Estimation of Chlorophyll in Tobacco Leaves by Direct Photometry

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