Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of trees

The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R _Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P _N on a leaf area basis (mean of 9.1–10.1 μmol CO₂ m⁻² s⁻¹) and Chl basis, which correlated well with the higher values of stomatal conductance G _s (range 105–180 mmol m⁻² s⁻¹), as compared to shade leaves (G _s range 25–77 mmol m⁻² s⁻¹; P _N: 3.2–3.7 μmol CO₂ m⁻² s⁻¹). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R _Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R _Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the leaf area, and in general to a higher extent in sun leaves than in shade leaves.     

不同年龄麻竹阴阳叶生态生理特性

麻竹是中国重要的大型经济竹种,其栽培已从过去河滩、四旁零散种植发展到规模化培育,通过山地麻竹发笋期内不同年龄植株阴阳叶养分和代谢动态的比较研究,结果表明麻竹阳叶氮素、磷素浓度比阴叶高,但钾素浓度阳叶低于阴叶;从发笋初期至末期阴阳叶氮、磷、钾素浓度都呈逐渐减少的变化趋势,阴阳叶氮、磷、钾素浓度差异逐渐减小;阳叶在净光合速率、暗呼吸速率、CO2补偿点、光补偿点、光饱和点等方面较阴叶高,光呼吸较低,但不同年龄麻竹之间各指标变化有所不同.     

Some ecophysiological features in leaves of plants in an oak-hornbeam forest

Six different leaf indexes, indicating the anatomical and ecophysiological features in leaves, were used for characterizing the three principal layers (tree, shrub and herb) of an oak-hornbeam forest in southwest Slovakia, Czechoslovakia. The most pronounced differences in the leaf indexes followed were found between those at the active surface of the forest canopy (sun leaves of tall trees) and those in the herb layer. Differences exist between individual layers as well as between species within each layer. They should be taken into consideration in ecological and ecophysio-logical studies and in modelling forest ecosystems.     

More manganese accumulates in maple sun leaves than in shade leaves

Nuclear magnetic resonance and neutron activation analysis were used to measure manganese concentrations in leaves of Acer platanoides. Mn was found to accumulate in both the vacuoles and the chloroplasts, with more Mn (per unit area) in sun leaves than in shade leaves. No Mn was lost at senescence. Different seasonal patterns of Mn accumulation were found in sun and shade leaves. The quantity of chloroplast reserve Mn (bound to the outer surface of thylakoid membranes) increased rapidly in sun leaves from bud-break through midsummer, and then remained approximately constant through senescence. In shade leaves, however, the quantity of reserve Mn increased slowly, and at approximately a constant rate throughout the growing season.     

The induction of sun and shade leaves of the European beech (Fagus sylvatica L.): anatomical studies

Summary Primordia from buds of sun and shade twigs of European beech (Fagus sylvatica L.) were collected six times a year for anatomical investigations. Differentiation into sun-leaf and shade-leaf primordia was first observed in early August. Sun-leaf primordia had five, and shade-leaf primordia four layers of mesophyll meristem cells. With potted graft unions of beeches possible structural changes of leaf primordia were investigated. Trees adapted to shade develop sun-leaf primordia when put into full daylight, provided the transfer happened before July. Trees adapted to full daylight developed leaf primordia which remained structurally sun-leaf primordia when the plant was kept under shade conditions. Shadeleaf branches of young beech trees cut in February in order to expose the shade buds to full daylight developed either shade leaves or intermediate shade/sun leaves. These experiments show that the subtending leaf may provide the developing axillary bud with photoassimilates, but its character, whether sun or shade leaf, has no influence on the character of the developing leaf primordia.     

Photomorphogenesis of leaves: shade-avoidance and differentiation of sun and shade leaves.

