Laser spectroscopic CT images at different regions of an intact cactus plant are reported using coherent detection imaging system based on the optical heterodyne detection method. The images were obtained at the wavelengths of 714.5nm and 1319nm with continuous wave and single frequency Ti: Al2O3 and Nd: YAG lasers, respectively. These laser CT images exhibit clear wavelength dependence that can differentiate the plant internal structure. We attribute the difference in the reconstructed images to the change in the water attenuation coefficients at the wavelengths used in our study. Our results demonstrate that the coherent, detection imaging method offers a novel means to image in noninvasive and non-contact ways the plant internal structure and to monitor functional aspects of plant tissues such as water transport and water content. The potential application of our technique is expected in the fields of agriculture, horticulture, forestry and environmental studies and monitoring in the future.