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, Lors de l'absorption d'un photon, la chlorophylle a passe d'un état fondamental à un état excité supérieur ou inférieur selon l'énergie du photon. Cet état est instable et afin de retrouver son état fondamental, la chlorophylle passe successivement de l'état excité supérieur à inférieur en émettant de la chaleur et de l'état excité inférieur à l'état fondamentale, soit en réémettant un photon (fluorescence), en transférant son énergie à une molécule voisine (résonnance) ou, enfin, en perdant un électron (photochimie), Synthèse sur les mesures fluorimétriques La photosynthèse est le processus photochimique qui permet aux organismes chlorophylliens de synthétiser de la matière organique à partir de dioxyde de carbone, d'eau et d'énergie lumineuse

. Kalaji, Le rendement quantique de fluorescence est donc variable. En effet, le changement brutal du niveau d'illumination induit une augmentation rapide du rendement quantique de fluorescence qui atteint un maximum en un temps de l'ordre de la seconde. L'augmentation du rendement de fluorescence est due à la diminution rapide des accepteurs d'électrons dans la chaîne d'oxydoréduction. Cette absence d'accepteurs disponibles diminue l'efficacité photosynthétique de la plante. Ce phénomène induit à court terme une augmentation du rendement de fluorescence qui est une voie de dissipation de l'excès d'énergie absorbée. Par la suite, le rendement de fluorescence diminue lentement jusqu'à atteindre un niveau stationnaire (Fs), ce spectre, les lumières bleues et rouges excitent la chlorophylle plus efficacement que la lumière verte, 2017.

. Schreiber, Cette courbe (classiquement appelées transitions « OJIP ») est généralement représentée sur une échelle de temps logarithmique, afin de permettre la visualisation des trois étapes sur un seul graphique. Ces étapes se rapportent à 3 processus différents, La mesure de la variation de l'intensité de fluorescence apporte donc une information sur la capacité du système photosynthétique à convertir l'énergie lumineuse, 1995.

, ? JI représente la réduction du pool de plastoquinone ? IP représente la réduction du côté accepteur d'électrons du photosystème I (PSI)

, Par leur sensibilité à l'état redox des composants de la chaine de transport d'électrons, les mesures de fluorescence permettent de suivre de manière indirecte et d'interpréter de nombreux processus ayant lieu durant le transport d'électrons