Photosynthetic adaptation of Solanum dulcamara L. to sun and shade environments

Summary The photosynthetic response properties of individuals of Solanum dulcamara L. collected from sun and shade habitats were compared in controlled environments. Light-saturated photosynthetic rates and seven additional parameters associated with photosynthetic and growth performance were measured over a range of 12 environmental conditions that simulated natural habitat differences in light intensity, moisture availability and daily temperature amplitude. In contrast to previous studies, the results suggest there is no ecotypic differentiation with respect to the sun and shade environments from which the individuals were collected. It appears that all but one of the field-collected individuals are capable of successfully inhabiting the full range of light environments from which the species was collected.     

Photosynthetic Adaptation of Solanum dulcamara L. to Sun and Shade Environments: II. Physiological Characterization of Phenotypic Response to Environment

Photosynthetic and growth properties of Solanum dulcamara L. were studied under controlled environments. The 200 experimentally tested plants were clonal replicates of five field-collected individuals, three from fully exposed habitats and two from deeply shaded habitats. After 4 weeks of growth in one of eight environmental treatments, each plant was measured for leaf adaxial and abaxial conductance to water vapor, specific leaf weight, chlorophyll per square decimeter of leaf, photosynthetic unit size, light-saturated photosynthetic rate, total leaf area, and total leaf, stem, and root dry weights. Changes in light level influenced photosynthesis and growth of each plant more than changes in water availability or temperature. It is strongly suggested that the primary adaptive response of the tested individuals to changes in levels of light involves the regulation of leaf thickness.     

Photosynthetic responses of C3 and C4 species from cool shaded habitats in Hawaii

Summary The C₄ species, Euphorbia forbesii, and the C₃ species, Claoxylon sandwicense, occupy cool, shaded habitats in Hawaii. Both of these species exhibit the photosynthetic characteristics of typical shade plants: low light-saturated photosynthetic rates, low dark respiration rates, low light levels for saturation of photosynthesis, and low light compensation points. In addition, the quantum yields of the two species are similar at leaf temperatures near 22°C, reflecting a significant increase in the quantum yield of E. forbesii over that of C₄ species from open habitats. C. sandwicense has a lower dark respiration rate than E. forbesii. Hence, since the quantum yields of the two species are similar at cool temperatures, C. sandwicense has a higher photosynthetic rate than E. forbesii at low incident photon flux densities. As a consequence, C. sandwicense should have a greater carbon gain than E. forbesii under the diffuse radiation conditions of their native habitat. However, since E. forbesii has a higher light-saturated photosynthetic rate than C. sandwicense, E. forbesii may have a greater carbon gain than C. sandwicense during sunflecks.     

Photosynthetic apparatus of pea thylakoid membranes : response to growth light intensity

We investigated the effect of growth light intensity on the photosynthetic apparatus of pea (Pisum sativum) thylakoid membranes. Plants were grown either in a growth chamber at light intensities that ranged from 8 to 1050 microeinsteins per square meter per second, or outside under natural sunlight. In thylakoid membranes we determined: the amounts of active and inactive photosystem II, photosystem I, cytochrome b/f, and high potential cytochrome b₅₅₉, the rate of uncoupled electron transport, and the ratio of chlorophyll a to b. In leaves we determined: the amounts of the photosynthetic components per leaf area, the fresh weight per leaf area, the rate of electron transport, and the light compensation point. To minimize factors other than growth light intensity that may alter the photosynthetic apparatus, we focused on peas grown above the light compensation point (20-40 microeinsteins per square meter per second), and harvested only the unshaded leaves at the top of the plant. The maximum difference in the concentrations of the photosynthetic components was about 30% in thylakoids isolated from plants grown over a 10-fold range in light intensity, 100 to 1050 microeinsteins per square meter per second. Plants grown under natural sunlight were virtually indistinguishable from plants grown in growth chambers at the higher light intensities. On a leaf area basis, over the same growth light regime, the maximum difference in the concentration of the photosynthetic components was also about 30%. For peas grown at 1050 microeinsteins per square meter per second we found the concentrations of active photosystem II, photosystem I, and cytochrome b/f were about 2.1 millimoles per mol chlorophyll. There were an additional 20 to 33% of photosystem II complexes that were inactive. Over 90% of the heme-containing cytochrome f detected in the thylakoid membranes was active in linear electron transport. Based on these data, we do not find convincing evidence that the stoichiometries of the electron transport components in the thylakoid membrane, the size of the light-harvesting system serving the reaction centers, or the concentration of the photosynthetic components per leaf area, are regulated in response to different growth light intensities. The concept that emerges from this work is of a relatively fixed photosynthetic apparatus in thylakoid membranes of peas grown above the light compensation point.     

