Cold stress effects on organelle ultrastructure in polar Caryophyllaceae species

Abstract: This study investigated leaf mesophyll cells of Caryophyllaceae plants growing in polar regions – Cerastium alpinum and Silene involucrata from the Hornsund region of Spitsbergen island (Svalbard Archipelago, Arctic), and Colobanthus quitensis from the Ad− miralty Bay region on King George Island (South Shetland Islands, West Antarctic). Ultra− structural changes were analyzed in mesophyll protoplasts of plants growing in natural Arctic and Antarctic habitats and plants grown in a greenhouse, including plants exposed to short−term cold stress under semi−controlled conditions. Cell organelles of plants growing in natural polar habitats and greenhouse−grown plants were characterized by significant mor− phological plasticity.Chloroplasts of plants studied in this work formed variously shaped pro− trusions and invaginations that visibly increased the contact area between adjacent cell com− partments and reduced the distance between organelles. S. involucrata plants grown under greenhouse conditions, tested by us in this work, were characterized by highly dynamic cell nuclei with single or multiple invaginations of the nuclear membrane and the presence of channels and cisternae filled with cytoplasm and organelles. Crystalline inclusion proteins were observed in the cell nuclei of C. quitensis between nuclear membranes and in the direct proximity of heterochromatin. Our study revealed significant conformational dynamics of organelles, manifested by variations in the optical density of matrices, membranes and envelopes, in particular in C. quitensis, which could suggest that the analyzed Caryophyllaceae taxa are well adapted to severe climate and changing conditions in polar regions

Cold stress effects on organelle ultrastructure in polar Caryophyllaceae species

Abstract: This study investigated leaf mesophyll cells of Caryophyllaceae plants growing in polar regions -Cerastium alpinum and Silene involucrata from the Hornsund region of Spitsbergen island (Svalbard Archipelago, Arctic), and Colobanthus quitensis from the Ad− miralty Bay region on King George Island (South Shetland Islands, West Antarctic). Ultra− structural changes were analyzed in mesophyll protoplasts of plants growing in natural Arctic and Antarctic habitats and plants grown in a greenhouse, including plants exposed to short−term cold stress under semi−controlled conditions. Cell organelles of plants growing in natural polar habitats and greenhouse−grown plants were characterized by significant mor− phological plasticity. Chloroplasts of plants studied in this work formed variously shaped pro− trusions and invaginations that visibly increased the contact area between adjacent cell com− partments and reduced the distance between organelles. S. involucrata plants grown under greenhouse conditions, tested by us in this work, were characterized by highly dynamic cell nuclei with single or multiple invaginations of the nuclear membrane and the presence of channels and cisternae filled with cytoplasm and organelles. Crystalline inclusion proteins were observed in the cell nuclei of C. quitensis between nuclear membranes and in the direct proximity of heterochromatin. Our study revealed significant conformational dynamics of organelles, manifested by variations in the optical density of matrices, membranes and enve− lopes, in particular in C. quitensis, which could suggest that the analyzed Caryophyllaceae taxa are well adapted to severe climate and changing conditions in polar regions

Changes in soluble carbohydrates in polar Caryophyllaceae and Poaceae plants in response to chilling

