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.
Spearmint cultivars MSS-5, Arka, and Neera grown in nutrient culture in controlled conditions differed in plant height, number of tillers, internodal position, fresh mass, dry mass, leaf stem ratio, and chlorophyll contents. Initial transpiration rate, stomatal conductivity, and CO2 exchange rate showed better increase in MSS-5 genotype. Mn stress decreased oil content whereas the content of oil constituent carvone increased in MSS-5 and Arka. and P. Singh, A. Misra, N. K. Srivastava.
Seedlings of chile ancho pepper were grown in pots containing a pasteurized mixture of sand and a low phosphorus (P) sandy loam soil, and either inoculated (VAM) or not inoculated (NVAM) with the endomycorrhizal fungus Glomus intraradices. Long Ashton nutrient solution (LANS) was modified to supply P to the seedlings at 0, 11, and 44 g(P) m-3 (P0, P11, P44, respectively). Low P depressed net photosynthetic rate (PN), stomatal conductance (gs), phosphorus use efficiency (PN/P), and internal CO2 concentration (Ci). The mycorrhiza alleviated low P effects by increasing PN, gs, PN/P, and decreasing Ci. At P0, Ci of NVAM plants was equal to or higher than that of VAM plants, suggesting nonstomatal inhibition of photosynthesis. Gas exchange of VAM plants at P0 was similar to that of NVAM plants at P11. Endomycorrhiza increased leaf number, leaf area, shoot, root and fruit mass at P0 and P11 compared to NVAM plants. Reproductive growth was enhanced by 450 % in mycorrhizal plants at P44. Root colonization (arbuscules, vesicles, internal and extraradical hyphae development) was higher at lower P concentrations, while sporulation was unaffected. The enhanced growth and gas exchange of mycorrhizal plants was in part due to greater uptake of P and greater extraradical hyphae development. and L. Aguilera-Gomez ... [et al.].
In cotton (Gossypium hirsutum L.) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied. After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate (PN) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply. Decreased leaf PN of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves. Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading. K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues. and Duli Zhao, D. M. Oosterhuis, C. W. Bednarz.
The effects of potassium nutrition [0, 6.25, 12.50, 25.00 g(K) m-2 of K2SO4 or KCl] on gas exchange characteristics and water relations in four cultivars (CIM-448, CIM-1100, Karishma, S-12) of cotton were assessed under an arid environment. Net photosynthetic rate (PN) and transpiration rate (E) increased with increased K supply. The leaf pressure potential (Ψp) increased significantly by the addition of 25.00 g(K) m-2 compared to zero K level. The water use efficiency (PN/E) was improved by 24.6 % under the highest K dose compared to zero K. There were positive correlations (0.99**, 0.98**, 0.95**, 0.97**) between K-doses and PN, E, Ψp, and PN/E, respectively. and H. Pervez, M. Ashraf, M. I. Makhdum.
We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψw) and leaf osmotic potential (Ψs) decreased. Leaf Ψw was at least -0.32 MPa lower than the Ψw of solution. Na+ and K+ ions explained about 78 % of decrease in Ψs. K+ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely, Na+ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate
(PN) and stomatal conductance (gs) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO2 concentration (Ci) followed the same trend. The PN as a function of Ci showed that both the initial linear slope and upper plateau of the PN vs. Ci curve were markedly affected by high salinity (40 and 55 ‰). and N. Suárez, E. Medina.
We examined, under laboratory conditions, the influence of temperature (2 °C vs. 10 °C) on the physiological responses of two aquatic bryophytes from a mountain stream to artificially enhanced UV-B radiation for 82 d. These organisms may be exposed naturally to relatively low temperatures and high levels of UV-B radiation, and this combination is believed to increase the adverse effects of UV-B radiation. In the moss Fontinalis antipyretica, UV-B-treated samples showed severe physiological damages, including significant decreases in chlorophyll (Chl) and carotenoid (Car) contents, Chl a/b and Chl/phaeopigment ratios, Chl a fluorescence parameters Fv/Fm and ΦPS2, electron transport rate (ETRmax), and growth. In the liverwort Jungermannia cordifolia, UV-B radiation hardly caused any physiological change except for growth reduction. Thus, this liverwort seemed to be more tolerant to UV-B radiation than the moss under the specific experimental conditions used, maybe partly due to the accumulation of UV-B absorbing compounds. The influence of temperature on the effects of UV-B radiation depended on the species: the higher the UV-B tolerance, the lower the influence of temperature. Also, different physiological variables showed varied responses to this influence. Particularly, the lower temperature used in our study enhanced the adverse effects of UV-B radiation on important physiological variables such as Fv/Fm, growth, and Chl/phaeopigment ratios in the UV-B-sensitive F. antipyretica, but not in the more UV-B-tolerant J. cordifolia. Thus, the adverse effects of cold and UV-B radiation were apparently additive in the moss, but this additiveness was lacking in the liverwort. The Principal Components Analyses (PCA) conducted for both species with the physiological data obtained after 36 and 82 d of culture confirmed the above results. Under natural conditions, the relatively high water temperatures in summer might facilitate the acclimation of aquatic bryophytes from mountain streams to high levels of UV-B radiation. This may be relevant to predict the consequences of concomitant global warming and increasing UV-B radiation. and E. Nuñez-Olivera ... [et al.].
