Effects of zinc and soil moisture on photosynthetic rate and chlorophyll fluorescence parameters of maize

Effects of zinc [0 and 5.0 mg Zn kg⁻¹ (soil)] on photosynthetic rate (P_N), and chlorophyll fluorescence in leaves of maize (Zea mays L.) cv. Zhongdan 9409 seedlings grown under different soil moisture regimes (40–45 % and 70–75 % of soil saturated water content) were studied. Zn application did not enhance maize plant adaptation to drought stress. The relative water content and the water potential of leaves were not affected by Zn treatment. Moreover, The P_N of drought-stressed plants was not improved by Zn supply. The increases of plant biomass, stomatal conductance and quantum yield of photosystem 2 due to Zn addition were notable in well-watered plants.     

Diurnal variation of gas exchange, chlorophyll fluorescence, and xanthophyll cycle components of maize hybrids released in different years

Diurnal variation of gas exchange, chlorophyll (Chl) fluorescence, and xanthophyll cycle components of three maize (Zea mays L.) hybrids released in different years, i.e. Baimaya (1950s), Zhongdan2 (1970s), and Nongda108 (1990s), were compared. On cloudless days, the newer hybrids always had higher net photosynthetic rate (P _N), especially at noon, than the older ones. At noon, all the hybrids decreased their maximal yield of photosystem 2 (PS2) photochemistry (F_v/F_m) and actual quantum yield of PS2 (Φ_PS2), the newer ones always showing higher values. Generally, the newer hybrids displayed higher photochemical quenching of Chl (q_P) and lower non-photochemical quenching (NPQ). The interhybrid differences in P _N may be owing to their differential photochemical efficiency. A midday depression in P _N occurred in all hybrids, which might be caused by serious photoinhibition or by decreased stomatal conductance. However, midday depression in P _N was more obvious in the older hybrids, especially when leaves were senescent. The higher de-epoxidation state of the xanthophylls was noted in older hybrids, which was confirmed by their larger NPQ. The newer maize hybrids did not need a strong de-epoxidation state since they had a better photosynthetic quantum conversion rate and a lower NPQ.     

Effects of drought stress on photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean plants

Changes in plant growth, photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean [Glycine max (L.) Merr.] plants under drought stress were studied. Total plant dry mass was reduced by 30 % compared to well-watered control plants. Leaf water potential was slightly decreased by water stress. Water stress induced daytime shrinkage and reduced night-time expansion of stem. Photosynthetic rate, stomatal conductance and transpiration rate were significantly declined by water stress, while the intercellular CO₂ concentration was changed only slightly at the initiation of stress treatment. The maximum photochemical efficiency of photosystem 2 and apparent photosynthetic electron transport rate were not changed by water stress.     

Different photosynthetic responses of wild and cultivated plants to high irradiance

In addition to other factors, high altitude (HA) environment is characterized by high photosynthetic photon flux density (PPFD). Photosynthetic characteristics of wild and cultivated plants were studied at different irradiances at Losar, India (altitude 4 200 m). Wild plants were tolerant to high PPFDs. Slopes of curve between net photosynthetic rate (P _N) and intercellular CO₂ concentration (C _i) or stomatal conductance (g _s) increased with increase in irradiance suggesting insensitivity or tolerance of these plants to higher PPFD. Cultivated plants, however, were sensitive to higher PPFD, their slopes of curves between P _N and C _i or g _s decreased with increased PPFD. Tolerance or insensitivity to higher PPFD was an important parameter affecting plant performance at HA.     

Comparative effects of salt-stress and alkali-stress on the growth,photosynthesis, solute accumulation,and ion balance of barley plants

We compared the effects of salt-stresses (SS, 1: 1 molar ratio of NaCl to Na₂SO₄) and alkali-stresses (AS, 1: 1 molar ratio of NaHCO₃ to Na₂CO₃) on the growth, photosynthesis, solute accumulation, and ion balance of barley seedlings, to elucidate the mechanism of AS (high-pH) damage to plants and the physiological adaptive mechanism of plants to AS. The effects of SS on the water content, root system activity, membrane permeability, and the content of photosynthetic pigments were much less than those of AS. However, AS damaged root function, photosynthetic pigments, and the membrane system, led to the severe reductions in water content, root system activity, content of photosynthetic pigments, and net photosynthetic rate, and a sharp increase in electrolyte leakage rate. Moreover, with salinity higher than 60 mM, Na⁺ content increased slowly under SS and sharply under AS. This indicates that high-pH caused by AS might interfere with control of Na⁺ uptake in roots and increase intracellular Na⁺ to a toxic level, which may be the main cause of some damage emerging under higher AS. Under SS, barley accumulated organic acids, Cl⁻, SO₄ ²⁻, and NO₃ ⁻ to balance the massive influx of cations, the contribution of inorganic ions to ion balance was greater than that of organic acids. However, AS might inhibit absorptions of NO₃ ⁻ and Cl⁻, enhance organic acid synthesis, and SO₄ ²⁻ absorption to maintain intracellular ion balance and stable pH.     

