.

This case report describes the neuro-opthalmologic and respiratory manifestations of xanthoma disseminatum, a rare histiocytosis syndrome characterized by disseminated lesions in a young male adult. Multimodality management of this disease, including the role of local radiotherapy, is discussed accompanied by a review of the literature.

The geometry of light interception by shoots of Heteromeles arbutifolia: morphological and physiological consequences for individual leaves.

The influence of leaf orientation and position within shoots on individual leaf light environments, carbon gain, and susceptibility to photoinhibition was studied in the California chaparral shrub Heteromeles arbutifolia with measurements of gas exchange and chlorophyll fluorescence, and by application of a three-dimensional canopy architecture model. Simulations of light absorption and photosynthesis revealed a complex pattern of leaf light environments and resulting leaf carbon gain within the shoots. Upper, south-facing leaves were potentially the most productive because they intercepted greater daily photon flux density (PFD) than leaves of any other orientation. North-facing leaves intercepted less PFD but of this, more was received on the abaxial surface because of the steep leaf angles. Leaves differed in their response to abaxial versus adaxial illumination depending on their orientation. While most had lower photosynthetic rates when illuminated on their abaxial as compared to adaxial surface, the photosynthetic rates of north-facing leaves were independent of the surface of illumination. Because of the increasing self-shading, there were strong decreases in absorbed PFD and daily carbon gain in the basipetal direction. Leaf nitrogen per unit mass also decreased in the basipetal direction but on a per unit area basis was nearly constant along the shoot. The decrease in leaf N per unit mass was accounted for by an increase in leaf mass per unit area (LMA) rather than by movement of N from older to younger leaves during shoot growth. The increased LMA of older lower leaves may have contributed directly to their lower photosynthetic capacities by increasing the limitations to diffusion of CO2 within the leaf to the sites of carboxylation. There was no evidence for sun/shade acclimation along the shoot. Upper leaves and especially south-facing upper leaves had a potential risk for photoinhibition as demonstrated by the high PFDs received and the diurnal decreases in the fluorescence ratio F v/F m. Predawn F v/F m ratios remained high (>0.8) indicating that when in their normal orientations leaves sustained no photoinhibition. Reorientation of the leaves to horizontal induced a strong sustained decrease in F v/F m and CO2 exchange that slowly recovered over the next 10-15 days. If leaves were also inverted so that the abaxial surface received the increased PFDs, then the reduction in F v/F m and CO2 assimilation was much greater with no evidence for recovery. The heterogeneity of responses was due to a combination of differences between leaves of different orientation, differences between responses on their abaxial versus adaxial surfaces, and differences along the shoot due to leaf age and self-shading effects.

Stomatal behavior and photosynthetic performance under dynamic light regimes in a seasonally dry tropical rain forest.

Rates of photosynthetic induction upon exposure to high light and rates of induction loss after darkening the leaf were measured in the field for four species of tropical shrubs in the family Rubiaceae. During wet season mornings, stomatal conductance (g s) in the shade prior to induction was generally high enough so that the time course of induction was determined primarily by rates of activation of biochemical processes. During wet season afternoons, however, g s values in the shade tended to be considerably lower and photosynthetic induction following a light increase exhibited a slower time course. In the afternoon, the time course of induction was determined by a combination of stomatal opening time and the rates of activation of light regulated enzymes. Stomatal behavior was also correlated with patterns of induction loss following a transfer from high light to darkness. In the afternoon, maximum g s was lower for all species, and for a given time in the darkness, leaves showed a greater loss of induction in the afternoon than in the morning. During the dry season, maximum g s and average values for g s in the shade were reduced in all species. Along with these shifts in stomatal behavior, reduced rates of photosynthetic induction were observed. In the high-light species, the lower maximum g s values observed during the dry season were also correlated with increased induction loss for a given time in the darkness. For all species, stomatal behavior was affected by season and time of day and, with the exception of wet season mornings, stomata appeared to exert significant control over rates of induction and patterns of induction loss. The results of simulation modeling suggest that the observed seasonal and diurnal changes in rates of induction and induction loss can have significant consequences on sunfleck carbon gain under a dynamic light regime.

