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The effect of water shortage on growth and gas exchange of maize grown on sandy soil (SS) and clay soil was studied. The lower soil water content in the SS during vegetative growth stages did not affect plant height, above-ground biomass, and leaf area index (LAI). LAI reduction was observed on the SS during the reproductive stage due to early leaf senescence. Canopy and leaf gas exchanges, measured by eddy correlation technique and by a portable photosynthetic system, respectively, were affected by water stress and a greater reduction in net photosynthetic rate (A N) and stomatal conductance (g s) was observed on SS. Chlorophyll and carotenoids content was not affected by water shortage in either condition. Results support two main conclusions: (1) leaf photosynthetic capacity was unaffected by water stress, and (2) maize effectively endured water shortage during the vegetative growth stage. © 2008 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.

Photosynthesis and photoprotective mechanisms were investigated in the field on Laurus nobilis L. and Quercus ilex L. leaves exposed to summer drought (July) and winter cold (February) conditions compared with no-stress conditions (May). In July, net photosynthetic rate (A) and stomatal conductance (g s) decreased significantly compared with May in both species; conversely the highest ETR/A ratio and no difference in non-photochemical quenching (NPQ) was observed. In February A, g s and ETR/A declined compared with May but the highest NPQ were found in both species. Our data suggest that during summer, an increase of photochemical alternative pathways to carbon reduction, were able to effectively protect the photosynthetic apparatus under drought. In winter, the thermal dissipation of excess absorbed light constitutes the main safety valve for the photosynthetic apparatus.

This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 μmol(CO2) mol−1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m−2 s−1 (control light) or 1,900 μmol m−2 s−1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (P N) and a rise in the ratio of intercellular to ambient CO2 concentration (C i/C a) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (ΦPSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in P N, C i/C a, ΦPSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE.

Gas exchange and chlorophyll a fluorescence measurements were performed simultaneously on leaves of Phillyrea angustifolia L. to assess the effects of heat stress (30 min at 40 °C) on photosynthesis and photosystem II (PSII) photochemical efficiency of plants grown at ambient CO2 and exposed to an elevated CO2 concentration (800 µmol·mol–1) and 300 µmol photons·m–2·s–1. No significant difference was found in the heat-induced decreases of net photosynthesis (PN), quantum yield of PSII electron transport (ΦPSII), and maximum PSII photochemical efficiency (Fv/Fm) between plants exposed to ambient and elevated CO2 concentrations, showing that elevated CO2 was not able to reduce the potential for photoinhibition at high temperatures under moderate light conditions. The heat-induced decrease of PN was higher than that of ΦPSII indicating that reductive power was more utilized in non-assimilatory processes than in CO2 fixation at both CO2 treatments. This result suggested that impairment of the Calvin cycle rather than electron transport inhibition was the main cause of the limitation in CO2 fixation.

Quercus ilex plants grown on two different substrates, sand soil (C) and compost (CG), were exposed to photosynthetic photon flux densities (PPFD) at 390 and 800 µmol(CO2) mol−1 (C390 and C800). At C800 both C and CG plants showed a significant increase of net photosynthetic rate (P N) and electron transport rate (ETR) in response to PPFD increase as compared to C390. In addition, at C800 lower non-photochemical quenching (NPQ) values were observed. The differences between C390 and C800 were related to PPFD. The higher P N and ETR and the lower dissipative processes found in CG plants at both CO2 concentrations as compared to C plants suggest that substrate influences significantly photosynthetic response of Q. ilex plants. Moreover, short-term exposures at elevated CO2 decreased nitrate photo-assimilation in leaves independently from substrate of growth.

This research aimed to investigate the physiological strategies that allow Phillyrea angustifolia, a sclerophyllous shrub widespread in the Mediterranean maquis, to cope successfully with the most stressful conditions of the Mediterranean climate i.e. summer drought and winter cold. Gas exchange and chlorophyll a fluorescence measurements as well as pigment content determinations were performed periodically throughout one whole year (spring 2004–spring 2005) on plants growing outdoor in the Botanical Garden of the Naples University. In June and July 2004 and in February 2005 the light-saturated net photosynthetic rate (P N) and stomatal conductance (gH2O) were lower compared to May and October 2004. Carboxylation rate (v c) was negatively affected by summer drought and low temperature. The quantum yield (¦PSII) and maximum photochemical efficiency of PSII (F v/F m) significantly declined in February. All monitored parameters increased after each stressful period. The highest carotenoid content was detected in July whereas total pigment content was lower both in July and in February as compared to May and October, respectively. The photosynthetic apparatus of P. angustifolia is able to cope with summer drought and winter cold by different strategies: in summer, efficient stomatal control reduces water loss whereas in winter, PSII efficiency is down-regulated to avoid irreversible damage.

