Effects Of Growth Irradiance Research Articles

Effects of growth irradiance on photosynthesis and photorespiration of Phoebe bournei leaves

Light intensity is a major environmental factor affecting the growth and survival of trees in a forest. The effect of light reduction on photosynthesis and photorespiration of an evergreen broad-leaved tree, Phoebe bournei (Hemsley) Yang was examined with three levels of full light, 50.5% light, and 21.8% light. The results showed that shading led to significant increase in plant height and crown diameter. Light-saturated leaf photosynthetic rate (Amax), maximal carboxylation activity (Vcmax), maximum electron transfer rate (Jmax), stomatal conductance (gs), mesophyll conductance (gm) and chloroplast CO2 concentration (Cc) significantly increased in response to shade. Photorespiratory CO2 release rate (PR) was higher in plants grown under shade conditions than under full light. The relative limitations of gm (lm) was higher than the relative limitations of gs (ls) and the relative limitations of biochemical factors (lb) in leaves of P. bournei grown under full light, whereas lm was lower than ls and lb under shade. Our results suggest that increase of photosynthesis in P. bournei leaves grown under shade is associated with enhanced CO2 diffusion and biochemistry. And we propose that enhancement of the photorespiratory is essential for shade leaves to improve photosynthesis.

Response of plasmodesmata formation in leaves of C4 grasses to growth irradiance.

Rapid metabolite diffusion across the mesophyll (M) and bundle sheath (BS) cell interface in C4 leaves is a key requirement for C4 photosynthesis and occurs via plasmodesmata (PD). Here, we investigated how growth irradiance affects PD density between M and BS cells and between M cells in two C4 species using our PD quantification method, which combines three-dimensional laser confocal fluorescence microscopy and scanning electron microscopy. The response of leaf anatomy and physiology of NADP-ME species, Setaria viridis and Zea mays to growth under different irradiances, low light (100μmolm-2 s-1 ), and high light (1,000μmolm-2 s-1 ), was observed both at seedling and established growth stages. We found that the effect of growth irradiance on C4 leaf PD density depended on plant age and species. The high light treatment resulted in two to four-fold greater PD density per unit leaf area than at low light, due to greater area of PD clusters and greater PD size in high light plants. These results along with our finding that the effect of light on M-BS PD density was not tightly linked to photosynthetic capacity suggest a complex mechanism underlying the dynamic response of C4 leaf PD formation to growth irradiance.

Orchid Conservation in Singapore under Natural Conditions: Responses of Grammatophyllum Speciosum to Growth Irradiances

Grammatophyllum speciosum orchid plants were grown both on the ground and on trees under high light (HL) and low light (LL) conditions in Pasir Ris Park, Singapore. This paper studied photosynthetic energy utilization investigated by chlorophyll (Chl) fluorescence and photosynthetic pigments; plant water status measured by leaf relative water content (RWC) and stomatal conductance (gs). All plants had midday leaf RWC greater than 80%, indicating no severe water deficit occurred in any plants. Except for plants grown on trees under LL, midday depression of Fv/Fm ratios occurred in all other plants, indicating dynamic photoinhibiton. There was no chronic photoinhibition in any plants as Fv/Fm ratios recovered to healthy level at early morning. Grown on the ground under HL, G. speciosum had higher photochemical quantum yield (ΔF/Fm’), greater electron transport rate (ETR) and non-photochemical quenching (NPQ), indicating their higher efficiency in utilization and dissipation excess energy. Plants grown on the ground under HL had lower Chl and Chl/Car ratio, but higher content of carotenoids and Chl a/b ratio compared to the other plants, implying their acclimation to HL conditions. The highest gs was recorded at 1000 h, suggesting the avoidance of drought stress by widely opening stomata only for a short period of time in the early morning. Higher gs was related to higher leaf temperature, indicating that the role of gs in moderating leaf temperature. Understanding the effects of growth irradiance on photosynthesis of G. speciosum would be an important step towards a sustainable conservation of native orchids in Singapore.

