Effects Of Exogenous Spermidine On Ultrastructure And Function Of Chloroplast Of Salicornia Bigelovii Torr. Suffering Salt Stress

Polyamine is a kind of important antioxidants which have close relationship with the tolerance of plant under stress. S. bigelovii were chosen as experimental materials in this paper. The effects of exogenous spermidine on ultrastructure of chloroplast, polyamine content in leaves and chloroplasts and photosynthetic efficiency of S. bigelovii under salt stress were investigated. The results are as follows:First, seedlings of S. bigelovii were treated with different concentrations of NaCl (0, 100,200,300,400,500 mM). Three kind of polyamines (Put, Spm and Spd) and their different forms (free, perchioric acid soluble and insoluble conjugated) were investigated under NaC1 and exogenous spermidine treatment. The results showed that three forms of the Put both increased at first and then decreased under salt treatment. The free form of Spd and the bound state of Spm increased all the time. The free form of Spd, the conjugated state of the content of Spd and Spm and the bound state of Spd both increased at first and then decreased. Ultimately, the final total PAs of the free and bound was both increased all the time, while the the conjugated state content increased at first and then decreased. All the three forms of the three polyamines of (Spd+Spm)/Put ratio increased at first and then decreased, while the Put/PAs ratio was opposite.Exogenous Spd increased the conjugated and bound form of the polyamines contents. At the same time, exogenous Spd also increased the free and bound states of (Spd+Spm)/Put ratio,In addition, exogenous Spd could accelerate the free form of Spd transforming to spm and also be beneficial to the combination of small molecules and large molecules which could lead to the increace of conjugated states and bound states, indicating that exogenous Spd could be involved in the regulation of PAs metabolism and play an important role in enhancing salt tolerance in seedlings.Second, the effects of exogenous spermidine on ultrastructure of chloroplast and levels of thylakoid proteins of chloroplasts were measured. The data showed that soluble protein content increased at first and then decreased with the increasing of NaC1 concentration. Exogenous spermidine could increase the soluble protein content of S. bigelovii under salt stress. The results of transmission electron micros observation indicated that the optimal concentration of S. bigelovii was 300 mM. The structure of chloroplast was both damaged under and over 300 mM. However, exogenous spermidine alleviated the salt-induced membranes injury of chloroplast. The results of SDS-PAGE revealed that the amounts of 33 kD,23 kD and 17 kD subunits were reduced under NaC1 treatment especially at 0 and 100mM NaCl contention. The amounts of 47kD,43kD,33 kD,23 kD and 17 kD subunits increased with different degrees with treatment of exogenous spermidine. However, there was no markedly change of 28 kD and 25 kD subunits with treatment of exogenous spermidine.Third, the effects of exogenous sermdine (Spd) on the three polyamines in chloroplast and photosynthetic efficiency of S. bigelovii was studied present. The results showed that the chlorophyll content, photosynthetic rate (Pn), stomatal conductance (Gs) both increased at first with with the increasing of NaCl concentration and then decreased with high NaCl concentration. However, intercellular CO2 concentration (Ci) decreased at first and then increased. Exogenous spermidine enhanced the content of chlorophyll, Pn, Gs. The free form of Put in chloroplast decreased at first and then increased with single NaCl treatment. In contrast, Spd increased all the time and spm increased at first and then decreased. With the different change of three polyamines, the PAs and (Spd+Spm)/Put of chloroplast increased at first and then decreased, while the Put/PAs ratio was opposite. Exogenous Spd significantly increased chloroplast bound state of three levels of polyamines which suggest that exogenous Spd can be beneficial to the accumulation of polyamines in chloroplast and alleviate the metabolic disturbance of polyamines caused by NaCl in S. bigelovii.