The scenarios for the long-term habitation of space platforms and planetary stations involve plants as fundamental part of Bioregenerative Life Support Systems (BLSS) to support the crew needs. Several constraints may limit plant growth in space: among them ionizing radiation is recognized to severely affect plant cell at morphological, physiological and biochemical level. In this work, plants of Phaseolus vulgaris L. were subjected to four different doses of X-rays (0.3, 10, 50 and 100 Gy) in order to assess the effects of ionizing radiation on this species and to analyze possible mechanisms carried out to overcome the radiation injuries. The effects of X-rays on plant growth were assessed by measuring stem elongation, number of internodes and leaf dry weight. The integrity of photosynthetic apparatus was evaluated by photosynthetic pigment composition and ribulose 1,5-bisphosphate carboxylase (Rubisco) activity, whereas changes in total antioxidant pool and glutathione S transferase activity (GST) were utilized as markers of oxidative stress. The distribution of phenolic compounds in leaf tissues as natural shielding against radiation was also determined. Irradiation of plants at 0.3 and 10 Gy did not determine differences in all considered parameters as compared to control. On the contrary, at 50 and 100 Gy a reduction of plant growth and a decrease in photosynthetic pigment content, as well as an increase in phenolic compounds and a decrease in total antioxidant content and GST activity were found. Only a slight reduction of Rubisco activity in leaves irradiated at 50 and 100 Gy was found. The overall results indicate P. vulgaris as a species with a good potential to face ionizing radiation and suggest its suitability for utilization in BLSSs.

A mixture of ryegrass (Lolium italicum A. Braun) and clover (Trifolium alexandrinum L.) was sown in Eboli (Salerno, Southern Italy) in September 2007. Crop growth, leaf and canopy gas exchange and ecophysiological traits were monitored throughout the growth cycle. The gross primary production (GPP) was not affected by air temperature (Tair); on the contrary the ecosystem respiration (Reco) decreased as Tair decreased while net ecosystem CO2 exchange (NEE) increased. When was normalized with leaf area index (LAI), GPP decreased with Tair, a likely response to cold that down-regulated canopy photosynthesis in order to optimize the light use at low winter temperatures. Net photosynthetic rates (PN), the effective quantum yield of PSII (?PSII) and photosynthetic pigment content were higher in clover than ryegrass, in relation to the higher leaf N content. The lower ?PSII in ryegrass was linked to lower photochemical quenching coefficient (qP) values, due to a reduced number of reaction centres, in agreement with the lowest Chl a content. This behaviour can be considered as an adaptive strategy to cold to avoid photooxidative damage at low temperature rather than an impairment of PSII complexes.

Winter cold and high irradiance represent natural constraints in Mediterranean-type ecosystems that may limit plant growth and productivity, resulting often in photoinhibition of photosynthetic apparatus. However, evergreen species of Mediterranean maquis are able to adapt successfully to low temperatures adopting both physiological strategies and anatomical modifications. The aim of this study was to investigate in Cistus incanus L. subsp. incanus, a shrub widely diffused in Mediterranean maquis of Southern Italy, the role of photochemical and non-photochemical strategies in reducing the excess of light energy to reaction centres, as well as the leaf structural modifications related to cold acclimation. To this purpose, chlorophyll a fluorescence measurements were conducted on fully expanded leaves at midday, under saturating light intensity, on plants grown indoor at 20-25°C and outdoor during the winter. Anatomical and cytological features of leaves were also determined on both plant groups through light and fluorescence microscopy. Data obtained showed that leaf photochemical behaviour and structure change significantly in response to different growth temperatures: in outdoor plants we observed a significant decrease of electron transport rate (ETR), photochemical quenching (qP), photochemical efficiency of open PSII reaction centres (Fv'/Fm') and an increase of non-photochemical quenching (qN) and total chlorophyll and carotenoids content, accompanied by changes in tissue density. Conversely indoor plants exhibited a better capacity in photochemistry. However, the decrease of photochemical processes under cold did not lead to photodamage risks in outdoor plants, because no difference in maximal photochemical efficiency (Fv/Fm) was detected as compared to indoor plants. The overall analysis of data suggests that in outdoor plants the photoprotection at low winter temperatures is obtained by means of a combination of thermal dissipation processes and alteration of leaf structural characteristics.