Inter-relationships between light and respiration in the control of ascorbic acid synthesis and accumulation in Arabidopsis thaliana leaves.

The effects of growth irradiance and respiration on ascorbic acid (AA) synthesis and accumulation were studied in the leaves of wild-type and transformed Arabidopsis thaliana with modified amounts of the mitochondrial alternative oxidase (AOX) protein. Plants were grown under low (LL; 50 micromol photons m(-2) s(-1)), intermediate (IL; 100 micromol photons m(-2) s(-1)), or high (HL; 250 micromol photons m(-2) s(-1)) light. Increasing growth irradiance progressively elevated leaf AA content and hence the values of dark-induced disappearance of leaf AA, which were 11, 55, and 89 nmol AA lost g(-1) fresh weight h(-1), from LL-, IL-, and HL-grown leaves, respectively. When HL leaves were supplied with L-galactone-1,4-lactone (L-GalL; the precursor of AA), they accumulated twice as much AA and had double the maximal L-galactone-1,4-lactone dehydrogenase (L-GalLDH) activities of LL leaves. Growth under HL enhanced dehydroascorbate reductase and monodehydroascorbate reductase activities. Leaf respiration rates were highest in the HL leaves, which also had higher amounts of cytochrome c and cytochrome c oxidase (CCO) activities, as well as enhanced capacity of the AOX and CCO electron transport pathways. Leaves of the AOX-overexpressing lines accumulated more AA than wild-type or antisense leaves, particularly at HL. Intact mitochondria from AOX-overexpressing lines had higher AA synthesis capacities than those from the wild-type or antisense lines even though they had similar L-GalLDH activities. AOX antisense lines had more cytochrome c protein than wild-type or AOX-overexpressing lines. It is concluded that regardless of limitations on L-GalL synthesis by regulation of early steps in the AA synthesis pathway, the regulation of L-GalLDH activity via the interaction of light and respiratory controls is a crucial determinant of the overall ability of leaves to produce and accumulate AA.

The effect of growth irradiance on leaf anatomy and photosynthesis in Acer species differing in light demand

AbstractVariation in light demand is a major factor in determining the growth and survival of trees in a forest. There is strong relation between the light‐demand and the effect of growth irradiance on leaf morphology and photosynthesis in three Acer species: A. rufinerve (light‐demanding), A. mono (intermediate) and A. palmatum (shade‐tolerant). The increase in mesophyll thickness and surface area of chloroplasts facing the intercellular airspaces (Sc) with growth irradiance was highest in A. rufinerve. Although the increase in light‐saturated photosynthesis (Amax) was similar among the species, the increase in water use efficiency (WUE) was much higher in A. rufinerve than that in the other species, indicating that the response to water limitation plays an important role in leaf photosynthetic acclimation to high light in A. rufinerve. The low CO2 partial pressure at the carboxylation site (Cc) in A. rufinerve (130 µmol mol−1) at high irradiance was caused by low stomatal and internal conductance to CO2 diffusion, which minimized the increase in Amax in A. rufinerve despite its high Rubisco content. Under shade conditions, interspecific differences in leaf features were relatively small. Thus, difference in light demand related to leaf acclimation to high light rather than that to low light in the Acer species.

Effects of temperature, nitrogen, and light limitation on the optical properties of the marine diatom Thalassiosira pseudonana

