Changes In Photosynthetic Apparatus Research Articles

Comparative Study between the Photosynthetic Parameters of Two Avocado (Persea americana) Cultivars Reveals Natural Variation in Light Reactions in Response to Frost Stress

Avocado is a commercially important fruit tree which is sold worldwide. Originating in subtropical regions of the South America, this species is now grown worldwide and is sometimes exposed to cold temperatures. Specifically, frost stress harms the crop yield and its quality. While it is known in general that the photosynthetic apparatus changes in response to cold conditions, there is still not much information regarding the photosynthetic apparatus response to sporadic frost stress. In this study, we tracked the photosynthetic apparatus’ light reaction of ‘Hass’ and ‘Ettinger’ avocado cultivars to frost stress, with Ettinger being known to be more resilient to cold than Hass. We found that in avocado trees, the photosynthetic apparatus’ response to frost occurs at the level of photosystem II (PSII) itself, rather than a photoprotective response to a stress. The Hass apparatus incorrectly interprets the reduction in electron transport rate activity and by that increases its light harvesting complex size at the expense of its reaction centers which then increases the apparatus’ probability to generate reactive oxygen species. The results of this study open opportunities to further research the process which regulates the feedback mechanism that controls the photosynthetic unit’s size in Hass when compared to the Ettinger cultivar, and whether it is part of a feedback regulation from the carbon assimilation step or indirectly from a stomatal limitation which arises in these subtropical species. While corroborating past studies performed on avocados, this study suggests using advanced chlorophyll a fluorescence protocols when researching natural variation in crops.

APPLICATION OF OJIP CHLOROPHYLL FLUORESCENCE TRANSIENT ANALYSIS TO STUDY THE POSTHARVEST CHANGES IN PHOTOSINTHETIC APPARATUS IN CUT FOLIAGE SPECIES

Chlorophyll fluorescence (ChlF) is a non-invasive technique that can be potentially used in postharvest research to gain useful information on early responses to postharvest stresses. This study was conducted to validate the application of ChlF transient analysis in determining the postharvest changes in photosynthetic apparatus in three ornamental foliage species, i.e., Cordyline fruticosa ‘Willy’s Gold’ and ‘Rubra’, Dracaena sanderiana ‘White’, and Nephrolepis exaltata. Salicylic acid (100 and 300 mg·L−1), glucose (10 g·L−1), and their combinations were used as holding solutions with control treatment (distilled water) at room temperature (25±2°C). Vase life was evaluated using OJIP analysis. OJIP parameters, i.e., specific energy fluxes per reaction center (ABS/RC, TR/RC, ET/RC, and DI/RC), flux ratios (maximum quantum yield of primary photochemistry-φPo), electron transport efficiency (ψo), and quantum yield of electron transport (φEo), and performance index (PI) were recorded every other day, using a fluorometer (FluorPen 100). Leaf chlorophyll contents of all species and anthocyanin contents of two cordyline cultivars were determined. Data were subjected to ANOVA in a completely randomized design. Mean separation was done by DMRT (p ≤ 0.05). Clear variations in ChlF were observed in every foliage species with the time. OJIP analysis showed species-depended variations. The higher ABS/RC and DI/RC were recorded for D. sanderiana and N. exaltata compared to the PI of those species. At the end of the experiment, the chlorophyll contents were decreased, while anthocyanin contents were increased. Consequently, chlorophyll fluorescence changes in photosynthetic apparatus can be used for the prediction of the postharvest stresses and longevity of cut foliage.

