The aim of our study was to investigate the underlying molecular mechanisms of exogenously supplied trehalose affecting wheat photosynthesis under heat stress. The amount of ATP synthase (ATPase), oxygen-evolving enhancer protein (OEE), PsbP, Rubisco, chloroplast fructose-bisphosphate aldolase (FBPA), and ferredoxin-NADP(H) oxidoreductase (FNR) were downregulated, while PSI reaction center subunits were upregulated under heat stress. However, in the trehalose-pretreated groups, the amount of FNR, cytochrome b6f complex, PSI reaction center subunits, ATPase, FBPA, and Rubisco were upregulated under normal growth conditions and heat stress. Besides, during the recovery period, the upregulation in CAB, PsbP, OEE2, and ATPase suggested that trehalose pretreatment might help to the recovery of PSII and PSI. These results indicate that trehalose pretreatment effectively regulates the levels of the photosynthesis-related proteins and relieves the damage of heat stress to wheat chloroplast., Y. Luo, H. Y. Liu, Y. Z. Fan, W. Wang, Y. Y. Zhao., and Obsahuje bibliografii
Chlorophyll a fluorescence, water potential (Ψs), and root system of Juniperus oxycedrus ssp. macrocarpa, Juniperus phoenicea ssp. turbinata, and Pinus pinea were studied in Mediterranean coastal dunes of SW Spain during summer drought and after fall rains in 1999, the driest year in the 90's. A strong and reversible depression in the photochemical efficiency of photosystem 2 of the three species was recorded, which happened concomitantly with the diurnal increase and decrease in radiation. J. phoenicea, with superficial root system, was the most affected species by summer drought. It showed high rates of down-regulation of photosynthesis by photoinhibition and positive correlation between Ψs and Fv/Fp, with Ψs lower than -7 MPa. However, it tolerated this high stress, showing a fast recovery of its physiological state after fall rains. On the other hand, J. oxycedrus and P. pinea, both with deep root systems, kept their Ψs values up to -3 MPa, showing lower stress during summer drought. On the other hand, J. oxycedrus and J. phoenicea were more sensible to changes in edaphic water content than P. pinea. These specific responses to summer drought would be determined by their root distributions and stomatal control of transpiration, conditioning the efficiency in getting and using the available water resources. Ecophysiological responses indicate that these species are well-adapted to long periods of drought in Mediterranean climate areas, developing different strategies: J. phoenicea tolerates high stress with a fast recovery after fall rains, while J. oxycedrus and P. pinea are less affected by summer drought since their deep root systems would allow them to reach deep water resources. and J. M. Castillo ... [et al.].
The effects of potassium (K) deficiency on chlorophyll (Chl) content, photosynthetic gas exchange, and photosystem II (PSII) photochemistry during the seedling stage were investigated in two soybean [Glycine max (L.) Merr.] cultivars, low-K sensitive Tiefeng31 and low-K tolerant Shennong6. The cultivars were grown hydroponically in K-sufficient (KS) and K-deficient (KD) solutions. Photosynthetic gas exchange and Chl content in Tiefeng31 were severely affected by the low K condition, but were almost unaffected in Shennong6. This difference is in accordance with the PSII photochemistry in the plants, indicating that the photosynthetic apparatus of Shennong6 is more tolerant to low-K stress than that of Tiefeng31. and X.-T. Li ... [et al.].
In Huanshandak Sandland, China, net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), water use efficiency (WUE), photochemical efficiency of photosystem 2 (Fv/Fm), and leaf nitrogen content were compared for Hedysarum fruticosum var. mongolicum (H.f.m.), a nitrogen fixing shrub, and Salix gordejevii (S.g.), a nitrogen non-fixing shrub. PN, E, and gs of the two shrubs were similar in trends, i.e. two peaks were observed in diurnal courses. However, except Ci, other parameters of H.f.m. were higher during the measured days than those of S.g. The midday depression of PN was mainly due to decrease in stomata conductance and to reduction of Fv/Fm at midday. The higher PN of H.f.m. was consistent with the higher leaf N content and there was a positive relation between them. In addition, several C4 traits were found in H.f.m., i.e. high saturation irradiance and WUE, low dark respiration rate, and Ci, which partly resulted in higher PN. This seems to indicate that the C3 plant H.f.m. may have C4 photosynthesis pathway or C4 enzymes. and S. L. Niu ... [et al.].
