Salt stress impact on the molecular structure and function of the photosynthetic apparatus--the protective role of polyamines.

In the present study the green alga Scenedesmus obliquus was used to assess the effects of high salinity (high NaCl-concentration) on the structure and function of the photosynthetic apparatus and the possibility for alleviation by exogenous putrescine (Put). Chlorophyll fluorescence data revealed the range of the changes induced in the photosynthetic apparatus by different NaCl concentrations, which altogether pointed towards an increased excitation pressure. At the same time, changes in the levels of endogenous polyamine concentrations, both in cell and in isolated thylakoid preparations were also evidenced. Certain polyamine changes (Put reduction) were correlated with changes in the structure and function of the photosynthetic apparatus, such as the increase in the functional size of the antenna and the reduction in the density of active photosystem II reaction centers. Thus, exogenously added Put was used to compensate for this stress condition and to adjust the above mentioned changes, so that to confer some kind of tolerance to the photosynthetic apparatus against enhanced NaCl-salinity and permit cell growth even in NaCl concentrations that under natural conditions would be toxic.