Impact of lead on the amount of chlorophyll and carotenoids in the leaves of Triticum durum and T. aestivum, Hordeum vulgare and Avena sativa

Lead is one of the most dangerous pollutants to both the environment and humans. It causes structural changes in photosynthetic apparatus and reduced biosynthesis of chlorophyll pigments inhibits carbon metabolism. The aim of our study was to determine the dynamics of photosynthetic pigments in leaves of wheat (Triticum durum and T. aestivum), barley (Hordeum vulgare) and oats (Avena sativa) at different lead acetate, Pb(CH3COO)2 levels: 0, 0.15, 0.30 and 0.60 g/L. The results of this research indicate that these concentrations significantly affected chlorophyll content of H. vulgare and A. sativa as compared to T. durum and T. aestivum. Analysis of variance showed that lead concentration and interaction between cereal species had a significant effect on all chlorophyll characteristics at 0.1% probability and on carotenoids contents at 1% significance. Lead acetate in 0.3 and 0.6 g/L concentrations had a highly significant effect on chlorophyll a, b and carotenoids in H. vulgare seedlings, its carotenoid contents increased from 0.002 mg/g FW at 0 g/L to 0.107 mg/g FW at 0.6 g/L, whereas its chlorophyll content decreased under heavy metal stress, corresponding to the concentration of the metal ion. Carotenoids of A. sativa were not affected compared to Chl a and Chl b, while higher concentrations significantly increased chlorophyll contents of the seedlings from 1.384 mg/g FW of total chlorophyll at 0 g/L to 1.883 mg/g FW at 0.6 g/L. The increased amount of carotenoids was indicative of the formation of free radicals in plants under heavy metal stress, while decreased levels of chlorophyll content were an indication of reduction in the growth of the plants leading to decrease in the yield. It is suggested that chlorophyll content can be adopted as a very useful in vivo indicator of heavy metal toxicity.

Special issue in honour of Prof. Reto J. Strasser - JIP-test as a tool for early detection of the macronutrients deficiency in Miscanthus plants

The optimization of cultivation process and improving the yield of perspective energy crops in Europe could be one of the ways to overcome the problem of limited amount of conventional fuel. The aim of this work was to check if the use of JIP-test, as a noninvasive method for early detection of the changes in photosynthetic apparatus, can be applied to detect nutrients deficiency in miscanthus (Miscanthus × gigantheus Anderss.) plants. The experiment was performed in fully randomized design with the following experimental variants: CaNPK (full fertilization, control), NPK (without calcium), CaKN (phosphorus poor), CaPK (nitrogen poor), CaPN (potassium poor), and Ca (without NPK). Our results revealed that the reaction of photosynthetic apparatus of miscanthus plants grown under certain macronutrient deficiency was associated with exclusive significant modifications in the measured chlorophyll fluorescence signals, analysed further by JIP-test. Analysis of chlorophyll fluorescence induction curves discovered substantial deficiency of phosphorus and potassium ahead of the standard chemical method.

Can just one-second measurement of chlorophyll a fluorescence be used to predict sulphur deficiency in radish (Raphanus sativus L. sativus) plants?

Nutrients deficiency (ND) in plants is one of the main factors adversely affecting plant growth and yield of agricultural and horticultural production. Usually detection of NDs in plants is based on visible symptoms or destructive chemical analysis. Recently chlorophyll a fluorescence is one of the most used approaches to investigate photosynthesis light-dependent reactions. It is widely accepted that it can inform about structural and functional changes in photosynthetic apparatus, especially under abiotic stresses including NDs. The aim of this research was to study the influence of sulphur deficiency on photosynthetic efficiency of two cultivars radish (Raphanus sativus L. sativus) – ‘Fluo HF1’ and ‘Suntella F1’, and to assess the potential of chlorophyll a fluorescence measurements in early detection of this stress. Our results showed the sulphur deficiency has decreased the electron transport rate, chlorophyll content, grana size, and, at some degree, net photosynthesis and stomatal conductance. The changes in photosynthetic machinery performance were observed earlier than the visible effects of sulphur deficiency. However, the photosynthetic apparatus of radish plants was not considerably affected by this stress. Some sensitive parameters of OJIP test were altered but we were not able to identify the sulphur deficiency stress based on the alteration of only one of these parameters. We conclude that the detection of specific stress reactions of plants to sulphur deficiency should be based on integrative analysis of the response of the photosynthetic machinery. Such stress induced reactions can be detected by Principal Component Analysis of a large number of JIP-test parameters.

