Depression Of PN Research Articles

Diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response of six parental lines of maize released in three eras

Over the past seven decades, the grain yield of maize (Zea mays L.) has increased continuously in China, mostly due to hybridization innovations, particularly recent genetic improvements in photosynthesis. In order to reveal photosynthetic characters of elite inbred lines in different ears, a field experiment was conducted at the North China Plain of Shandong Province in China. Six parental lines of maize introduced in three eras (the 1960s, 1980s, and 2000s) were investigated diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response characteristic at the grain filling stage. Compared to earlier parental lines, the 2000s parental lines always had higher net photosynthetic rate (Pn) throughout the day, especially at noon, and a mid-day depression in Pn did not occur in all hybrids parental lines. Moreover, the stomatal conductance (Gs) and water use efficiency (WUE) of the 2000s’ lines showed higher value than those of the 1960s’ and 1980s’ lines. The inbred lines differences in photosynthetic parameters were partly owing to their different quantum carboxylation efficiencies and light synthase activities. Simultaneously, the 2000s parental lines exhibited lower light and CO2 compensation points, and their higher apparent quantum yield, and carboxylation efficiency. These suggested that the modern parental lines required lower light intensity and less CO2 to maintain a relatively high photosynthetic capacity, substantially increasing leaf physical quality and stress resistance. It provided crucial information of high photo-efficiency and stress-resistance breeding in maize.

Light stress-induced chloroplast movement and midday depression of photosynthesis in sorghum leaves

ABSTRACTPlants are exposed to high light intensity, high leaf temperatures and high air-to-leaf water vapor pressure deficit (ALVPD) during the day. These environmental stresses cause stomatal closure and photoinhibitory damage, leading to midday depression of photosynthesis. Chloroplast positioning is essential for the efficient operation of photosynthesis. However, chloroplast behavior before, during, and even after the midday depression of photosynthesis remains unknown. We investigated changes in the intracellular positioning of chloroplasts and photosynthetic traits under a diurnal pattern of light. Sorghum leaves were exposed to a 12-h regime of light mimicking the natural light environment, with constant leaf temperature and ALVPD. Net photosynthetic rate (Pn) showed a diurnal pattern, and midday depression in Pn was observed at 3.8 h of irradiation. Depression in Pn was attributed to stomatal limitation because the decrease in Pn was in accordance with the decrease in stomatal conductance. The maximum efficiency of photosystem II decreased with the increase in light intensity and remained low after 12 h of irradiation. Bundle sheath chloroplasts swelled after 8 h of irradiation, representing the accumulation of starch. Conversely, mesophyll chloroplasts exhibited avoidance response after 4 h of irradiation, and the avoidance position was maintained during the remainder of the daytime. These data suggest that chloroplasts are subject to light stress during and after the midday depression of photosynthesis. The intensity of natural light is excessive for most of the day and this light stress induces chloroplast avoidance response and depression of photosynthesis.

Low sink-induced stomatal closure alters photosynthetic rates of source leaves in beans as dependent on H2O2 and ABA accumulation in guard cells

Low sink demand provided by pod removal and stem girdling of beans (Vicia faba, cv. Daqingshan) (-Sink) induced a significantly lower net photosynthetic rate (Pn), stomatal conductance (gs), internal CO2 concentration (Ci), and transpiration rate (E) compared with pod and root sink retention (CK). This depression in Pn was due to stomatal limitation. Low sink demand of -Sink plants resulted in a higher leaf sucrose content, but a lower sucrose content in guard cells. Moreover, the significant accumulation of H2O2 and ABA were observed in both leaves and guard cells of -Sink plants. The most intensive electron dense deposit of cerium perhydroxides, produced by H2O2 reaction with cerium chloride, was present in the cell walls, especially the dorsal walls of guard cells. Immunogold electron-microscopy localization of ABA showed that ABA was distributed in ventral walls of guard cells and the intercellular space of mesophyll cells of -Sink leaves in contrast to CK plants. Application of exogenous sucrose to isolated bean leaves increased H2O2 and ABA contents. H2O2 and ABA in leaves was likely generated by two independently regulated pathways, each affected by the high sucrose concentration induced by low sink demand. Increased sucrose in leaves in response to low sink demand may have caused the increase of H2O2 and ABA, and their accumulation in mesophyll cells and guard cells was likely the primary cause for stomatal closure under low sink demand.