Leaf shape is an important factor in optimal plant growth, because leaves are the main photosynthetic organs. Plants exhibit plasticity in leaf shape and structure, allowing them to optimize photosynthetic efficiency. In Arabidopsis thaliana(L.) Heynh., several types of leaves develop differentially, according to light intensity and quality. When shaded, the expansion of leaf lamina is inhibited, while the petiole elongation is enhanced. This phenomenon is part of the so-called shade-avoidance syndrome. Under low light, A. thaliana develops shade leaves with only one layer of palisade tissue, whereas under high light, it develops sun leaves that have nearly two complete layers of palisade tissue. Although the molecular mechanisms of these photomorphogenic phenomena in leaves are not well understood, recent studies of A. thaliana have provided some insight. For example, some cytochrome P450s may be involved in the specific control of the petiole length during photomorphogenesis. On the other hand, switching between sun and shade leaves is regulated by long-distance signaling from mature leaves in Chenopodium album. Here we provide an overview of the mechanisms of photomorphogenesis in leaves based on recent findings.     

Photosynthetic symmetry of sun and shade leaves of different orientations

Summary The photosynthetic responses to light of leaves irradiated on the adaxial or abaxial surfaces, were measured for plants with contrasting leaf orientations. For vertical-leaf species of open habitats (Eryngium yuccifolium and Silphium terebinthinaceum), photosynthetic rates were identical when irradiated on either surface. However, for horizontal-leaf species of open habitats (Ambrosia trifida and Solidago canadensis), light-saturated rates of photosynthesis for adaxial irradiation were 19 to 37% higher than rates for abaxial irradiation. Leaves of understory plants (Asarum canadense and Hydrophyllum canadense) were functionally symmetrical although they had horizontal orientation. Photosynthetic rates were measured at saturating CO₂, thus differences in the response to incident irradiance presumably resulted from complex interactions of light and leaf optical properties rather than from stomatal effects. Differences in absorptance (400–700 nm) among leaf surfaces were evident for horizontal-leaf species but the primary determinant of functional symmetry was leaf anatomy. Functionally symmetrical leaves had upper and lower palisade layers of equal thickness (vertical leaves of open habitats) or were composed primarily of a single layer of photosynthetic cells (horizontal leaves of understory habitats). Photosynthetic symmetry of vertical-leaf species may be an adaptation to maximize daily integrated carbon gain and water-use efficiency, whereas asymmetry of horizontal-leaf species may be an adaptation to maximize daily integrated carbon gain and photosynthetic nutrient-use efficiency.     

Water is allocated differently to chloroplasts in sun and shade leaves

Hydrogen-1 nuclear magnetic resonance spectroscopy was used to study water allocation in cell compartments of sun and shade leaves. NMR spectra of Acer platanoides were resolved into two peaks that were assigned to chloroplast and nonchloroplast water. Sun leaves contained 1.7 times more water per unit area of surface than shade leaves, and the water was allocated differently. Chloroplasts in sun leaves contained 17% of the total leaf water versus 47% in shade leaves. Comparing equal leaf surface areas, the chloroplasts in shade leaves contained 60% more water than those in sun leaves.     

Chlorophyll and light gradients in sun and shade leaves of Spinacia oleracea

Abstract. Light gradients were measured and correlated with chlorophyll concentration and anatomy of leaves in spinach (Spinacia oleracea L.). Light gradients were measured at 450, 550 and 680 nm within thin (455 μm) and thick (630 μm) leaves of spinach grown under sun and shade conditions. The light gradients were relatively steep in both types of leaves and 90% of the light at 450 and 680 nm was absorbed by the initial 140 μm of the palisade. In general, blue light was depleted faster than red light which, in turn was depleted faster than green light. Light penetrated further into the thicker palisade of sun leaves in comparison to the shade leaves. The distance that blue light at 450 nm travelled before it became 90% depleted was 120 μm in sun leaves versus 76 μm in shade leaves. Red light at 680 nm and green light at 550 nm travelled further but the trends were similar to that measured at 450nm. The steeper light gradients within the palisade-of shade leaves were caused by increased scattering of light within the intercellular air spaces and/or cells which were less compact than those in sun leaves. The decline in the amount of light within the leaf appeared to be balanced by a gradient in chlorophyll concentration measured in paradermal sections. Progressing from the adaxial epidermis, chlorophyll content increased through the palisade and then declined through the spongy mesophyll. Chlorophyll content was similar in the palisade of both sun and shade leaves. Chloroplast distribution within both sun and shade leaves was relatively uniform so that the chlorophyll gradient appeared to be caused by greater amounts of chlorophyll within chloroplasts located deeper within the leaf. These results indicate that the anatomy of the palisade may be of special importance for controlling the penetration of photo-synthetically active radiation into the leaf. Changing the structural characteristics of individual palisade cells or their arrangement may be an adaptation that maximizes the absorption of light in leaves with varying mesophyll thickness due to different ambient light regimes.     