A gradual reduction in leaf water potential (Ψleaf), net photosynthetic rate (PN), stomatal conductance, and transpiration rate was observed in two drought tolerant (C 306 and K 8027) and two susceptible (RW 893 and 899) genotypes subjected to water stress. The extent of reduction was lower in K 8027 and C 306 and higher in RW 893 and RW 899. Rewatering the plants after 5 d of stress restored PN and other gas exchange traits in all four cultivars. Water stress had no significant effect on variable to maximum fluorescence ratio (Fv/Fm) indicating that water stress had no effect on primary photochemistry of photosystem 2 (PS2). However, water stress reduced the efficiency of excitation energy transfer (F'v/F'm) and the quantum yield of electron transport (ΦPS2). The reduction was more pronounced in susceptible cultivars. Water stress had no significant effect on photochemical quenching, however, the non-photochemical quenching increased by water stress. and D. Subrahmanyam ... [et al.].
Chlorophyll fluorescence kinetics was used to investigate the effect of 1,4-dithiothreitol (DTT) on the distribution of excitation energy between photosystem 1 (PS1) and photosystem 2 (PS2) in soybean leaves under high irradiance (HI). The maximum PS2 quantum yield (Fv/Fm) was hardly affected by the presence of DTT, however, photon-saturated photosynthesis was depressed distinctly. Photochemical efficiency of open PS2 reaction centres during irradiation (Fv'/Fm') was enhanced by about 30-40 % by DTT treatment, whereas photochemical quenching (qP) was depressed by about 40 % under HI. DTT treatment caused a 30 % decrease in allocation of excitation energy to PS1 under HI and a 20 % increase to PS2. An obvious shift in the balance of excitation energy distribution between photosystems was observed in DTT-treated leaves. Though high excitation pressure (1 - qP) resulted from DTT treatment, non-photochemical quenching (qN) was lower. DTT completely inhibited the formation of zeaxanthin and also distinctly depressed the state transition (qT). The shift in the balance of excitation distribution between the two photosystems induced by DTT was mainly due to the enhancement of excitation energy capture by PS2 antenna and the inhibition of state transition. It might be the shift in the balance between the two photosystems that mainly induced the depression of photosynthesis. Thus, to keep high utilization efficiency of absorbed photon energy, it is necessary to maintain the balance of excitation distribution between PS2 and PS1. and C.-D. Jiang ... [et al.].
Effects of benzyladenine (BA) and abscisic acid (ABA) applied separately or simultaneously on parameters of gas exchange of Phaseolus vulgaris L. leaves were studied. In the first two experimental sets) 100 μM ABA and 10 μM BA were applied to plants sufficiently supplied with water. Spraying of leaves with ABA decreased stomatal conductance (gs) and in consequence transpiration rate (E) and net photosynthetic rate (PN) already 1 h after application, but 24 h after application the effect almost disappeared. 10 μM BA slightly decreased gas exchange parameters, but in simultaneous application with ABA reversed the effect of ABA. Immersion of roots into the same solutions markedly decreased gas exchange parameters and 24 h after ABA application the stomata were completely closed. The effect of ABA was ameliorated by simultaneous BA application, particularly after 1-h treatment. In the third experimental set, plants were pre-treated by immersing roots into water, 1 μM BA, or 100 μM ABA for 24 h and then the halves of split root system were dipped into different combinations of 1 μM BA, 100 μM ABA, and water. In plants pre-treated with ABA all gas exchange parameters were small and they did not differ in plants treated with H2O+H2O, H2O+BA, or BA+BA. In plants pre-treated with BA or H2O, markedly lower values of PN were found when both halves of roots were immersed in ABA. Further, the effects of pre-treatment of plants with water, 1 μM BA, 100 μM ABA, or ABA+BA on the development of water stress induced by cessation of watering and on the recovery after rehydration were followed. ABA markedly decreased gas exchange parameters at the beginning of the experiment, but in its later phase the effect was compensated by delay in development of water stress. BA also delayed development of water stress and increased PN in water-stressed leaves. BA reversed the effect of ABA at mild water stress. Positive effects of BA and ABA pre-treatments were observed also after rehydration.