Brassinosteroids (BRs) and polyamines, well-established growth regulators, play a key role in abiotic stress response in plants. In the present study, we examined the role of 24-epibrassinolide (EBL, an active BR) and/or putrescine (Put) in the salt-induced stress in cucumber. The 15-d-old plants were exposed to 100 mM NaCl and they were subsequently treated by exogenous EBL and/or Put. The salt stress reduced significantly plant growth and gas-exchange parameters, and increased proline content and electrolyte leakage in the leaves. Toxic effects induced by salt stress were completely overcome by the combination of EBL and Put. EBL and/or Put treatments improved the growth parameters of the NaCl-treated plants, such as shoot length, root length, fresh and dry mass. Our data also indicated that applications of EBL and Put upregulated the activities of the antioxidant enzymes, such as catalase, peroxidase, and superoxide dismutase under salt stress., Q. Fariduddin, B. A. Mir, M. Yusuf, A. Ahmad., and Obsahuje bibliografii
Seedlings of the hypoxia-sensitive cucumber cultivar were hydroponically grown under hypoxia for 7 d in the presence or absence of 24-epibrassinolide (EBR, 2.1 nM). Hypoxia significantly inhibited growth, while EBR partially counteracted this inhibition. Leaf net photosynthetic rate (PN), stomatal conductance, transpiration rate, and water-use efficiency declined greatly, while the stomatal limitation value increased significantly. The maximum net photosynthetic rate was strongly reduced by hypoxia, indicating that stomatal limitation was not the only cause of the PN decrease. EBR markedly diminished the harmful effects of hypoxia on PN as well as on stomata openness. It also greatly stimulated CO2 fixation by the way of increasing the carboxylation capacity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), ribulose-1,5-bisphosphate regeneration, Rubisco activity, and the protection of Rubisco large subunit from degradation. Our data indicated that photosystem (PS) II was damaged by hypoxia, while EBR had the protective effect. EBR further increased nonphotochemical quenching that could reduce photodamage of the PSII reaction center. The proportion of absorbed light energy allocated for photochemical reaction (P) was reduced, while both nonphotochemical reaction dissipation of light energy and imbalanced partitioning of excitation energy between PSI and PSII increased. EBR increased P and alleviated this imbalance. The results suggest that both stomatal and nonstomatal factors limited the photosynthesis of cucumber seedlings under hypoxia. EBR alleviated the growth inhibition by improving CO2 asimilation and protecting leaves against PSII damage., Y. H. Ma, S. R. Guo., and Obsahuje bibliografii
Leaf chlorophyll (Chl) concentration can be an indicator of plant health, including photosynthetic potential and nutrient status. In some cases, this measure can indicate the degree to which plants are water-stressed. Traditional methods of measuring Chl concentration have involved a destructive sampling technique: extraction and spectrophotometric analysis. A compatible nondestructive method to measure leaf Chl concentration exists and applies transmittance spectroscopy to plants with a Minolta SPAD-502 meter. These techniques were evaluated by comparing leaf Chl concentration in big bluestem (Andropogon gerardii). Leaves were sampled from plants representing three ecotypes (originating from Central Kansas, Eastern Kansas, and Illinois, USA) and two cultivars of A. gerardii growing in Hays, Kansas, USA. Leaf Chl concentration was measured using nondestructive and destructive techniques. We documented a saturating relationship between destructively measured leaf Chl concentration and SPAD index resulting from a decelerating change in SPAD index as Chl concentration increased. The comparison of A. gerardii ecotypes and cultivars demonstrated highest Chl concentration in the ecotype and cultivar from areas with historically low precipitation, Central Kansas and A. gerardii var. hallii, respectively. A high ratio of Chl a to Chl b is an index of drought adaptation and was also manifested in A. gerardii from drier regions. Thus, drought-adapted ecotypes and cultivars might be able to maintain high photosynthetic productivity and protect photosystem II during dry periods. Conversely, the ecotypes and cultivar originating from areas with higher precipitation had lower leaf Chl and a lower Chl a/b ratio., K. L. Caudle, L. C. Johnson, S. G. Baer, B. R. Maricle., and Obsahuje bibliografii
A differential mechanical technique for tissue separation, based on the different physical resistance to grinding between mesophyll (M) and bundle sheath (BS) cells, was tested on dicotyledonous C4 plants A triplex canscens, A triplex halimus, Gomphrena globosa, Amaranthus retroflexus, Amaranthus caudatus and Portulaca oleracea. A metal sieve (35 mesh) was placed inside a mortar and pieces of leaves (0.5 cm2) were ground in an aqueous medium on the sieve to obtain a homogenate. The homogenate was at first collected below the sieve and was then filtered through six layers of muslin. Microscopic examination showed that the filtrate was enriched by the M cells and the residue was enriched by BS cells, few of which were broken. The BS cell fraction was then vigorously ground and filtered; this second filtrate was named the BS cell fraction and the first filtrate was named the M cell fraction. Ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) (RuBPC) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) (PEPC) were assayed, and chlorophyll determinations and protein estimations were made on both fractions. As expected, PEPC showed higher activities in the M fractions; contrary to expectation RuBPC was present in M cell fractions in the six dicotyledonous C4 plants tested. The relative high RuBPC activities found in the M fraction could not be explained in terms of bundle sheath contamination.