Stomatal versus biochemical limitations to dynamic photosynthetic performance in four tropical rainforest shrub species.

Photosynthetic performance under dynamic light regimes was assessed in four different species of tropical shrubs from the family Rubiaceae via field gas exchange measurements conducted on Barro Colorado Island, Panamá. Rates of photosynthetic induction and induction loss were assessed throughout the day in both the wet and dry seasons in order to determine the relative roles of stomata and biochemistry in limiting photosynthetic performance under transient light conditions. A high degree of coordination was observed between stomatal conductance and biochemical capacity for CO2 assimilation during induction. Rates of biochemical and overall photosynthetic induction sharply decreased when initial stomatal conductance fell below a narrow range of critical values. Time of day or season did not affect rates of biochemical deactivation upon shading, but did influence stomatal closure, which often exerted a significant influence over induction loss in the darkness. In measurements of total assimilation due to a 60-s light pulse, both biochemical activity and stomatal conductance were linearly related to total CO2 uptake. Only during the mornings of the wet season was stomatal conductance consistently high enough to be non-limiting to dynamic photosynthetic performance. At all other times, stomatal behavior exercised significant influence over induction times, photosynthetic induction loss, and total CO2 uptake from 60-s light pulses.

Leaf movement, stress avoidance and photosynthesis in Vitis californica.

Gas exchange and chlorophyll fluorescence techniques were used to evaluate the hypothesis that leaf movement in Vitis californica Benth. (California wild grape) allows a compromise between sunlight interception and stress damage in order to maximize photosynthetic carbon gain over the life of the leaf. Leaves that were restrained horizontally tolerated their increased radiation loads if critical temperatures were not exceeded. Reductions in photosynthetic capacity and the F V/F M fluorescence ratio only occurred in leaves that attained high temperatures. Leaf orientation and canopy position were important determinants of leaf temperature. These results indicate that excessive leaf temperature, not high PFD, can be a principle cause of reduced carbon gain and senescence in this species in the wild. Leaf movement appears to protect photosynthetic components in midsummer.

Seasonal changes in net photosynthesis of Atriplex hymenelytra shrubs growing in Death Valley, California.

Field measurements of CO2 and water vapor exchange were made on Atriplex hymenelytra (Torr.) Wats. shrubs growing in Death Valley, California during March 1971 and July 1972. Rates of CO2 uptake and leaf conductances were substantially higher in March as compared to July. In spite of the large differences in ambient temperatures in March and July, no adaptive acclimation response was apparent in the temperature dependence of photosynthesis. Photosynthesis transpiration ratios at typical midday leaf temperatures were much higher in March than in July. High water use efficiency results from a combination of the C4 photosynthetic pathway, relatively low leaf conductances, and maximum growth and photosynthetic activity during the cooler months of the year.

Gas exchange responses of Chesapeake Bay tidal marsh species under field and laboratory conditions.

Laboratory and field gas exchange measurements were made on C3 (Scirpus olneyi Gray) and C4 (Spartina patens (Ait.) Mahl., Distichlis spicata (L.) Green) species from an irregularly flooded tidal marsh on the Chesapeake Bay. Laboratory measurements were made on plants grown from root stocks that were transplanted to a greenhouse and grown under high light and high nutrient conditions. The two C4 species were similar in their laboratory gas exchange characteristics: both had higher net carbon exchange rates, higher mesophyll conductances, higher photosynthetic temperature optima and lower leaf conductances than the C3 species. The laboratory photosynthetic water use efficiency of the C4 species was approximately three times that of the C3 species.Field gas exchange responses of the above species were measured in situ a Chesapeake Bay tidal marsh. Despite differences in biological potential measured in the laboratory, all three species had similar in situ carbon exchange rates on a leaf area basis. On a dry weight basis, leaves of the two C4 species had about 1.4 times higher light saturated CO2 assimilation rates than the C3 species. Light saturation of CO2 exchange occurred at photosynthetic photon flux densities of 80 n Einstein cm-2s-1, compared with 160 n Einstein cm -2s-1 in the laboratory grown plants. Spartina patens and Scirpus olneyi had similar daily CO2 assimilation rates, but the daily transpiration rate of the C3 species was almost twice that of the C4 species. Spartina patens showed greater seasonal decrease in photosynthesis than Distichlis spicata and Scirpus olneyi. The two C4 grass species maintained higher mesophyll conductances and photosynthetic water use efficiencies than the C4 sedge.