A series of laboratory experiments were conducted to examine the optical properties of the marine diatom Thalassiosira pseudonana for a broad range of growth rates (µ from 0.22 to 2 d−1) under temperature‐, nitrogen‐, and light‐limited conditions. The effects of temperature and nitrogen limitation on spectral absorption cross‐sections expressed on a per cell basis, σa(λ), were similar. With the reduction in growth rate, σa at a light wavelength λ = 674 nm showed an equivalent decrease regardless of whether the cells were limited by temperature or nitrogen. The effect of growth irradiance was distinctively different, since σa increased with light limitation. The chlorophyll a (Chl a)—specific absorption coefficient showed the opposite trends than those of σa. These patterns resulted primarily from the acclimative strategies of T. pseudonana involving an increase in Chl a content in response to light limitation and a decrease in Chl a under temperature and nitrogen limitation. The scattering cross‐sections, σb(λ), and carbon‐specific scattering coefficients, b*c(λ), were generally not a strong function of growth rate with the exception of lower values of b*c for light‐limited cells. While T. pseudonana exhibited some changes in cell size, variations in the refractive index had the major influence on cell optical properties. The imaginary part of the refractive index (at λ = 674 nm) showed a strong correlation with intracellular Chl a concentration, and the real part of the refractive index (at λ = 660 nm) was correlated with the intracellular carbon concentration. Our results indicate that integrated studies of the effects of various environmental factors such as light, nutrients, and temperature are needed to adequately describe optical variability in phytoplankton.

The effect of growth irradiance on leaf anatomy and photosynthesis in maple species

The capacity in using irradiance is decisive for the success of tree species in forests. Tree species that have different capacities in using irradiance are classified as light-adapted and shade-tolerant species. When grown under low or high light, these species sometimes show contrast photosynthetic response, which indicates that the changes in the processes that limit photosynthesis may differ between these two types. We compared the leaf morphological and physiological acclimation to growth irradiance among the three maple species having different light adaptation. Seedlings of sun-adapted (Acer rufinerve), intermediate (Acer mono), and shade-adapted (Acer palmatum) maple species were grown under 100% and 17% of full sun. When grown under full sun, thickness of mesophyll and surface area of chloroplasts facing to intercellular airspaces (Sc) were larger in A. rufinerve compared to A. mono and A. palmatum. In contrast, interspecific difference in light-saturated photosynthesis (Amax) was not significant. CO2 partial pressure at the carboxylation site (Cc) was lower in A. rufinerve compared to those in A. palmatum and A. mono, because both stomatal and mesophyll conductance to CO2 diffusion were tended to be small in this species. This low Cc in A. rufinerve may minimize the increase of Amax irrespective of large Rubisco contents. On the other hand, A. rufinerve had large water use efficiency (WUE) compared to the other species, which may be advantageous under full sun where midday VPD would be large. Under low growth irradiance, interspecific difference in leaf anatomy and photosynthesis was less significant compared to full sun.

Effect of growth irradiance on plastocyanin levels in barley

Plastocyanin levels in barley (Hordeum vulgare cv Boone) were found to be dependent on growth irradiance. An immunochemical assay was developed and used to measure the plastocyanin content of isolated thylakoid membranes. Barley grown under 600 μmole photons m(-2)s(-1) contained two- to four-fold greater quantities of plastocyanin per unit chlorophyll compared with plants grown under 60 μmole photons m(-2)s(-1). The plastocyanin/Photosystem I ratio was found to be 2 to 3 under high irradiance compared with 0.5 to 1.5 under low irradiance. The reduced plastocyanin pool size in low light plants contributed to a two-fold reduction in photosynthetic electron transport activity. Plastocyanin levels increased upon transfer of low light plants to high irradiance conditions. In contrast, plastocyanin levels were not affected in plants transferred from high to low irradiance, suggesting that plastocyanin is not involved in the acclimation of photosynthesis to shade.

Effects of Growth Irradiance and Nitrogen Limitation on Photosynthetic Energy Conversion in Photosystem II