Summary The effects of high irradiance (700 and 1400 μmol photons m −2 s −1 ) on the regulation of photochemistry in leaves and stems of the CAM plant Cissus quinquangularis Chiov. were investigated by chlorophyll a fluorescence parameters. Significant decreases in F o , F m and F v were observed in the leaf and in the stem tissues with increasing light intensity and exposure time. F v /F m , the PS II photochemical efficiency, decreased at an higher extent in stems and leaves at 1400 μmol photons m −2 s −1 . Non-photochemical quenching increased with the intensity and duration of light exposure, being higher in leaves than in stems. Upon high-light stress, a slighter reduction in quantum yield of the PS II electron transport was observed in the stem than in the leaf tissue. A significant decrease of photochemical quenching was observed in leaves but not in stems, thus suggesting a different strategy in the regulation of photochemistry in leaves and stems of C. quinquangularis plants exposed to high-light stress.

In plants, the decline of poly(ADP-ribosyl)ation activity is involved in energy homeostasis and stress tolerance. By reducing stress-induced poly(ADP-ribosyl)ation activity, NAD(+) breakdown is inhibited preventing high energy consumption. Under these conditions, plants preserve their energy homeostasis without an overactivation of mitochondrial respiration, thus avoiding the production of reactive oxygen species. Therefore, plants with lowered poly(ADP-ribosyl)ation activity appear tolerant to multiple stresses. In this study, the evergreen species Cistus incanus L. was used as a model because of its capacity to overcome successfully the environmental constraints of the Mediterranean climate. The aim of the present work was to characterize and assess the role of poly(ADP-ribosyl)ation in C. incanus plants kept under different temperature in greenhouse (GH), outdoor during winter (WO) and outdoor during spring (SO). Data showed that in C. incanus polyADPribose metabolism occurs. The enzyme responsible for poly(ADP-ribose) chains synthesis is a poly(ADP-ribose)polymerase of about 80 kDa, lacking "zinc finger" N-terminal domain and able to automodify. The lowest PARP activity, as well as the lowest quantum yield of PSII linear electron transport (Φ(PSII)) and photochemical quenching (q(P)), was found in WO plants. Instead, in SO plants the recovery of photochemical activity associated to a poly(ADP-ribose)polymerase activity increase of about 50%, as compared to GH plants, was observed. Taking into account both biochemical and eco-physiological responses, a possible explanation for the poly(ADP-ribosyl)ation deficiency in WO plants has been hypothesized.

Non-photochemical quenching (NPQ) is a complex and still unclear mechanism essential for higher plants. The intensive research on this subject has highlighted three main components of NPQ: energy-dependent process (qE); state transitions to balance the excitation of PSII and PSI (qT); and photoinhibitory processes (qI). Recently, these components have been resolved as quantum yields according to the energy partitioning approach that takes into account the rate constants of every process involved in the quenching mechanisms of excited chlorophylls. In this study a fully extended quantum yield approach and the introduction of novel equations to assess the yields of each NPQ component are presented. Furthermore, a complete analysis of the yield of NPQ in Beta vulgaris exposed to different irradiances has been carried out. In agreement with experimental results here it is shown that the previous approach may amplify the yield of qE component and flatten the quantitative results of fluorescence analysis. Moreover, the significance of taking into account the physiological variability of NPQ for a correct assessment of energy partitioning is demonstrated.

The contribute of paraheliotropism in PSII photoprotection at high light and temperature was assessed by gas exchange and chlorophyll fluorescence. Measurements were performed at 10:00, 12:00, 15:00 and 18:00 on blocked leaves (BL) and on control unblocked leaves (UL) of R. pseudoacacia. In BL at midday as well as at 15:00 and 18:00, An, gCO2, ΦPSII, IPO and F'q/F'v declined compared to 10:00 whereas Ci/Ca ratio and qN increased significantly. Differently from BL, UL maintained an higher An, IPO and ΦPSII as well as a lower qN throughout the day. At 18:00, An, gCO2, ΦPSII and F'q/F'v of BL recovered as compared to 15:00 even if the values remained lower than 10:00 and UL. Moreover, conversely to UL, a significant decrease of Fv/Fm was observed in the evening. Data suggest that in R. pseudoacacia leaf movements represent an efficient strategy to face the photoinhibition at no cost for plant in terms of An reduction.

