An open-top chamber experiment was carried out from April through October 2006 to examine the effects of elevated (80 nmol mol-1) atmospheric O3 on Ginkgo biloba (4-years-old) in urban area. The air with ambient O3 (AA, ≈ 45 nmol mol-1) was used as control. The leaf mass and size, leaf area index, net photosynthetic rate (PN), apparent quantum yield, transpiration rate, and stomatal conductance were decreased by elevated O3 (EO) exposure. Visible foliar injury, which is light-brown flecks, was observed in the EO OTCs after 90 d of exposure. Carboxylation efficiency (ΦCO2) and photorespiration and dark respiration rates were enhanced by EO exposure in the first half of the season, but all of them turned to be lower than those of the AA control at the end of experiment. Stomata limitation of photosynthesis was significantly higher than control in the whole season (p<0.05). Chlorophyll (Chl) content was lower in EO variant than in the control and the difference became more and more apparent through the season. Hence the decrease in PN of G. biloba exposed to EO was the result of both stomatal and non-stomatal limitations. In the early season, the inhibition of photosynthesis was mainly caused by the stomatal limitation, and the earliest response was photoprotective down-regulation of photosynthesis but not photodamage. However, at the end of the season, the non-stomatal limiting factors such as decrease in Chl content, decrease in ΦCO2, and anti-oxidative enzyme activity became more important. and X.-Y. He ... [et al.].
Photosynthesis, photorespiration, and chlorophyll (Chl) fluorescence in green and red Berberis thunbergii leaves were studied with two different measuring radiations, red (RR) and "white" (WR). The photosynthetic and photorespiration rates responded differently to the different radiation qualities, which indicate that the carboxylase and oxygenase activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were affected. Differences in photosynthetic rate between the two color leaves were less under RR than under WR. However, this reduced difference in photosynthetic rate was not correlated with the stomatal response to the measuring radiation qualities. Compared with the WR, the RR reduced the differences in dark-adapted minimum and maximum fluorescence, steady-state fluorescence, light-adapted maximum fluorescence, and actual photochemical efficiency (ΦPS2) of photosystem 2 (PS2), but enlarged the difference in non-photochemical quenching between the two color leaves. Differences in both maximum quantum yield of PS2 and ratio of ΦPS2 to quantum yield of CO2 fixation between the two color leaves were similar under the two measuring radiations. To exclude disturbance of radiation attenuation caused by anthocyanins, it is better to use RR to compare the photosynthesis and Chl fluorescence in green versus red leaves. and P.-M. Li ... [et al.].
Using a radiogasometric method the rates of photorespiratory and respiratory decarboxylations of primary and stored photosynthates in the leaves of two groups of C3 species, differing in the ability of starch accumulation, were determined. One group included starch-accumulating (SA) species with rates of starch synthesis on the average 38 % the rate of photosynthesis [Solanum tuberosum L., Arabidopsis thaliana (L.) Heynh, Helianthus annuus L., and Plantago lanceolata L.]. The second group represented starch-deficient (SD) species with rates of starch synthesis less than 8 % the rate of photosynthesis (Secale cereale L., Triticum aestivum L., Hordeum vulgare L., and Poa trivialis L.). In SA species the rate of respiration in the dark was significantly higher than in SD species. No differences were found in the rates of photosynthesis, photorespiration, and respiration under irradiation. Thus, the degree of inhibition of respiration by irradiation was in SA species higher than in SD species. It is concluded that starch does not provide substrates for respiratory and photorespiratory decarboxylations in irradiated photosynthesizing leaves. and H. Ivanova ... [et al.].