The pericarp of cereal crops is considered a photosynthetically active tissue. Although extensive studies have been performed on green leaves, the photosynthetic role of the pericarp in cereal caryopsis development has not been well investigated. In the present study, we investigated the anatomy, ultrastructure, chlorophyll (Chl) fluorescence, and oxygen evolution of the pericarp during caryopsis ontogenesis in field wheat (Triticum aestivum L.). The results showed that wheat pericarp cross-cells contained Chl; the grana stacks and thylakoid membranes in the cross-cells were more distinct in the pericarp than those in the flag leaves as shown by transmission electron microscopy. Chl fluorescence revealed that the photosynthetic efficiency, which was indicated by values of maximum efficiency of PSII photochemistry and effective PSII quantum yield, was lower in the pericarp compared to that of the flag leaf eight days after anthesis (DAA), whereas similar values were subsequently observed. The nonphotochemical quenching values were lower from 8-16 DAA but significantly increased in the pericarp from 24-32 DAA compared to the flag leaf. The oxygen evolution rate of the flag leaves was consistently higher than that of pericarp; notably, isolated pericarps released more oxygen than intact pericarps during caryopsis development. These results suggest that the pericarp plays a key role in caryopsis development by performing photosynthesis as well as by supplying oxygen to the endosperm and dissipating excessive energy during the
grain-filling stages., L. A. Kong , Y. Xie, M. Z. Sun, J. S. Si, L. Hu., and Obsahuje seznam literatury
The diurnal trends of gas exchange and chlorophyll fluorescence parameters in four Lycoris species (L. houdyshelii, L. aurea, L. radiata var. pumila and L. albiflora) were determined and compared with a portable photosynthesis analysis system. Our study revealed that L. houdyshelii had the lowest light compensation point (LCP), while the other three species had higher LCP (12.37-14.99 μmol m-2 s-1); L. aurea had the highest light saturation point (LSP) (1,189 μmol m-2 s-1), and L. houdyshelii and L. albiflora had lower LSP with the values being 322 and 345 μmol m-2 s-1, respectively, and L. radiata var. pumila showed the intermediate LSP. Both the species L. houdyshelii and L. albiflora exhibited a typical and obvious decline in net photosynthetic rate (PN) during midday, which was not observed in L. aurea. This indicated a possible photoinhibition in L. houdyshelii and L. albiflora as the ratio of variable to maximum fluorescence (Fv/Fm) values were higher in these two species. The minimal fluorescence (F0) values were lower in L. aurea and L. radiata var. pumila. The diurnal changes of transpiration rate (E) in all four species presented only one peak, appearing between 11:00 h or 13:00 h. By using simple correlation analyses, it was observed that the environmental factors affecting
PN were different among four species and the main factors were photosynthetic photon flux density (PPFD) and relative humidity especially for L. aurea and L. radiata. The results of studying indicated that the four species could be divided into two groups. The species L. radiata var. pumila and L. aurea were more adapted to a relatively high irradiance, and L. houdyshelii and L. albiflora could be grown in moderate-shade environment in order to scale up their growth and productivity., K. Liu ... [et al.]., and Obsahuje bibliografii
To probe the role of xanthophylls in non-photochemical quenching (NPQ) and the compensatory acclimated photoprotection mechanisms, a tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) Xa mutant with deficit in lutein (L) and neoxanthin (N) contents was used. The Xa mutant showed lowered NPQ, an increased degree of de-epoxidation state [(A+Z)/(V+A+Z)], and decreases of photosystem 2 (PS2) antenna size. Although the Xa mutant had a CO2 assimilation rate similar to that of Ailsa Craig, it exhibited a much larger stomatal conductance (gs) than Ailsa Craig. Decreased electron flux in PS2 (J PS2) for the Xa mutant was associated with electron flux for photorespiratory carbon oxidation (Jo) and alternative electron flux in PS2 (Ja) while electron flux for photosynthetic carbon reduction (Jc) was not different from Ailsa Craig. Moreover, the Xa mutant also exhibited higher activities of antioxidant enzymes, higher contents of ascorbate and glutathione, and lower contents of reactive oxygen species. Hence some compensatory acclimated mechanisms of photoprotection operated properly in the lack of NPQ and xanthophylls. and Y. J. Wang ... [et al.].
