Maize plant inbred lines, one Al-sensitive (B-73) and two Al-tolerant (F-2 and L-2039), were grown hydroponically in the presence of 200 µM Al. After 13 d of growth, root and shoot lengths, photosystem 2 (PS2) activity, chlorophyll (Chl) content, 5-aminolevulinic acid (5-ALA) synthesis rate, chlorophyllase (Chlase) activity, and N, Mg, Fe, and Mn contents in leaves were determined. PS2 activity and Chl content were most severely affected by Al in B-73, but F-2 was almost unaffected. This was in accordance with Al-accumulation in the plants. The observed changes in B-73 coincided with 5-ALA synthesis inhibition, Chlase activation, and leaf deprivation of Fe and Mg. In Al-treated L-2039 plants, the leaf Mg and Mn contents were decreased. Also, an excessive Chlase activation was found in Al-treated L-2039, without a substantial Chl loss. This may indicate the activation of different enzyme pools in tolerant and sensitive genotypes under low-stress conditions. and N. Mihailovic, G. Drazic, Z. Vucinic.
Cr(VI) significantly reduced rates of net photosynthesis and transpiration and of stomatal conductance. Cr(VI) did not affect the Fv/Fm ratio of chlorophyll fluorescence implying that the primary photochemical processes in photosystem 2 were not affected. However, the efficiency of excitation capture by open PS2 centres, in vivo quantum yield of PS2 photochemistry, and electron transport rate were significantly reduced by Cr(VI). The coefficient of photochemical quenching was reduced with a concomitant increase in coefficient of non-photochemical quenching, suggesting reduced demand for ATP and NADPH due to inhibition of CO2 assimilation. Lipid peroxidation was increased by Cr(VI) and the activities of superoxide dismutase and catalase (CAT) were increased. However, the CAT activity was reduced by high Cr(VI) concentration. The activities of ascorbate peroxidase and glutathione reductase were significantly reduced by Cr(VI) treatment.
A greenhouse experiment examined whether clonal integration improves photosynthesis of ramets of alligator weed [Alternanthera philoxeroides (Mart.) Griseb.], a widespread invasive clonal plant in China, in heterogeneous (He) nutrient habitats. The connected pairs of ramets experienced different nutrient levels [high homogeneous (Ho) nutrient, low Ho nutrient, and two He nutrient treatments]. Clonal integration significantly improved the net photosynthetic rate, stomatal conductance, transpiration rate, and minimal and maximal chlorophyll fluorescence of ramets of alligator weed in low nutrient condition. These characteristics may contribute to the success of the ramets of alligator weed in invading contrasting habitats. The clonal integration of the invasive clonal plants may contribute significantly to their invasiveness. and J. Liu ... [et al.].
Six months old in vitro-grown Anoectochilus formosanus plantlets were transferred to ex-vitro acclimation under low irradiance, LI [60 µmol(photon) m-2 s-1], intermediate irradiance, II [180 µmol(photon) m-2 s-1], and high irradiance, HI [300 µmol(photon) m-2 s-1] for 30 d. Imposition of II led to a significant increase of chlorophyll (Chl) b content, rates of net photosynthesis (PN) and transpiration (E), stomatal conductance (gs), electron transfer rate (ETR), quantum yield of electron transport from water through photosystem 2 (ΦPS2), and activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBPCO, EC 4.1.1.39). This indicates that Anoectochilus was better acclimated at II compared to LI treatment. On the other hand, HI acclimation led to a significant reduction of Chl a and b, PN, E, gs, photochemical quenching, dark-adapted quantum efficiency of open PS2 centres (Fv/Fm), probability of an absorbed photon reaching an open PS2 reaction centre (Fv'/Fm'), ETR, ΦPS2, and energy efficiency of CO2 fixation (ΦCO2/ΦPS2). This indicates that HI treatment considerably exceeded the photo-protective capacity and Anoectochilus suffered HI induced damage to the photosynthetic apparatus. Imposition of HI significantly increased the contents of antheraxanthin and zeaxanthin (ZEA), non-photochemical quenching, and conversion of violaxanthin to ZEA. Thus Anoectochilus modifies its system to dissipate excess excitation energy and to protect the photosynthetic machinery. and D. M. Pandey ... [et al.].
Net photosynthetic rate (PN) of tobacco plants grown with NH4-N as the only N source was the lowest all the times, while PN grown only with NO3-N was the greatest until 22nd day, and PN grown with both NO3-N and NH4-N (1 : 1) was the greatest. Maximal photochemical efficiency of photosystem 2 (PS2), Fv/Fm, and actual quantum yield of PS2 under actinic irradiation (ΦPS2) in plants grown with only NH4-N were greatest at early stage and then decreased and were smaller than those of other treatments. Photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qNP) in the NH4-N plants were the greatest at all times. Hence excessive NH4-N can decrease not only photochemical efficiency but also the efficiency of utilization of photon energy absorbed by pigments for photosynthesis. Therefore, excessive NH4-N is a hindrance to photosynthesis of flue-cured tobacco. On the other hand, tobacco cultured with an appropriate mixture of NO3-N with NH4-N can sufficiently utilize photon energy and increase the efficiency of energy transformation. and H. X. Guo, W. Q. Liu, Y. C. Shi.