Зміни у фотосинтетичному апараті бобових культур, уражених збудниками бактеріозів та фітоплазмозів

Зміни у фотосинтетичному апараті бобових культур, уражених збудниками бактеріозів та фітоплазмозів

Drought-induced changes in photosynthetic apparatus and antioxidant components of wheat (Triticum durum Desf.) varieties

Water deficit is a key factor influencing the yield and quality of crops. In the present study, the photosynthetic responses by means of chlorophyll fluorescence of chloroplasts, thylakoid membrane proteins, and antioxidant components were analyzed in wheat (Triticum durum Desf.) plants differing in their tolerance to drought. Two durum winter wheat varieties, Barakatli 95 (drought tolerant) and Garagylchyg 2 (drought sensitive) were grown under field well-watered and drought conditions. It was found that contents of the PS I core (CPI) with Mr of 123 kD and apoprotein P700 with Mr of 63 kD were relatively higher in Barakatli 95 variety under drought stress compared with the control plants. Synthesis of α- and β-subunits of CF1 ATP-synthase complex with Mr of 55 and 53.5 kD also slightly increased in the tolerant Barakatli 95 and decreased in the drought sensitive variety Garagylchyg 2. A decrease in the intensity of 30 kD band and a significant increase were found in the content of the 25-16 kD region in Garagylchyg 2 variety. The synthesis of 60 kD and content of low molecular mass polypeptides (21.5 and 12 kD) were increased in the tolerant genotype Barakatli 95. The intensity of peaks at 687, 695, and 742nm considerably increases in the fluorescence spectra (77K) of chloroplasts isolated from the sensitive variety Garagylchyg 2, and there is a stimulation of the ratio of fluorescence band intensity F687/F740. At the same time, higher level of glycine betaine was found in the drought tolerant variety compared with the control one throughout the different periods of growth.

Comparison of population growth and photosynthetic apparatus changes in response to different nutrient status in a diatom and a coccolithophore.

In many marine ecosystems, diatoms dominate in nutrient-rich coastal waters while coccolithiophores are found offshore in areas where nutrients may be limiting. In lab-controlled batch cultures, mixed-species competition between the diatom Phaeodactylum tricornutum and the coccolithophore Emiliana huxleyi and the response of each species were examined under nitrate (N) and phosphate (P) starvation. Based on the logistic growth model and the Lotka-Volterra competition model, E.huxleyi showed higher competitive abilities than P.tricornutum under N and P starvation. For both species, cell growth was more inhibited by P starvation, while photosynthetic functions (chl a fluorescence parameters) and cellular constituents (pigments) were impaired by N starvation. The decline of photosynthetic functions occurred later in E.huxleyi (day 12) than in P.tricornutum (day 9); this time difference was associated with greater damage of the photosynthetic apparatus in P.tricornutum compared with E.huxleyi. Xanthophyll cycle pigment accumulation and the transformation from diadinoxanthin to diatoxanthin was more active in E.huxleyi than P.tricornutum, under similar N and P starvation. We concluded that E.huxleyi and P.tricornutum have different mechanisms to allocate resources and energy under nutrient starvation. It appears that E.huxleyi has a more economic strategy to adapt to nutrient depleted environments than P.tricornutum. These findings provided additional evidence explaining how N versus P limitation differentially support diatom and coccolithophore blooms in natural environments.

Physiological performance of a foliose macrolichen Umbilicaria antarctica as affected by supplemental UV-B treatment

To date, a limited knowledge is available about Umbilicaria antarctica responses when it is exposed high doses of UV-B radiation. It is well established that resistance of Antarctic lichens to natural UV-B levels including increased doses during ozone hole period is high, thanks to numerous photoprotective mechanism. Capacity of the photoprotective processes, however, is not well known This study attempts to determine changes on the photosynthetic efficiency and on the synthesis of UV-B absorbing compounds of U. antarctica when exposed to low photosynthetically active radiation and extremely high intensity of UV-B light: 3.0 W m-2, of UV-B for 3 hours, 6 hours and 7 days. During the experiment, chlorophyll fluorescence was measured to evaluate changes in photosynthetic apparatus of intrathalline alga. After 7 d exposition, amount of UV-B absorbing compounds was evaluated in U. antarctica. Heavy UV-B stress let to an increase in chlorophyll fluorescence kinetics (OJIPs), however, majority of parameters related to functioning of PS II remained unchanged indicating high resistance of U. antarctica to UV-B stress. Potential (FV/FM) and actual (ФPSII) yields of PS II were not affected by the UV-B treatment as well. In majority of cases, heavy UV-B treatment led to a decrease in the amount of UV-B absorbing compounds extracted from treated thalli.

