Detoxification of cadmium in tobacco plants: formation and active excretion of crystals containing cadmium and calcium through trichomes

• Published in: Planta Vol. 213; no. 1; pp. 45 - 50
• Main Authors: Choi, Y.-E., Harada, E., Wada, M., Tsuboi, H., Morita, Y., Kusano, T., Sano, H.
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-05-2001; Springer
• Subjects: Aluminum; Biological and medical sciences; Biotransformation; Cadmium; Cadmium - metabolism; Cadmium - toxicity; Calcium; Calcium - metabolism; Carbon; Cell Membrane - metabolism; Cell Surface Extensions - ultrastructure; Chemical Precipitation; Crystallization; Crystals; Fundamental and applied biological sciences. Psychology; Heavy metals; Nicotiana - physiology; Physiological diseases. Varia; Phytopathology. Animal pests. Plant and forest protection; Plant cells; Plant Epidermis - cytology; Plant Epidermis - metabolism; Plant Leaves - physiology; Plant Leaves - ultrastructure; Plants; Seedlings; Trichomes; Vacuoles - chemistry; Vacuoles - metabolism; Cadmium; Excretion; Calcium; Tolerance; Stimulant plant; Detoxication; Nicotiana tabacum; Soil pollution; Trichome; Stress; Heavy metal; Pollutant; Sensitivity resistance; Phytotoxicity; Dicotyledones; Morphology; Angiospermae; Spermatophyta; Solanaceae; Ionic crystals; Adaptation
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s004250000487

In tobacco (Nicotiana tabacum L.), long and short trichomes can be distinguished morphologically. The established function of long trichomes is to exude a sticky gum containing diterpenes, whereas that of short trichomes is not known. When tobacco seedlings were exposed to toxic levels of cadmium (Cd), growth was retarded, but trichome number was increased up to 2-fold in comparison with untreated samples. Observation by variable-pressure scanning electron microscopy (VP-SEM) indicated that large crystals of 150 μm in size were formed on head cells of both short and long trichomes. An energy-dispersive X-ray analysis system fitted with VP-SEM revealed the crystals to contain amounts of Cd and calcium (Ca) at much higher concentrations than in the head cells themselves. Transmission electron microscopy demonstrated crystal formation in amorphous osmiophilic deposits in vacuoles. When seedlings were treated with Cd in the presence of Ca, tolerance was increased in proportion to the increase in Ca concentration. These results indicate that tobacco plants actively exclude toxic Cd by forming and excreting Cd/Ca-containing crystals through the head cells of trichomes.