A long growing season, mediated by the ability to grow at low temperatures early in the season, can result in higher yields in biomass of crop Miscanthus. In this paper, the chilling tolerance of two highly productive Miscanthus genotypes, the widely planted Miscanthus × giganteus and the Miscanthus sinensis genotype ‘Goliath’, was studied. Measurements in the field as well as under controlled conditions were combined with the main purpose to create basic comparison tools in order to investigate chilling tolerance in Miscanthus in relation to its field performance. Under field conditions, M. × giganteus was higher yielding and had a faster growth rate early in the growing season. Correspondingly, M. × giganteus displayed a less drastic reduction of the leaf elongation rate and of net photosynthesis under continuous chilling stress conditions in the growth chamber. This was accompanied by higher photochemical quenching and lower nonphotochemical quenching in M. × giganteus than that in M. sinensis ‘Goliath’ when exposed to chilling temperatures. No evidence of impaired stomatal conductance or increased use of alternative electron sinks was observed under chilling stress. Soluble sugar content markedly increased in both genotypes when grown at 12°C compared to 20°C. The concentration of raffinose showed the largest relative increase at 12°C, possibly serving as a protection against chilling stress. Overall, both genotypes showed high chilling tolerance for C4 plants, but M. × giganteus performed better than M. sinensis ‘Goliath’. This was not due to its capacity to resume growth earlier in the season but rather due to a higher growth rate and higher photosynthetic efficiency at low temperatures., S. Fonteyne, P. Lootens, H. Muylle, W. van den Ende, T. de Swaef, D. Reheul, I. Roldan-Ruiz., and Obsahuje seznam literatury
We compared the sensitivity to cold stress, in terms of photosynthetic capacity and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern United States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than the deciduous species, Quercus michauxii. Short-term cold stress in both species lead to greater than 50 % reduction in maximum photosynthetic rates, 60-70 % reduction in electron transport, and irreversible quenching of PS2 fluorescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 µmol m-2 s-1) and chilling (5 °C) showed that the evergreen Q. virginiana exhibited more protective qE and less irreversible quenching (qI) than the deciduous Q. michauxii. The large qE which we observed in Q. virginiana suggests that the capacity for photoprotection at low temperatures is not induced by a long-term acclimation to cold but preexists in evergreen leaves. This capacity may contribute to the ability of this species to maintain leaves during the winter. and J. Cavender-Bares ... [et al.].
This work aimed to evaluate if chilling stress may be mitigated by elevated CO2 (EC) in Beta vulgaris L. plants. Photosynthetic rate was measured at 21% and 2% O2 after a short-term exposure of 5 h at four different treatments: 360 μmol(CO2) mol-1/25°C (AC); 360 μmol(CO2) mol-1/4°C (AC+LT); 700 μmol(CO2) mol-1/25°C (EC); 700 μmol(CO2) mol-1/4°C (EC+LT). Compared to AC+LT, EC+LT plants showed higher values of CO2 fixation, photochemical activity, and Rubisco amount. These latter invest a higher portion of photosynthetic electron flow to O2, differently from AC+LT plants that promote the regulated thermal dissipation processes. In EC+LT plants, the photosynthetic electron flow to O2 acts as a safety mechanism against the excess of absorbed light, upon return to prechilling conditions, allowing photosynthetic apparatus to maintain its efficiency. In AC+LT plants, the increase of thermal dissipation processes was not adequate to guarantee the PSII photoprotection and the photosynthetic recovery after chilling., C. Arena, L. Vitale., and Obsahuje bibliografii
Simultaneous measurements of chlorophyll (Chl) fluorescence and photosynthetic O2 evolution {P^ in leaf disks from Vicia faba (cv. Reina Blanca) leaves were doně during the first weeks of growth in order to evaluate the damage caused by methabenzthiazuron (MBT) under field conditions. The plants were treated at preemergence with two doses of MBT (0.25 .and 0,40 g m'^). Measurements were carried out at constant temperature and saturating CO2 concentration. During the first weeks after plant emergence both doses of herbicide were followed by a drop in and in some fluorescence parameters, such as Fy/Fn, and AF/Fn,' ratios, and in photochemical and non-photochemical quenching, qp and q^. At the same time, increases in minimal fluorescence (Fq and Fq') and in maximal (Fj„') and steady-state fluorescence (Fj) were aiso observed on application of saturating pulses. Fluorescence parameters gave a better indication of the damage caused to the photosynthetic systém than the measurements. The linear relationship found between OO2 and the effective quantum yield, AF/Fn,', suggests that the latter is a good measure of the quantum efficiency of photosynthesis in herbicide-treated plants. Moreover, plant tissues detoxified the herbicide and, one month after plant emergence, photosynthesis was fully recovered in herbicide-treated plants; biomass production recovered and even increased at the end of the growth period.
The effect of inorganic (IC) depletion on fluorescence quenching was studied under laboratory conditions using the chlorococcal alga Scenedesmus quadricauda strain Greifswald/15. The absence of IC caused a decrease in photochemical quenching (^p), fluorescence yield and the photosystem 2 photochemical yield (dF/F^), and an increase of non-photochemical quenching {q^). High extemal pH (about 11), which accompanies the IC-depletion, did not háve any remarkable effect on the algae. Fluorescence parameters were reversed by a resupply of CO2. The IC-defícient algae when exposed to high irradiance appeared to be less sensitive to the photoinhibition than the algae supplied with CO2. Increased thermal dissipation of the excitation energy (non-photochemical quenching) in the absence of IC is one of the probable protective mechanisms against photoinhibitory damage.