Chlorophyll fluorescence as an indicator of age-dependent changes in photosynthetic apparatus of wheat leaves

Wheat (Triticum sativus L.) seedlings of various ages (2- to 16-day-old plants) were used to study age-dependent changes in the chlorophyll fluorescence induction (CFI) at various light intensities during flu- orescence measurements. Plants were raised in a growth chamber using hydroponics with expanded clay, controlled environmental conditions, and 690 µmol/(m2 s) photon flux density (PFD) of photosynthetically active radiation (PAR). Parameters of CFI were determined under actinic PFD of 380, 580, 820, and 1340 µmol/(m2 s) PAR. The fifth leaf from the stem base, exposed to uniform lighting, was sampled for measurements. This leaf emerged at the plant age of 16 days. Based on fluorescence data, we calculated the maximal photochemical quantum yield of photosystem II (F v/F m), the effective photochemical quantum yield of PSII (Yield), parameters of photochemical (qP) and non-photochemical (qN and NPQ) quenching of chlorophyll fluorescence, the F p/F t ratio, and the “vitality index” (fluorescence decrease ratio, R fd). At moderate actinic PFD, applied commonly in PAM fluorometers (about 380 µmol/(m2 s)), age-dependent changes in NPQ, F p/F t, and R fd were observed. Analysis of CFI parameters in wheat leaves of different ages at PFD increasing from 380 to 820 µmol/(m2 s) revealed that R fd, NPQ, and qN are the most sensitive markers of the leaf age among all parameters tested. These suitable indicators can be used for rapid assessment of the leaf age.

Influences of growth cessation and photoacclimation on winter survival of non-native Lolium–Festuca grasses in high-latitude regions

Autumnal growth cessation in non-native grass species is inadequate for sufficient cold acclimation. Cold acclimation is influenced to various degrees by growth cessation and photoacclimation. The effects of both factors on winter survival were investigated by measuring photosynthetic activity with Handy Pea fluorimeter and leaf elongation growth rate (LER) and their effects on winter survival. Triplicate field trials were established at two locations in Norway: Fureneset (61°N) and Vågønes (67°N). In total, ten entries of perennial ryegrass (Lolium perenne), Festulolium hybrids and introgression lines, and meadow fescue (Festuca pratensis) were investigated weekly by measuring selected leaves (n=3×10) of the regrowth after the third harvest taken in late August in two successive years.The results showed that the relationship between photosynthetic performance in autumn, LER and winter survival differed between the locations. In the south (Fureneset), there was a positive correlation between photosynthetic activity before winter and winter survival. In the north (Vågønes), there was no correlation or even a negative correlation between photosynthetic activity before winter and winter survival. Low photosynthetic activity in autumn was associated with a higher level of winter survival in the north for F. pratensis cv. Norild and two northern-adapted cultivars of L. perenne. Northern-adapted forage grasses can be assumed to have an alternative mechanism for growth inhibition, since in the north the amount of light seems to be insufficient to trigger the changes in photosynthetic apparatus that are responsible for growth cessation in the south. Moreover, with progressing climate change, this adaptation pattern will increasingly be required in more southerly areas of the Nordic region because the light intensity decrease and temperature increase predicted for these areas will delay cold acclimation.

