0012-4966/03/0304- $25.00 © 2003 MAIK “Nauka / Interperiodica” 0176 Doklady Biological Sciences, Vol. 389, 2003, pp. 176–179. Translated from Doklady Akademii Nauk, Vol. 389, No. 6, 2003, pp. 842–845. Original Russian Text Copyright © 2003 by Trunova, Astakhova, Deryabin, Sabel’nikova. According to the reaction induced by exposure to low temperature, plants fall into the following groups: frost-resistant, cold-tolerant, and cold-sensitive. Frost- resistant plants are able to withstand the formation of extracellular ice. Cold-tolerant plants are tolerant to low temperatures at which ice is not formed, and cold- sensitive plants are not tolerant to low positive temper- atures. Depending on specific genetic features and characteristics of temperature stress, the plants of these groups during the adaptation period produce cells of specific ultrastructure. It was shown that, in cells of frost-adapted plants of winter wheat and rye [1, 2] and wintering trees and shrub plants [3] exposed to hypothermia, there was cytoplasm proliferation, a decrease in the vacuole vol- ume, an increase in the vacuole electron density, an increase in the number of cell elements, and an increase in the number of plastoglobules. This prevented intrac- ellular ice formation and caused an increase in the plant resistance to the formation of extracellular ice. Exposure of cold-sensitive plants to low positive temperatures induces destructive changes in the cell ultrastructure: swelling of chloroplast stroma [4], rup- ture of chloroplast envelope and lamellae [5], a decrease in the number of ribosomes, and failure in the tonoplast intactness [6]. The changes in the structure of cells of cold-tolerant tomato plants (cultivar Sibirskii Skorospelyi) induced by long-term exposure to low positive temperatures were mainly manifested as the formation of xeromor- phous structure [7]. The following changes in the ultra- structure of plant cells were observed after the exposure at 6°C: a decrease in the areas of the cell, cytoplasm, chloroplast, grana, and starch grains; a decrease in the section count of chloroplasts, mitochondria, starch grains, and granal structures; and a decrease in the number of thylakoids per grana. It was suggested that these changes in the ultrastructure of tomato cells and chloroplasts should be regarded as manifestation of adaptive or protection responses rather than cell dam- age. It is well known that adaptation to hypothermia is accompanied by accumulation of sugars in cells of both frost-resistant and cold-tolerant plants. The main role in this process is played by invertase (β-D-fructofurano- side fructohydrolase, EC 3.2.1.26), the key enzyme of carbon metabolism. The activity of this enzyme is directly correlated with the ability of the plant to toler- ate exposure to low temperatures [8]. The monosaccha- rides produced as a result of hydrolysis not only pro- vide cryoprotective and osmoregulatory functions, but also are the main substrates of plastic and energy sub- stances required for the reorganization and formation of the resistance of cell structures to temperature stress [9]. To test this suggestion, we studied cold-tolerant potato plants transformed with the yeast invertase (YI) gene. It was shown in our earlier work that the trans- genic plants were characterized by a high invertase activity and an enhanced content of monosaccharides and disaccharides [10]. The goal of this work was to study the effect of transformation of potato plants with the YI gene on the chloroplast ultrastructure under normal conditions and after exposure to low temperature. Potato (Solanum tuberosum L., cv. Desiree) plants carrying the yeast invertase gene were the object of this study. The yeast invertase gene in the transgenic potato plants was controlled by the patatin class I promoter (B33) and contained the leader peptide sequence of pro- teinase II for the apoplast location of the enzyme. The plants transformed with the marker gene GUS (encod- ing β-glucoronidase) under the control of the 35S CaMV promoter were used as control. Transgenic plants also contained the canamycin resistance gene. Plants were obtained from Max-Plank Institut für Molekulare Pflanzenphysiologie (Germany). Plants were propagated by microcutting and grown for five weeks at a temperature of 22°C and a photope- riod of 16 h (light intensity, 5 klx) on the Murashige– Skoog agar medium (0.7%) containing 2% sucrose and GENERAL BIOLOGY Ultrastructural Organization of Chloroplasts of the Leaves of Potato Plants Transformed with the Yeast Invertase Gene at Normal and Low Temperature T. I. Trunova, N. V. Astakhova, A. N. Deryabin, and E. P. Sabel’nikova Presented by Academician L.N. Andreev December 9, 2002 Received December 16, 2002 Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, ul. Botanicheskaya 35, Moscow, 126276 Russia