Developmental process of sun and shade leaves in Chenopodium album L.

The authors’ previous study of Chenopodium album L. revealed that the light signal for anatomical differentiation of sun and shade leaves is sensed by mature leaves, not by developing leaves. They suggested that the two‐cell‐layered palisade tissue of the sun leaves would be formed without a change in the total palisade tissue cell number. To verify that suggestion, a detailed study was made of the developmental processes of the sun and shade leaves of C. album with respect to the division of palisade tissue cells (PCs) and the data was expressed against developmental time (leaf plastochron index, LPI). The total number of PCs per leaf did not differ between the sun and shade leaves throughout leaf development (from LPI ?1 to 10). In both sun and shade leaves, anticlinal cell division of PCs occurred most frequently from LPI ?1 to 2. In sun leaves, periclinal division of PCs occurred synchronously with anticlinal division. The constancy of the total number of PCs indicates that periclinal divisions occur at the expense of anticlinal divisions. These results support the above suggestion that two‐cell‐layered palisade tissue is formed by a change of cell division direction without a change in the total number of PCs. PCs would be able to recognize the polarity or axis that is perpendicular to the leaf plane and thereby change the direction of their cell divisions in response to the light signal from mature leaves.     

Inclination of sun and shade leaves influences chloroplast light harvesting and utilization

Light harvesting and utilization by chloroplasts located near the adaxial vs the abaxial surface of sun and shade leaves were examined by fluorometry in two herbaceous perennials that differed in their anatomy and leaf inclination. Leaves of Thermopsis montana had well-developed palisade and spongy mesophyll whereas the photosynthetic tissue of Smilacina stellata consisted of spongy mesophyll only. Leaf orientation depended upon the irradiance during leaf development. When grown under low-light levels, leaves of S. stellata and T. montana were nearly horizontal, whereas under high-light levels, S. stellata leaves and T. montana leaves were inclined 60⁰ and 30⁰, respectively. Leaf inclination increased the amount of light that was intercepted by the lower leaf surfaces and affected the photosynthetic properties of the chloroplasts located near the abaxial leaf surface. The slowest rates of quinone pool reduction and reoxidation were found in chloroplasts located near the adaxial leaf surface of T. montana plants grown under high light, indicating large quinone pools in these chloroplasts. Chloroplasts near the abaxial surface of low-light leaves had lower light utilization capacities as shown by photochemical quenching measurements. The amount of photosystem II (PSII) down regulation, measured from each leaf surface, was also found to be influenced by irradiance and leaf inclination. The greatest difference between down regulation monitored from the adaxial vs abaxial surfaces was found in plants with horizontal leaves. Different energy dissipation mechanisms may be employed by the two species. Values for down regulation in S. stellata were 2–3 times higher than those in T. montana, while the portion of the PSII population which was found to be Q_B nonreducing was 4–6 times lower in high light S. stellata leaves than in T. montana. All values of Stern-Volmer type nonphotochemical quenching (NPQ) from S. stellata leaves were similar when quenching analysis was performed at actinic irradiances that were higher than the irradiance to which the leaf surface was exposed during growth. In contrast, with T. montana, NPQ values from the abaxial leaf surface were up to 45% higher than those from the adaxial leaf surface regardless of growth conditions. The observed differences in chloroplast properties between species and between the adaxial and abaxial leaf surfaces may depend upon a complex interaction among light, leaf anatomy and leaf inclination.     

