The effects of drought on thylakoid acyl lipid composition, photosynthetic capacity (P max), and electrolyte lekage were evaluated in two-months-old peanut cultivars (57-422, 73-30, GC 8-35) growing in a glasshouse. For lipid studies, plants were submitted to three treatments by withholding irrigation: control (C), mild water stress (S1), and severe water stress (S2). Concerning membrane and photosynthetic capacity stability, drought was imposed by polyethylene glycol (PEG 600). In the cv. 73-30 a sharp decrease in the content of thylakoid acyl lipids was observed, already under S1 conditions, whereas cv. 57-422 was strongly affected only under S2. Cv. GC 8-35 had the lowest content of acyl lipids under control conditions, a significant increase under S1 conditions, and only under S2 a decrease occurred. Thus concerning lipid stability, cv. 73-30 was the most sensitive. Among lipid classes, phospholipids and galactolipids were similarly affected, as was MGDG relatively to DGDG. Water deficit imposed by PEG induced a higher increase in electrolyte leakage in cv. 73-30 than in the other cvs. A positive relationship between acyl lipid concentration and membrane integrity was found in all studied cvs. A positive association between acyl lipid concentration, membrane integrity, and P max was found in the cvs. 57-422 and 73-30. and J. A. Lauriano ... [et al.].
Phlomis fruticosa is one of the main species of post-fire Mediterranean communities, occupying areas with post-fire grazing or altered precipitation pattern and consequently water stress imposed on seedlings of co-occurring species. Seedlings of woody perennials often differ from their mature individuals regarding their resistance of photosynthetic performance to environmental stresses. Such differences have been reported for tree species but there is a lack of information regarding shrub species. In the present study, we tried to detect changes in (PSII) activity imposed by water stress in P. fruticosa seedlings as well as its capability for recovery after rehydration. Maximum PSII photochemical efficiency decreased only under severe water stress exactly as in mature plants in the field. However, leaf chlorophyll (Chl) content was almost stable regardless of leaf relative water content (RWC). We assume that the photoprotective chlorophyll loss process, reported for many mature Mediterranean species (including P. fruticosa), has not yet been developed at the seedling stage. On the other hand, photoprotection through an increase of the relative amount of non-QB-reducing centers was found during dehydration. Non-photochemical quenching (NPQ) contributed to protection from photodamage until moderate water stress but was significantly suppressed under severe water stress. Both processes were reversed after rehydration. The above characteristics enabled seedlings not only to survive during aggravating drought but also to maintain a considerable part of their effective quantum yield and perform significant electron transport even at extremely low relative water content (RWC). This was confirmed with measurements in a semi-natural environment (pots) and under real steady state conditions regarding adaptation of the photosynthetic machinery to prevailing light intensities. and A. Petsas, G. Grammatikopoulos.
Global warming will likely exacerbate the negative effects of limited water availability in the Mediterranean area. The Italian Aleppo pine (Pinus halepensis Mill.) provenances are distributed along the coasts except Otricoli provenance growing in an unusual location between 300 and 1,000 m a. s. l., in Umbria (central Italy). The aim of the present study was to investigate the photosynthetic response to a 28-day-long drought and to a subsequent reestablishment of water availability in Otricoli and North Euboea (Greece) provenances, representing different locations along a rainfall gradient in the natural range of this species. Six-month-old seedlings were used in this experiment since at this age Aleppo pine plants in Mediterranean climate face their first water stress potentially affecting plant survival. Water potential (ψw), net photosynthesis and stomatal conductance decreased during drought in both provenances and showed minimal values 28 days after beginning the treatment (DAT). Otricoli seedlings adjusted ψw gradually as the stress level increased and 21 DAT showed a lower ψw than North Euboea. In contrast, in North Euboea seedlings ψw that was not affected until 21 DAT rapidly dropped to a minimum of -3.81 MPa 28 DAT. At the onset of the stress the intercellular CO2 concentration (Ci) was reduced, and the "instrinsic" water-use efficiency (WUEi) was enhanced in both provenances, as stomatal conductance decreased more rapidly than photosynthesis. However, 28 DAT, Ci increased and WUEi decreased as stomatal conductance and photosynthesis declined to minimum levels, revealing nonstomatal limitations of photosynthesis. A rapid decrease in PSII maximal photochemical efficiency estimated by chlorophyll (Chl) fluorescence (Fv/Fm) was also observed when the stress became severe. At the final stage of water stress, North Euboea seedlings maintained significantly higher values of Fv/Fm than Otricoli seedlings. Upon rewatering, photosynthesis did not fully recover in Otricoli seedlings (41 DAT), while all other parameters recovered to control levels in both provenances. No drought-induced physiological differences were consistent with the regional climatic features of these two provenances. Our results suggest that phenotypic plasticity in drought response may help Otricoli provenance cope with global warming, but that recurrent drought episode may slow down the primary productivity of this provenance. and M. Michelozzi ... [et al.].
The influence of drought stress (DS) upon whole-plant water content, water relations, photosynthesis, and water-use efficiency of Hibiscus rosa-sinensis cv. Leprechaun (Hibiscus) plants at three levels of potassium (K) nutritional status were determined after a 21-d gradually imposed DS treatment. Compared to K-deficient plants, adequate K supply improved the leaf water content (LWC) and leaf water relations of Hibiscus by decreasing the Ψ π, and generally sustained rates of net photosynthesis (PN) and transpiration (E), and stomatal conductance (gs), both in DS and non-DS plants. In K-deficient Hibiscus, LWC, turgor potential (Ψ P), and PN, E, and gs as well as instantaneous water-use efficiency, WUE (PN/E) were consistently lower, compared to K-sufficient plants. Carbon isotope discrimination (Δ) was lower (i.e. longterm WUE was greatest) in DS than non-DS plants, but K had no effect on Δ during the 21-d drought treatment period under glasshouse conditions. However, the trend in the Δ value of DS plants suggests that Δ could be a useful index of the response of Hibiscus to DS under glasshouse growing conditions. Thus the incorporation of a properly controlled fertilization regime involving sufficient levels of K can improve the acclimation of PN to low Ψleaf, increase PN/E of Hibiscus, and may have potential benefit for other woody plants species. and J. N. Egilla, F. T. Davies Jr., T. W. Boutton.
