Chlorophyll (Chl) α fluorescence induction (transient), measured by exposing dark-adapted samples to high light, shows a polyphasic rise, which has been the subject of extensive research over several decades. Several Chl fluorescence parameters based on this transient have been defined, the most widely used being the FV [= (FM-F0)]/FM ratio as a proxy for the maximum quantum yield of PSII photochemistry. However, considerable additional information may be derived from analysis of the shape of the fluorescence transient. In fact, several performance indices (PIs) have been defined, which are suggested to provide information on the structure and function of PSII, as well as on the efficiencies of specific electron transport reactions in the thylakoid membrane. Further, these PIs have been proposed to quantify plant tolerance to stress, such as by high light, drought, high (or low) temperature, or N-deficiency. This is an interesting idea, since the speed of the Chl α fluorescence transient measurement (<1 s) is very suitable for high-throughput phenotyping. In this review, we describe how PIs have been used in the assessment of photosynthetic tolerance to various abiotic stress factors. We synthesize these findings and draw conclusions on the suitability of several PIs in assessing stress responses. Finally, we highlight an alternative method to extract information from fluorescence transients, the Integrated Biomarker Response. This method has been developed to define multi-parametric indices in other scientific fields (e.g., ecology), and may be used to combine Chl α fluorescence data with other proxies characterizing CO2 assimilation, or even growth or grain yield, allowing a more holistic assessment of plant performance., A. Stirbet, D. Lazár, J. Kromdijk, Govindjee., and Obsahuje bibliografické odkazy
We present a chlorophyll fluorometer module system which adapts the intensity to the individual leaf sample by adjusting the quantum flux density of the excitation light so that the fluorescence signal is kept constant. This is achieved by means of a feedback power adjustment of the fluorescence exciting laser diode. Thus, the intensity of the excitation light is adapted to the actual need of a particular sample for quantum conversion without applying exaggeratedly high quantum flux density. We demonstrate the influence of the initial laser power chosen at the onset of irradiation and kept constant during fluorescence rise transient within the first second. Examples are shown for measuring upper and lower leaf sides, a single leaf with different pre-darkening periods, as well as yellow, light green and dark green leaves. The novel excitation kinetics during the induction of chlorophyll fluorescence can be used to study the yield and regulation of photosynthesis and its related non-photochemical processes for an individual leaf. It allows not only to sense the present state of pre-darkening or pre-irradiation but also the light environment the leaf has experienced during its growth and development. Thus, the individual physiological capacity and plasticity of each leaf sample can be sensed being of high importance for basic and applied ecophysiological research which makes this new methodology both innovative and informative. and A. Barócsi ... [et al.].
Excitation kinetics based on feedback regulation of chlorophyll (Chl) fluorescence of leaves measured with the chlorophyll fluorometer, FluoroMeter Modul (FMM), are presented. These kinetics showed the variation of excitation light (laser power, LP) regulated by the feedback mechanism of the FMM, an intelligent Chl fluorometer with embedded computer, which maintains the fluorescence response constant during the 300-s transient between the dark- and light-adapted state of photosynthesis. The excitation kinetics exhibited a rise of LP with different time constants and fluctuations leading to a type of steady state. The variation of excitation kinetics were demonstrated using the example of primary leaves of etiolated barley seedlings (Hordeum vulgare L. cv. Barke) during 48 h of greening in the light with gradual accumulation of Chl and development of photosynthetic activity. The excitation kinetics showed a fast rise followed by a short plateau at ca. 30 s and finally a slow constant increase up to 300 s. Only in the case of 2 h of greening in the light, the curve reached a stable steady state after 75 s followed by a slight decline. The final LP value (at 300 s of illumination) increased up to 12 h of greening and decreased with longer greening times. The active feedback mechanism of the FMM adjusted the excitation light during the measurement to the actual photosynthetic capacity of the individual leaf sample. In this way, the illumination with excessive light was avoided. The novel excitation kinetics can be used to characterize health, stress, disease, and/or product quality of plant material., C. Buschmann ... [et al.]., and Obsahuje bibliografii
a1_Imaging the four fluorescence bands of leaves, the red (F690) and far-red (F740) chlorophyll (Chl) fluorescence as well as the blue (F440) and green (F520) fluorescence of leaves and the corresponding fluorescence ratios is a fast and excellent nondestructive technique to detect the photosynthetic activity and capacity of leaves, of gradients over the leaf area as well as the effect of various strain and stress parameters on plants. This review primarily deals with the first and pioneering multi-colour fluorescence imaging results obtained since the mid-1990s in a cooperation with French colleagues in Strasbourg and in my laboratory in Karlsruhe. Together we introduced not only the joint imaging of the red and far-red Chl fluorescence but also of the blue and green fluorescence of leaves. The two instrumental setups composed for this purpose were (1) the Karlsruhe-Strasbourg UV-Laser Fluorescence Imaging System (Laser-FIS) and (2) the Karlsruhe Flash-Light Fluorescence Imaging System (FL-FIS). Essential results obtained with these instruments are summarized as well as the basic principles and characteristics of multi-colour fluorescence imaging. The great advantage of fluorescence imaging is that the fluorescence yield in the four fluorescence bands is sensed of several thousand up to 200,000 pixels per leaf area in one image. The multi-colour FIS technique allows to sense many physiological parameters and stress effects in plants at an early stage before a damage of leaves is visually detectable. Various examples of plant stress detection by the multi-colour FIS technique are given. Via imaging the Chl fluorescence ratio F690/F740 it is even possible to determine the Chl content of leaves. The FIS technique also allows to follow the successive uptake of diuron and loss of photosynthetic function and to screen the ripening of apples during storage., a2_Particularly meaningful and of high statistical relevance are the fluorescence ratio images red/far-red (F690/F740), blue/red (F440/F690), and blue/green (F440/F520) as well as images of the fluorescence decrease ratio RFd, which is an indicator of the net CO2 assimilation rates of leaves., H. K. Lichtenthaler., and Obsahuje bibliografické odkazy