Low temperature and hardening effects on photosynthetic apparatus efficiency and survival of forage grass varieties

Freezing tolerance is essential for perennial plants and ability to adapt to extreme temperature is crucial for their survival in many environments. Freezing tolerance of hardened and unhardened plants of Dactylis glomerata and Lolium perenne varieties was probed by their quantum photosynthetic efficiency using the chlorophyll fluorescence technique. Quantum yield of photosystem II (PSII) electron transport (Φ<sub>PSII</sub>), maximal (F<sub>m</sub>’) and steady-state (F<sub>s</sub>) chlorophyll fluorescence yields of light-adapted samples were measured. Φ<sub>PSII</sub> depended on developmental phase, temperature and hardening process. A clear decline in PSII activity, especially after –10°C application was observed. Plant hardening during emergence phase had a positive impact on PSII activity, especially after –5°C application. After 72 h of –5°C temperature treatment, hardened plants showed quicker recovery of their photosynthetic apparatus (0.527–0.697) as compared to unhardened ones (0.224–0.330). Stress temperature of –10°C caused irreversible changes of photosynthetic apparatus of hardened and unhardened plants independently of growth phases (0.003–0.014). Φ<sub>PSII</sub> and F<sub>m</sub>’ parameters were strongly correlated with shoots survival under stress. Our results suggest that perennial plants’ hardening allows them to survive low temperatures due inter alia enhancing their photosynthetic machinery performance.

Chlorophyll content, photosynthetic efficiency and genetic markers in two sour cherry (Prunus cerasus L.) genotypes under drought stress

Abstract - Drought is a limiting factor in fruit production today. Identification of sour cherry genotypes tolerant to drought will enable the sustainability of fruit production. The aim of our study was to select sour cherry genotypes according to their genetic background as well as drought tolerance and investigate possible mechanisms of drought tolerance through the changes in photosynthetic apparatus (i.e. photosynthetic pigment content) and photosynthesis process assessed through the chlorophyll fluorescence transient. All of them together with molecular markers (SSRs and AFLPs), relative water content (RWC) as indicator of plant water status distinguish two genotypes (Kelleris 16 and OS), which are the opposite in regards to drought tolerance. Down-regulation of photosynthesis in drought-treated Kelleris 16 plants was seen as changes in antenna complexes of PSII (decreased total chlorophylls content (a+b) and chlorophylls ratio (a/b)). Despite unchanged maximum quantum yield of PSII in drought-treated leaves of genotype OS, overall photosynthetic performance expressed as PIABS was down-regulated in both investigated genotypes. However, decrement of PIABS was much pronounced in genotype Kelleris 16, mainly because of changes in a certain fraction of RCs, which become dissipative centres, seen as increase in ABS/RC and DI0/RC, in order to avoid photooxidative damage of photosynthetic apparatus. Also, electron transport, seen as decrease in ET0/(TR0-ET0) and ET0/RC, was impaired which lead to impaired CO2 fixation and photosynthesis. The described changes in the functioning of photosynthetic apparatus in drought-treated plants of Kelleris 16 constitute the main distinction between the two investigated genotypes regarding drought adaptation mechanisms.

Structural and functional reorganization of the photosynthetic apparatus in adaptation to cold of wheat plants

In seedlings of a cold-resistant wheat variety, the dynamics was studied of the main structural-functional parameters of the photosynthetic apparatus (PSA) and of cold resistance of leaf cells in low-temperature plant adaptation. It has been established that a complex of structural-functional PSA changes takes place in seedling leaves under the influence of cold. As a result, as early as in the first hours of hardening, the formation of chloroplasts begins to occur in mesophyll cells of larger sizes and with a thylakoid system of the “sun type.” Owing to structural and functional readjustment (a change of content of pigments, stabilization of pigment-protein complexes, and enhancement of nonphotochemical quenching of excess energy) in the process of cold adaptation, the rate of photosynthesis stabilizes. It is suggested that the observed structural-functional PSA rearrangement is a necessary condition for formation of increased cold resistance of leaf cells; this, alongside with other physiological-biochemical changes occurring in parallel in cells and tissues of the plants, provides their survival under conditions of low temperatures.

