A solid-state device for the simultaneous measurement of prompt and delayed chlorophyll fluorescence induction transients in leaves

This paper describes a totally solid-state device designed to monitor simultaneously both prompt and delayed fluorescence transients in leaves. The light source is a filtered high intensity light emitting diode (LED) with a maximum usable output of 50 μE/m 2/sec. The sensor consists of a very sensitive photo-diode-operational amplifier combination (9 × 10 7 V/W; 0.25-msec response time). Circuitry was designed to pulse the LED (0- to 25-msec pulse) and to intensify the trace monitored with a storage oscilloscope. The probe unit containing the emitter and sensor was designed so that the effects of different gas atmospheres and different temperatures could be studied. The effects of temperature on the performance of the device are described. Examples of simultaneous traces of prompt and delayed fluorescence are shown to indicate that good resolution of both phenomena can be obtained. To illustrate the utility of the device the low-temperature kinetics of prompt and delayed fluorescence of avocado ( Persea americana Mill.) are contrasted with the kinetics at room temperature.