The alpine homoploid hybrid Pinus densata has greater cold photosynthesis tolerance than its progenitors

The diploid hybrid tree species Pinus densata inhabits high-altitude regions, usually at higher altitudes than its parental species, P. tabulaeformis and P. yunnanensis. Its success in alpine habitat has been hypothetically attributed to enhanced cold tolerance. We tested this hypothesis by subjecting all three species to cold stress for 33 days (12/5°C, day/night) and measuring changes in their photosynthetic function. Significant decreases in net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (E) were observed in all three species in response to cold stress. The depression of Pn was primarily attributable to stomatal closure in P. densata, but to both stomatal and non-stomatal limitations in its progenitors, as the parental species had increased intercellular CO2 concentrations (Ci) under the stress. Significant decreases in chlorophyll fluorescence parameters were also observed in both parental species, but they varied little throughout the experiment in P. densata. Furthermore, the chlorophyll and carotenoid concentrations decreased significantly under the cold stress, while anthocyanin concentrations increased, and the anthocyanin concentration in P. densata was significantly higher than in either parental species at the end of the exposure. Finally, P. densata recovered more quickly than its parental species when the cold treatment ended. These results show that P. densata maintains a high photosynthetic rate and exhibits elevated PSII activity and anthocyanin levels under cold stress. These adaptations suggest that P. densata is more cold-tolerant than its parental species and may have been important for its colonization of high alpine habitats.

Diurnal changes in photosynthetic parameters of Populus tremuloides, modulated by elevated concentrations of CO 2 and/or O 3 and daily climatic variation

The diurnal changes in light-saturated photosynthesis (Pn) under elevated CO 2 and/or O 3 in relation to stomatal conductance ( g s), water potential, intercellular [CO 2], leaf temperature and vapour-pressure difference between leaf and air (VPD L) were studied at the Aspen FACE site. Two aspen ( Populus tremuloides Michx.) clones differing in their sensitivity to ozone were measured. The depression in Pn was found after 10:00 h. The midday decline in Pn corresponded with both decreased g s and decreased Rubisco carboxylation efficiency, Vc max. As a result of increasing VPD L, g s decreased. Elevated [CO 2] resulted in more pronounced midday decline in Pn compared to ambient concentrations. Moreover, this decline was more pronounced under combined treatment compared to elevated CO 2 treatment. The positive impact of CO 2 on Pn was relatively more pronounced in days with environmental stress but relatively less pronounced during midday depression. The negative impact of ozone tended to decrease in both cases.

Photosynthesis and yield responses of ozone-polluted winter wheat to drought

Winter wheat (Triticum aestivum L. cv. Jingdong 8) was exposed to short-term high ozone treatment after anthesis and then was either well irrigated with soil water content (SWC) of 80–85 % (O3+W) or drought treated (SWC 35–40 %, O3+D). Short-term ozone exposure significantly decreased irradiance-saturated net photosynthetic rate (P N) of winter wheat. Under good SWC, P N of the O3-treated plant was similar to that of control on 2 d after O3-exposure (6 DAA), but decreased significantly after 13 DAA, indicating that O3 exposure accelerated leaf senescence. Meanwhile, green flag leaf area was reduced faster than that of control. As a result, grain yield of O3+W was significantly decreased. P N of O3+D was further notably decreased and green flag leaf area was reduced more than that in O3+W. Consequently, substantial yield loss of O3+D was observed compared to that of O3+W. Although P N was significantly positively correlated with stomatal conductance, it also had notable positive correlation with the maximum photochemical efficiency in the dark adapted leaves (Fv/Fm), electron transport rate (ETR), photochemical quenching (qP), as well as content of chlorophyll, suggesting that the depression of P N was mainly caused by non-stomatal limitation. Hence optimal soil water condition should be considered in order to reduce the yield loss caused by O3 pollution.