Functional properties of photosynthetic apparatus in three Fucus species inhabiting the White Sea: Effect of dehydration

Three species of Fucus inhabiting different zones at the littoral and sublittoral of the White Sea (F. vesiculosus L., F. serratus L., and F. distichus L.) were compared with regard to performance of the photosynthetic apparatus (PSA) and PSA changes upon prolonged desiccation of algae. The content of chlorophyll a and the total content of carotenoids were significantly higher in F. serratus than in F. vesiculosus. The potential quantum yield (F v/F m) of photosystem II (PSII) was 0.69–0.74 in all species. The highest effective quantum yield of PSII (Y II) was observed in F. vesiculosus plants inhabiting zones with the most intense insolation. The ratio of non-photochemical quenching to photochemical quenching (qN/qP) increased with the depth of algal habitats in the row from F. vesiculosus to F. serratus. The fluorescence parameters F. serratus deviated during desiccation from their normal values and did not recover upon the subsequent return to water. By contrast, the fluorescence parameters of F. vesiculosus and F. distichus recovered gradually after the return of algae from air to sea water. It is supposed that F. serratus plants, unlike other species, are characterized by comparatively low physiological plasticity.

Sensitivity of Photosynthetic Apparatus of Pea Plants to Heavy Metal Stress

ABSTRACTIn this work we studied the changes in photosynthetic apparatus on pea pants, exposed to cadmium toxicity in early stages in their development. Photosynthetic oxygen evolution (flash-induced oxygen yield patterns and oxygen burst under continuous irradiation) in isolated thylakoid membranes were measured in order to investigate structural organization and functional activity of PSII centers (PSIIα and PSIIβ). Decrease of the amplitude of the initial oxygen burst (A) and the ratio between the amplitudes of the fast and slow components (A1/A2) in Cd treated plants corresponds with decrease of the number and proportion of functionally active PSIIα and PSIIβ centers. The drastic decline of the amplitudes of the flash-induced oxygen yields and the loss of the characteristic oscillations were observed in treated plants. Changes in thermolumenescense characteristics confirmed damaged effect of Cd on PSII, namely decrease in intensity and loss of oscillations of the B-band.

Changes in photosynthetic apparatus of mustard (Sinapis alba) cotyledons following cycloheximide and kinetin treatments

Biochemical and accompanying structural characteristics of the photosynthetic process were studied in mustard seedlings cultivated on medium with increasing concentrations of cycloheximide alone as well as in combination with various kinetin concentrations. After 7 days of cultivation the contents of total chlorophyll, carotenoids and content of Rubisco in mustard cotyledons were determined. The content of chlorophyll pigments and carotenoids decreased in dependence of cycloheximide concentration. Following antibiotic treatment the content of both Rubisco subunits markedly decreased. In addition cycloheximide caused disturbance in mesophyll organization and chloroplast ultrastructure. Kinetin applied with cycloheximide increased the amount of photosynthetic pigments as well as of Rubisco, compared to the cycloheximide alone. In the seedlings treated with cycloheximide+kinetin the structure of leaf mesophyll and chloroplast membrane system was similar to control. Our results indicate that kinetin diminished the negative effects of cycloheximide on photosynthetic pigments and Rubisco as well as on the structural traits of the cotyledons.

The Effects of Cold Acclimation on Photosynthetic Apparatus and the Expression of COR14b in Four Genotypes of Barley (Hordeum vulgare) Contrasting in their Tolerance to Freezing and High-light Treatment in Cold Conditions