A comparison of the attitudes shown by general practitioners, hospital doctors and medical students towards alternative medicine.

The aim of this study was to compare and contrast the views of general practitioners (GPs), hospital doctors and medical students to alternative medicine. A questionnaire was sent to a random sample of 100 GPs and 100 hospital doctors in the South West Thames Regional Health Authority (SWTRHA). A convenience sample of 237 pre-clinical medical students at St George's Hospital Medical School was also given a questionnaire. Eighty-seven GPs and 81 hospital doctors replied. Five therapies were investigated: acupuncture; chiropractice; homeopathy; naturopathy; and osteopathy. All respondents were asked about their attitude towards and knowledge of these therapies. Doctors were asked how often they referred patients for such treatment and whether they practised it themselves. GPs and hospital doctors had similar levels of knowledge of the therapies. Medical students were the least informed but the most enthusiastic respondents. Seventy per cent of hospital doctors and 93% of GPs had, on at least one occasion, suggested a referral for alternative treatment. GPs were making these referrals more frequently and earlier. Twelve per cent of hospital doctors and 20% of GPs were practising alternative medicine. The majority of the respondents felt that alternative medicine should be available on the National Health Service (NHS) and that medical students should receive some tuition about alternative therapies. A considerable proportion of those doctors referring patients to alternative practitioners were ignorant of their official qualifications.

C(4) photosynthesis in tree form euphorbia species from hawaiian rainforest sites.

The (13)C (12)C isotope ratios and the leaf anatomy of 18 species and varieties of Euphorbia native to the Hawaian Islands indicated that all possess C(4) photosynthesis. These species range from small prostrate coastal strand shrubs to shrubs and trees in rainforest and bog habitats. The results show that C(4) photosynthesis occurs in plants from a much wider range of habitats and life-forms than has been previously reported.

Effect of Growth Temperature on the Fatty Acid Composition of the Leaf Lipids in Atriplex lentiformis (Torr.) Wats.

Plants of Atriplex lentiformis had more saturated leaf lipids when grown at 43 C day/30 C night as compared to 23/18 C temperatures. In monogalactosyl diglyceride, the major change was the presence of hexadecatrienoic acid (16:3) at low but not high growth temperatures. In other lipids investigated, the major change was a decrease in linolenic acid (18:3) and increases in the more saturated fatty acids at high growth temperatures. Growth temperatures had little effect on the relative proportions of the galacto- and sulfolipids in the leaf. The increased lipid saturation is correlated with the greater thermostability of the photosynthetic apparatus at high growth temperatures in A. lentiformis but any cause and effect relationship is uncertain.

Acclimation of Photosynthetic and Respiratory Carbon Dioxide Exchange to Growth Temperature in Atriplex lentiformis (Torr.) Wats.

Atriplex lentiformis plants collected from coastal and desert habitats exhibit marked differences in capacity to adjust photosynthetic response to changes in growth temperature. Plants from desert habitats grown at 43 C day/30 C night temperatures had higher CO(2) uptake rates at high temperatures but reduced rates at low temperatures as compared to plants grown at 23 C day/18 C night temperatures. In contrast, growth of the coastal plants at high temperatures resulted in markedly reduced photosynthetic rates at all measurement temperatures.Leaf conductances to CO(2) were not important in controlling either the differences in the temperature dependence of net CO(2) uptake or the differences in photosynthetic capacities at any measurement temperature. At low measurement temperatures, differences in photosynthetic capacities among plants acclimated to the contrasting growth regimes were correlated with differences in leaf ribulose diphophate carboxylase activities. At high measurement temperatures, the improved net photosynthetic performance of the high temperature acclimated desert plants appeared to be due to a combination of decreased respiration rates, decreased temperature dependence of respiration, and an apparent increased thermal stability of photosynthetic CO(2) exchange.