Genetic structure of European accessions of Solanum dulcamara L. (Solanaceae)

Solanum dulcamara (bittersweet) is one of the few native species of Solanum present in Europe. It is a common weed that occupies a wide range of habitats and is often found in the direct vicinity of cultivated potatoes (Solanum tuberosum), where it could transmit diseases. A broad sampling of European S. dulcamara accessions was carried out to gain insight into the population structure and crossing preferences of this species. Three amplified fragment length polymorphism (AFLP^®) primer combinations generating 288 polymorphic fragments were used to analyze 79 bittersweet accessions (245 individuals). Dendrograms revealed a low level of genetic polymorphism in the bittersweet populations, caused partially by the out-crossing nature of this species.     

Chlorophyll concentrations and a/b ratios in mosses collected from exposed and shaded habitats in Kansas

Abstract

Chlorophyll concentrations and a/b ratios of 31 moss species in 16 families collected from various habitats in Kansas were lower than those of most higher vascular plants. Most of the mosses examined had higher chlorophyll concentrations and lower chlorophyll a/b ratios when collected from habitats with low solar irradiance, relative to mosses collected from habitats characterized by high irradiance. This was true for mosses collected from under a forest canopy compared with those collected from exposed sandstone outcrops, and for the same populations of mosses collected before and after forest canopy closure. Such changes in the characteristics of the light-harvesting pigment system appear to represent adaptations enhancing the efficiency of light capture.     

Effect of light intensity and temperature on apparent photosynthesis of altitudinal ecotypes of Trifolium repens L.

Summary The dependence on light and temperature of the apparent photosynthetic rate was studied on ecotypes of Trifolium repens from different altitudes in the alps (600–2040 m above sea level). Due to the altitude, the natural habitats have different temperature conditions. At the higher altitudes the light conditions for the growing plants vary due to grazing or cutting management of these meadows. Accordingly, for this study the plants were grown at different temperatures and light intensities in growth cabinets.High altitude plants had higher photosynthetic rates, especially when measured at low temperatures. According to the light conditions, dependent on management, in the alpine habitats the ecotypes differed in their photosynthetic properties like sun and shade plants. It is stated, that the photosynthetic performance as well as the acclimation capacity to the growth conditions is related to the altitude of the habitats and probably also to the agricultural management.     

Photosynthetic responses of Zostera marina L. (Eelgrass) to in situ manipulations of light intensity

Summary Photosynthetic responses of the temperate seagrass, Zostera marina L., were examined by manipulations of photon flux density in an eelgrass bed in Great Harbor, Woods Hole, MA during August 1981. Sun reflectors and light shading screens were placed at shallow (1.3 m) and deep (5.5 m) stations in the eelgrass bed to increase (+35% to +40%) and decrease (-55%) ambient photon flux densities. The portion of the day that light intensities exceeding the light compensation point for Z. marina (H _comp) and the light saturation point (H _sat) were determined to assess the impact of the reflectors and shades. The H _comp and H _sat periods at the deep station shading screen were most strongly affected; H _comp was reduced by 11% and H _sat was reduced by 52%. Light-saturated photosynthetic rates, dark respiration rates, leaf chlorophyll content, chlorophyll a/b, PSU_{O 2} size, PSU density, leaf area, specific leaf area, leaf turnover times and leaf production rates were determined at the end of three sets of 1- to 2-week experiments. None of the measured parameters were affected by the photon flux density manipulations at the shallow station; however, at the deep station leaf production rates were significantly reduced under the shading screen and chlorophyll a/b ratios were higher at the reflector. These results indicate that adjustment to short-term changes in light regime in Z. marina is largely by leaf production rates. Further, the most dramatic changes in the periods of compensating or saturating photon flux densities had the greatest impact on the measured photosynthetic responses.     

Transformation and Characterization of Transgenic Plants of Solanum dulcamara L.--Incidence of Transgene Silencing