Effects of Genotypes and Plant Density on Yield, Yield Components and Photosynthesis in Bt Transgenic Cotton

AbstractBt (Bacillus thuringiensis) transgenic cotton (Gossypium hirsutumL.), including the introduced, indigenous Chinese non‐hybrid and hybrid cotton, is spreading very rapidly in China. Agronomic and photosynthetic performance as well as the optimum plant density for planting Bt cotton may vary with genotypes. With three types of commercial Bt cotton varieties, two field experiments were conducted to study yield performance and leaf photosynthetic rate (Pn) during 2000 and 2001, and yield interaction between variety and plant density during 2001 and 2002 in Yellow River region in northern China. The first experiment showed that the indigenous Chinese Bt cotton significantly differed from the introduced Bt cotton (IBtC) in plant growth and yield components. As a result of manipulation of boll numbers, boll weight and lint percentage, there was no significant difference in lint yield between Chinese non‐hybrid Bt cotton (CBtC) and the IBtC, but two Chinese hybrid Bt cotton (HBtC) varieties exhibited significantly higher lint yield than all other varieties in either 2000 or 2001. Hybrid cotton SCRC15 showed a one‐peak curvilinear change in diurnal course of Pn throughout the growing season, while non‐hybrid cotton 33B and SCRC16 exhibited severe mid‐day depression in Pn in squaring, flowering or boll‐setting stage. The second experiment showed that the main effect of plant population on lint yield was not significant, and yield difference among all treatments was derived from varieties and the interaction between plant density and variety. The optimal plant densities in terms of lint yield for the introduced, indigenous CBtC and HBtC genotypes were 6.0, 4.5 and 3.0 plants m−2respectively.

Physiological characteristics of photosynthesis in {\sl Iris lactea} Pall. var. {\sl chinensis} (Fisch.) Koidz grown in salt and alkali soil

The experiment was conducted to determine diurnal changes of net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), water use efficiency (WUE), and environmental factors in Iris lactea Pall. var. chinensis (Fisch.) Koidz grown in salt-alkali soil. The data acquired in this study showed that diurnal changes of Pn and Tr were two-peak-type-curve and were marked by a midday depression of Pn, which could be fully accounted for by Gs changes. Carboxylic efficiency (CE), photosynthetic rate at saturation for intercellular CO_(2) concentration (A_(350)), apparent quantum yield (AQY), and photosynthetic rate at light saturation (Pmax) all decreased at midday. The results indicated that the midday depression could be attributed to the rising leaf temperature caused by increased strong solar radiation (PAR).

Comparison of photosynthetic activity of Orychophragmus violaceus and oil-seed rape

Orychophragmus violaceus, Brassica campestris cv. Chuanyou No.8, and Brassica juncea cv. Luzhousileng diurnal changes of net photosynthetic rate (PN) and activities of carbonic anhydrase (CA) of leaves were studied. One uni-modal curve occurred at the diurnal changes of PN in O. violaceus, but bimodal curves were found in B. campestris and B. juncea. Thus photosynthetic midday depression was not found in O. violaceus but in both Brassica species. Midday depression of PN in O. violaceus was not related to high temperature or low humidity at midday but to the activity of CA.

Comparison of Photosynthetic Traits Between Two Typical Shrubs: Legume and Non-Legume in Hunshandak Sandland

In Huanshandak Sandland, China, net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), water use efficiency (WUE), photochemical efficiency of photosystem 2 (Fv/Fm), and leaf nitrogen content were compared for Hedysarum fruticosum var. mongolicum (H.f.m.), a nitrogen fixing shrub, and Salix gordejevii (S.g.), a nitrogen non-fixing shrub. PN, E, and gs of the two shrubs were similar in trends, i.e. two peaks were observed in diurnal courses. However, except Ci, other parameters of H.f.m. were higher during the measured days than those of S.g. The midday depression of PN was mainly due to decrease in stomata conductance and to reduction of Fv/Fm at midday. The higher PN of H.f.m. was consistent with the higher leaf N content and there was a positive relation between them. In addition, several C4 traits were found in H.f.m., i.e. high saturation irradiance and WUE, low dark respiration rate, and Ci, which partly resulted in higher PN. This seems to indicate that the C3 plant H.f.m. may have C4 photosynthesis pathway or C4 enzymes.

