Investigation of photosynthesis and light protective mechanisms in sun and shade leaves using chlorophyll fluorescence measurements

Light response, light utilization and regulation involving carotenoids 

Shade leaves receive much less light than sun leaves. For sun leaves investment into high photosynthetic capacity is paid back as carbon gain, for shade leaves it is only to a small extent, and the leaves develop accordingly. But not only the average light conditions, but also their short-term variations require adaptation: Light intensities in the field change rapidly and strongly, with light energy absorption by leaves inevitably varying in close proportion. In the shade, where light is scarce, the energy of each photon absorbed by light-harvesting antennae must be efficiently transferred to the reaction center, and this is accomplished almost completely. In full sun however, with more than 50-fold higher light intensity, a complete energy transfer would lead to immediate destruction of the reaction center. Thus, antennae have to be partially de-coupled from the reaction centers in high light. With intermittent clouds, or with light flecks in forest canopies, the light intensity can easily increase 50-fold within minutes. Fast regulation is thus vital and indispensable. Excess light energy in antennae and reaction centers not used for (1) photosynthesis has to be safely dissipated as (2) heat or (3) fluorescence light to avoid damage to cell constituents.  

Analysis of chlorophyll fluorescence intensity under various conditions using modern equipment provides a means to distinguish between the three pathways for absorbed excitation energy, to quantify regulated light-protective mechanisms involving carotenoids and to calculate light utilization efficiencies in different light environments. 

Modern PC-controlled fluorometers allow quantitative measurements and analyses of chlorophyll fluorescence. Students use them to obtain light response curves of electron transport rates in the light reactions of photosynthesis in sun and shade leaves of beech (Fagus sylvatica) or ivy (Hedera helix). They determine the efficiencies of light use and carotenoid-based light protective mechanisms under different light conditions. We also demonstrate how light curves of photosynthesis and transpiration are measured as CO2 uptake and H2O release with contemporary equipment using infrared gas analysis. 

Duration: 1 Tag
Number of Participants: max. 16

Anpassungen bei Sonnen- und Schattenblättern: Lichtabhängigkeit des Elektronentransports, Lichtnutzungseffizienz und Lichtschutzmechanismen. Untersuchung durch quantitative Chlorophyll-Fluoreszenzmessung mit PAM-Fluorometern

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Moderne, von Laptops gesteuerte PAM-Fluorometer ermöglichen die quantitative Messung der Chlorophyllfluoreszenz unter verschiedenen Belichtungsbedingungen. Damit nehmen wir Lichtkurven des Elektronentransports von Licht- und Schattenblättern auf, bestimmen ihre Licht-Nutzungseffizienz und untersuchen Schutzmechanismen zur Entsorgung überoptimaler Lichtenergie. Wir arbeiten in Kleingruppen mit Blättern der Buche oder des Efeu. Als Demonstration werden mit einem modernen Messgerät unter kontrollierten Bedingungen Lichtkurven der Photosynthese von Sonnen- und Schattenblättern durch Infrarot-Gas-Analyse gemessen.

Der Kurs ist geeignet für Schüler der Oberstufe und kann gut mit dem Kurs Anpassungen bei Licht- bzw. Schattenblättern: Quantitative Untersuchung der Pigment-Ausstattung, des Blattbaus und der Lichtabhängigkeit der Photosynthese kombiniert werden. 

Dauer: ½ Tag

Max. Teilnehmerzahl: 16

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