Morphological, anatomical, and physiological leaf traits of Corylus avellana plants growing in different light conditions within the natural reserve "Siro Negri" (Italy) were analyzed. The results highlighted the capability of C. avellana to grow both in sun and shade conditions throughout several adaptations at leaf level. In particular, the more than 100% higher specific leaf area in shade is associated to a 44% lower palisade to spongy parenchyma thickness ratio compared with that in sun. Moreover, the chlorophyll (Chl) a to Chl b ratio decreased in response to the 97% decrease in photosynthetic photon flux density. The results highlighted the decrease in the ratio of Chl to carotenoid content, the maximum PSII photochemical efficiency, and the actual PSII photochemical efficiency (ΦPSII) associated with the increase in the ratio of photorespiration to net photosynthesis (PN) in sun. Chl a/b ratio was the most significant variable explaining PN variations in shade. In sun, PN was most influenced by the ratio between the fraction of electron transport rate (ETR) used for CO2 assimilation and ETR used for photorespiration, by ΦPSII, nitrogen content per leaf area, and by total Chl content per leaf area. The high phenotypic plasticity of C. avellana (PI = 0.33) shows its responsiveness to light variations. In particular, a greater plasticity of morphological (PIm = 0.41) than of physiological (PIp = 0.36) and anatomical traits (PIa = 0.24) attests to the shade tolerance of the species., R. Catoni, M.U. Granata, F. Sartori, L. Varone, L. Gratani., and Obsahuje bibliografii
Walnut (Juglans regia L.) plantlets were incubated during micropropagation in standard vessels (quasi confmed vessels) or in aerated vessels flushed with 360 or 20 000 cm^(C02) under irradiances of 70 (LI) and 250 (HI) pmol m"^ s'*. Plantlet morphology was strongly affected by the environment; leaf surface was increased, but shoot elongation and number of stems were reduced after increasing the irradiance of culture. Gross photosynthesis (Pq) capacity measured by using the •®02 isotope and mass-spectrometry techniques was increased by increasing photosynthetic photon flux (PPF) and CO2 concentration. Plantlets exhibited a potential for photorespiratory activity and Mehler-type reaction and a high rate of mitochondrial respiration in all vessel types and irradiances. When a long-term HI was applied, gas exchange rates (Pq and O2 uptake) were reduced in most of the vessel and PPF conditions, except in quasi confmed vessels. Under all the growth conditions, net photosynthetic rate (P^) was zero or slightly positive and the dry matter accumulation was very similar. Changes in O2 exchange, growth rate or enzyme activities linked to carbon fixation that were induced by changes in PFD and CO2 concentration showed that the photosynthetic characteristics of plantlets were typical for hetero-mixotrophic tissues.
In order to evaluate the photosynthetic activity of a C3 leaf from the electron transport rate (ETR) of photosystem 2 (PS2), a new method was devised and examined using leaves of sweet potato. In this method, both surfaces of a leaf were sealed with transparent films to stop the gas exchange between the leaf and the atmosphere; hence the functions of both photosynthetic assimilation (CO2 uptake) and photorespiration (CO2 release) are restricted to the inside of the leaf. After both functional rates became equally balanced, ETR of the sealed leaf (ETRseal) was determined from the chlorophyll fluorescence. The measurements were conducted at different irradiances and leaf temperatures and by using leaves of different age. Under each measurement condition, ETRseal showed a close positive relationship with the photosynthetic potential, or the gross photosynthetic rate measured in the air of 2 % O2 (PG2%) before sealing. ETRseal may become an indicator to estimate or evaluate the photosynthetic activity of C3 leaves. and Haimeirong, F. Kubota, Y. Yoshimura.
