This contribution is a practical guide to the measurement of the different chlorophyll (Chl) fluorescence parameters and gives examples of their development under high-irradiance stress. From the Chl fluorescence induction kinetics upon irradiation of dark-adapted leaves, measured with the PAM fluorometer, various Chl fluorescence parameters, ratios, and quenching coefficients can be determined, which provide information on the functionality of the photosystem 2 (PS2) and the photosynthetic apparatus. These are the parameters Fv, Fm, F0, Fm', Fv', NF, and ΔF, the Chl fluorescence ratios Fv/Fm, Fv/F0, ΔF/Fm', as well as the photochemical (qP) and non-photochemical quenching coefficients (qN, qCN, and NPQ). qN consists of three components (qN = qE + qT + qI), the contribution of which can be determined via Chl fluorescence relaxation kinetics measured in the dark period after the induction kinetics. The above Chl fluorescence parameters and ratios, many of which are measured in the dark-adapted state of leaves, primarily provide information on the functionality of PS2. In fully developed green and dark-green leaves these Chl fluorescence parameters, measured at the upper adaxial leaf side, only reflect the Chl fluorescence of a small portion of the leaf chloroplasts of the green palisade parenchyma cells at the upper outer leaf half. Thus, PAM fluorometer measurements have to be performed at both leaf sides to obtain information on all chloroplasts of the whole leaf. Combined high irradiance (HI) and heat stress, applied at the upper leaf side, strongly reduced the quantum yield of the photochemical energy conversion at the upper leaf half to nearly zero, whereas the Chl fluorescence signals measured at the lower leaf side were not or only little affected. During this HL-stress treatment, qN, qCN, and NPQ increased in both leaf sides, but to a much higher extent at the lower compared to the upper leaf side. qN was the best indicator for non-photochemical quenching even during a stronger HL-stress, whereas qCN and NPQ decreased with progressive stress even though non-photochemical quenching still continued. It is strongly recommended to determine, in addition to the classical fluorescence parameters, via the PAM fluorometer also the Chl fluorescence decrease ratio RFd (Fd/Fs), which, when measured at saturation irradiance is directly correlated to the net CO2 assimilation rate (PN) of leaves. This RFd-ratio can be determined from the Chl fluorescence induction kinetics measured with the PAM fluorometer using continuous saturating light (cSL) during 4-5 min. As the RFd-values are fast measurable indicators correlating with the photosynthetic, activity of whole leaves, they should always be determined via the PAM fluorometer parallel to the other Chl fluorescence coefficients and ratios., and H. K. Lichtenthaler, C. Buschmann, M. Knapp.
Meteorological parameters inside and outside an open-top chamber (OTC) fumigation facility were recorded and the primary photosynthetic response of four tree species measured with chlorophyll (Chl) a fluorescence emission. Parameters extracted from the Chl a fluorescence transient were used to calculate photosynthetic activity of the leaves using a performance index. Measurements were made during the night throughout a single growing season. The seasonal primary photosynthetic performance in all species was significantly altered by growth in the OTCs, and the degree of response was dependent upon the species. Wind was an important effectual component of the altered environment. The average temperature was consistently 1.94±0.70 °C higher within the OTCs, whereas wind speed fluctuated substantially more between inside and outside the OTCs (0 to 8 m -1). There was a correlation between the photosynthetic performance index and wind speed in Fagus sylvatica, Fraxinus excelsior, and Prunus serotina. The response to wind was also particular to each species; the photosynthetic performance of F. sylvatica increased with wind speed (1 to 7 m s-1), decreased with F. excelsior (0 to 6.5 m s-1) and P. serotina (0 to 5.5 m s-1). Abies alba, in contrast, was almost insensitive to wind. A model was proposed and tested for the conversion of the photosynthetic performance values collected in OTCs to predict the photosynthetic performance outside OTCs. The wide variety of responses to wind and temperature of the four species conformed to linear functions that describe the relationship of the wind speed and temperature responses with the difference in photosynthetic performance between the OTC and open environments. Specific coefficients for wind and temperature were proposed. The photosynthetic response to wind of each species depends on its ecophysiological specialisation. and A. J. Clark ... [et al.].
The article deals with manuscript XIII G 25 of the National Library of the Czech Republic, which contains an explanation of part of the Book of Psalms (109-118). The explanation is attributed to the Master of the Prague University and preacher in the Prague Bethlehem Chapel Václav of Dráchov (about 1395-1469). The author analyses the contents of the codex, the relationship between it and further manuscripts, its provenience and finally, the research results in this field are summarized.