A transformation system is described for Solanum dulcamara usingthe supervirulentAgrobacterium tumefaciens strain 1065, carryingboth the ß-glucuronidase (gus) and neomycin phosphotransferaseII (npt II) genes adjacent to the right and left T-DNA borders,respectively. Leaf explants were more efficient for the productionof transformed plants compared to stem explants on medium containing50 mg l^-1of kanamycin sulphate. A 1:10 (v:v) dilution of anovernight culture ofAgrobacterium gave optimal transformationin terms of transgenic plant regeneration. From a total of 174kanamycin-resistant plants selected by their antibiotic resistance,16 failed to exhibit GUS activity. Southern analysis revealedthat these GUS-negative transformants originated from threeindependently transformed cell lines. Restriction enzyme analysesshowed that the GUS-negative plants had both the gus and nptII genes integrated into their genome (one plant had a singlecopy of each gene; the other two plants had multiple copies),with major rearrangement of the gus gene occurring in plantswith several copies of the transgene. GUS-negative plants showedleaf malformations, delayed flowering and a reduction in flower,fruit and seed production compared to GUS-positive and non-transformed(control) plants. Although gene silencing of the gus gene occurred,albeit at a low frequency (9.2%), the transformation systemdescribed generates large numbers of phenotypically normal,stably transformed plants. Copyright 2000 Annals of Botany Company Agrobacterium -mediated transformation, gene silencing, Solanum dulcamara L. (Bittersweet, Woody Nightshade), T-DNA truncation, transgene expression     

Photosynthetic response of seagrasses to ultraviolet-a radiation and the influence of visible light intensity

Inhibition of photosynthesis by ultraviolet-A radiation (UV-A, 315-380 nanometers) was examined in three marine angiosperms: Halophila engelmannii Aschers, Halodule wrightii Aschers, and Syringodium filiforme Kütz. Sensitivity to UV-A and photosensitization to UV-A by photosynthetically active radiation (PAR, 380-700 nanometers) were characterized.     

Photosynthetic responses to variable light: a comparison of species from contrasting habitats

Photosynthetic responses to variable light were compared for species from habitats differing in light availability and dynamics. Plants were grown under the same controlled conditions and were analysed for the kinetics of photosynthetic induction when photon flux density (PFD) was increased from 25 to 800 mol m^-2s^-1. Gas exchange techniques were used to analyse the two principal components of induction, opening of stomata and activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). On average, 90% of the final photosynthetic rate was attained after 7 min for obligate shade plants (two species), 18 min for fast-growing sun plants (seven species from productive habitats) and 32 min for slow-growing sun plants (nine species from unproductive habitats). The rapidity of response of the shade plants was explained by stomata remaining more open in the low-light period prior to induction. This was also observed in two species of deciduous trees, which therefore resembled shade plants rather than other fast-growing sun plants. The slow response of the slow-growing sun plants was the result of lower rates of both Rubisco activation and stomatal opening, the latter being more important for the final phase of induction. The lower rate of Rubisco activation was confirmed by direct, enzymatic measurements of representative plants. With increasing leaf age, the rate of stomatal opening appeared to decrease but the rate of Rubisco activation was largely conserved. Representative species were also compared with respect to the efficiency of using light-flecks relative to continuously high light. The shade plants and the slow-growing sun plants had a higher efficiency than the fast-growing sun plants. This could be related to the presence of a higher electron transport capacity relative to carboxylation capacity in the former group, which seems to be associated with their lower photosynthetic capacities. Representative species were also compared with respect to the ability to maintain the various induction components through periods of low light. Generally, the fast-growing sun plants were less able than the other two categories to maintain the rapidly reversible component. Thus, although the rate of induction appears to be related to the ecology of the plant, other aspects of photosynthetic dynamics, such as the efficiency of using lightflecks and the ability to maintain the rapidly reversible component, seem rather to be inversely related to the photosynthetic capacity.     

Comparative effects of light during growth on the photosynthetic properties of NADP-ME type C4 grasses from open and shaded habitats. II. Photosynthetic enzyme activities and metabolism*

Abstract The influences of shading during growth upon the activities of several photosynthetic enzymes were examined in NADP-ME type C₄ grasses from open (Zea mays L.) and shaded (Paspalum conjugation Berg.) habitats. The substantial species-difference in maximum photosynthetic rate observed under a high light regime was correlated with large differences in both enzyme activities and leaf protein contents. With the exception of RuBP carboxylase activity, other photosynthetic enzyme activities in Z. mays were reduced by shading to a similar extent as maximum photosynthetic rate. In contrast, only PEP carboxylase and pyruvate, P_i dikinase activities were decreased by shading in P. conjugatum. As with maximum photosynthetic rate, other photosynthetic enzyme activities in P. conjugatum were relatively insensitive to irradiance during growth. Under a low photon flux density of photosynthetically active radiation (50 μmol m^?2 s^?1), the flow of [¹⁴C] label through photosynthetic intermediates in intact, shade-grown leaves of P. conjugatum was typical of C₄ metabolism. This provides incontrovertible proof for the occurrence of C₄ photosynthesis in shaded habitats.     