The effects of enhanced UV-B radiation on growth and photosynthetic activities were investigated in fronds of the aquatic fern Azolla microphylla Kaulf. The fronds were exposed to UV-B radiation intermittently once in 3 d during 12 d. Biomass and relative growth rate of UV-B treated Azolla plants and the heterocyst frequency of the UV-B treated symbiont decreased resulting in an increase in doubling time over the control. The doubling time was 3.08 d for control and 3.35 d for UV-B irradiated plants. Chl and carotenoid contents per unit fresh mass and photosystem 2 (PS2) activity also decreased under UV-B treatment. Measurements of photosynthetic activity in terms of fluorescence kinetics and PS2 mediated O2 evolution showed that the aquatic fern Azolla is sensitive to UV-B damage. and M. Jayakumar ... [et al.].
The protein secondary structure and pigments' microenvironment in photosystem 1 (PS1) complexes were studied in the temperature range of 25-80 °C using Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy, respectively. Quantitative analysis of the component bands of the amide I band (1 700-1 600 cm-1) showed no significant change below 50 °C. However, apparent conformational changes occurred at 60 °C and further continued at 70 and 80 °C accompanied with transitions of secondary structure mainly from α-helix to the β-sheet structures. CD analysis demonstrated that the regular arrangement, viz. protein microenvironment of pigments of PS1 complexes, was destroyed by heat treatment which might come from the changes of protein secondary structure of PS1. The CD signals at 645 nm contributed by chlorophyll (Chl) b of light-harvesting complex 1 (LHC1) were easily destroyed at the beginning of heat treatment (25-60 °C). When temperature reached 70 and 80 °C, the CD signals at 478 nm contributed mainly by Chl b of LHC1 and 498 nm contributed by carotenoids decreased most rapidly, indicating that LHC1 was more sensitive to high temperature than core complexes. In addition, the oxygen uptake rate decreased by 90.81 % at 70 °C and was lost completely at 80 °C showing that heat treatment damaged the regular function of PS1 complexes. This may be attributed to heat-induced changes of pigment microenvironment and protein secondary structure, especially transmembrane α-helix located in PsaA/B of PS1. and Z.-H. Hu ... [et al.].
Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000-2001 and 2001-2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (PN), maximal activity of photosystem 2, PS2 (Fv/Fm), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as PN×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK. and D. Jiang ... [et al.].
Gas exchange, chlorophyll (Chl) fluorescence, and contents of photosynthetic pigments, soluble proteins (ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO), and antioxidant enzymes were characterized in the fully expanded 6th leaves in rice seedlings grown on either complete (CK) or on nitrogen-deficient nutrient (N-deficiency) solutions during a 20-chase period. Compared with the control plants, the lower photosynthetic capacity at saturation irradiance (Pmax) was accompanied by an increase in intercellular CO2 concentration (Ci), indicating that in N-deficient plants the decline in Pmax was not due to stomatal limitation but due to the reduced carboxylation efficiency. The fluorescence parameters ΦPS2, Fv'/Fm', electron transport rate (ETR), and qP showed the same tendency as Pmax in N-deficient plants. Correspondingly, a higher qN paralleled the rise of the ratio of carotenoid (Car) to Chl contents. However, Fv/Fm was still diminished, suggesting that photoinhibition did occur in the photosystem 2 (PS2) reaction centres. In addition, the activities of antioxidant enzymes on a fresh mass basis were gradually lowered, leading to the aggravation of membrane lipid peroxidation with the proceeding N-deficiency. The accumulation of malonyldialdehyde resulted in the lessening of Chl and soluble protein content. Analyses of regression showed PS2 excitation pressure (1 - qP) was linearly correlated with the content of Chl and inversely with soluble protein (particularly RuBPCO) content. There was a lag phase in the increase of PS2 excitation pressure compared to the decrease of RuBPCO content. Therefore, the increased excitation pressure under N-deficiency is probably the result of saturation of the electron transport chain due to the limitation of the use of reductants by the Calvin cycle. Rice plants responded to N-deficiency and high irradiance by decreasing light-harvesting capacity and by increasing thermal dissipation of absorbed energy. and Z.-A. Huang ... [et al.].
Six-year-old Scots pine (Pinus sylvestris L.) seedlings were grown in open top chambers (OTCs) at ambient (AC) or elevated (ambient + 400 µmol mol-1; EC) CO2 concentration for three years (1996-1998). Chlorophyll (Chl) a fluorescence of current and one-year-old needles was measured in the field at two-weekly intervals in the period July-October 1998. In addition, Chl, carbon (C), and nitrogen (N) concentrations in both needle age classes were determined monthly during the same period. Chl fluorescence parameters were not significantly affected by EC, suggesting there was no response of the light reactions and the photochemical efficiency of photosystem 2. Chl concentrations were not significantly different but a reduced N concentration was observed in needles of EC treatment. Significant differences between needle age classes were observed for all parameters, but were most apparent under EC and toward the end of the growing season, possibly due to an acclimation process. As a result, significant interactions between CO2 treatment, needle age class, and season were found. This study emphasizes the importance of repeated measures including different leaf/needle age classes to assess the photosynthetic response of trees under EC. and B. Gielen, M. E. Jach, R. Ceulemans.