In plants, hydrogen peroxide (H2O2) acts as a signalling molecule that facilitates various biochemical and physiological processes. H2O2 is a versatile molecule, involved in several cellular processes both under stress and stress-free conditions. In regulating plant metabolism under stress conditions, exogenous application of H2O2 also plays a pivotal role which is manifested in improved growth, photosynthetic capacity, and antioxidant protection. Abiotic stress is an inevitable environmental factor that extensively affects and reduces growth, quality, yield, and productivity of plants. Several signalling pathways involved in H2O2-mediated stress and defense responses have been extensively studied and there is ample scope of additional research that could further clarify the mechanism and modulating factors which regulate these pathways. An attempt has been made to dissect the role of H2O2 under low temperature stress and how it affects plant growth and development, photosynthetic capacity, regulation of antioxidant system, and signalling., T. A. Khan, M. Yusuf, Q. Fariduddin., and Obsahuje bibliografii
Hypobaria (low total atmospheric pressure) is essential in sustainable, energy-efficient plant production systems for long-term space exploration and human habitation on the Moon and Mars. There are also critical engineering, safety, and materials handling advantages of growing plants under hypobaria, including reduced atmospheric leakage from extraterrestrial base environments. The potential for producing crops under hypobaria and manipulating hypoxia (low oxygen stress) to increase health-promoting bioactive compounds is not well characterized. Here we showed that hypobaric-grown lettuce plants (25 kPa ≈ 25% of normal pressure) exposed to hypoxia (6 kPa pO2 ≈ 29% of normal pO2) during the final 3 d of the production cycle had enhanced antioxidant activity, increased synthesis of anthocyananins, phenolics, and carotenoids without reduction of photosynthesis or plant biomass. Net photosynthetic rate (PN) was not affected by total pressure. However, 10 d of hypoxia reduced PN, dark respiration rate (RD),
PN/RD ratio, and plant biomass. Growing plants under hypobaria and manipulating hypoxia during crop production to enhance health-promoting bioactive compounds is important for the health and well-being of astronauts exposed to space radiation and other stresses during long-term habitation. and C. He ... [et al.].
Dendrobium is one of the three largest genera in the Orchidaceae and is distributed throughout various habitats. We investigated photosynthesis in seven Dendrobium species and cultivars by comparing their leaf δ13C values, titratable acidity, and CO2 exchange in well-watered and drought-stressed conditions. In addition, the leaf thickness and mesophyll succulence index (Sm) were measured in well-watered conditions. Our results indicate that Dendrobium loddigesii is a typical obligate (or constitutive) CAM plant because the leaf δ13C values were -14.47 and -14.66‰ in both conditions, respectively. Others showed the leaf thickness of 0.31-0.89 mm and their δ13C values ranged from -25.68 to -28.37‰. These are not the CAM plants but they could not be classified as obligate C3 or C3/CAM intermediate plants. Dendrobium crepidatum and Dendrobium fimbriatum were further identified as the obligate C3 plants because the net CO2 uptake was positive during daytime and negative during nighttime in both conditions. In contrast, Dendrobium chrysotoxum, Dendrobium nobile, and D. nobile ‘V1’ and ‘V4’, showed no positive net CO2 uptake and low ΔH+ values during nighttime under well-watered conditions, indicating C3 photosynthesis. However, they showed the positive net CO2 uptake and large ΔH+ values during nighttime after drought-stress (21 or 28 days without H2O), indicating CAM photosynthesis. Therefore, these four species and cultivars were identified as C3/CAM intermediate (inducible or facultative) plants. In brief, obligate CAM, C3/CAM intermediate, and obligate C3 plant types all exist in the section of Dendrobium. To the best of our knowledge, this is the first report of the obligate C3 plants in Dendrobium, and these diverse photosynthetic pathways may explain their varied environmental adaptations., S. Qiu, S. Sultana, Z. D. Liu, L. Y. Yin, C. Y. Wang., and Obsahuje bibliografii
Quantification of chlorophyll (Chl) fluorescence is a versatile tool for analysing the photosynthetic performance of plants in a non-intrusive manner. A pulse-amplitude modulated fluorometer was combined with a CNC router for the automated measurement of the effective quantum yield of photosystem 2 (Φ2) of Arabidopsis thaliana plants. About 90 000 individual plants representing 7 500 lines derived from En-transposon and T-DNA mutagenised Arabidopsis populations were screened for mutants with altered Φ2. Forty-eight recessive Φ2 mutations were identified of which most exhibit also altered pigmentation and increased photosensitivity. For three Φ2 mutants the corresponding mutated genes were identified that code all for chloroplast-located proteins. Comparison of the Φ2 mutant screen with other screening methods based on the measurement of Chl fluorescence shows that the Φ2 mutants identified are different to mutants identified by high Chl fluorescence. Some Φ2 mutants, on the contrary, are common to mutants identified by screens based on non-photochemical quenching. and C. Varotto ... [et al.].