The effects of drought and the diurnal changes in photosynthetic electron transport were studied in non-nodulated plants of Casuarina equisetifolia. The induction of fluorescence showed a slightly higher I step in water-stressed than control plants, and the time from the start of irradiation to the P step of induction was significantly shortened by drought. The quantum efficiency of photosystem 2 (PS2) in the dark-adapted state (Fv/Fm) was generally not affected by drought, whereas it decreased during the central hours of the day. The decrease in quantum yield of PS2 electron transport (Φ2) in water-stressed plants was associated with decreases in the photochemical efficiency of open (oxidised) PS2 centres (Fv'/Fm') and increases in non-photochemical quenching (qN) rather than with increased closure of PS2 centres (lowered photochemical quenching, qP). In contrast, the changes in quantum yield of electron transport during the day were related to changes in qP rather than in Fv'/Fm'. When chlorophyll fluorescence was measured at the same irradiance during the day, a greater qN was observed at the end of the drying cycle than after watering, and early and late in the photoperiod than in the central hours of the day. The greater qN at the beginning and end of the day did not prevent an increase in energy not used photochemically nor dissipated non-photochemically. Drought did not affect this excess of photon energy. and R. Martínez-Carrasco, J. Sánchez-Rodriguez, P. Pérez.
In the seasonally flooded forest of the Mapire River, a tributary of the Orinoco, seedlings remain totally covered by flood water for over six months. In order to characterize the physiological response to flooding and submergence, seedlings of the tree Pouteria orinocoensis, an important component of the forest vegetation, were subjected experimentally to flooding. Flooding was imposed gradually, the maximum level of flood including submerged and emerged leaves. After 45 d a severe reduction of net photosynthetic rate (PN) and stomatal conductance (g s) was observed in emerged leaves, whereas leaf water potential remained constant. The decrease in PN of emerged leaves was associated to an increase in both relative stomatal and non-stomatal limitations, and the maintenance of the internal/air CO2 concentration (C i/C a) for at least 20 d of flooding. After this time, both PN and gs became almost zero. The decrease in photosynthetic capacity of emerged leaves with flooding was also evidenced by a decrease in carboxylation efficiency; photon-saturated photosynthetic rate, and apparent quantum yield of CO2 fixation. Oxygen evolution rate of submerged leaves measured after three days of treatment was 7 % of the photosynthetic rate of emerged leaves. Submersion determined a chronic photoinhibition of leaves, viewed as a reduction in maximum quantum yield in dark-adapted leaves, whereas the chlorophyll fluorescence analysis of emerged leaves pointed out at the occurrence of dynamic, rather than chronic, photoinhibition. This was evidenced by the absence of photochemical damage, i.e. the maintenance of maximum quantum yield in dark-adapted leaves. Nevertheless, the observed lack of complementarity between photochemical and non-photochemical quenching after 12 d of flooding implies that the capacity for photochemical quenching decreased in a non-co-ordinate manner with the increase in non-photochemical quenching.
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.].
The effect of water deficit on chlorophyll fluorescence, sugar content, and growth parameters of strawberry (Fragaria×ananassa Duch. cv. Elsanta) was studied. Drought stress caused significant reductions in leaf water potential, fresh and dry masses, leaf area, and leaf number. A gradual reduction of photochemical quenching (qP) and quantum efficiency (ΦPS2) was observed under drought stress while non-photochemical quenching (qN) increased. Maximum efficiency of photosystem 2 (Fv/Fm) was not affected by drought stress. and F. Razavi ... [et al.].
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.
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.
Influence of manganese (Mn) toxicity on photosynthesis in ricebean (Vigna umbellata) was studied by the measurement of gas exchange characteristics and chlorophyll fluorescence parameters. The net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) were reduced with increasing Mn concentration in nutrient solution. The reduction in gs and E was more pronounced at 6 d of Mn treatment. However, PN declined at 2 d of Mn treatment implying that the reduction in photosynthesis was not due to the direct effect of Mn on stomatal regulation. Mn did not affect the maximum efficiency of photosystem 2 (PS2) photochemistry (Fv/Fm). A reduction in photochemical quenching (qP) and excitation capture efficiency of open PS2 (Fv'/Fm') with a concomitant increase in qN was observed. This implies that reduced demand for ATP and NADPH due to the reduction in photosynthesis causes a down-regulation of PS2 photochemistry and thus a high pH gradient (increase in qN) and limited electron transport (decreased qP). and Desiraju Subrahmanyam, V. S. Rathore.