As compared with the swamp reed (SR) ecotype of Phragmites communis growing in the desert region of northwest China, plants of the dune reed (DR) ecotype from the same region possessed lower chlorophyll (Chl) content in leaves, and less thylakoids and grana stacks in chloroplasts. Tube gel electrophoresis without stain showed that the contents of Chl-protein (Pro) components related to photosystem 2 (PS2) were markedly lower in the DR thylakoid membranes than in the SR thylakoid membranes, while the contents of Chl-Pro components associated with PS1 were almost the same in both types. SDS-PAGE analysis indicated that the content of polypeptides of the light-harvesting Chl a/b complex of PS2 (LHC2) was lower in the DR thylakoids. Besides, the conformation of LHC2 within the DR thylakoid membranes was also altered as indicated by circular dichroism spectra. Hence in the DR, reduced energy harvesting by declining the size of LHC2 might be responsible for the down-regulated PS2 activity. Chl fluorescence parameters. Fv/Fm and quantum efficiency of PS2 (ΦPS2), were lower in the DR leaves than in the SR ones. However, non-photochemical quenching coefficient (qN) was greater in DR than that in SR, implying other energy dissipation way exists in the DR photosynthetic membranes. and X. Y. Zhu, S. M. Wang, C. L. Zhang.
The proportional light absorptance by photosynthetic tissue (α) is used with chlorophyll (Chl) fluorescence methods to calculate electron transport rate (ETR). Although a value of α of 0.84 is often used as a standard for calculating ETR, many succulent plant species and species with crassulacean acid metabolism (CAM) have photosynthetic tissues that vary greatly in color or are highly reflective, and could have values of α that differ from 0.84, thus affecting the calculation of ETR. We measured ETR using Chl fluorescence and α using an integrating sphere in 58 plant species to determine the importance of applying a measured value of α when calculating ETR. Values of α varied from 0.55-0.92 with a mean of 0.82 across species. Differences between ETR values calculated with measured α values ranged from 53% lower to 12% greater than ETR values calculated with a standard α value of 0.84 and were significantly different in 39 out of 58 species. While measurements of ETR using Chl fluorescence represent a rapid and effective assessment of physiological performance, the value of α needs to be considered. Measurements of α, especially on species with light-colored or reflective photosynthetic tissue, will allow more accurate determination of photosynthesis in succulent and CAM species. and J. A. Stemke, L. S. Santiago
Growth, net photosynthetic rate (PN), chlorophyll fluorescence induction kinetics, and stromal fructose-1,6-bisphosphatase (sFBPase) in annual legumes native to the Mediterranean region, two clovers (Trifolium subterraneum L. ssp. oxaloides Nyman cv. Clare and T. michelianum Savi cv. Giorgia) and two Medicago species (M. polymorpha L. cv. Anglona and M. truncatula Gaertn. cv. Paraggio), shifted from 20 to 10 °C for 1 d or developed at 10 °C were compared with controls kept at 20 °C. Cold development produced a larger stimulation of growth in the clover cv. Giorgia and the Medicago cv. Paraggio. Transferring plants to low temperatures affected PN relatively less in clovers than in Medicago plants. Development at 10 °C relieved the inhibition of photosynthesis in Giorgia and Paraggio, but not in Clare and Anglona, which correlated with increases in the maximum rate of carboxylation by ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO (Vcmax), and the photon-saturated rate of electron transport (Jmax). In Medicago, transfer from high to low temperature inhibited photosynthesis in a lesser extent in Anglona than in Paraggio, which showed severe limitations at level of Vcmax and Jmax. Development at 10 °C in Paraggio produced an efficient photosynthetic cold acclimation, this being associated with a two-fold increase of quantum yield of photosystem 2 electron transport (ΔF/F'm) and with the activity of sFBPase. By contrast, Anglona showed an irreversible inhibition of PN coupled with the reduction of carbon metabolism by impairment of Calvin cycle enzyme activities such as RuBPCO and sFBPase, resulting in a poor cold acclimation of photosynthesis in this cultivar. and M. C. Antolín, M. Hekneby, M. Sánchez-Díaz.