The effect of heat stress (35 to 50 °C) on photosynthesis was investigated in heat tolerant (N 22) and heat sensitive (IR 8) cultivars of rice {Oryza sativa L.). The net photosynthetic rate showed greater thermal stability in N 22 than in IR 8. The relative dechne of the rate of whole chain electron transport and photosystem 2 (PS2) activity was more pronounced in IR 8 than N 22. In both cultivars photosystem (PSI) activity was stimulated by thermal treatment. Chlorophyll (Chl) a fluorescence transient arising ffom PS2 showed inhibition in both cultivars at 45 and 50 °C. Maximum fluorescence decreased more in IR 8 than in N 22 by high temperature treatment.
In a field experiment, two winter wheat (Triticum aestivum L.) cultivars, Tainong 18 (a large-spike cultivar) and Jinan 17 (a multiple-spike cultivar), were treated with 78% (S1), 50% (S2), and 10% (S3) of full sunshine (S0, control) from anthesis to maturity to determine the responses of photosynthetic characteristics and antioxidative enzyme activities in a flag leaf. Compared with S0 treatment, the chlorophyll (Chl) content and maximal efficiency of photosystem II (PSII) photochemistry (Fv/Fm) of flag leaves were enhanced in treatments S1 and S2. From 0 to 7 d post flowering, the Chl content and Fv/Fm in S3 were also higher than those in S0, but significantly lower than those in controls, respectively. With the increase of shading intensity, the effective quantum yield of PSII (ΦPSII) was promoted; whereas, the ratio of Chl a/b declined. Compared with S0, treatments S2 and S3 significantly suppressed the activities of superoxide dismutase (SOD) and peroxidase (POD), net photosynthetic rate (PN), and contents of total soluble sugar, nevertheless, S1 treatment showed positive effects on the above parameters. Under the same shading condition, Jinan 17 had larger Chl content and higher activities of PSII and antioxidative enzymes, but lower malondialdehyde (MDA) content than Tainong 18. The results indicated that multiple-spike cultivar was more advantageous for the Huang-Huai-Hai Plain, where shading problem occurs later during the growth period, than the large-spike cultivar, because of the lesser damage in a flag leaf and better photosynthetic function of the former one. Wheat plants under S1 shading condition had relatively high activities of antioxidative enzymes and a low degree of membrane lipid peroxidation, which was in favor of stress resistance, maintaining high PN duration, and accumulation of photosynthates in wheat plants., C. Xu ... [et al.]., and Obsahuje bibliografii
o reveal the dynamics of short-term photosynthetic acclimation to increased irradiance, the light response of photochemical (qp), non-photochemical (q^) and Fo (qo) quenchings of chlorophyll (Chl) fluorescence and Chl and carotenoids compositíon in Norway spruce needles were monitored within three days after transfer of saplings ffom low diffuse irradiance (maximum photosynthetic photon fluence density PPFD 50 pmol m'^ s'i) to direct sun radiation (maximum PPFD 2000 pmol m‘2 s'*). Irradiance responses of fluorescence quenching coefficients revealed the occurrence of substantíal changes in partítioning of excitation energy between photochemical reactions and radiatíonless dissipation within two days. The saturating irradiance for qj,j and the capacity of non-radiatíve dissipation processes was shifted from about 450 pmol m'^ s** to 1620 pmol m-2 s'L Whereas immediately after exposure to ťull sunlight was completely reduced at 1620 pmol m'^ s'*, two days later 40 % of was stíll present in oxidized form at this irradiance. A fast pigment photobleaching at noon prevented the over-reduction of and thus it was one of the possible short-term acclimation processes. No severe photoinhibition of photosystem 2 (PS 2) photochemistry occurred within the period of investigation as can be judged from the high F^/F^ value.
The widespread Mediterranean Pinus pinea showed exceptionally low genetic diversity and low differentiation between traits in the adult phase. We explored the adaptation potential of seedlings from four main Iberian provenances during their regeneration phase. We assessed the variability of shoot growth, allometry, physiological traits, and phenotypic plasticity to the interactive effect of light and water environments during 8-month moderate water-stress cycle and after one-week heat wave. The effect of shade and drought was mainly orthogonal whatever the provenance. The inland La Mancha provenance showed higher shoot growth and biomass compared to the southern coastal Depresión-del-Guadalquivir provenance. Following the heat wave, La Mancha presented higher net photosynthetic rates, a lower decrease in maximal quantum efficiency of PSII, and a higher accumulated relative height growth, thus, showing an adaptive advantage. The observed differences corroborated the ecological grouping of the provenances along latitudinal and inland-coastal gradients. We confirmed the high adaptive plasticity of Pinus pinea to the unpredictable Mediterranean environment., M. Pardos, R. Calama., and Obsahuje bibliografii
We compared responses of maize, tomato, and bean plants to water stress. Maize reached a severe water deficit (leaf water potential -1.90 MPa) in a longer period of time as compared with tomato and bean plants. Maize stomatal conductance (gs) decreased at mild water deficit. gs of tomato and bean decreased gradually and did not reach values as low as in maize. The protein content was maintained in maize and decreased at low water potential (ψw); in tomato it fluctuated and also decreased at low ψw; in bean it gradually decreased. Ribulose-1,5-bisphosphate carboxylase/oxygenase activity remained high at mild and moderate stress in maize and tomato plants; in bean it remained high only at mild stress. and M. Castrillo ... [et al.].