Effects of Growth Temperature on the Thermal Stability of the Photosynthetic Apparatus of Atriplex lentiformis (Torr.) Wats.

High growth temperatures induced a substantial increase in the thermal stability of the photosynthetic apparatus of Atriplex lentiformis. This was manifested as a much reduced inhibition of light-saturated photosynthesis and the initial slope of the light-dependence curves by exposure to high temperatures in high as compared to moderate temperature-grown plants. Heat treatment at 46 C of leaves from moderate temperature-grown plants resulted in a marked reduction in photosystem II activities of chloroplasts isolated from them. In contrast, heat treatment of leaves from high temperature-grown plants resulted in no reduction of photosystem II activities. In vivo estimates of photosystem II functioning, the 515 nm light-induced absorbance change, and the ratio initial to maximum fluorescence (F(0)/F(max)) indicated a similar increase in the thermal stability of photosystem II in high temperature-grown plants.

Petiole twisting in the crowns of Psychotria liminesis: implications for light interception and daily carbon gain.

We used Y-plant, a computer-based model of crown architecture, to examine the implications of leaf reorientation resulting from petiole bending in Psychotria limonensis (Rubiaceae) seedlings. During this reorientation process, bending of the petioles of lower leaves that are potentially self-shaded by the upper leaves rotates the lamina around the stem's orthotropic axis so that self-shading is reduced. Simulations of daily light capture and assimilation revealed a 66% increase in daily C gain due to reorientation of the leaves as compared to simulations where the leaves remained in their characteristic opposite decussate pattern set by the phyllotaxy. This was due to enhanced carbon (C) gain of the lower leaves because of the reduction of shading by upper developing leaves in the same vertical plane. The light signal for this movement was experimentally examined by placing leaf-shaped filters above already fully expanded leaves and following the resulting shade-avoiding movements. The filters were either neutral density shade cloth that reduced the photon flux density (PFD) but did not alter the red to far red ratio (R:FR) or a film that reduced the PFD equivalently but also reduced the R:FR. Leaf reorientation was much more rapid and complete under the low R:FR as compared to the high R:FR indicating involvement of a phytochrome photosensory system that detected the presence of a shading leaf. Plants in gaps were found to lack a reorientation response indicating that the reorientation is specific to the shaded understory environment.

Photoinhibition in Vitis californica: The Role of Temperature during High-Light Treatment.

Leaves of Vitis californica Benth. (California wild grape) exposed to a photon flux density (PFD) equivalent to full sun exhibited temperature-dependent reductions in the rates or efficiencies of component photosynthetic processes. During high-PFD exposure, net CO(2) uptake, photon yield of oxygen evolution, and photosystem II chlorophyll fluorescence at 77 Kelvin (F(m), F(v), and F(v)/F(m)) were more severely inhibited at high and low temperatures than at intermediate temperatures. Sun leaves tolerated high PFD more than growth chamber-grown leaves but exhibited qualitatively similar temperature-dependent responses to high-PFD exposures. Photosystem II fluorescence and net CO(2) uptake exhibited different sensitivities to PFD and temperature. Fluorescence and gas exchange kinetics during exposure to high PFD suggested an interaction of multiple, temperature-dependent processes, involving both regulation of energy distribution and damage to photosynthetic components. Comparison of F(v)/F(m) to photon yield of oxygen evolution yielded a single, curvilinear relationship, regardless of growth condition or treatment temperature, whereas the relationship between F(m) (or F(v)) and photon yield varied with growth conditions. This indicated that F(v)/F(m) was the most reliable fluorescence indicator of PSII photochemical efficiency for leaves of different growth conditions and treatments.