Photosynthetic photon flux density,carbon dioxide concentration,and vapor pressure deficit effects on photosynthesis in cacao seedlings

Independent short-term effects of photosynthetic photon flux density (PPFD) of 50–400 μmol m⁻² s⁻¹, external CO₂ concentration (C _a) of 85–850 cm³ m⁻³, and vapor pressure deficit (VPD) of 0.9–2.2 kPa on net photosynthetic rate (P _N), stomatal conductance (g _s), leaf internal CO₂ concentration (C _i), and transpiration rates (E) were investigated in three cacao genotypes. In all these genotypes, increasing PPFD from 50 to 400 μmol m⁻² s⁻¹ increased P _N by about 50 %, but further increases in PPFD up to 1 500 μmol m⁻² s⁻¹ had no effect on P _N. Increasing C _a significantly increased P _N and C _i while g _s and E decreased more strongly than in most trees that have been studied. In all genotypes, increasing VPD reduced P _N, but the slight decrease in g _s and the slight increase in C _i with increasing VPD were non-significant. Increasing VPD significantly increased E and this may have caused the reduction in P _N. The unusually small response of g _s to VPD could limit the ability of cacao to grow where VPD is high. There were no significant differences in gas exchange characteristics (g _s, C _i, E) among the three cacao genotypes under any measurement conditions.     

Effects of water stress and high temperature on gas exchange and chlorophyll fluorescence in Triticum aestivum L.

Wheat plants grown in controlled growth chambers were exposed to drought stress (DS) and high temperature (HT) singly and in combination (DS+HT). The effects of these two stresses on net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), quantum efficiency of photosystem 2 (Φ_PS2), variable to maximum chlorophyll (Chl) fluorescence (F_v/F_m), photochemical (q_p) and non-photochemical (NPQ) Chl fluorescence, and yield were investigated. Grain yield was decreased by 21 % due to DS, while it was increased by 26 % due to HT. P _N, g _s, C _i, and Chl fluorescence were dramatically reduced to DS, HT, and their interaction, except NPQ which showed an increase due to HT.     

Effects of the interaction between ozone and carbon dioxide on gas exchange,ascorbic acid content,and visible leaf symptoms in rice leaves

Tropospheric ozone (O₃) decreases photosynthesis, growth, and yield of crop plants, while elevated carbon dioxide (CO₂) has the opposite effect. The net photosynthetic rate (P _N), dark respiration rate (R _D), and ascorbic acid content of rice leaves were examined under combinations of O₃ (0, 0.1, or 0.3 cm³ m⁻³, expressed as O⁰, O^0.1, O^0.3, respectively) and CO₂ (400 or 800 cm³ m⁻³, expressed as C⁴⁰⁰ or C⁸⁰⁰, respectively). The P _N declined immediately after O₃ fumigation, and was larger under O^0.3 than under O^0.1. When C⁸⁰⁰ was combined with the O₃, P _N was unaffected by O^0.1 and there was an approximately 20 % decrease when the rice leaves were exposed to O^0.3 for 3 h. The depression of stomatal conductance (g _s) observed under O^0.1 was accelerated by C⁸⁰⁰, and that under O^0.3 did not change because the decline under O^0.3 was too large. Excluding the stomatal effect, the mesophyll P _N was suppressed only by O^0.3, but was substantially ameliorated when C⁸⁰⁰ was combined. Ozone fumigation boosted the R _D value, whereas C⁸⁰⁰ suppressed it. An appreciable reduction of ascorbic acid occurred when the leaves were fumigated with O^0.3, but the reduction was partially ameliorated by C⁸⁰⁰. The degree of visible leaf symptoms coincided with the effect of the interaction between O₃ and CO₂ on P _N. The amelioration of O₃ injury by elevated CO₂ was largely attributed to the restriction of O₃ intake by the leaves with stomatal closure, and partly to the maintenance of the scavenge system for reactive oxygen species that entered the leaf mesophyll, as well as the promotion of the P _N.     