Morphological and ultrastructural changes, the chlorophyll (Chl) content and Chl a fluorescence induction were studied in primary leaves of runner beán plants (Phaseolus coccineus L. cv. Pi?kny Jaš) grown in Knop solution and treated with excess Cu [20 g(CuS04 x 5 H2O) m"^] at difíerent growth stages. The plants were exposed to the metal for 12 d. Cu added to the nutrient solution at the beginning growth stage induced significant leaf area reduction (31 %) as well as increase of Chl accumulation (148 %) and leaf density (122 %). No ultrastructural changes of chloroplasts were seen. Application of Cu at the advanced growth stage caused relatively smáli changes except local disturbances in stroma lamellae and leaf reduction to 70 % of control. Significant disorganization of chloroplast ultrastructure, smáli leaf area reduction (80 %) but specific leaf area increase (163 %) and leaf density decrease (67 %) were seen only in the primary leaves of plants treated with Cu at the finál stage of growth. These changes, similar to senescence response, were accompanied by Fy/Fo ratio decrease to 67 % in comparison with control.
Physiological responses of two wheat (Triticum aestivum L.) genotypes (salt-tolerant DK961 and salt-sensitive JN17) to increased salt concentrations (50, 100, 150 mM NaCl: NaCl50, NaCl100, NaCl150) were studied. Photosynthetic capacity, irradiance response curves, contents of soluble sugars, proteins, and chlorophyll (Chl), K+/Na+ ratio, and activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) in flag leaves were measured on 7 d after anthesis. In control (NaCl0) plants, non-significant (p>0.05) differences were found in gas exchange and saturation irradiance (SI) between salt-tolerant (ST) and salt-sensitive (SS) wheat genotypes. However, we found higher soluble sugar and protein contents, K+/Na+ ratio, and antioxidant enzyme activities, but lower Chl content and yield in ST wheat. Salinity stresses remarkably increased soluble sugar and protein contents and the antioxidant activities, but decreased K+/Na+ ratio, Chl contents, SI, photosynthetic capacities, and yield, the extent being considerably larger in JN17 than DK961. Although the soluble sugar and protein contents and the antioxidant activities of JN17 elevated more evidently under salt stresses, those variables never reached the high levels of DK961. The antioxidant enzyme activities of SS wheat increased in NaCl50 and NaCl100, but decreased rapidly when the NaCl concentration reached 150 mM. Thus the ST wheat could maintain higher grain yield than the SS one by remaining higher osmoregulation and antioxidative abilities, which led to higher photosynthetic capacity. Hence the ST wheat could harmonize the relationship between CO2 assimilation (source) and the grain yield (sink) under the experimental conditions. and Y. H. Zheng ... [et al.].
Soybean [Glycine mctx (L.) Merr. cv. Jack] was grown in the field in rain-prolected plots to study effects of drought and atmospheric CO2 enrichnient on leaf gas exchange. Midday depressions in leaf photosynthetic CO2 exchange rates were found in drought-sfressed plants and the diumal changes were inostly stoinatal- regulated, although accumulated drought stress eventually resulted in some non- stomatal limitations. However, seasonal changes in were mostly limited by non- stomatal factors. Water use efficiency was always higher for drought stiessed plants and depended on the severity of stress and associated stomatal or nonstoinatal limitations. At enriched atmospheric CO2 levels, stomatal limitations to Pyj under drought stress were less important than at ambient atmospheric CO2 levels. Morning and aftemoon leaf starch levels were enhanced in both irrigated and nonirrigated plants in enriched CO2. Aftemoon starch levels were higher in stiessed leaves than in non-stressed leaves at normál CO2 levels.
Ultrastructural and physiological effects of exposure to 1 ppm and 5 ppm of cadmium (Cd) on cultured cells of Koliella antarctica, a green microalga from Antarctica, were investigated. The amount of Cd in the alga rose with the increase of the metal concentration in the growth medium and most Cd remained outside the cells, bound to the components of the cell walls. The increase of Cd in the microalga was concomitant with the decrease of other elements, mainly calcium (Ca). Exposure to 1 ppm Cd slowed culture growth by inhibiting cell division and also caused the development of some misshapen cells with chloroplast showing disordered thylakoids. However, this concentration did not substantially affect the chlorophyll (Chl) content or photosystem (PS) activity. At 5 ppm, Cd cell growth suddenly stopped and some cells lysed. After a week of Cd contamination, the cells were enlarged and severely damaged. The chloroplasts showed great ultrastructural alterations and a reduced Chl content. Cd exposure negatively affected PSII, whose activity was almost completely lost after four days. and N. La Rocca ... [et al.].
Changes in the activities of enzymes involved in scavenging active oxygen species were followed after exposing bean seedling leaves (Phaseolus vulgaris L.) to various cross stresses of irradiance and temperature. The activities of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (AsAPOD, EC 1.11.1.11) increased to different extent with prolonged irradiation of the leaves, and were stimulated by high temperature (HT). The activity of catalase (CAT, 1.11.1.6) decreased when exposed to strong irradiance (HI), and the decrease was further exacerbated when HI was combined with HT. CAT activity was more sensitive to HT than to HI. Ascorbate (AsA) content slightly decreased and then increased during the treatment of HI, but decreased under the cross stress of HI and HT. On the contrary, glutathione (GSH) content increased all the time during various treatments of irradiance and temperature. The increase in the combined stress was even more pronounced. Irradiance is the major reason in triggering the operation of xanthophyll cycle, which was difficult to be started by HT. The antioxidant systems tended to be inactivated with prolonged exposure to the cross stress of HI and HT. The de-expoxidated state of xanthophyll cycle, however, was increasing all the time, which indicated that the zeaxanthin-dependent thermal dissipation was one major energy dissipation pathway during the cross stress of HI and HT. and Liang Ye, Hui-yuan Gao, Qi Zou.