A portable, microprocessor operated instrument for measuring chlorophyll fluorescence kinetics in stress physiology

Abstract

A portable instrument for measuring chlorophyll fluorescence induction kinetics is described and examples of measurements are given. The instrument is centered around a statistically‐mixed bifurcated optical fiber. One fiber branch guides the actinic light to the sample, whereas the other branch carries the emitted chlorophyll fluorescence to the photodetector. Scattered actinic light is cut out from the detector by a red interference filter. The instrument measures fast as well as slow fluorescence induction kinetics, but is particularly well designed for analyzing fast kinetics. The high time resolution and strong, variable actinic light mean that both F o (non‐variable fluorescence) and F m (maximal fluorescence at the P‐peak) are well defined. A built in microprocessor unit with attached memory stores the fluorescence induction curve and calculates key fluorescence parameters such as F o , F m , F v (variable fluorescence equals F m −F o ), F v /F m (the photochemical efficiency of photosystem II) and t 1/2 (half rise time from F o , to F m ). These values are digitally displayed after each recording and they (or the whole induction curve) can be stored in a memory and later retrieved. Because of a flexible setting of the instrument it can be used with high accuracy both for optically thick leaves and for diluted suspensions of algae or chloroplasts. A simple, light weight clamp cuvette for dark adaptation of leaves has been developed. It is equipped with a gate allowing the optical fiber to be inserted without daylight reaching the dark adapted portion of the leaf. The instrument has been developed for rapid monitoring of changes in activities and organization of the photosynthetic apparatus in vivo when plants are exposed to environmental stress both in the field and in the laboratory. Examples of measurements are given for differently treated leaves of Pinus sylvestris, Salix sp., Betula verrucosa, Zea mays, Epilobium angustifo‐lium and for chloroplast thylakoids isolated from Spinacia oleracea.