Antioxidants in sun and shade leaves of sour orange trees (Citrus aurantium) after long-term acclimation to elevated CO2

Antioxidative systems and the contents of pigments, malondialdehyde,soluble protein, and carbohydrate were investigated in sun-and shade-acclimated leaves of sour orange (Citrus aurantium)trees that had been grown for 7.5 years under ambient and elevated(+300 µmol mol^–1) atmospheric CO₂ concentrations.Sunacclimated leaves contained higher ascorbate, glutathioneand soluble carbohydrate contents and higher catalase activitiesthan shade-acclimated leaves. The activities of superoxide dismutases,which belonged to the family of Cu/Zn-isozymes, were similarin sunand shade-acclimated leaves and decreased in responseto enhanced CO₂. In shade-acclimated leaves, none of the otherparameters studied was affected by elevated CO₂. In sun-acclimatedleaves elevated CO₂ caused increases in carbohydrate and ascorbatecontents. There was no evidence for enhanced lipid peroxidationas assessed from the determination of the malondialdehyde contentsunder either conditions. Key words: Ascorbate, catalase, CO₂ enrichment, global change, glutathione, superoxide dismutase     

Chlorophyll fluorescence kinetics, photosynthetic activity, and pigment composition of blue-shade and half-shade leaves as compared to sun and shade leaves of different trees

The chlorophyll (Chl) fluorescence induction kinetics, net photosynthetic CO₂ fixation rates P _N, and composition of photosynthetic pigments of differently light exposed leaves of several trees were comparatively measured to determine the differences in photosynthetic activity and pigment adaptation of leaves. The functional measurements were carried out with sun, half-shade and shade leaves of seven different trees species. These were: Acer platanoides L., Ginkgo biloba L., Fagus sylvatica L., Platanus x acerifolia Willd., Populus nigra L., Quercus robur L., Tilia cordata Mill. In three cases (beech, ginkgo, and oak), we compared the Chl fluorescence kinetics and photosynthetic rates of blue-shade leaves of the north tree crown receiving only blue sky light but no direct sunlight with that of sun leaves. In these cases, we also determined in detail the pigment composition of all four leaf types. In addition, we determined the quantum irradiance and spectral irradiance of direct sunlight, blue skylight as well as the irradiance in half shade and full shade. The results indicate that sun leaves possess significantly higher mean values for the net CO₂ fixation rates P _N (7.8–10.7 μmol CO₂ m^?2 s^?1 leaf area) and the Chl fluorescence ratio R _Fd (3.85–4.46) as compared to shade leaves (mean P _N of 2.6–3.8 μmol CO₂ m^?2 s^?1 leaf area.; mean R _Fd of 1.94–2.56). Sun leaves also exhibit higher mean values for the pigment ratio Chl a/b (3.14–3.31) and considerably lower values for the weight ratio total chlorophylls to total carotenoids, (a + b)/(x + c), (4.07–4.25) as compared to shade leaves (Chl a/b 2.62–2.72) and (a + b)/(x + c) of 5.18–5.54. Blue-shade and half-shade leaves have an intermediate position between sun and shade leaves in all investigated parameters including the ratio F _v/F _o (maximum quantum yield of PS2 photochemistry) and are significantly different from sun and shade leaves but could not be differentiated from each other. The mean values of the Chl fluorescence decrease ratio R _Fd of blue-shade and half-shade leaves fit well into the strong linear correlation with the net photosynthetic rates P _N of sun and shade leaves, thus unequivocally indicating that the determination of the Chl fluorescence decrease ratio R _Fd is a fast and indirect measurement of the photosynthetic activity of leaves. The investigations clearly demonstrate that the photosynthetic capacity and pigment composition of leaves and chloroplasts strongly depend on the amounts and quality of light received by the leaves.     

The spatial distribution of chloroplast water in Acer platanoides sun and shade leaves

We evaluated a new, two-dimensional (2-D) nuclear magnetic resonance (NMR) imaging technique as a method for measuring the distribution of chloroplasts in leaves. NMR images that showed the distribution of chloroplast water and of total water as a function of depth into Acer platanoides sun and shade leaves were compared with the distribution of chlorophyll in the same leaf types (as measured by fluorescence microscopy), with the cellular structure (by scanning electron microscopy), and with published information. Results showed that the volume fraction of chloroplast water was much larger in shade than in sun leaves, and that it averaged about one-third larger in the palisade than in the spongy parenchyma region of both leaf types. Chlorophyll fluorescence was more intense in shade than in sun leaves. In sun leaves, fluorescence was maximal in the palisade region near the junction with the spongy parenchyma, while in shade leaves, fluorescence was maximal in the upper part of the spongy layer. We concluded that 2-D NMR imaging reliably indicates the location of chloroplast water.     

