Photosynthetic characteristics of two hybrid rice combinations, Peiai 64S/E32 and Shanyou 63, were compared at the panicle differentiation stage. As compared with Shanyou 63, the new combination Peiai 64S/E32 showed a significantly higher net photosynthetic rate (PN), apparent quantum yield of carbon assimilation (Φc), carboxylation efficiency (CE), and photorespiratory rate (RP) as well as leaf chlorophyll content, but a significantly lower dark respiration rate (RD) and compensation irradiance (Ic). It also showed a slightly higher photochemical efficiency (Fv/Fm and ΔF/Fm') of photosystem 2, a lower non-photochemical quenching (qN), and a similar CO2 compensation concentration (Γ) as compared to Shanyou 63. and Hua Jiang ... [et al.].
Seedlings of Chloris virgata were treated with varying (0-160 mM) salt-stress (SS; 1 : 1 molar ratio of NaCl to Na2SO4) or alkali-stress (AS; 1 : 1 molar ratio of NaHCO3 to Na2CO3). To compare these effects, relative growth rates (RGR), stored energy, photosynthetic pigment contents, net photosynthetic rates, stomatal conductance, and transpiration rates were determined. Both stresses did not change significantly the photosynthetic parameters of C. virgata under moderate stress (below 120 mM). Photosynthetic ability decreased significantly only at high stress (160 mM). Thus C. virgata, a natural alkali-resistant halophyte, adapts better to both kinds of stress. The inhibition effects of AS on RGR and energy storage of C. virgata were significantly greater than that of SS of the same intensity. The energy consumption of C. virgata was considerably greater while resisting AS than while resisting SS. and C. W. Yang ... [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
In whole cells of the wild type of Synechocystis 6714 exposed to high irradiance (Hl) the electron transfer to Qb was inhibited before the transfer to Qa In the mutant AzV with two point mutations in the Qg pocket (Ala 251 Val and Phe 211 Ser) the inhibition of electron transport to Qb had about the same rate as in the wild type but the transport to Qa was inhibited faster in the mutant. In the mutant also the repair of photosystem 2 (PS 2) reaction centres was slower after a moderate photoinhibitory damage. In contrast degradation of the Dl protein in the course of photoinhibition in vitro was slower with thylakoids from the mutant than with those of the wild type. In CMamydomonas cells photoinhibited at low temperature (5 °C) and in spinách thylakoids under anaerobic conditions a fast inhibition of electron transfer developed in PS 2 simultaneously with a State characteiized by a high level of F^. This high fluorescent statě disappeared and electron transport activity was restored in the dark without protein synďiesis when photoinhibited samples were soon transferred to higher temperature (25 °C) or to aerobic conditions, respectively. On the other hand, the irreversible photoinhibitory damage characteiized by the dechne of was slowed down by lowering of the temperature in all the objects tested.
In the present study, we investigated the antioxidative potential in leaves of the chromatic (CC) versus green (GC) Amaranthus tricolor L. under moderate high-temperature stress at 45°C. Before heat stress, CC had significantly higher levels of betacyanins [about 3.2 mg g-1(FM)] than the green [1.8 mg g-1(FM) (p<0.01), while similar chlorophyll (Chl) content [about 2 mg g-1(FM)] was observed between both cultivars. After exposure to high temperature (45°C) for 6 days, betacyanins in leaves of CC were remarkably increased (about 2 times of that in control samples grown at 30°C). In contrast, betacyanins in GC significantly decreased by 56% in comparison with that of the control. Chl level in CC was higher than that in GC after heat stress for 6 days. Flavonoids and total phenolics in both cultivars were increased, but much more in CC. Significantly less H2O2 accumulation was observed in the leaves and stems of CC than in those of GC under heat stress. Interestingly, much stronger circadian oscillation in fluorescence was observed in both cultivars after treatment at 45°C, which suggested that heat stress stimulates endogenous rhythms of photosystem II (PSII). Under moderate high-temperature stress, Chl fluorescence parameters Fv/Fm (maximum quantum yield of PSII), qP (coefficient of photochemical quenching), ΦPSII (effective PSII quantum yield), and ETR (electron transport rate) exhibited a gradual decrease, NPQ (nonphotochemical quenching) showed a slight increase followed by a gradual decline, whereas Fo (minimum fluorescence of a dark-adapted leaf) increased continuously. In contrast to GC, after 120 h of high-temperature treatment, CC exhibited significantly lower Fo level, and higher levels of Fv/Fm and NPQ. It is clear that PSII in CC was more stable than that in GC. The results indicate that betacyanins are an effective antioxidant, and probably contribute greatly to the higher thermal stability of PSII and higher tolerance to heat stress. and Z. Shu ... [et al.].