Abstract Four species of flowering plants comprising Arctic populations of Cerastium alpinum and Poa arctica var. vivipara and indigenous Antarctic species Colobanthus quitensis and Deschampsia antarctica were investigated. Plants derived from natural origins were grown in an experimental greenhouse in Poland (53�470N and 20�300E latitude). Plants for experiment were collected during spring of 2010. Soluble carbohydrates in the intact shoots of C. alpinum and C. quitensis, polar plants of the family Caryophyllaceae, and D. antarctica and P. arctica var. vivipara, representatives of the family Poaceae, were analyzed by gas chromatography, and their involvement in the plants’ response to chilling stress was examined. Plant tissues of the examined families growing in a greenhouse conditions (18–20 �C, short day 10/14 h light/darkness) differed in the content and composition of soluble carbohydrates. In addition to common monosaccharides, myo-inositol and sucrose, Caryophyllaceae plants contained raffinose family oligosaccharides (RFOs), D-pinitol and mono-galactosyl pinitols. RFOs and D-pinitol were not detected in plants of the family Poaceae which contain 1-kestose, a specific tri-saccharide. The accumulation of significant quantities of sucrose in all investigated plants, RFOs in Caryophyllaceae plants and 1-kestose in Poaceae plants in response to chilling stress(4 �C for 48 h with a long day photoperiod, 20/4 h) indicates that those compounds participate in the stress response. The common sugar accumulating in cold stress response and probably most important for chilling tolerance of four investigated plants species seems to be sucrose. On the other hand, the accumulation of above-mentioned carbohydrates during chilling stress can be a return to sugars metabolism, occurring in natural environmental conditions. No changes in D-pinitol concentrations were observed in the tissues of C. alpinum and C. quitensis plants subjected to both low and elevated temperatures, which probably rules out the protective effects of D-pinitol in response to cold stress

The influence of short-term cold stress on the metabolism of non-structural carbohydrates in polar grasses

Plants adapt to extremely low temperatures in polar regions by maximizing their photosynthetic efficiency and accumulating cryoprotective and osmoprotective compounds. Flowering plants of the family Poaceae growing in the Arctic and in the Antarctic were investigated. Their responses to cold stress were analyzed under laboratory conditions. Samples were collected after 24 h and 48 h of cold treatment. Quantitative and qualitative changes of sugars are found among different species, but they can differ within a genus of the family Poaceae. The values of the investigated parameters in Poa annua differed considerably depending to the biogeographic origin of plants. At the beginning of the experiment, Antarctic plants were acclimatized in greenhouse characterized by significantly higher content of sugars, including storage reserves, sucrose and starch, but lower total protein content. After 24 h of exposure to cold stress, much smaller changes in the examined parameters were noted in Antarctic plants than in locally grown specimens. Total sugar content and sucrose, starch and glucose levels were nearly constant in P. annua, but they varied significantly. Those changes are responsible for the high adaptability of P. annua to survive and develop in highly unsupportive environments and colonize new regions

Glutathione Transferase U13 Functions in Pathogen-Triggered Glucosinolate Metabolism

Glutathione (GSH) and indole glucosinolates (IGs) exert key functions in the immune system of the model plant Arabidopsis (Arabidopsis thaliana). Appropriate GSH levels are important for execution of both pre-and postinvasive disease resistance mechanisms to invasive pathogens, whereas an intact PENETRATION2 (PEN2)-pathway for IG metabolism is essential for preinvasive resistance in this species. Earlier indirect evidence suggested that the latter pathway involves conjugation of GSH with unstable products of IG metabolism and further processing of the resulting adducts to biologically active molecules. Here we describe the identification of Glutathione-S-Transferase class-tau member 13 (GSTU13) as an indispensable component of the PEN2 immune pathway for IG metabolism. gstu13 mutant plants are defective in the pathogen-triggered biosynthesis of end products of the PEN2 pathway, including 4-O-b-D-glucosyl-indol-3-yl formamide, indole-3-ylmethyl amine, and raphanusamic acid. In line with this metabolic defect, lack of functional GSTU13 results in enhanced disease susceptibility toward several fungal pathogens including Erysiphe pisi, Colletotrichum gloeosporioides, and Plectosphaerella cucumerina. Seedlings of gstu13 plants fail also to deposit the (1,3)-b-glucan cell wall polymer, callose, after recognition of the bacterial flg22 epitope. We show that GSTU13 mediates specifically the role of GSH in IG metabolism without noticeable impact on other immune functions of this tripeptide. We postulate that GSTU13 connects GSH with the pathogen-triggered PEN2 pathway for IG metabolism to deliver metabolites that may have numerous functions in the innate immune system of Arabidopsis