Under the conditions of long-term storage of seeds in gene banks, seeds are subjected to natural aging process that results in decrease of their viability. Center for plant genetic resources of Moldova pays much attention to the development and introduction of physical and chemical methods that increase viability of seeds of different plant species under ex situ conservation. This work presents the results of investigations on use of millimeter radiation (MMR) for activation of germination processes of datura seeds (Datura stramonium L.) belonging to nightshade family (Solanaceae). In order to determine protective effect on seeds, temperature stress was additionally applied, namely – positive low temperature (LT). Separate and combined influence of these factors was studied in direct and reversed combinations (MMR+LT and LT+MMR). Experiments were carried at LT (2-4 оС) and MMR with the wavelength of 5.6 mm, power density of 6.6 mW/cm2 and 8- and 30-min exposures. These exposures in our preceding experiments have caused stimulating effects on seeds of other plant species (cereals, grains, vegetables, pulse and technical crops) [1,2,3]. Imbibed datura seeds were exposed to said treatment (for 14 hours). Morphophysiological parameters of seeds and seedlings were studied (germinating energy and germinability of seeds, length of rootlets, dry biomass of seedlings) in accordance with the International Rules of ISTA [4], in addition peroxidase enzyme activity in seedling rootlets was measured [5]. As much as 200 seeds were used in each variant. Stimulating effect of millimeter radiation was revealed in all studied parameters, maximum effect was observed at 30-min exposure. With respect to seed germinating energy stimulation was 35.5% as compared to control, with respect to seed germinability it was 3.9%, length of rootlets – 28.5%, dry biomass of rootlets – 55.0% (Fig.1). With separate influence of low temperature on seeds, viability of seeds assessed by studied parameters remained at the level of control. Combined influence of factors (MMR+LT and LT+MMR) on seeds caused stimulation of germination processes in all variants, i.e. both reparative and protective effects of MMR were manifested. It should be noted that radioprotective and radioreparative effects of MMR were discovered in preceding works on maize and triticale seeds with the use of millimeter radiation and gamma-radiation [6]. Fig.1. Morphophysiological parameters of datura seedlings exposed to treatment with MMR and LT Legend: 1 – control; 2 – MMR 8 min; 3 – MMR 30 min; 4 – LT; 5 – MMR 8 min + LT; 6 – MMR 30 min + LT; 7 – LT + MMR 8 min; 8 – LT + MMR 30 min Comparison of direct and reversed combinations of factors has demonstrated a more prominent protective effect of millimeter radiation, i.e. when seeds were treated with low temperature following their treatment with millimeter radiation. In this case (MMR 8 min + LT) seed germinating energy exceeded germinating energy in reversed combination (LT + MMR 8 min) by 20%, and the variant with MMR 30 min + LT exceeded reversed combination by 23.2% by this parameter. Similar patterns were noted with respect to seed germinability. Stimulation of seed germinability in these variants was 13.6 and 24.0%, respectively. Measurement of such morphophysiological parameters as length of rootlets and dry biomass of rootlets also allowed to make a conclusion on protective effect of millimeter radiation. Evaluation of datura seed viability by peroxidase enzyme activity in seedlings also was indicative of reparative and protective effects of millimeter radiation but protective effect on this parameter was more prominent than reparative effect. With the following combinations of factors: MMR 8 min + LT and MMR 30 min + LT peroxidase activity in seedlings exceeded that in reversed combinations by 1.6 and 1.5 times (Fig.2). Thus we can conclude that treatment of datura seeds with millimeter radiation with 30-min exposure after their long-term storage in gene bank results in significant increase of morphophysiological and biochemical parameters of seeds and seedlings. Combined application of physical factors makes stimulating effect of millimeter radiation even more prominent. Significant protective effect of millimeter radiation was noted when it was used in combination with low temperature. Fig.2. Perosidase enzyme activity in datura seedlings after treatment with MMR and LT. Legend: 1 – control; 2 – MMR 8 min; 3 – MMR 30 min; 4 – LT; 5 – MMR 8 min + LT; 6 – MMR 30 min + LT; 7 – LT + MMR 8 min; 8 – LT + MMR 30 min Therefore it seems appropriate to recommend this physical method for increase of datura seed viability under its ex situ conservation.