Estimation of Chlorophyll in Tobacco Leaves by Direct Photometry

A simple portable instrument utilizing a cadmium sulphide light-dependentresistor in a bridge circuit, and its use in the in vivo estimationof total chlorophyll content of tobacco leaves, are described.The method has wide applicability in plant physiological andnutritional research, and in agriculture. The relationship betweeninstrument readout and chlorophyll content (calibration curve)was nearly parabolic and was determined largely by the light-scatteringproperties of the leaf. The effects of some environmental andplant parameters on this relationship and on the precision ofthe estimation were analysed. The importance of sampling procedurewas emphasized by a marked heterogeneity of chlorophyll distributionfound within leaves of all ages. A scattered-transmission spectrophotometerwas found to give the same type of calibration curve, and wasused to demonstrate that the ‘reference wavelength’correction used by previous authors has no effect on the shapeof the curve or the precision of the method.