Volatile Metabolites and External CO2Exchange of Wheat Cenoses under Optimal Conditions and Thermal Stress

The effects of elevated temperature (35 and 45°C) on photosynthesis, respiration, and both the qualitative and quantitative compositions of volatile emissions (VE) of wheat (Triticum aestuvumL. cultivar 232) cenoses at light intensities of 70, 150, or 240 W/m²of photosynthetically available radiation (PAR) were studied. At a PAR of 240 W/m², the thermal stabilities of photosynthesis and respiration increased at 35°C and decreased at 45°C. Elevated temperatures nonuniformly changed the rates and direction of VE syntheses. In this process, the highest increase in VE evolution was observed at 70 W/m²and 35°C; the lowest, at 240 W/m². In addition, the concentrations and composition of VE during the repair period differed from the initial values.     

Heat-Induced Increase in the Tolerance of the Wheat Photosynthetic Apparatus to Combined Action of High Temperature and Visible Light: CO2 Fixation,Photosynthetic Pigments,and Chloroplast Ultrastructure

Heating of the leaves of 15-day-old wheat (Triticum aestivum L.) plants at 42°C in the light (370 W/m² PAR) suppressed their ability to fix CO₂ twice stronger than heating in darkness. Heat hardening (3 h at 38–39°C) improved the tolerance of photosynthesis to combined action of high light and temperature but did not affect the tolerance to photoinhibition at 30°C. Hardening did not induce changes in the levels of photosynthetic pigments and their ratios. De-epoxidation of violaxanthin turned out to be more tolerant to photoinhibition at 42°C than CO₂ fixation. Protective effect of hardening was not related to the accumulation of zeaxanthin and activation of the xanthophyll cycle. Hardening protected the most sensitive population of chloroplasts against heat-induced photodamage and simultaneously increased the number and length of thylakoids. An increase in the volume of the thylakoid system was also induced by heating at 42°C and exposure to high light at 30°C. The formation of additional thylakoids and grana of shade type was not associated with improved tolerance of photosynthesis to heat and light stresses.     

Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280–320 nm; 60 μmol m⁻² s⁻¹) exposure alone and in combination with photosynthetically active radiation (PAR; 400–800 nm; 200 μmol m⁻² s⁻¹) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O₂ evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples.     

Effects of weather during leaf development on photosynthetic characteristics of soybean leaves

Net photosynthetic rates and mesophyll conductances at 25 °C at light saturation and air levels of carbon dioxide and oxygen were measured on recently fully expanded leaflets of second trifoliolate leaves of soybeans (Glycine max cv. Kent). Plants were grown outdoors in pots at Beltsville, Maryland with 14 planting times from May through August, 1983. Air temperature and humidity, and photosynthetically active radiation (PAR) were measured for the expansion periods of the second trifoliolate leaves. Rates of net photosynthesis ranged from 24 to 33 mol m^–2 s^–1, and mesophyll conductances from 0.24 to 0.35 cm s^–1 for the different planting dates. Mean 24-h air temperatures ranged from 20.6 to 29.0 °C, and mean daily PAR ranged from 29.4 to 58.4 mol m^–2 d^–1 for the leaf expansion periods. There was a positive relationship between photosynthetic characteristics and PAR during leaf expansion, and a negative relationship between photosynthetic characteristics and leaf expansion rates, with 96% of the variation in photosynthetic characteristics accounted for by these two variables. Leaf expansion rates were highly correlated with air temperature.     

Structural and Functional Characteristics of Ajuga reptansPhotosynthesis under Cold Climate Conditions

Structural, functional, and biochemical characteristics of the photosynthetic apparatus of a nemoral herbaceous perennial plant Ajuga reptansL. inhabiting the middle taiga subzone were investigated. Plant leaves were characterized by a high content of green (3.1 mg/dm²) and yellow (0.64 mg/dm²) pigments and contained moderate-sized chloroplasts with grana consisting of ten thylakoids or more. The maximum rate of photosynthesis in summergreen leaves (5–8 mg CO₂/(dm²h)) was observed at 14–16°C under a saturating photosynthetically active radiation of 50 W/m². At 6–7°C, the rate of CO₂assimilation was reduced to 60–80% of the maximum one. The temperature optimum of photosynthesis was not constant and shifted by 2–6°C depending on the changes in the ambient temperature. Wintergreen leaves were capable of photosynthesis in late autumn after heavy freezes and in early spring after a long winter. The accumulation of soluble carbohydrates and free amino acids in leaves helps to maintain the functional activity of the photosynthetic apparatus.     