Diurnal Changes in Photosynthesis, Sugars, and Nitrogen of Wheat and Mungbean Grown Under Elevated CO<sub>2</sub> Concentration

The diurnal changes in leaf net photosynthetic rate (PN) and sugar and nitrogen contents in wheat [Triticum aestivum (L.) cv. HD 2285] and mungbean [Vigna radiata (L.) Wilczek cv. PS 16] were analysed under ambient, AC [350±25 µmol mol-1] and elevated, EC [600±50 µmol mol-1] CO2 concentrations. In both mungbean and wheat PN of AC- and EC-grown plants compared at the same CO2 concentration showed that PN was higher under EC. However, increased PN in EC-plants declined in the afternoon and approached PN of AC-plants. Depression in PN, however, was less in mungbean compared with the large depression in wheat. Greater down regulation of PN in wheat was associated with the accumulation of large amount of sugars and low nitrogen content in wheat leaves. Mungbean leaves accumulated mostly starch under EC and the difference in N content in AC- and EC-plants was relatively less than in wheat.

Photosynthetic Acclimation to Elevated CO<sub>2</sub> in Relation to Leaf Saccharide Constituents in Wheat and Sunflower

Wheat (T. durum cvs. HD 4502 and B 449, T. aestivum cvs. Kalyansona and Kundan) and sunflower (Helianthus annuus L. cv. Morden) were grown under atmospheric (360±10 cm3 m-3, AC) and elevated CO2 (650±50 cm3 m-3, EC) concentration in open top chambers for entire period of growth and development till maturity. Leaf net photosynthetic rate (PN) of EC-grown plants of wheat measured at EC was significantly decreased in comparison with AC-plants of wheat measured at EC. Sunflower, however, showed no significant depression in PN in EC-plants. There was a decrease in ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, its activation state and amount in EC-plants of wheat, whereas no significant decrease was observed in sunflower. The above different acclimation to EC in wheat and sunflower was related with saccharide constituents accumulated in the leaves. Under EC, sunflower accumulated in the leaves more starch, whereas wheat accumulated more sugars.

Different Patterns of Gas Exchange and Photochemical Efficiency in Three Desert Shrub Species Under Two Natural Temperatures and Irradiances in Mu Us Sandy Area of China

Field studies of gas exchange and chlorophyll fluorescence of three desert shrub species, Hedysarum fruticosum var. mongolicum, Artemisia ordosia, and Salix pasmmophylla, showed different patterns under different leaf temperature (T1) and incident photosynthetic photon flux density (PPFD). H. fruticosum var. mongolicum and A. ordosia exhibited higher PN and gs than S. pasmmophylla, especially under very high T1 (>46 °C) and high PPFD (>2 100 µmol m-2 s-1) in hot summer. The decreases of PN with the diurnal course were due mainly to stomata closure. However, PN of S. pasmmophylla was seriously depressed by very high temperature from midday to evening as shown by the negative PN in hot summer, whereas none of such depression was found in spring. Maximal spring photochemical efficiency of photosystem 2 (PS2), i.e, Fv/Fm, was the lowest at 16:00, indicating the injury of PS2 by heat at this stage. In hot summer again, all the three shrubs underwent pronounced midday depression of PN and gs, while in spring they showed a one-peak response. And the first peak appeared 2 h earlier in hot summer than in spring for all the three shrubs. It was the high temperature that led to the different patterns of gas exchange and the serious depression of PN in S. pasmmophylla. H. fruticosum var. mongolicum and A. ordosia were much more tolerant to heat and high irradiance than S. pasmmophylla, which fixed most of CO2 at the fast growing stage in spring. Nevertheless, in hot summer it had to survive the severe hot environment through strong respiration and storage of CO2 only in the early morning.