Zea mays is cultivated in the Mediterranean regions where summer drought may lead to photoinhibition when irrigation is not available. In this work the response of maize to water stress was evaluated by gas exchange measurements at the canopy and leaf level. Leaf gas exchange was assessed before, during and after water stress, while canopy turbulent fluxes of mass and energy were performed on a continuous basis. In the early growth period, a linear increment of net ecosystem photosynthetic rate (PNE) to incoming of photosynthetic photon flux density (PPFD) was found and net leaf photosynthetic rate (PNL) showed the tendency to saturate under high irradiance. During water stress, the relationship between PNE and PPFD became curvilinear and both PNE and PNL saturated in a range between 1,000 and 1,500 mu mol (photons) m(-2) s(-1). Leaf water potential (psi(1)) dropped from -1.50 to -1.88 MPa during water stress, indicating that leaf and canopy gas exchanges were limited by stomatal conductance. With the restoration of irrigation, P-NE, P-NL and psi(1) showed a recovery, and P-NE and P-NL reached the highest values of whole study period. Leaf area index (LAI) reached a value of 3.0 m(2)m(-2). The relationship between P-NE and PPFD remained curvilinear and PNE values were lower than those of a typical well-irrigated maize crop. The recovery in PNE and P-NL after stress, and psi(1) values during stress indicate that the photosynthetic apparatus was not damaged while soil moisture stress after-effects resulted in a sub-optimal LAI values, which in turn depressed P-NE.

Photosynthesis, excitation energy dissipation and alternative electron sinks to carbon assimilation at different temperatures (5–35 °C range) were studied in plants of Beta vulgaris L. grown outdoors at springtime. Gas exchange and chlorophyll fluorescence measurements were performed in plants exposed to different temperatures for two hours at saturating irradiance (1000 μmol photons m −2 s −1 ). The photosynthetic rate decreased significantly either by lowering the temperature below 25 °C or by increasing it above 25 °C. At low temperatures (5, 10 and 15 °C) a significant decrease of electron transport rate (ETR) was found and processes alternative to CO 2 fixation, as sinks of electrons, occurred but they were not affected by the temperature. However, at 5 °C a low and statistically significant photorespiratory rate was observed and the non-photochemical quenching (NPQ) was the highest. At higher temperature (30–35 °C) ETR saturated and hence non-assimilative processes, alternative to CO 2 fixation, sustained the photochemical activity. Among processes consuming O 2 photorespiration increased at 30–35 °C, while processes non-consuming O 2 were non-affected. By increasing the temperature up to 30–35 °C NPQ values did not show appreciable differences compared to 25 °C. The obtained results indicate that in B. vulgaris plants the thermal dissipation represents the main dissipative process of the excess excitation energy at low temperatures. On the contrary, at high temperatures (30–35 °C) the main dissipation of the excess excitation energy is due to alternative pathways to CO 2 assimilation.

Gas exchange and fluorescence parameters were measured simultaneously in two Zea mays L. cultivars (Liri and 121C D8) to assess the relationship between the quantum yield of electron transport (??PS2) and the quantum yield of CO2 assimilation (??CO2) in response to photosynthetic photon flux density (PPFD). The cv. Liri was grown under controlled environmental conditions in a climate chamber (CC) while cv. 121C D8 was grown in CC as well as outdoors (OT). By exposing the two maize cultivars grown in CC to an increasing PPFD, higher photosynthetic and photochemical rates were evidenced in cv. Liri than in cv. 121C D8. In Liri plants the ??PS2/??CO2 ratio increased progressively up to 27 with increasing PPFD. This suggests that the reductive power was more utilised in non-assimilatory processes than in CO2 assimilation at high PPFD. On the contrary, by exposing 121C D8 plants to increasing PPFD, ??PS2/??CO2 was fairly constant (around 11???13), indicating that the electron transport rate was tightly down regulated by CO2 assimilation. Although no significant differences were found between ??PS2/??CO2 of the 121C D8 maize grown under CC and OT by exposing them to high PPFD, the photosynthetic rate and photochemical rates were higher in OT maize plants

