Measurement of non-photochemical quenching using the JTS-150 pump probe spectrometer – Application Note 5.

Introduction

In this application note, we describe how to measure Non- Photochemical Quenching (NPQ) using the JTS-150. This method has been long utilized by the previous models of JTS and provides data that is analogous to a pulsed-amplitude modulated (PAM) fluorometer. PAM fluorometers have been powerful tools that were based on the model that absorbed solar radiation which has 3 possible fates: to be released as heat, fluorescence, or drive photochemistry. The photochemical pathway leads to a quenching of observed fluorescence that is therefore referred to as photochemical quenching.

Chlorophyll fluorescence is a widely used technique and has been the subject of several excellent reviews that we would recommend before starting experiments if the techniques are unfamiliar, please see [1, 2, 3]. Separation of fluorescence quenching into photochemical and non-photochemical components was first achieved by the addition of 3-(3,4- dichlorophenyl)-1,1-dimethylurea (DCMU) to intact chloroplasts and Chlorella cells at points throughout the fluorescence induction curve. DCMU inhibits electron transfer from Q_A to the secondary quinone acceptor of PSII (Q_B), which results in a rapid reduction of Q_A and an in-crease in fluorescence as photochemical quenching is prevented. The development of PAM flu- orometers that use weak modulated measuring beams in which phase and frequency decoding are used to detect fluorescence yield changes enabled the routine, nondestructive, quantitative determination of photochemical and non-photochemical processes in leaves.