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

Abstract

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 microm 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.

Alleviation by calcium of cadmium-induced root growth inhibition in Arabidopsis seedlings

“…In tobacco, Cd tolerance was increased in the presence of Ca, probably due to the active exclusion of toxic Cd by the formation and excretion of Cd/Ca containing crystals through the head cells of trichomes (Choi et al 2001). It was also previously reported that the accumulation of Cd on seed germination of radish is reduced by high concentration of Ca (Rivetta et al 1997).…”

“…Extraction and measurement of Cd was performed as previously described (Harada et al 2001). Two-week-old Arabidopsis seedlings, which were cultivated in 10 ml half strength MS medium supplemented with 1% sucrose, were treated with 500 mM CdCl 2 in the presence or absence of 30 mM CaCl 2 for 24 h. At first, the sample was washed twice with distilled water, and then five volumes of precooled Tris-HCl (50 mmol/L, pH 7.2) buffer and sea sand C (Nakalai Tesque) were added.…”

“…Tissues were homogenized with sea sand C and the crude extract was centrifuged at 12,500ϫg for 15 min. The supernatant was diluted with 19 volumes of the buffer solution and the concentration of Cd was measured with an atomic absorption/film emission spectrophotometer (AA-6500S, Shimadzu, Kyoto, Japan) as described (Harada et al 2001). …”

Investigation of metal exudates from tobacco glandular trichomes under heavy metal stresses using a variable pressure scanning electron microscopy system

“…The culture conditions of plants were described in Choi et al (2001) and Sarret et al (2006). Briefly, for the hydroponic cultures, seeds were germinated on solid medium-filled PCR tubes and transferred after 3 weeks to 1.5-L pots (three plants per pot) filled with one-tenthstrength Hoagland medium.…”

Comparative Metabolomics of Transgenic Tobacco Plants (Nicotiana tabacum var. Xanthi) Reveals Differential Effects of Engineered Complete and Incomplete Flavonoid Pathways on the Metabolome

“…In addition, oxalic acid accumulated at higher levels in ANR plants in a pattern similar to that of the cembranoids. Oxalate, which accumulates in glandular trichomes and idioblast cells of Nicotiana species (Choi et al 2001;Sarret et al 2006;VolkA and Franceschi 2000), is the calcium salt of oxalic acid and has important defensive activities against chewing insects (Korth et al 2006). We microscopically examined trichomes, but did not observe changes of their morphology and density on the surfaces of stems and leaves between transgenic and WT tobacco plants (Fig.…”