Bean plants Phaseolus vulgaris L. (cv. Carioca and Negro Huasteco) and Vigna unguiculata L. Walp (cv. Epace-10) were grown in a growth chamber with a photosynthetic photon flux density of 200 μmol m-2 s-1 at leaf level and air temperature of 25+1 °C. Fully expanded, first pair leaves of 12-d-old plants were submitted for 90 min to high temperature (25, 30, 35, 40, 45, and 48 °C). Chlorophyll a fluorescence parameters (ETR, qP, qN, and F0) were investigated using a modulated fluorimeter at 25 °C during recovery considered here as 48 h after stress induction period. An accentuated decrease in qP and an increase in qN at 48 °C in Carioca and Negro Huasteco was not observed in Epace-10. In response to excitation irradiance a great potential for ETR was found in Negro Huasteco at 25 °C, also demonstrated by net photosynthetic rate. At 48 °C ETR was high for Epace-10 while it was equal to zero for Carioca and Negro Huasteco. Tolerance to high temperature observed in Epace-10 provided important information about the adaptative characteristics of Vigna cultivars to warm climates. and E. S. Costa ... [et al.].
Photosystem II (PSII) photochemistry was examined by chlorophyll (Chl) a fluorescence analysis in high-yield rice LYPJ flag leaves during senescence. Parameters deduced from the JIP-test showed that inhibition of the donor side of PSII was greater than that of the acceptor side in hybrid rice LYPJ. The natural senescence process was accompanied by the increased inactivation of oxygen-evolving complex (OEC) and a lower total number of active reaction centers per absorption. It indicated that the inhibition of electron transport caused by natural senescence might be caused partly by uncoupling of the OEC and/or inactivation of PSII reaction centers. Chl fluorescence parameters analyzed in this study suggested that energy dissipation was enhanced in order to protect senescent leaves from photodamage. Nevertheless, considerably reduced PSI electron transport activity was observed at the later senescence. Thus, natural senescence inhibited OEC-PSII electron transport, but also significantly limited the PSII-PSI electron flow., Y. W. Wang, C. Xu, C. F. Lv, M. Wu, X. J. Cai, Z. T. Liu, X. M. Song, G. X. Chen, C. G. Lv., and Seznam literaruty
The effect of Potato virus Y NTN (PVY) infection upon photosynthesis was analysed in transgenic Pssu-ipt tobacco overproducing endogenous cytokinins in comparison with control, nontransgenic Nicotiana tabacum plants. The course of the infection from the early to the late stage was monitored by measuring of photosynthetic gas exchange and fast chlorophyll (Chl) a fluorescence induction kinetics. Leaf photosynthesis was also analysed using Chl fluorescence imaging (Chl-FI). From the different fluorescence parameters obtained using Chl-FI, the nonphotochemical quenching (NPQ) proved to be the most useful parameter to assess the effect of PVY infection. On the other hand, Chl-FI was found to be inapplicable for any presymptomatic detection of PVY infection in tobacco. The lower accumulation of the virus was found in transgenic plants and corresponded also with the presence of visible symptoms of PVY infection. The net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) significantly decreased with the progress of the infection in both control plant types and transgenic rooted plants, while transgenic grafts were much less affected. The analysis of the Chl fluorescence transient revealed higher number of silent dissipative reaction centres, higher nonphotochemical dissipation, and significantly lower performance index, PI(abs), in the healthy transgenic grafts. Chl-FI also confirmed significantly higher NPQ in transgenic grafts., P. Spoustová ... [et al.]., and Obsahuje bibliografii
The lichens Parmelia quercina, Parmelia sulcata, Evernia prunastri, Hypogymnia physodes, and Anaptychia ciliaris were exposed to ozone (O3) in controlled environment cuvettes designed to maintain the lichens at optimal physiological activity during exposure. Measurements of gas exchange, modulated chlorophyll (Chl) fluorescence, and pigment analysis were conducted before and after exposure to 300 mm3 (O3) m-3, 4 h per d for 14 d. No changes in the efficiency of photosystem 2 (PS2) photochemistry, the reduction state of QA, or the electron flow through PS2, measured by Chl fluorescence, were detected in any of the five lichen species studied. Additionally, neither photosynthetic CO2 assimilation nor xanthophyll cycle activity or photosynthetic pigment concentration were affected by high O3 concentrations. Thus the studied lichen species have significant capacities to withstand oxidative stresses induced by high concentration of O3. and A. Calatayud, P. J. Temple, E. Barreno.
Alhagi sparsifolia Shap. is exposed to a high-irradiance environment as the main vegetation found in the forelands of the Taklamakan Desert. We investigated chlorophyll a fluorescence emission of A. sparsifolia seedlings grown under ambient (HL) and shade (LL) conditions. Our results indicated that the fluorescence intensity in the leaves was significantly higher for LL-grown plants than that under HL. High values of the maximum quantum yield of PSII for primary photochemistry (φPo) and the quantum yield that an electron moves further than QA - (φEo) in the plants under LL conditions suggested that the electron flow from QA - (primary quinone electron acceptors of PSII) to QB (secondary quinone acceptor of PSII) or QB - was enhanced at LL compared to natural HL conditions. The efficiency/probability with which an electron from the intersystem electron carriers was transferred to reduce end electron acceptors at the PSI acceptor side and the quantum yield for the reduction of end electron acceptors at the PSI acceptor side were opposite to φPo, and φEo. Thus, we concluded that the electron transport on the donor side of PSII was blocked under LL conditions, while acceptor side was inhibited at the HL conditions. The PSII activity of electron transport in the plants grown in shade was enhanced, while the energy transport from PSII to PSI was blocked compared to the plants grown at HL conditions. Furthermore, PSII activity under HL was seriously affected in midday, while the plants grown in shade enhanced their energy transport., L. Li, X. Y. Li, F. J. Zeng, L. S. Lin., and Seznam literatury