Effect of abscisic acid on photosynthetic parameters during <Emphasis Type="Italic">ex vitro</Emphasis> transfer of micropropagated tobacco plantlets

The aim of this research was to determine whether exogenous abscisic acid (ABA) applied immediately after ex vitro transfer of in vitro grown plants can improve their acclimatization. Tobacco (Nicotiana tabacum L.) plantlets were transferred into pots with Perlite initially moistened either by water or 50 μM ABA solution and they were grown under low (LI) or high (HI) irradiance of 150 and 700 μmol m⁻² s⁻¹, respectively. Endogenous content of ABA in tobacco leaves increased considerably after ABA application and even more in plants grown under HI. Stomatal conductance, transpiration rate and net photosynthetic rate decreased considerably 1 d after ex vitro transfer and increased thereafter. The gas exchange parameters were further decreased by ABA application and so wilting of these plants was limited. Chlorophyll (a+b) and β-carotene contents were higher in ABA-treated plants, but the content of xanthophyll cycle pigments was not increased. However, the degree of xanthophyll cycle pigments deepoxidation was decreased what also suggested less stress in ABA-treated plants. No dramatic changes in most chlorophyll a fluorescence parameters after ex vitro transfer suggested that the plants did not suffer from restriction of electron transport or photosystem damage.     

Up-regulation of cyclic electron flow and down-regulation of linear electron flow in antisense-<Emphasis Type="Italic">rca</Emphasis> mutant rice

To investigate how excess excitation energy is dissipated in a ribulose-1,5-bisphospate carboxylase/oxygenase activase antisense transgenic rice with net photosynthetic rate (P _N) half of that of wild type parent, we measured the response curve of P _N to intercellular CO₂ concentration (C _i), electron transport rate (ETR), quantum yield of open photosystem 2 (PS2) reaction centres under irradiation (F_v′/F_m′), efficiency of total PS2 centres (Φ_PS2), photochemical (q_P) and non-photochemical quenching (NPQ), post-irradiation transient increase in chlorophyll (Chl) fluorescence (PITICF), and P700⁺ re-reduction. Carboxylation efficiency dependence on C _i, ETR at saturation irradiance, and F_v′/F_m′, Φ_PS2, and q_P under the irradiation were significantly lower in the mutant. However, NPQ, energy-dependent quenching (q_E), PITICF, and P700⁺ re-reduction were significantly higher in the mutant. Hence the mutant down-regulates linear ETR and stimulates cyclic electron flow around PS1, which may generate the ΔpH to support NPQ and q_E for dissipation of excess excitation energy.     

Effects of root temperature on leaf gas exchange and xylem sap abscisic acid concentrations in six Cucurbitaceae species

Roots of six Cucurbitaceae species were exposed to low (14 °C), middle (24 °C), and high (34 °C) temperatures while aerial parts of plants were maintained at ambient temperatures between 23 and 33 °C. The highest dry mass (DM), photon-saturated rate of net photosynthesis (P _Nsat), and stomatal conductance (g _s) were found at 14 °C in figleaf gourd and turban squash plants, at 24 °C in cucumber and melon plants, while bitter melon and wax gourd plants had lower DM, P _Nsat, and g _s at 14 °C than at 24 or 34 °C. Sub-or supra-optimum root temperatures did not induce photoinhibition but induced slight changes in the quantum efficiency of photosystem 2, PS2 (Φ_PS2) and photochemical quenching (q_p). Meanwhile, xylem sap abscisic acid (ABA) concentration followed a contrasting change pattern to that of g _s. Thus the change in P _Nsat was mainly due to the change in g _s and roots played an important role in the regulation of stomatal behaviour by delivering increased amount of ABA to shoots at sub-or supra-optimum root temperatures.     

Leaf gas exchange,water relations,nutrient content and growth in citrus and olive seedlings under salinity

The effects of salinity on growth, leaf nutrient content, water relations, gas exchange parameters and chlorophyll fluorescence were studied in six-month-old seedlings of citrus (Citrus limonia Osbeck) and rooted cuttings of olive (Olea europaea L. cv. Arbequina). Citrus and olive were grown in a greenhouse and watered with half strength Hoagland’s solution plus 0 or 50 mM NaCl for citrus, or plus 0 or 100 mM NaCl for olive. Salinity increased Cl⁻ and Na⁺ content in leaves and roots in both species and reduced total plant dry mass, net photosynthetic rate and stomatal conductance. Decreased growth and gas exchange was apparently due to a toxic effect of Cl⁻ and/or Na⁺ and not due to osmotic stress since both species were able to osmotically adjust to maintain pressure potential higher than in non-salinized leaves. Internal CO₂ concentration in the mesophyll was not reduced in either species. Salinity decreased leaf chlorophyll a content only in citrus.     