A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relation to grain formation and leaf senescence in two different senescent types of maize (Zea mays L.), one stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55). In comparison with Hokkou 55, P3845 had a higher N concentration (Nc) in the leaves and a higher specific N absorption rate by roots (SARN), which indicated that a large amount of N was supplied to the leaves from the roots during maturation. This resulted in a higher photosynthetic rate, which supports saccharide distribution to roots. Thus, stay-green plants maintained a more balanced C and N metabolism between shoots and roots. Moreover, the coefficients of the relationship between the relative growth rate (RGR) and Nc, and between the photon-saturated photo-synthetic rate (Psat) and Nc were lower in P3845. The Psat per unit Nc in leaves was lower in the stay-green cultivars, which indicated that high yield was attained by longer green area duration and not by a high Psat per unit Nc in the leaf. Consequently, a high Psat caused a high leaf senescence rate because C and N compounds will translocate actively from the leaves. and Ping He ... [et al.].
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.].
We determined the interactive effects of irradiance, elevated CO2 concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 µmol m-2 s-1), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO2 concentrations (Ca), AC and EC (350 and 750 µmol mol-1, respectively). Rates of net photosynthesis (PN) and transpiration (E) and stomatal conductance (gs) were measured, along with water use efficiency (WUE) and ratio of internal and external CO2 concentrations (Ci/Ca). PN revealed an interactive effect between PAR and Ca. As PAR increased so did PN under both C a regimes. The gs showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15 °C and 1 200 µmol m-2 s-1 PAR under EC. The Ci /Ca was influenced independently by temperature and Ca. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO2 concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on PN and WUE. and A. Thiagarajan, R. Lada, P. Joy.
Leaf tissue damaging to seedlings can limit their subsequent growth, and the effects may be more extensive. Compensatory photosynthesis responses of the remnant cotyledon and primary leaf of Pharbitis purpurea to clipping and the effect of clipping on seedling growth were evaluated in a pot-cultivated experiment. Three treatments were conducted in the experiment, which were clipped cotyledon (CC), clipped second leaf (CL), and control group (CG). The area, thickness, mass, and longevity of the remaining cotyledon of CC exhibited over-compensatory growth. In contrast, seedlings of CC had under-compensatory growth in seedling height, root length, seedling mass, and root to shoot ratio. However, the traits of remnant cotyledon and seedling in CL treatment exhibited equal-compensatory growth. Net photosynthetic rate of the cotyledon of CC was significantly higher than those of CL and CG treatments, and the diurnal changes in photosynthetic rates showed significantly different patterns which were unimodal curve (CC) and bimodal curve (CL and CG), respectively. There was no significant difference between CL and CG treatment. Net photosynthetic rate of the primary leaf of CL was significantly higher than that of CG treatment. However, the photosynthetic rates of primary leaves of CL and CG treatments showed similar photosynthetic patterns characterized by a bimodal curve. P. purpurea seedlings used a compensatory growth strategy in the remaining cotyledon or the primary leaf to resist leaf loss and minimize any adverse effects. and W. Zheng ... [et al.].