UV spectra represent a unique observational tool to investigate both physics and chemistry of stars owing to the occurence, in this wavelength range, of the resonance spectral transitions, i.e. the most intense transitions for most common atoms, ions and molecules. WSO-UV spectrographs will provide good opportunities of such studies. In the figure above the spectral energy distributions for three Main Sequience stars with different effective temperatures are presented. Blue area shows spectral range covered by WSO-UV spectrographs.