Leaf photosynthetic characteristics of seedlings of actinorhizal Alnus spp. and Elaeagnus spp.

Single leaf photosynthetic characteristics of Alnus glutinosa, A. incana, A. rubra, Elaeagnus angustifolia, and E. umbellata seedlings conditioned to ambient sunlight in a glasshouse were assessed. Light saturation occurred between 930 and 1400 mol m^-2s^-1 PAR for all species. Maximum rates of net photosynthesis (Pn) measured at 25°C ranged from 12.8 to 17.3 mol CO₂m^-2s^-1 and rates of dark respiration ranged from 0.74 to 0.95 mol CO₂m^-2s^-1. These values of leaf photosynthetic variables are typical of early to midsuccessional species. The rate of Pn measured at optimal temperature (20°C) and 530mol m^-2s^-1 PAR was significantly (p<0.01) correlated with leaf nitrogen concentration (r=0.69) and negatively correlated with the mean area of a leaf (r=–0.64). We suggest that the high leaf nitrogen concentration and rate of Pn observed for Elaeagnus umbellata and to a lesser degree for E. angustifolia are genetic adaptations related to their crown architecture.Abbreviations Pn net photosynthesis     

Net photosynthetic response patterns of the basidiomycete lichen Cora pavonia (Web.) E. Fries from the tropical volcano La Soufrière (Guadeloupe)

Summary The response of net photosynthesis to temperature, moisture, and light was examined in thalli of the tropical basidiomycete lichen Cora pavonia from recent lahar flows on the volcanic summit La Soufrière (Guadeloupe, French West Indies). Although thalli of C. pavonia are typically exposed to only low light intensities and isothermal temperature conditions under prevailing cloud/shroud conditions on La Soufrière, their photosynthetic response matrix reveals an unexpected breadth of response. The temperature optimum of net photosynthetic uptake in C. pavonia rises from 6°C at a photon flux area density of 25 mol m^–2 s^–1 PAR to 27°C at 1000 mol m^–2 s^–1 PAR, with rates of maximal net photosynthetic uptake exceeding 25 mg CO₂ g^–1 h^–1. Net photosynthesis was optimal at thallus moisture contents of 250 to 350 percent water content by weight, declining only slightly in fully saturated thalli. These response patterns pose an apparent paradox, as on most days they will act to severely restrict net photosynthetic uptake by thalli of C. pavonia on La Soufrière. This paradox is discussed in context of those selective pressures faced by lichen thalli in later successional stages as well as those imposed by brief periods of atypical weather conditions.     

Influence of excitation light intensity and leaf age on the slow chlorophyll fluorescence transient in radish

The temporal characteristics of the slow phase of chlorophyll fluorescence induction-T _0.5 (half-decay time) and t _min (an integral-based index of the variable emission rate)-as well as the popular amplitude index F _P/F _S were determined at different excitation light intensities (I _ex [400?C500 nm] of 20?C80 W/m²) in dark-adapted leaves of different age (3?C24 days) taken from radish plants grown under continuous light of 100 W/m² PAR. All the profiles thus obtained were mutually consistent, and the age-related variations were minimized at I _ex > 40 W/m²; at that the age-averaged temporal indices proved to be more light-responsive than the standard amplitude ratio.     

The effect of different night conditions on the CO2 fixation in a lichen Xanthoria parietina

CO₂ fixation was studied in a lichen, Xanthoria parietina, kept in continuous light, and with cyclic changes in light intensity, dark period or temperature. The diurnal and seasonal courses of CO₂ exchange were followed. The rate of net photosynthesis was observed to fall from morning to evening, and this decline was more pronounced in winter than in summer. The maximal net photosynthetic rate, 223 ng CO₂g^-1dws^-1, occured in winter and the minimum, 94 ng CO₂g^-1dws^-1, late in spring. The light compensation point in summer was four times as high as in winter. In continuous light (180 or 90 mol photons m^-2s^-1, 15°C) net photosynthesis decreased noticeably during one week, falling below the level maintained in a 12 h light: 12 h dark cycle. Photosynthetic activity did not decrease, however, in lichens held in continuous light (90 mol photons m^-2s^-1) with cyclic changes of temperature (12 h 20 °C: 12 h 5 °C). Active photosynthesis was also maintained in light of cyclically changing intensity (12 h: 12 h, 15 °C) when night-time light was at least 75% lower than illumination by day. A dark period of 4 hours in a 24-h light:dark cycle was sufficient to keep CO₂ fixation at the control level. It seems that plants need an unproductive period during the day to survive and this can be induced by fluctuations in light and/or temperature.     