Differential expression of photosynthesis-related genes of reed ecotypes in response to drought and saline habitats

Three ecotypes of reed (Phragmites communis Trinius), swamp reed (SR), dune reed (DR), and heavy salt meadow reed (HSMR), growing in desert regions of northwest China were simultaneously investigated in their natural state for gas exchange patterns and the expression of three photosynthesis-related genes, cab (the gene for the light-harvesting chlorophyll a/b binding protein, LHC), psbA (the gene for the reaction centre D1 protein of photosystem 2, PS2), and 16S rDNA (the gene for plastid 16S rRNA). Stomatal conductance (gs) and intercellular CO2 concentration (ci) were markedly lower in the two terrestrial ecotypes (DR and HSMR) as compared to SR, paralleling a similar observed depression in net photosynthetic rate (PN). However, DR with the lowest measured gs and ci still exhibited a higher PN compared to HSMR. These results suggest that both stomatal and non-stomatal factors account for the comparatively low carbon assimilation in the terrestrial ecotypes. An increase in the expression of photosynthesis-related genes was observed in DR compared to SR, whereas the reverse situation was true in HSMR. The expression of photosynthesis-related genes may contribute to reed plants' photosynthetic capacity per leaf area under natural water deficits, but the levels of photosynthesis-related gene expression are not directly correlated with reed plants' general ability for survival and adaptation under water deficient conditions.     

Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability

Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P_max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes Scenedesmus quadricauda, Chlamydomonas globosa, cryptophyte Cryptomonas ovata and ochrophyte Cyclotella meneghiniana. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in S. quadricauda and Cry. ovata. Cry. ovata can be characterized as a low light-acclimated species, whereas S. quadricauda and Cyc. meneghiniana can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P_max with PUFAs and light. In S. quadricauda and Cyc. meneghiniana, PUFAs negatively affected the relationship between P_max and light. In Chl. globosa, lower light coincided with higher PUFAs and lower P_max, but PCA also indicated that PUFAs had no direct influence on P_max. PUFAs and P_max were unaffected by light in Cry. ovata. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation.     

Photosynthetic adaptation ofSolanum dulcamara L. to sun and shade environments. III. Characterization of genotypes with differing photosynthetic performance

Summary Clone mal9, a genotype ofSolanum dulcamara L. having photosynthetic characteristics similar to previously hypothesized shade ecotypes, is compared to five other genotypes having photosynthetic characteristics similar to previously hypothesized sun ecotypes. The primary differences are a 35% reduction in total leaf conductance and a 15% reduction in leaf chlorophyll content in mal9. Both factors contribute to a 44% reduction in lightsaturated photosynthetic rate in mal9. In relation to the 5 other genotypes, mal9 appears to be poorly adapted for growth in the normal range of natural habitats.     

Nitrogen supply as a factor influencing photoinhibition and photosynthetic acclimation after transfer of shade-grown Solanum dulcamara to bright light

We have compared the ability of shadegrown clones of Solamum dulcamara L. from shade and sun habitats to acclimate to bright light, as a function of nitrogen nutrition before and after transfer to bright light. Leaves of S. dulcamara grown in the shade with 0.6 mM NO ₃ ^- have similar photosynthetic properties as leaves of plants grown with 12.0 mM NO ₃ ^- . When transferred to bright light for 1–2 d the leaves of these plants show substantial photoinhibition which is characterized by about 50% decrease in apparent quantum yield and a reduction in the rate of photosynthesis in air at light saturation. Photoinhibition of leaf photosynthesis is associated with reduction in the variable component of low-temperature fluorescence emission, and with loss of in-vitro electron transport, especially of photosystem II-dependent processes.We find no evidence for ecotypic differentiation in the potential for photosynthetic acclimation among shade and sun clones of S. dulcamara, or of differentiation with respect to nitrogen requirements for acclimation. Recovery from photoinhibition and subsequent acclimation of photosynthesis to bright light only occurs in leaves of plants provided with 12.0 mM NO ₃ ^- . In these, apparent quantum yield is fully restored after 14 d, and photosynthetic acclimation is shown by an increase in light-saturated photosynthesis in air, of light-and CO₂-saturated photosynthesis, and of the initial slope of the CO₂-response curve. The latter changes are highly correlated with changes in ribulose-bisphosphate-carboxylase activity in vitro. Plants supplied with 0.6 mM NO ₃ ^- show incomplete recovery of apparent quantum yield after 14 d, but CO₂-dependent leaf photosynthetic parameters return to control levels.Symbols and abbreviations F_o initial level of fluorescence at 77 K - F_m maximum level of fluorescence at 77 K - F_v variable components of fluorescence at 77 K (F_v=F_m-F_o) - PSI, PSII photosystem I and II, respectively - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39)