Diurnal changes in needle gas exchange in alpine Pinus pumila during snow‐melting and summer seasons

Pinus pumila (Pallas) Regel. is a dominant dwarf tree in alpine regions of Japan. The possible factors limiting the net photosynthetic rate (Pn) of the needles of P. pumila were examined in the snow‐melting (May) and the summer (August) seasons. In August, in situ maximum Pn was 20 μmol kg−1 needle s−1 in the current‐year needles and 25 μmol kg−1 needle s−1 in the 1‐year‐old needles. Diurnal trends of Pn in August were positively related to fluctuations in photosynthetic photon flux density (PPFD) and no midday depression of Pn was found, indicating that a decrease in PPFD rather than an increase in needle‐to‐air vapor pressure deficit (ΔW) might cause the reduction of Pn. Both stomatal conductance (gs) and Pn were lower in May than in August. In May, Pn and gs were almost zero in the morning, but gradually increased with decreasing ΔW, reaching maximum Pn values (4 μmol kg−1 needle s−1) and gs (60 mmol kg−1 needle s−1) at 16.00 hours. The daytime Pn in May was positively related to gs. Relative water content in the exposed needles above the snow in May was 83%, which was far above the lethal level. This indicates that the water flow from stems or soils to needles was enough to compensate for a small amount of water loss due to the low gs in May, although the water supplied to needles would be impeded by the low temperatures. Thus, the reduced gs in May would be important for avoiding needle desiccation, and would result in a reduced Pn.

Diurnal Changes of Gas Exchange, Chlorophyll Fluorescence, and Stomatal Aperture of Hybrid Poplar Clones Subjected to Midday Light Stress

Diurnal changes in net photosynthetic rate (PN), chlorophyll (Chl) fluorescence, and stomatal aperture of several hybrid poplar clones subjected to midday light stress were measured in July and August of 1996. Midday depression of PN, photosystem 2 (PS2) efficiency, stomatal conductance (gs), and stomatal aperture was observed in all clones, though at differing rates among them. Non-uniform stomatal closure occurred at noon and at other times, requiring a modification of intercellular CO2 concentration (C1). A linear relationship was found between gs and stomatal aperture. More than half of the photons absorbed by PS2 centre dissipated thermally when subjected to light stress at noon. There was a linear relationship between the rate of PS2 photochemical electron transport (PxPFD) and PN. There was a consensus for two fluorescence indicators (1 - qP/qN and (Fm' - F)/Fm') in assessment of susceptibility of photoinhibition in the clones. According to PN, Chl fluorescence, and stomatal aperture, we conclude that midday depression of photosynthesis can be attributed to both stomatal and non-stomatal limitations.

Diurnal and Seasonal Changes in Prunus Amygdalus Gas Exchanges

Diurnal courses in net photosynthetic rate (PN), stomatal conductance (gs), leaf water potential (ψ), internal CO2 concentration (ci), and water use efficiency (WUE) were studied as season progressed, in relation to environmental factors in field grown Prunus amygdalus. In sun leaves PN reached maximum between 09:00 to 11:00 h and subsequently declined when high temperature and low humidity occurred. An increase was observed late in the afternoon. A decrease in gs and ψ was found as season progressed in both years of measurements. In periods of high evaporative demand, ψ was very low, however, it did not explain the reductions of PN in all the three periods (spring, early and late summer). Midday depression of PN and gs seemed to be related with leaf temperature (Tl) and high irradiance. Increase in ci and F0 and decrease in Fv/Fm found between 12:00 and 14:00 h corresponded to the decrease in PN. Therefore, a transient modification of photosynthetic machinery might be considered. WUE was negatively correlated with vapour pressure difference of leaf to air, that decreased during the day. The September values, higher than in the previous months, were due to the lower seasonal decreases in PN than in gs.