Photosynthetic energy conversion was investigated in five species of marine unicellular algae, (Dunaliella tertiolecta, Thalassiosira pseudonana, T. weisflogii, Skeletorema costatum, Isochrysis galbana) representing three phylogenetic classes, which were grown under steady state conditions with either light or inorganic nitrogen as a limiting factor. Using a pump and probe fluorescence technique we measured the maximum change in variable fluorescence yields, the flash intensity saturation curves for the change in fluorescence yields and the kinetics of the decay in fluorescence yields. Under all growth irradiance levels nutrient replete cells exhibited approximately the same changes in fluorescence yields and similar fluorescence decay kinetics. The apparent relative absorption cross-section of photosystem II, calculated from the slope of the flash intensity saturation curves, generally increased as cells shade adapted. The decay kinetics of the fluorescence yield following a saturating pump flash can be expressed as the sum of three exponential components, with half-times of 160 and 600 microseconds and 30 to 300 milliseconds. The relative contribution of each component did not change significantly with growth irradiance. As cells became more nitrogen limited, however, the maximum change in fluorescence yield decreased, and was accompanied by a decrease in the proportion of a 160 microsecond fluorescence decay component, which corresponds to the transfer of electrons from Q(a) (-) to Q(b). Changes in fluorescence yields were also accompanied by changes in the levels of D1, a protein which is integral in reaction center II, and CP47, a chlorophyll protein forming part of the core of photosystem II. These results are consistent with a loss of functional photosystem II reaction centers. Moreover, in spite of losses of total cellular chlorophyll, which invariably accompanied nitrogen limitation, the apparent absorption cross-sections of photosystem II increased. Our results suggest that nitrogen limitation leads to substantial decreases in photosynthetic energy conversion efficiency.

Chlorophyll-Protein Complexes from the Red-Tide Dinoflagellate, Gonyaulax polyedra Stein

A comparision of high (330 microeinsteins per meter squared per second) and low (80 microeinsteins per meter squared per second) light grown Gonyaulax polyedra indicated a change in the distribution of chlorophyll a, chlorophyll c(2), and peridinin among detergent-soluble chlorophyll-protein complexes. Thylakoid fractions were prepared by sonication and centrifugation. Chlorophyll-protein complexes were solubilized from the membranes with sodium dodecyl sulfate and resolved by Deriphat electrophoresis. Low light cells yielded five distinct chlorophyll-protein complexes (I to V), while only four (I' to IV') were evident in preparations of high light cells. Both high molecular weight complexes I and I' were dominated by chlorophyll a absorption and associated with minor amounts of chlorophyll c. Both complexes II and II' were chlorophyll a-chlorophyll c(2)-protein complexes devoid of peridinin and unique to dinoflagellates. The chlorophyll a:c(2) molar ratio of both complexes was 1:3, indicating significant chlorophyll c enrichment over thylakoid membrane chlorophyll a:c ratios of 1.8 to 2:1. Low light complex III differed from all other high or low light complexes in that it possessed peridinin and had a chlorophyll a:c(2) ratio of 1:1. Low light complexes IV and V and high light complexes III' and IV' were spectrally similar, had high chlorophyll a:c(2) ratios (4:1), and were associated with peridinin. The effects of growth irradiance on the composition of chlorophyll-protein complexes in Gonyaulax polyedra differed from those described for other chlorophyll c-containing plant species.

Effects of growth irradiance on the photosynthetic action spectra of the marine dinoflagellate, Glenodinium sp.

Whole cell absorption curves of the marine dinoflagellate Glenodinium sp., cultured at irradiances of 250μW/cm(2) (low light) and 2500μW/cm(2) (high light), were measured and their difference spectrum determined. Absorption by low light grown cells exceeded that of high light grown cells throughout the visible spectrum by a factor which ranged from 2 to 4. The difference spectrum supported the view that increased pigmentation, resulting from low light conditions, was largely due to an increase in cell content of a peridinin-chlorophyll a-protein (PCP) and an unidentified chlorophyll a component of the chloroplast membrane. Photosynthetic action spectrum measurements indicated that chlorophyll a, peridinin, and very likely chlorophyll c, were effective light-harvesting pigments for photosynthesis in both high and low light grown cultures of Glenodinium sp. Comparison of action spectra and absorption spectra suggested that low light grown cells selectively increased cellular absorption in the 480 nm to 560 nm region, and effectively utilized this spectral region for the promotion of oxygen evolution.