We investigated the strategies of four co-occurring evergreen woody species Quercus ilex, Quercus coccifera, Pinus halepensis, and Juniperus phoenicea to cope with Mediterranean field conditions. For that purpose, stem water potential, gas exchange, chlorophyll (Chl) fluorescence, and Chl and carotenoid (Car) contents were examined. We recognized two stress periods along the year, winter with low precipitation and low temperatures that led to chronic photoinhibition, and summer, when drought coincided with high radiation, leading to an increase of dynamic photoinhibition and a decrease of pigment content. Summer photoprotection was related to non-photochemical energy dissipation, electron flow to alternative sinks other than photosynthesis, decrease of Chl content, and proportional increase of Car content. Water potential of trees with deep vertical roots (Q. coccifera, Q. ilex, and P. halepensis) mainly depended on precipitation, whereas water potential of trees with shallow roots (J. phoenicea) depended not only on precipitation but also on ambient temperature. and F. J. Baquedano, F. J. Castillo.
Apple rootstock seedling M.9-T337 was selected to explore the effect of drought stress. The findings indicated that the relative water content of both the leaf and soil gradually decreased with an increase in drought stress. The water-use efficiency of the leaves increased gradually but decreased sharply after 20 d of drought. Changes in the gas-exchange parameters and chlorophyll fluorescence parameters reflected the gradual decrease in the photosynthetic capacity of the plants with drought stress duration. Infrared thermal imaging showed significant temperature differences between the drought-stressed and control plants after 15 d of drought treatment. When irreversible damage occurred under drought stress, the crop water-stress index and relative water content of the leaf and soil were 0.7, 60.5, and 17.8%, respectively. Based on the results, we formulated a drought stress-grade standard. Further, we established that the best time for irrigation is when drought stress reaches grade 3., D. T. Gao, C. Y. Shi, Q. L. Li, Z. F. Wei, L. Liu, J. R. Feng., and Obsahuje bibliografické odkazy
Maize (Zea mays) seedlings were exposed for 6 h to strong irradiance (1 000 μmol m-1 s-1 of PPFD) at 5, 12, 17, or 25 °C, followed by an exposure to the darkness for 6 h at 22 °C. Leaf chlorophyll fluorescence, net photosynthetic rate (PN), and the amount of superoxide radicals (O2-⋅) in relation to chilling-induced photoinhibition were investigated. During the photophase, a good correlation (r=-0.879) was observed between ΦPS2 (relative quantum efficiency of PS2 electron transport) and the amount of O2-⋅. Treatment with exogenous O2-⋅ reduced the PN and ΦPS2 as the chilling stress did, that was inhibited by specific scavenger of O2-⋅. Hence chilling-induced photoinhibition might be due to the production of O2-⋅. In contrast, in the dark period, PN and ΦPS2 of the seedlings treated with the exogenous O2-⋅ were enhanced, but they were inhibited by the specific scavenger of O2-⋅, showing the photoprotective role of O2-⋅ in the recovery phase. Furthermore, in terms of the effect of exogenous O2-⋅ on the xanthophyll cycle, the O2-⋅ production suggested a promotion effect for the de-epoxidation of violaxanthin during the photophase, the epoxidation of zeaxanthin at the dark stage, and the increase of the xanthophyll pool both in the photophase and dark phase, resulting in an enhancement of the ability of non-photochemical quenching to avoid or alleviate the damage to photosynthetic apparatus. and D. Ke, G. Sun, Y. Jiang.
Lichen thalli were exposed to 4 regimes differing in irradiance and duration of irradiation. Photosynthetic efficiency of thalli was monitored by chlorophyll fluorescence parameters and xanthophyll cycle analysis. Maximal quantum yield of photosystem 2 (FV/FM) decreased gradually with time in long-term treatment. The effect of additional short-term high irradiance (HI) treatment applied each 24 h was not significant. Nevertheless, short-term HI applied repeatedly on thalli kept in the dark led to a significant decrease of FV/FM. Non-photochemical quenching recorded during the long-term treatment corresponded to the content of zeaxanthin (Z). In short-term treatment, however, proportion of Z (and antheraxanthin) to total amount of xanthophyll cycle pigments recovered to the initial values every 24 h after each repeated short-term HI event in thalli kept in dark. Thus duration of irradiation rather than irradiance and frequency of HI events is important for a decrease in primary photosynthetic processes in wet thalli of Lasallia pustulata. Rapidly responding photoprotective mechanisms, such as conversion of xanthophyll cycle pigments, are involved mainly in short-term irradiation events, even at HI. and M. Barták ... [et al.].
Based on new experimental data of linear and nonlinear spectroscopic investigations of LHC2 complexes, both the energy transfer and energy relaxation of excitons were studied in the limiting cases of strong pigment-pigment and pigment-protein interactions, respectively. Consequences of the structural basis and the dominance of strong pigment-pigment interactions in monomers were independently established by different optical measurements. In this model, the energy relaxation of excitons was determined by dynamical processes of exciton interactions with the radiation fíeld and the long-wave protein vibrations, respectively, in particular with the mode having the wave number of 43 cm'f