Strong light elevates thermotolerance of photosynthetic apparatus and the content of membranes and polar lipids in wheat leaves

The influence of excess irradiance on resistance of wheat (Triticum aestivum L.) photosynthetic apparatus to heating in darkness and in the light was investigated and compared with changes in leaf cell ultra-structure and composition of cell lipids and fatty acids. The leaves of 14- to 16-day-old plants grown at low irradiance (about 20 W/m²) were exposed for 1 h to irradiance of 370 or 600 W/m² PAR. Using infrared gas analysis, we found that the preexposure of leaves to excess irradiation elevated resistance of apparent photosynthesis to 10-min heat treatment at 40–45°C. The rate of Hill reaction (reduction of 2,6-dichlorophenolindophenol by isolated chloroplasts) was higher for leaves heated at high irradiance than for leaves heated in darkness. During illumination of leaves with strong light, mesophyll cells became more abundant in mitochondria and peroxysomes, as well as in cisternae of endoplasmic reticulum and Golgi complex. The chloroplast thylakoids and grana became more extensive and numerous. At the same time, the leaf content of main classes of membrane glycerolipids increased in parallel with the increase in the phospholipid/glycolipid and lipid/chlorophyll ratios. The unsaturation index of fatty acids of membrane lipids increased because of the elevated content of linolenic acid. Thus, excessive light (not fully utilized in photosynthesis) induced in wheat leaves a series of nonspecific adaptive changes that were similar to those occurring under the action of other environmental factors, such as heat shock, cooling, salinity, and osmotic stresses.     

Effect of Temperature and Illumination on Growth and Reproduction of the Green Alga Ulva fenestrata

The combined effect of temperature (5, 10, 15, and 20°C) and illumination (40 and 60 mE/(m² s)) on growth and reproduction of the green marine alga Ulva fenestrata P. et R. from the sublittoral zone of Amursky Bay, Sea of Japan, was studied in the laboratory environment in the months April–July, 2000. It was demonstrated that the temperature of 5°C and illumination of 40 mE/(m² s) are the most favorable for maintaining the vegetative mass of the algae. A water temperature of 10°C and illumination of 40 mE/(m² s) are the optimum conditions for vegetative growth of U. fenestrata thalli. A temperature decrease and increase by 5°C reduces the growth rate on average by 30%. Sporo- and gametogenesis in U. fenestrata are the most regular (every 10 days) and occupy the greatest disk area at a water temperature of 15°C and illumination of 40 mE/(m² s). Vegetative growth of thalli is sharply inhibited at the stage of cell preparation to gametogenesis a day before the beginning of gamete formation.     

Temperature and irradiance and the total daily photosynthetic production of the crown of a Pinus radiata tree

Summary Carbon dioxide exchange rates were recorded for different ages and positions of foliage and parts of the main stem of a 7-m tall Pinus radiata D. Don tree growing in a large, artificially lit, controlled-environment room. Irradiance levels were varied from dark to approximately full sunlight, and air temperatures from 10° to 35°C in 5°C steps. Leaf temperatures within the cuvettes used for CO₂ exchange measurements, however, were up to 5°C higher than the room air temperature set but this varied with position in the tree crown, the shaded lower crown being at approximately room temperature. A balance sheet was prepared to show the photosynthetic gains and respiratory losses of different parts of the crown over 24 h at each air temperature and at irradiances of 400, 270, and 135 W m^-2 during the 8-h photosynthetic period. The greatest daily photosynthetic gain was at 10° C, although this temperature is considered sub-optimal for growth. At temperatures greater than 25° C, even at the greatest irradiance level for 8 h, total respiration was greater than photosynthesis.     

Radish plant behaviour under short-term elevated ozone fumigation

Effects of short-term ozone (O₃) fumigation on radish (Raphanus sativus L.) plants were examined in growth chambers under controlled environment conditions. Plants were exposed to 0 μg/m³ (reference), 80 μg/m³, 160 μg/m³ and 240 μg/m³ O₃ concentrations for 7 h per day for five days. Day/night temperature was 21°C/14°C and photoperiod 16 h. Chlorophyll content was evaluated spectrophotometrically. Chromatographic analysis of saccharides was also undertaken. The results showed that elevated O₃ inhibited the growth of radish rhizocarps, net assimilation rate and biomass accumulation. O₃ induced leaf desiccation, necrosis and premature senescence, but a typical reaction of plants to O₃ stress was the rapid regeneration of new leaves. O₃ inhibited accumulation of carotenoids more than chlorophylls. The higher photosynthetic pigment content in newly generated radish leaves may be regarded as an adaptation of the photosynthetic system to O₃. Leaf saccharide metabolism and incorporation depended on O₃ concentration. Rapid regeneration of new leaves and increased content of photosynthetic pigments is the typical reaction of radish plants to O₃ stress.     