Photosynthesis in different types of transgenic tobacco plants with elevated cytokinin content

Photosynthetic parameters were compared in three types of transgenic tobacco plants: ipt-transgenic plants with slightly elevated endogenous cytokinin (CK) content, Pssu-ipt-transgenic plants with markedly increased CK content, and zmp-transgenic plants with slightly elevated CK content accompanied by elevated auxin content. Slightly increased CK content promoted net photosynthetic rate (PN) in both ipt- and zmp-transgenic plants, and chlorophyll (Chl) and carotenoid contents in zmp-transgenic plants. Morphology, growth characteristics, stomatal conductance, and parameters of Chl a fluorescence kinetics were similar in control and transgenic plants with slightly higher CK content. No significant effect of increased level of endogenous auxin (indole-3-acetic acid) on development of zmp-transgenic plants and measured parameters was found. Pssu-ipt-transgenic plants with highly increased CK content revealed suppressed root development, wilting of plants, and depression of PN and stomatal conductance; however, Chl content was slightly increased and parameters of Chl a fluorescence kinetics did not indicate damage to photosynthetic apparatus.

Midday depression in photosynthesis: Effect on sucrose-phosphate synthase and ribulose-1,5-bisphosphate carboxylase in leaves of Prosopis juliflora (Swartz) DC

The midday depression in net photosynthetic rate (PN) and stomatal conductance (gs) in Prosopis juliflora was studied in relation to two key enzymes of carbon metabolism. Diurnal gas exchange measurements carried out in autumn on P. juliflora showed a pronounced depression in PN and gs along with a decrease in apparent carboxylation efficiency (CE*) during midday. The activities of sucrose-phosphate synthase (SPS) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) also showed large diurnal fluctuations. Initial RuBPCO activity (that present in vivo) and total activity (fully carbamylated activity) increased gradually with increase in irradiance, in the morning reaching a maximum by 08:00 h. The RuBPCO activity declined sharply during midday due to decrease in initial activity. The drop in the % activation of RuBPCO indicated that the deactivation of RuBPCO was achieved via a decarbamylation mechanism. There was a marked similarity in the diurnal patterns of SPS activity and the PN. During a diurnal rhythm, SPS activity increased after irradiation, reaching a maximum at 08:00 h and then declined during midday. Diurnal fluctuations in SPS activity could be due to the changes in the amount of protein (changes in Vmax) as well as to the changes in kinetic properties (changes in Vlim). Hence the midday decline in photosynthesis is closely associated with the regulation of RuBPCO and SPS activities.

Photosynthetic responses of greenhouse tomato plants to high solution electrical conductivity and low soil water content

SUMMARYGreenhouse tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in a peal-moss based substrate and supplied with nutrient solutions of high (4.5 mS cm-1) or low (2.3 mS cm-1) electrical conductivity (EC) and under high (95 ± 5%) or low (55 ± 8% of capillary capacity) soil water content, to elucidate how EC and soil water status affect plant photosynthesis and related physiological processes. Two weeks after beginning the treatments, photosynthesis (Pn) was measured during changes of photo-synthetic photon flux (PPF) from 0 to 1200 u.mol m-2 s-1 using a gas exchange method. The rectangular hyperbolic model (Pn = Pmax KI (1-KI)-2 -r) provided a good fit for the photosynthetic light-response curve. High EC treatment changed the curve by increasing the initial slope (quantum yield) and decreasing photosynthetic capacity at high PPF. However, soil water deficit not only decreased the photosynthetic capacity, but also decreased quantum use efficiency. Depression of Pn was attributed to de...

ナシ赤星病り病葉の光合成•呼吸特性

Net photosynthesis (Pn) and dark respiration (Rd) were determined on detached leaves of pear (Pyrus serotina, cvs. Suishu, Chojuro, Doitsu, Nijisseiki, Pyrus communis cv. Bartlett and Pyrus betulaefolia) infected by Japanese pear rust (Gymnosporangium asiaticum MIYABE et YAMADA).In the resistant cultivar (Bartlett), very few symptoms in leaves occurred. Pn and Rd were unaffected by infection. However, in susceptible cultivars (Suishu, Chojuro, Doitu) and P. betulaefolia, depression in Pn and stimulation of Rd accompanying an increase in size of lesions on leaves occurred.In Japanese pear cv. Nijisseiki, no significant differences were found either in Pn and Rd rate or in degree of infection by shading treatment.