An unexpectedly large proportion of C4 grasses was found in a moderately temperate and moist Himalayan location during monsoon period. 79 % of total grasses occurring in the area were found to be C4. Several grasses hitberto unreported as C4 háve now been recorded. The principál cause for the natural abundance of C4 species is presumably low atmospheric CO2 levels rallua' tlian the aridity and warmer temperatures. The finding adds a new dimension to our knowledge of natural distribution of the C4 species.
Iron is an essential limiting factor for primary production in many marine systems. The present study investigated differential regulation of protein expression in marine phytoplankton Prymnesium parvum under low Fe concentration. The phytoplankton was grown in f/2 culture medium in artificial seawater with low (0.0025 μM) and high (0.05 μM) Fe concentrations. Two-dimensional differential gel electrophoresis and matrix-assisted laser desorption-ionization-time of flight-mass spectrometer analysis were performed for protein identification and characterization. The growth of the alga declined substantially under the low Fe compared to the high Fe concentration. Under low Fe conditions, P. parvum upregulated 10 proteins including chloroplastic ATP synthase subunit b, D2 protein of PSII, D1 protein of PSII reaction centre, and light harvesting complex II protein, most of which are associated with photosynthetic activities in PSII. The results suggest that the marine alga P. parvum altered the biosynthesis of several photosynthetic proteins in order to cope with low Fe conditions., M. M. Rahman, M. A. Rahman, T. Maki, T. Nishiuchi, T. Asano, H. Hasegawa., and Obsahuje bibliografii
A simple method of a bicolor (multicolor), fast-Fourier, PAM chlorophyll fluorometry has been developed to obtain fluorescence induction curves. Quantum yields of PSII photochemistry were determined with blue and red simultaneously applied pulsed measuring lights for three subsequent 20-min periods of dark-, light-adaptation under actinic light and dark recovery. Measuring lights were cross-combined with blue and red actinic lights and saturation pulses. Coefficients of chromatic divergence were calculated as a ratio of the quantum yields obtained by red measuring light to that obtained by blue measuring light. Adaptation of Ficus benjamina and Hordeum vulgare leaves under blue (but not red) actinic light resulted in the sufficient increase of chromatic divergence. In addition, fraction of active, non(photo)inhibited, PSII centers was shown to be dependent on the color of measuring light. Thus, color of the light sources should be considered when reporting results of parameters evaluated from fluorescence induction curves., V. Lysenko, D. Lazár, T. Varduny., and Obsahuje bibliografii
Modelling the exchange and transformation of matter and energy in ecosystems requires the development of hierarchical structured models of the considered ecosystem compartments. In this context, a model describing the coupled CO2 and H2O gas exchange of a winter wheat canopy was developed and calibrated. The formidation of the model was related to the problems of linking processes at different systém levels. For model calibration, ecophysiological gas exchange characteristics and micro-meteorological data were obtained on both leaf and canopy levels and completed by results of structural and Chemical plant analysis. The gas exchange was measured by a computer-controlled multi-channel systém. On the basis of this data pool, the canopy gas fluxes were calculated by the model as the integrál of the corresponding local fluxes over the area elements of the canopy. The model describes correctly physiological interactions and gas exchange characteristics at both the leaf and canopy levels.
Chlorophyll index and leaf nitrogen status (SPAD value) was incorporated into the nonrectangular hyperbola (NRH) equation for photosynthetic light-response (PLR) curve to establish a modified NRH equation to overcome the parameter variation. Ten PLR curves measured on rice leaves with different SPAD values were collected from pot experiments with different nitrogen (N) dosages. The coefficients of initial slope of the PLR curve and the maximum net photosynthetic rate in NRH equation increased linearly with the increase of leaf SPAD. The modified NRH equation was established by multiplying a linear SPAD-based adjustment factor with the NRH equation. It was sufficient in describing the PLR curves with unified coefficients for rice leaf with different SPAD values. SPAD value, as the indicator of leaf N status, could be used for modification of NRH equation to overcome the shortcoming of large coefficient variations between individual leaves with different N status. The performance of the SPAD-modified NRH equation should be further validated by data collected from different kinds of plants growing under different environments., J. Z. Xu, Y. M. Yu, S. Z. Peng, S. H. Yang, L. X. Liao., and Obsahuje bibliografii