Watermelon (Citrillus lanatus) plants were grown for two consecutive years in open-top chambers with three different ozone concentrations (O3-free air, O3 ambient, and air with additional O3; CFA, NFA, and NFA+O3) and three nitrogen fertilizer concentrations [0, 14.0, and 29.6 g N per pot; N0, N1, and N2). There was an interaction between ozone and N fertilizer for the major parameters studied. O3 and N2 treatments led to a significant decrease in maximum efficiency of photosystem 2 (PS2) photochemistry (Fv/Fm), and induced a significant decrease in the actual quantum yield of PS2 (ΦPS2), due mainly to the increased closure of PS2 reaction centres (qP) and to an increase in the non-photochemical quenching (NPQ). On the other hand, these plants exhibited an increased susceptibility to photoinhibition, which could be associated with an increased fraction of reduced QA. An increase in lipid peroxidation indicated that damage was occurring at the membrane levels. High N concentration enhanced the detrimental effects of ozone on the fluorescence parameter induction and lipid peroxidation. All these negative alterations led to a decreased yield. and A. Calatayud, F. Pomares, E. Barreno.
The influence of chilling (8 °C, 5 d) at two photon flux densities [PFD, L = 200 and H = 500 μmol(photon) m-2 s-1] on the gas exchange and chlorophyll fluorescence was investigated in chilling-tolerant and chilling-sensitive maize hybrids (Zea mays L., K383×K130, K185×K217) and one cultivar of field bean (Vicia faba L. minor, cv. Nadwiślański). The net photosynthetic rate (PN) for the both studied plant species was inhibited at 8 °C. PN of both maize hybrids additionally decreased during chilling. Changes in the quantum efficiency of PS2 electron transport (ΦPS2) as a response to chilling and PFD were similar to PN. Measurements of ΦPS2/ΦCO2 ratio showed that in field bean seedlings strong alternative photochemical sinks of energy did not appear during chilling. However, the high increment in ΦPS2/ΦCO2 for maize hybrids can indicate reactions associated with chill damage generation. At 8 °C the non-photochemical quenching (NPQ) increased in all plants with chilling duration and PFD. The appearance of protective (qI,p) and damage (qI,d) components of qI and a decrease in qE (energy dependent quenching) took place. NPQ components of field bean and maize hybrids differed from each other. The amount of protective NPQ (qE + qI,p) components as part of total NPQ was higher in field bean than in maize hybrids at both PFD. On 5th day of chilling, the sum of qE and qI,p was 26.7 % of NPQ in tolerant maize hybrids and 17.6 % of NPQ in the sensitive one (averages for both PFD). The increased PFD inhibited the ability of all plants to perform protective dissipation of absorbed energy. The understanding of the genotypic variation of NPQ components in maize may have implications for the future selection of plants with a high chilling tolerance. and J. Kościelniak, J. Biesaga-Kościelniak.
Unlike mulberry (Morus alba, M.a.), paper mulberry (Broussonetia papyrifera, B.p.) can acclimate to Karst soil and incline to alien invasion. The photosynthetic parameters, diurnal changes of carbonic anhydrase, and chlorophyll fluorescence induction, and water potential were measured on sunny days (SD) and cloudy days (CD). Photosynthetic midday depression occurred in B.p. but not in M.a. The irradiance-and CO2-saturated photosynthetic rates of B.p. were significantly higher than those of M.a. There was no significant difference in water use efficiency between the two species on a SD. The maximum fluorescence, maximum quantum yield, photochemical quenching, and relative electron transport rate in the leaves of B.p. were much higher than those in M.a. The activity of carbonic anhydrase (CA) of B.p., on either an SD or a CD, was much greater than that of M.a. Higher transpiration rate (E) and net photosynthetic rate (PN) of B.p. resulted in the lack of water in mesophyll cells. Although a higher CA activity of B.p. supplied both water and CO2 for the photosynthesis of mesophyll cells, water in mesophyll cells was the factor limiting photosynthesis, and the intercellular CO2 concentration of B.p. was high and stable. and Y.-Y. Wu ... [et al.].