Cold acclimation modifies the balance of the energy absorbed and metabolized in the dark processes of photosynthesis, which may affect the expression of cold-regulated (COR) genes. At the same time, a gradual acclimation to the relatively high light conditions is observed, thereby minimizing the potential for photo-oxidative damage. As a result, the resistance to photoinhibition in the cold has often been identified as a trait closely related to freezing tolerance. Using four barley genotypes that differentially express both traits, the effect of cold acclimation on freezing tolerance and high-light tolerance was studied together with the expression of COR14b, one of the best-characterized barley COR genes. Plants were cold acclimated for 2 weeks at 2 degrees C. Freezing tolerance was studied by means of electrolyte leakage. Changes in photosynthetic apparatus and high-light tolerance were monitored by means of chlorophyll fluorescence. Accumulation of COR14b and some proteins important in photosynthetic acclimation to cold were studied with western analysis. COR14b transcript accumulation during cold acclimation was assessed with real-time PCR. Cold acclimation increased both freezing tolerance and high-light tolerance, especially when plants were treated with high light after non-lethal freezing. In all plants, cold acclimation triggered the increase in photosynthetic capacity during high-light treatment. In two plants that were characterized by higher high-light tolerance but lower freezing tolerance, higher accumulation of COR14b transcript and protein was observed after 7 d and 14 d of cold acclimation, while a higher transient induction of COR14b expression was observed in freezing-tolerant plants during the first day of cold acclimation. High-light tolerant plants were also characterized with a higher level of PsbS accumulation and more efficient dissipation of excess light energy. Accumulation of COR14b in barley seems to be important for resistance to combined freezing and high-light tolerance, but not for freezing tolerance per se.

Bioenergetic changes in the microalgal photosynthetic apparatus by extremely high CO2 concentrations induce an intense biomass production

Unicellular green alga Chlorella minutissima, grown under extreme carbon dioxide concentrations (0.036-100%), natural temperature and light intensities (Mediterranean conditions), strongly increase the microalgal biomass through photochemical and non-photochemical changes in the photosynthetic apparatus. Especially, CO(2) concentrations up to 10% enhance the density of active reaction centers (RC/CS(o)), decrease the antenna size per active reaction center (ABS/RC), decrease the dissipation energy (DI(o)/RC) and enhance the quantum yield of primary photochemistry (F(v)/F(m)). Higher CO(2) concentrations (20-25%) combine the above-mentioned photochemical changes with enhanced non-photochemical quenching of surplus energy, which leads to an enhanced steady-state fraction of 'open' (oxidized) PSII reaction centers (q(p)), and minimize the excitation pressure of PSII (1 - q(p)) under very high light intensities (approximately 1700 micromol m(-2) s(-1) maximal value), avoiding the photoinhibition and leading to an enormous biomass production (approximately 2500%). In conclusion, these extreme CO(2) concentrations - about 1000 times higher than the ambient one - can be easily metabolized from the unicellular green alga to biomass and can be used, on a local scale at least, for the future development of microalgal photobioreactors for the mitigation of the factory-produced carbon dioxide.

Acclimation of mesophyll and bundle sheath chloroplasts of maize to different irradiances during growth

The regulation by light of the photosynthetic apparatus, and composition of light-harvesting complexes in mesophyll and bundle sheath chloroplasts was investigated in maize. Leaf chlorophyll content, level of plastoquinone, PSI and PSII activities and Lhc polypeptide compositions were determined in plants grown under high, moderate and low irradiances. Photochemical efficiency of PSII, photochemical fluorescence quenching and non-photochemical fluorescence quenching over a range of actinic irradiances were also determined, using chlorophyll a fluorescence analysis. Acclimation of plants to different light conditions caused marked changes in light-harvesting complexes, LHCI and LHCII, and antenna complexes were also reorganized in these types of chloroplasts. The level of LHCII increased in plants grown in low light, even in agranal bundle sheath chloroplasts where the amount of PSII was strongly reduced. Irradiance also affected LHCI complex and the number of structural polypeptides, in this complex, generally decreased in chloroplasts from plants grown under lower light. Surprisingly moderate and low irradiances during growth do not affect the light reaction and fluorescence parameters of plants but generated differences in composition of light-harvesting complexes in chloroplasts. On the other hand, the changes in photosynthetic apparatus in plants acclimated to high light, resulted in a higher efficiency of photosynthesis. Based on these observations we propose that light acclimation to high light in maize is tightly coordinated adjustment of light reaction components/activity in both mesophyll and bundle sheath chloroplasts. Acclimation is concerned with balancing light utilization and level of the content of LHC complexes differently in both types of chloroplasts.