The kinetics of P515 in relation to the lipid composition of the thylakoid membrane

Flash-induced P515 absorbance changes have been studied in dark-adapted chloroplasts isolated from spinach plants grown under two different light intensities. The slow component (reaction 2), normally present in the P515 response of chloroplasts isolated from plants grown at an intensity of 60 W · m^–2, was largely reduced in chloroplasts isolated from plants grown at an intensity of 6 W · m^–2. This reduction of the slow component in the P515 response appeared to be coincident with an alteration in the lipid composition of the thylakoid membrane. Mainly the ratio monogalactosyldiacylglycerol to digalactosyldiacylglycerol appeared to be altered. In thylakoids from plants grown at 6 W · m^–2, the ratio was approximately 35% lower than that of plants grown at 60 W · m^–2. The amount of both cytochromeb ₅₆₃ and cytochromef was largely reduced in chloroplasts isolated from plants grown at low light intensity. These results may indicate a possible correlation between structural organization of the thylakoid membrane and the kinetics of the flash-induced P515 response.     

CO2 environment,microclimate and photosynthetic characteristics of the moss Hylocomium splendens in a subarctic habitat

Summary In order to document the natural CO₂ environment of the moss Hylocomium splendens, and ascertain whether or not the moss was adapted to this, and its interactions with other microenvironmental factors, two studies were carried out. Firstly, the seasonal variations of CO₂ concentration, photosynthetically active radiation (PAR), tissue water content and temperature were measured in the natural microenvironment of H. splendens in a subarctic forest during the summer period (July–September). Secondly, the photosynthetic responses of the species to controlled CO₂ concentrations, PAR, temperature, and hydration were measured in the laboratory. CO₂ concentrations around the upper parts of the plant, when PAR was above the compensation point (30 mol m^–2 s^–1), were mostly between 400 and 450 ppm. They occasionally increased up to 1143 ppm for short periods. PAR flux densities below saturating light levels for photosynthesis (100 mol m^–2 s^–1), occurred during 65% (July), 76% (August) and 96% (September) of the hours of the summer period. The temperature optimum of photosynthesis was 20° C: this temperature coincided with PAR above the compensation point during 5%, 6% and 0% of the time in July, August and September, respectively. Optimal hydration of tissues was infrequent. Hence PAR, temperature and water limit CO₂ uptake for most of the growing season. Our data suggest that the higher than normal ambient CO₂ concentration in the immediate environment of the plant counteracts some of the limitations in PAR supply that it experiences in its habitat. This species already experiences concentrations of atmospheric CO₂ predicted to occur over the next 50 years.     

Recovery of photosynthetic reactions after high-temperature treatments of a heat-tolerant cactus

Inhibition and recovery of net CO₂ uptake and three photosynthetic electron transport reactions as well as plant survival following high-temperature treatments were investigated for Opuntia ficus-indica. For plants maintained at 30°C/20°C day/night air temperatures, treatment at 60°C for 1 h irreversibly inhibited net CO₂ uptake and photosynthetic electron transport, resulting in plant death in about 60 days. When a plant maintained at 30°C/20°C was treated at 55°C for 1 h, net CO₂ uptake was completely inhibited 1 d after the treatment but fully recovered in 60 d. Differential inactivation of photosystem (PS) I, PSII, and whole chain electron transport activities occurred; PSI was the most tolerant of 55°C and took the least time (45 d) for total recovery. All 30°C/20°C plants survived a 1-h treatment at 55°C, although some pale green areas were observed on the cladode surfaces. In contrast to growing at 30°C/20°C, plants acclimated to 45°C/35°C survived 60°C for 1 h without showing any necrotic or pale green areas on the cladode surfaces. When such a plant was transferred to 30°C/20°C following the high-temperature treatment, recovery in net CO₂ uptake began in 1 d and progressed to complete recovery by 30 d. Growth temperatures thus influence the possibility for recovery of photosynthetic reactions and ultimately the survival of O. ficus-indica following a high-temperature exposure.Abbreviations DCPIP 2,6-dichlorophenol indophenol - MV methyl viologen - PAR photosynthetically active radiation - PSI or PSII photosystem I or II - WC whole chain     

