Chlorophyll Fluorescence: A Physiological Mechanism and a Physical Tool in Plant Eco-Physiological Studies

Abstract

The equation E = mc2 is universal and is equally applicable in all physical, chemical and biological occurrences. Chlorophyll a fluorescence is one of the best examples of such phenomenons occurring in photosynthetically active biological systems which work on a very simple principle. Being the exclusive photoactive chromophore of all reaction centres and which also converts and store incoming excitation energy in the form of an oxidoreduction potential, the main photoactive pigment Chlorophyll a, is invariably present in all oxygenic photosynthetic organisms. The transport of electrons and protons from water to nicotinamide-adenine-dinucleotide-phosphate (NADP) and also in the phosphorylation of ADP to ATP is the main route through which the absorbed light energy is utilized. Light energy absorbed by chlorophyll molecules in a leaf can be utilized for one of the three mechanisms: a bio-chemical mechanism in which it can be used in photochemistry, or a bio-physical mechanism in which either the excess energy can be dissipated as heat through xanthophylls or can be re-emitted as light-induced chlorophyll fluorescence. Due to the competition among all three bio-chemical and bio-physical processes, any decrease in the efficiency of one is always associated with a corresponding increase in one or both of the remaining processes. Therefore, changes in the efficiency of photochemistry and heat dissipation can be gained through determining the yield of chlorophyll fluorescence.