Water-water cycle involved in dissipation of excess photon energy in phosphorus deficient rice leaves

The water-water cycle which may be helpful for dissipating the excitation pressure over electron transport chain and minimizing the risk of photoinhibition and photodamage was investigated in rice after 10-d P-deficient treatment. Net photosynthetic rate decreased under P-deficiency, thus the absorption of photon energy exceeded the energy required for CO₂ assimilation. A more sensitive response of effective quantum yield of photosystem 2 (Φ_PS2) to O₂ concentration was observed in plants that suffered P starvation, indicating that more electrons were transported to O₂ in the P-deficient leaves. The electron transport rate through photosystem 2 (PS 2) (J_f) was stable, and the fraction of electron transport rate required to sustain CO₂ assimilation and photorespiration (J_g/J_f) was significantly decreased accompanied by an increase in the alternative electron transport (J_a/J_f), indicating that a considerable electron amount had been transported to O₂ during the water-water cycle in the P-deficient leaves. However, the fraction of electron transport to photorespiration (J_o/J_f) was also increased in the P-deficient leaves and it was less sensitive than that of water-water cycle. Therefore, water-water cycle could serve as an efficient electron sink. The higher non-photochemical fluorescence quenching (q_N) in the P-deficient leaves depended on O₂ concentration, suggesting that the water-water cycle might also contribute to non-radiative energy dissipation. Hence, the enhanced activity of the water-water cycle is important for protecting photosynthetic apparatus under P-deficiency in rice.     

Photosynthesis,water use efficiency,and δ<Superscript>13</Superscript>C in two rice genotypes with contrasting response to water deficit

The effects of water deficit and re-irrigation were studied in glasshouse-grown rice plants (cvs. Cimarrón and Fonaiap 2000) which differ in their susceptibility to water deficit. Relative water content decreased from >90 to 67–69 % and recovered to pre-stress values within 24 h after re-irrigation. The irradiance-saturated rate of photosynthesis (P _sat), transpiration rate (E), and stomatal conductance (g _s) decreased with water deficit. E and g _s decreased similarly in both cultivars, but P _sat was more strongly inhibited in Cimarrón than in Fonaiap 2000. Water deficit increased water use efficiency (WUE_T) over 2-fold in Fonaiap 2000 and by 1.5-fold in Cimarrón. The ratio of intercellular to ambient CO₂ concentration (C _i/C _a) decreased in Fonaiap 2000 during mild stress but increased at severe stress. Contrarily, Cimarrón did not change C _i/C _a with water deficit. After re-irrigation Fonaiap 2000 recovered P _sat to ca. 80 % of control values 24 h after re-irrigation, whereas Cimarrón recovered to 60 % of control values 48 h after re-irrigation. E and g _s recovered to a lesser extent (50 %) than P _sat, after 48 h of re-irrigation in both cultivars. Total aboveground and green (live) biomass were unaffected by water deficit in Fonaiap 2000 but were reduced by 21 and 40 % in Cimarrón, respectively. Dead biomass increased in stressed plants of both cultivars but to a larger extent in Cimarrón than in Fonaiap 2000. Water deficit increased δ¹³C in Fonaiap 2000, whereas Cimarrón was unaffected by water deficit showing lower values than those of Fonaiap 2000. δ¹³C was highly and linearly correlated to the ratio C _i/C _a. WUE_T was also significantly correlated to δ¹³C.     

Response of photosynthesis and chlorophyll fluorescence quenching to leaf dichotocarpism in Ligustrum vicaryi, an ornamental herb

Net photosynthetic rate of yellow upper leaves (UL) of Ligustrum vicaryi was slightly, but not significantly higher than that of green lower leaves (LL). Diurnally, maximum photochemical efficiency of photosystem 2, PS2 (F_v/F_m) of LL did not significantly decline but the UL showed fairly great daily variations. Yield of PS2 of UL showed an enantiomorphous variation to the photosynthetically active radiation and was significantly lower than in the LL. Unlike F_v/F_m, the efficiency of energy conversion in PS2 and both non-photosynthetic and photosynthetic quenching did not differ in UL and LL. Significant differences between UL and LL were found in contents of chlorophyll (Chl) a, b, and carotenoids (Car) and ratios of Chl a/b, Chl b/Chl (a+b), and Car/Chl (a+b). Leaf colour dichotocarpism in L. vicaryi was mainly caused by different photon utilization; sunflecks affected the LL.     