Pseudocyphellaria dissimilis: a desiccation-sensitive,highly shade-adapted lichen from New Zealand

Summary Pseudocyphellaria dissimilis, a foliose, cyanobacterial lichen, is shown not to fit into the normal ecological concept of lichens. This species is both extremely shade-tolerant and also more intolerant to drying than aquatic lichens previously thought to be the most desiccation-sensitive of lichens. Samples of P. dissimilis from a humid rain-forest site in New Zealand were transported in a moist state to Germany. Photosynthesis response curves were generated. The effect of desiccation was measured by comparing CO₂ exchange before and after a standard 20-h drying routine. Lichen thalli could be equilibrated at 15° C to relative humidities (RH) from 5% to almost 100%. Photosynthesis was saturated at a photosynthetically active radiation (PAR) level of 20 mol m^-2 s^-1 (350 bar CO₂) and PAR compensation was a very low 1 mol m^-2 s^-1. Photosynthesis did not saturate until 1500 bar CO₂. Net photosynthesis was relatively unaffected by temperature between 10° C and 30° C with upper compensation at over 40° C. Temporary depression of photosynthesis occurred after a drying period of 20 h with equilibration at 45–65% relative humidity (RH). Sustained damage occurred at 15–25% RH and many samples died after equilibration at 5–16% RH. Microclimate studies of the lichen habitat below the evergreen, broadleaf forest canopy revealed consistently low PAR (normally below 10–20 mol m^-2 s^-1) and high humidities (over 80% RH even during the day time). The species shows many features of an extremely deep shade-adapted plant including low PAR saturation and compensation, low photosynthetic and respiratory rates and low dry weight per unit area.     

Effect of salinity on photosynthetic activity of Nodularia spumigena

The aim of the study was to determine the influence of total dissolvedsolids/salinity (mg L^-1 TDS) on photosynthetic activity of Nodularia spumigena strain 001E isolated from Lake Alexandrina, SouthAustralia, using photosynthesis-irradiance (PI) curves. N. spumigena001E cultures were grown in ASM medium at a range of TDSconcentrations (360, 6,600, 13,200, 19,800, 26,400 mg L^-1)at an irradiance of 30 mol m^-2 s^-1 (PAR, 400–700 nm) at 25 °C. The PI relationship was determined at 25 °Cfor irradiances between 0 and 500 mol photon m^-2s^-1 (PAR). The initial slope of PI curve, , a function of lightharvesting efficiency and photosynthetic energy conversion, decreasedproportionally with an increase in salinity from 360 to 26,400 mgL^-1 TDS. The maximum rate of photosynthesis (P_max),occurred at 6,600 mg L^-1 TDS. No influence of salinity onI_k, the irradiance at which P_max was measured, or on R_d, the dark respiration rate, was identified.     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

Effects of temperature and CO2 enrichment on kinetic properties of NADP+-malate dehydrogenase in two ecotypes of Barnyard grass (Echinochloa crus-galli (L.) Beauv.) from contrasting climates

Summary The apparent energy of activation (E _a), Michaelis-Menten constant (K _mfor oxaloacetate), V _max/K _mratios and specific activities of NADP⁺-malate dehydrogenase (NADP⁺-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Québec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22°C, 21/15°C, and grown under two CO₂ concentrations, 350 l l^-1 and 675 l l^-1. E _avalues of NADP⁺-MDH extracted from QUE plants were significantly lower than those of MISS plants. K _mvalues and V _max/K _mratios of the enzyme from both ecotypes were similar over the range of 10–30°C but reduced V _max/K _mratios were found for the enzyme of QUE plants at 30 and 40°C assays. MISS plants had higher enzyme activities when measured on a chlorophyll basis but this trend was reversed when activities were expressed per fresh weight leaf or per leaf surface area. Activities were significantly higher in plants of both populations acclimated to 22/28°C. CO₂ enrichment did not modify appreciably the catalytic properties of NADP⁺-MDH and did not have a compensatory effect upon catalysis or enzyme activity under cool acclimatory conditions. NADP⁺-MDH activities were always in excess of the amount required to support observed rates of CO₂ assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold temperature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP⁺-malate dehydrogenase among these ecotypes.