| Tobacco (Nicotiana tabacum) is an important cash crop in our country. Cadmium (Cd) is a main factor which can affect its quality. Tobacco can accumulate Cd easily and the majority of Cd absorbed by it accumulates in its leaves, which is a danger to our healthy. Cd can not only affect the growth of tobacco, but also do affect the quality of it. The present study was conducted to investigate the effect abscisic acid (ABA) on the growth and Cd accumulation between two varieties of N. tabacum L.,’MS yunyan87’and’MSK326’. Experiments were also conducted to research metallothionein of Elsholtzia haichowensis on growth and cadmium accumulation of tobacco. Moreover, a pot experiment was conducted to study the effects of five different amendments on the fractions of Cd and available Cd concentration in a polluted soil and Cd concentration in shoot of N. tabacum L.’MSK326’.1. Hydroponic cultures were conducted to investigate the effect of ABA on tolerance and accumulation of Cd between two varieties of N. tabacum L.,’MS yunyan87’and ’MSK326’. A significant decrease in the dry weight, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration and transpiration rate was found in two varieties of N. tabacum L.. The dry weight of’MSK326’was higher than that of’MS yunyan87’when exposed to 50 μM Cd. With the same treatment, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration and Cd accumulation in shoots of ’MSK326’were higher than those of’MS yunyan87’. The Cd concentration in shoots and roots of two varieties of N. tabacum L. increased with the increasing Cd treatment concentration. In all treatments, Cd concentrations were higher in the roots than that in the shoots. Abscisic acid (ABA) is an important phytohormone involved in stress resistance of plants, which can help the stoma close when the plants are under stress. The results showed that in the presence of 50 μM CdCl2, exogenous ABA treatment increased the Cd concentration in roots and reduced Cd concentration in shoots.The transport of Cd from root to the shoots was also inhibited. The percentage of shoot/total Cd content showed a significantly correlation between the transpiration rate.2. In order to explain the role of MT in the process of Cd tolerance, hydroponic cultures were conducted to investigate the difference of Cd-tolerance and accumulation of Cd between wild-type and the transgenic tobacco over-expressed EhMTl. The net root length, dry weight and net photosynthetic rate of the transgenic type were higher^than the wild-type when exposed 20 μM CdCl2. All this showed that the transgenic type was more tolerant to Cd. The Cd concentration in shoots and roots of two genetype of tobacco increased with the increasing Cd treatment concentration. In all treatments, Cd concentrations in the roots were higher than that of the shoots. We also found that the transgenic type tend to turn Cd mainly stored in the cytoplasm, while the wild-type turn Cd stored in the organelles. This may related to the transgenic type have more expression of MT in the cytoplasm, which could combine more Cd.3. A pot experiment was conducted to study the effects of five different amendments on the fractions of Cd in a polluted soil and Cd concentration in shoot of N. tabacum L.’MSK326’. The result showed that the main fraction of Cd was exchange-able in the soil. Addition of amendments increased soil pH to some extent, and thereby the available Cd concentration in the soil was reduced. The transformation of Cd fractions caused by the amendments was mainly between exchangeable Cd and residual Cd, and this led to the decline of Cd bioavailability. Compared with the control treatment, amendments reduced the content of Cd in shoot to some extent, and biochar was best among all amendments. The Cd concentration in shoot showed a significantly correlation between the available Cd concentration in soil. |
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