Carotenoid composition in sun and shade leaves of plants with different life forms

The carotenoid composition of sun leaves of nine species of annual crop plants (some with several varieties) was compared with sun and shade leaves of several other groups of plants, among those sun and shade leaves of several species of perennial shrubs and vines and deep-shade leaves of seven rainforest species. All sun leaves contained considerably greater amounts of the components of the xanthophyll cycle violaxanthin, antheraxanthin and zeaxanthin as well as of β-carotene than the shade leaves, as had previously been reported for a variety of other species by Thayer & Björkman (Photosynthesis Research, 1990, 23, 331–343). Therefore, high light specifically stimulated β,β-carotenoid synthesis. The sun leaves of these crop species did not contain α-carotene which was, however, present in large amounts in all shade leaves and in smaller amounts in sun leaves of three of the four species of perennial shrubs and vines. There was no difference in neoxanthin content on a chlorophyll basis between sun and shade leaves, and there was no consistent general difference in the lutein content between all sun and all shade leaves. The zeaxanthin (and antheraxanthin) content at peak irradiance and the xanthophyll cycle pool size were compared for sun leaves from the different groups of plants with different life forms and different metabolic activities. When growing in full sunlight the annual crop species and a perennial mesophyte had high rates of photosynthesis whereas the perennial shrubs and vines had relatively low photosynthesis rates. More zeaxanthin (and antheraxanthin) were accumulated at noon in full sunlight in those species with the lower photosynthesis rates. However, it was not such that those species also possessed the larger pools of violaxanthin + antheraxanthin + zeaxanthin. Instead, the xanthophyll cycle pools of sun leaves of the annual crop species and the perennial mesophyte were not smaller, and were even possibly larger, than those of sun leaves of the perennial shrubs and vines with low photosynthesis rates. This was so in spite of the fact that the crop species experienced much lesser degrees of excessive light at full sun than the shrubs and vines. Thus, many of the crop species converted only about 30–50% of their xanthophyll cycle pool to zeaxanthin at noon, whereas the shrubs and vines typically converted more than 80% of their pool into zeaxanthin. The crop species also had larger pools of β-carotene than the shrubs and vines but smaller pools of lutein than the majority of the latter species.     

Herbivory in sun and shade

Observations of several plant species suggest that individuals incur greater herbivore damage in shaded than in nearby sunny areas. Two hypotheses are presented to explain this pattern of herbivory; a preliminary test of one suggests that plants growing in the sun are usually tastier, although eaten less, than those in the shade. The phenomenon has several implications for the nature of plant-herbivore interactions in terrestrial communities.     

Response of mitochondria to light intensity in the leaves of sun and shade species

The present authors have shown previously that both respiration rates and in vivo activities of the alternative oxidase (AOX) of leaves of Alocasia odora, a shade species, are lower than those in sun species, thereby optimizing energy production under limited light conditions (Noguchi et al., Australian Journal of Plant Physiology 28, 27–35, 2001). In the present study, mitochondria isolated from A. odora leaves were examined in order to investigate the biochemical basis for the differences in respiratory parameters. Alocasia odora and spinach plants were cultivated under both high and low light intensities, mitochondria were isolated from their leaves, and their respiratory properties compared. Mitochondrial content of leaf extracts from the two species was estimated using fumarase activities and antibody detection of porin (the voltage-dependent anion channel of the outer mitochondrial membrane). On a mitochondrial protein basis, spinach leaves showed higher capacities of the cytochrome pathway and cytochrome c oxidase (COX) than A. odora leaves. However, on a mitochondrial protein basis, A. odora showed higher capacities of AOX, which had a high affinity for ubiquinone when activated by pyruvate. Alocasia odora also had larger amounts of mitochondrial protein per leaf dry weight, even under severely shaded conditions, than spinach. Lower growth light intensity led to lower activities of most pathways and proteins tested in both species, especially glycine-dependent oxygen uptake. In the low light environment, most of the AOX protein in A. odora leaves was in its inactive, oxidized dimer form, but was converted to its reduced active form when plants were grown under high light. This shift may prevent over-reduction of the respiratory chain under photo-oxidative conditions.