Irradiance stress responses of gas exchange and antioxidant enzyme contents in pariparoba [<Emphasis Type="Italic">Pothomorphe umbellata</Emphasis> (L.) Miq.] plants

We evaluated the growth and development of the medicinal species Pothomorphe umbellata (L.) Miq. under different shade levels (full sun and 30, 50, and 70 % shade, marked as I₁₀₀, I₇₀, I₅₀, and I₃₀, respectively) and their effects on gas exchange and activities of antioxidant enzymes. Photosynthetically active radiation varied from 1 254 μmol m⁻² s⁻¹ at I₁₀₀ to 285 μmol m⁻² s⁻¹ at I₃₀. Stomatal conductance, net photosynthetic rate, and relative chlorophyll (Chl) content were maximal in I₇₀ plants. Plants grown under I₁₀₀ produced leaves with lower Chl content and signs of chlorosis and necrosis. These symptoms indicated Chl degradation induced by the generation of reactive oxygen species. Stress related antioxidant enzyme activities (Mn-SOD, Fe-SOD, and Cu/Zn-SOD) were highest in I₁₀₀ plants, whereas catalase activity was the lowest. Hence P. umbellata is a shade species (sciophyte), a feature that should be considered in reforestation programs or in field plantings for production of medicinal constituents.     

MPEC: an important gene in the chlorophyll biosynthesis pathway in photosynthetic organisms

One of the least understood enzymatic steps in chlorophyll biosynthesis is the formation of isocyclic ring, which is catalyzed by the Mg-protoporphyrin IX monomethyl ester (MgPME) cyclase that is involved in the conversion of MgPME to protochlorophyllide. Several genes encoding part of this enzyme have been identified and functional analysis of them has been performed. The enzyme plays important roles in higher plants and photosynthetic bacteria. The review focuses on the current knowledge of MgPME cyclase coding genes, with emphasis on their organization, expression pattern, and functional analysis obtained from mutants.     

Low concentration of bisulfite enhances photosynthesis in tea tree by promoting carboxylation efficiency in leaves

Tea tree (Melaleuca alternifolia) canopy was sprayed with low concentration of NaHSO₃ or mixture of NaHSO₃+ KH₂PO₄. The treatments significantly enhanced net photosynthetic rate (P _N), carboxylation efficiency (CE), and the maximum response of P _N to intercellular CO₂ concentration. The enhancement of P _N by foliar application of low concentrations of bisulfite was due to increasing CE relevant to ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase activity and regeneration rate of RuBP depending on ATP formation.     

Irreversible changes in barley leaf chlorophyll fluorescence detected by the fluorescence temperature curve in a linear heating/cooling regime

The chlorophyll fluorescence (F) temperature curves in a linear time-temperature heating/cooling regime were used to study heat-induced irreversible F changes in primary green leaves of spring barley (Hordeum vulgare L. cv. Akcent). The leaf segments were heated in a stirred water bath at heating rates of 0.0083, 0.0166, 0.0333, and 0.0500 °C s⁻¹ from room temperature up to maximal temperature T _m and then linearly cooled to 35 °C at the same rate. The F intensity was measured by a pulse-modulated technique. The results support the existence of the two critical temperatures of irreversible F changes postulated earlier, at 45–48 and 53–55 °C. The critical temperatures are slightly dependent on the heating rate. Two types of parameters were used to characterize the irreversibility of the F changes: the coefficient of irreversibility μ defined as the ratio of F intensity at 35 °C at the starting/ending parts of the cycle and the slopes of tangents of linear parts of the F temperature curve. The dependence of μ on T _m revealed a maximum, which moved from 54 to 61 °C with the increasing heating/cooling rate v from 0.0083 to 0.0500 °C s⁻¹, showing two basic phases of the irreversible changes. The Arrhenius and Eyring approaches were applied to calculate the activation energies of the initial increase in μ. The values varied between 30 and 50 kJ mol⁻¹ and decreased slightly with the increasing heating rate.