The effects of chilling treatment (4 °C) under low irradiance, LI (100 μmol m-2 s-1) and in the dark on subsequent recovery of photosynthesis in chilling-sensitive sweet pepper leaves were investigated by comparing the ratio of quantum yields of photosystem (PS) 2 and CO2 assimilation, ΦPS2/ΦCO2, measured in normal air (21 % O2, NA) and low O2-air (2% O2, LOA), and by analyzing chlorophyll (Chl) a fluorescence parameters. Chilling treatment in the dark had little effect on Fv/Fm and ΦPS2/ΦCO2, but it caused the decrease of net photosynthetic rate (PN) under saturating irradiance after 6-h chilling treatment, indicating that short-term chilling alone did not induce PS2 photoinhibition. Furthermore, photorespiration and Mehler reaction also did not obviously change during subsequent recovery after chilling stress in the dark. During chilling treatment under LI, there were obvious changes in Fv/Fm and ΦPS2/ΦCO2, determined in NA or LOA. Fv/Fm could recover fully in 4 h at 25 °C, and ΦPS2/ΦCO2 increased at the end of the treatment, as determined in both NA and LOA. During subsequent recovery, ΦPS2/ΦCO2 in LOA decreased faster than in NA. Thus the Mehler reaction might play an important role during chilling treatment under LI, and photorespiration was an important process during the subsequent recovery. The recovery of PN under saturating irradiance determined in NA and LOA took about 50 h, implying that there were some factors besides CO2 assimilation limiting the recovery of photosynthesis. From the progress of reduced P700 and the increase of the Mehler reaction during chilling under LI we propose that active oxygen species were the factors inducing PS1 photoinhibition, which prevented the recovery of photosynthesis in optimal conditions because of the slow recovery of the oxidizable P700. and X.-G. Li ... [et al.].
Five decades ago, a novel mode of CO2 assimilation that was later described as C4-photosynthesis was discovered on mature leaves of maize (Zea mays L.) plants. Here we show that 3- to 5-day-old developing maize leaves recapitulate the evolutionary advance from the ancient, inefficient C3 mode of photosynthesis to the C4 pathway, a mechanism for overcoming the wasteful process of photorespiration. Chlorophyll fluorescence measurements documented that photorespiration was high in 3-day-old juvenile primary leaves with non-specialized C3-like leaf anatomy and low in 5-day-old organs with the typical "Kranz-anatomy" of C4 leaves. Photosynthetic gas (CO2)-exchange measurements on 5-day-old leaves revealed the characteristic features of C4 photosynthesis, with a CO2 compensation point close to zero and little inhibition of photosynthesis by the normal oxygen concentration in the air. This indicates a very low photorespiratory activity in contrast to control experiments conducted with mature C3 sunflower (Helianthus annuus L.) leaves, which display a high rate of photorespiration. and U. Kutschera ... [et al.].
Tea tree (Melaleuca alternifolia) canopy was sprayed with low concentration of NaHSO3 or mixture of NaHSO3+ KH2PO4. The treatments significantly enhanced net photosynthetic rate (PN), carboxylation efficiency (CE), and the maximum response of PN to intercellular CO2 concentration. The enhancement of PN by foliar application of low concentrations of bisulfite was due to increasing CE relevant to ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase activity and regeneration rate of RuBP depending on ATP formation. and W.-J. Yang ... [et al.].
Photosynthetic assimilatíon of CO2 in a four-year-old plant of lilac, measured in April and in July, was compared. The results were calculated with regard to the surface area of the particular year groups of the stems and to the total surface area of the stems as well as to the globál surface area of the leaves of the plant. In April the stems were the only site of photosynthesis. In July the main organs of CO2 assimilatíon were the leaves, while the participation of the shoots in that period amounted to 2 %. In the process of photosynthesis in the stems mainly the endogenous CO2 was utilized, while the share of exogenous CO2 was 0.02 %. The potential photosynthesis was determined also on the basis of measurements of oxygen release by chloroplasts isolated from the bark and leaves. In July the production of oxygen by chloroplasts ffom the bark of all stems was 5 % of the amount of oxygen released by the chloroplasts isolated from the leaves. In April the production of oxygen by chloroplasts isolated from the bark of the particular year groups of the stems was higher than in July. In the process of CO2 assimilatíon by the bark and leaves the potential Chemical activity of chloroplasts was not fully utilized. The potential CO2 assimilatíon by chloroplasts isolated from the bark was 8.5 times greater than the measured results of CO2 exchange in July and 35.8 times greater in April.