Plants of Mediterranean-type ecosystems are exposed to climatic conditions that may limit carbon metabolism resulting in limitation of productivity and growth. During springtime, photosynthetic activity and plant growth are promoted, while they are constrained by aridity in summer and by low temperatures in winter. To overcome such stressful conditions, Mediterranean species have developed strategies expressed by phenological, physiological and structural modifications. Among the various woody species of the Mediterranean maquis in Southern Italy, Cistus incanus L. shows its phenology and cambial activity strictly related to the annual fluctuations of the environmental conditions. In this study, several structural, functional and eco-physiological characteristics were investigated on plants of C. incanus sampled during the autumn development in the Castevolturno Nature Reserve (NA, Italy). Anatomical and cytological features of leaves and twigs were analysed through light and fluorescence microscopy, mainly focusing on traits associated to a) regulation of water relations and b) protection of tissues from excessive irradiation and permanent injuries due to drought and predation. Efficiency and safety of the vascular system were evaluated on the basis of a detailed analysis of the xylem cell types. As regards eco-physiological behaviour, simultaneous measurements of gas exchange and chlorophyll fluorescence were conducted on fully expanded leaves at midday under saturating light intensity. The following parameters were analyzed: net photosynthesis (PN), stomatal conductance (gtH2O), water use efficiency (A/E) and quantum yield of PSII electron transport (Fe). All data were interpreted under ecological and functional perspectives.

Sedum dasyphyllum L. leaves of well-watered plants kept outdoors and under controlled conditions show diurnal malic acid fluctuations. In well-watered plants growing outdoors the malate accumulation undergoes seasonal variations and seems to be inhibited by short photoperiod and/or by low temperature. The seasonal variations of CAM activity correspond to seasonal variations of mesophyll succulence. Water stress markedly depressed CAM activity. In fact, plants of S. dasyphyllum show, under controlled conditions, a decrease of malate accumulation as relative water content decreases. Recovery from water stress is fairly slow. Water potential quickly increases during rewatering and exceeds the original value after few days, suggesting a consumption of osmotic compounds during the water stress period. © Taylor & Francis Group, LLC.

Crassulacean acid metabolism (CAM) and succulence were compared in two species of Peperomia (Piperaceae) and six species of Cissus and Cyphostenz ma (Vitaceae). The species include thin-leaved plants, leaf succulents, and stem succulents. Succulence at the organ or the cellular level mesophylll succulence [Sm]) does not appear to be causally related to CAM. Peperomia, with high Sm, shows low CAM activity, while Cypizostenima, with relatively low Sm, exhibits very high CAM activity. Overnight accumulation of malic acid as high as 332 µeq/g fresh weight was measured in the nonsucculent, thin leaves of Cissus sp., while only 50 µeq of malic acid per gram fresh weight accumulated in the succulent, photosynthesizing stem of the same plant. In the thin-leaved species of Cissus, CAM does not appear to be related to drought adaptation. Succulence in the CAM species Cissus may be a new acquisition that has allowed the genus to spread from the wet tropics to arid environments. We suggest that CAM and succulence are often associated in drought-adapted plants because both characters have been selected for in arid environments.

Ecological aspects of C3, C4 and CAM photosynthetic pathways. - Three different photosynthetic CO2 fixation pathways are known to occur in higher plants. However all three pathways ultimately depend on the Calvin-Benson cycle for carbon reduction. The oxygenase activity of RuBP carboxilase is responsible for photorespiratory CO2 release. Both C4 and CAM pathways behave as a CO2 concentrating mechanism which prevent photorespiration. The CO2-concentrating mechanism in C4 plants is based on intracellular symplastic transport of C4 dicarboxylic acids from mesophyll-cells to the adjacent bundle-sheath cells. On the contrary in CAM plants the CO2-concentrating mechanism is based on the intracellular transport of malic acid into and out of the vacuole. The C4 photosynthetic pathway as compared to the C3 pathway permits higher rates of CO2 fixation in high light and high temperature environments at low costs in terms of water loss, given the stability of the photosynthetic apparatus under such condition...

Stem chlorenchymatous cells from well‐watered and water‐stressed plants of Cissus quadrangularis L. were examined to evaluate the effect of drying on cell structure and metabolism. At a stem relative water content as low as 52‐58%, cellular integrity was maintained, but some qualitative and quantitative alterations occurred. Chlorophyll coment was higher in stressed plants, and the intact photosynthetic apparatus exhibited an increased degree of thylakoid stacking paralleled by a lower chlorophyll a/h ratio. Overnight malate accumulation was very low. Starch was retained but its day/night fluctuation was practically suppressed. Plastosomes were smaller and fewer, and the range of their daily fluctuation was very reduced. Vacuoles underwent fragmentation and accumulated osmiophilic deposits. The maintenance of the cellular integrity accounts for the ability of C. quadrangularis to recover rapidly from water stress. Copyright © 1984, Wiley Blackwell. All rights reserved