scholarly journals Winter survival of the unicellular green alga Micrasterias denticulata: insights from field monitoring and simulation experiments

PROTOPLASMA ◽  
2021 ◽  
Author(s):  
Philip Steiner ◽  
Othmar Buchner ◽  
Ancuela Andosch ◽  
Andreas Holzinger ◽  
Ursula Lütz-Meindl ◽  
...  
Keyword(s):  
Water Temperature ◽  
Cold Acclimation ◽  
Freezing Stress ◽  
Ultrastructural Changes ◽  
Peat Bog ◽  
Unicellular Green Alga ◽  
Micrasterias Denticulata ◽  
Ice Encasement ◽  
Peat Bog Pools ◽  
Acclimation Treatment

AbstractPeat bog pools around Tamsweg (Lungau, Austria) are typical habitats of the unicellular green alga Micrasterias denticulata. By measurement of water temperature and irradiation throughout a 1-year period (2018/2019), it was intended to assess the natural environmental strain in winter. Freezing resistance of Micrasterias cells and their ability to frost harden and become tolerant to ice encasement were determined after natural hardening and exposure to a cold acclimation treatment that simulated the natural temperature decrease in autumn. Transmission electron microscopy (TEM) was performed in laboratory-cultivated cells, after artificial cold acclimation treatment and in cells collected from field. Throughout winter, the peat bog pools inhabited by Micrasterias remained unfrozen. Despite air temperature minima down to −17.3 °C, the water temperature was mostly close to +0.8 °C. The alga was unable to frost harden, and upon ice encasement, the cells showed successive frost damage. Despite an unchanged freezing stress tolerance, significant ultrastructural changes were observed in field-sampled cells and in response to the artificial cold acclimation treatment: organelles such as the endoplasmic reticulum and thylakoids of the chloroplast showed distinct membrane bloating. Still, in the field samples, the Golgi apparatus appeared in an impeccable condition, and multivesicular bodies were less frequently observed suggesting a lower overall stress strain. The observed ultrastructural changes in winter and after cold acclimation are interpreted as cytological adjustments to winter or a resting state but are not related to frost hardening as Micrasterias cells were unable to improve their freezing stress tolerance.

Fluorescence as a tool in photosynthesis research: application in studies of photoinhibition, cold acclimation and freezing stress

1989 ◽  
Vol 323 (1216) ◽  
pp. 281-293 ◽  
Keyword(s):  
Quantum Yield ◽  
Cold Acclimation ◽  
Spinacia Oleracea ◽  
Photosynthetic Apparatus ◽  
Fluorescence Induction ◽  
High Light ◽  
Thermal Dissipation ◽  
Freezing Stress ◽  
Chlorophyll Fluorescence Induction ◽  
Freezing And Thawing

Chlorophyll fluorescence induction (at 20 °C and 77 K) and quenching were analysed in relation to effects of environmental stresses imposed by chilling in high light and by freezing and thawing of spinach ( Spinacia oleracea L.) leaves. The data indicate that cold acclimation of spinach plants, which leads to increased frost tolerance of the leaves, results in decreased susceptibility to photoinhibition of photosynthesis at chilling temperatures. When plants acclimated to 18 °C and 260-300 µmol quanta m -2 s -1 were exposed to higher light (550 µmol quanta m -2 s -1 ) at 4 °C, they developed strong photoinhibition, as characterized by decreased quantum yield of O 2 evolution and decreased ratio of variable: maximum fluorescence (F V /F M ) of photosystem II. The decrease in F V /F M resulted from a decline in F V and an increase in F 0 . The F V /F M ratio was lowered to a significantly greater extent when induction was recorded at 20 °C, as compared with 77 K. The effects related to photoinhibition were fully reversible at 18 °C in dim light. Plants that had been cold-acclimated for 10 days exhibited slightly decreased quantum yield and lowered F V /F M ratio. However, they did not show further photoinhibition on exposure to 550 µmol quanta m -2 s -1 at 4 °C. The reversible photoinhibition is discussed as a protective pathway serving for thermal dissipation of excessive light energy. It is hypothesized that such a mechanism prevents destruction of the photosynthetic apparatus, until other means of protection become effective during long-term acclimation to high light. Inhibition of photosynthetic carbon assimilation caused by freezing and thawing of leaves in the dark was closely correlated with inhibition of photochemical fluorescence quenching (q Q ). As a sensitive response of the thylakoid membranes to freezing stress, the energy-dependent quenching, q E , was inhibited. Only more severe impact of freezing caused a significant decline in the F V /F M ratio. It is concluded that measurements of fluorescence induction signals ( F V /F M ratios) provide a sensitive tool with which to investigate photoinhibition, whereas freezing damage to the photosynthetic system can be detected more readily by the quenching coefficients q Q and q E than by F V /F M ratios.

Ultrastructural changes in shoot apex cells of winter wheat seedlings during ice encasement

1978 ◽  
Vol 56 (7) ◽  
pp. 786-794 ◽  
Author(s):  
M. Keith Pomeroy ◽  
Chris J. Andrews
Keyword(s):  
Endoplasmic Reticulum ◽  
Winter Wheat ◽  
Structural Integrity ◽  
Triticum Aestivum L ◽  
Ultrastructural Changes ◽  
Wheat Seedlings ◽  
Contrast Exposure ◽  
Ice Encasement ◽  
Cold Hardy ◽  
Cellular Organelles

The decline in viability of cold-hardy Kharkov winter wheat (Triticum aestivum L.) seedlings during ice encasement at −1 °C was accompanied by characteristic ultrastructural changes. A dramatic increase in endoplasmic reticulum was observed within a few days. This proliferation of endoplasmic reticulum often resulted in the formation of an elaborate series of parallel membranes, either dispersed randomly throughout the cytoplasm or in the form of concentric whorls. However, the structural integrity of many cellular organelles was largely unaffected even by prolonged ice encasement resulting in death of the plants. In contrast, exposure of cold-hardy seedlings to near lethal, subfreezing temperature resulted in severe disorganization of cellular organelles. Ice encasement of nonhardened seedlings resulted in complete kill within 4 h. After 16 h ice encasement, occasional concentric whorls of endoplasmic reticulum and copious amounts of osmiophilic material were observed in the cytoplasm. Upon removal of the ice encasement stress, the accumulated endoplasmic reticulum disappeared rapidly during recovery at either2 or20 °C.

scholarly journals Fusion of Mitochondria to 3-D Networks, Autophagy and Increased Organelle Contacts are Important Subcellular Hallmarks during Cold Stress in Plants

2020 ◽  
Vol 21 (22) ◽  
pp. 8753
Author(s):  
Philip Steiner ◽  
Othmar Buchner ◽  
Ancuela Andosch ◽  
Gerhard Wanner ◽  
Gilbert Neuner ◽  
...  
Keyword(s):  
Low Temperature ◽  
Temperature Stress ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Low Temperature Stress ◽  
Freezing Stress ◽  
Electron Microscopic ◽  
Natural Habitats ◽  
Ultrastructural Alterations ◽  
Micrasterias Denticulata

Low temperature stress has a severe impact on the distribution, physiology, and survival of plants in their natural habitats. While numerous studies have focused on the physiological and molecular adjustments to low temperatures, this study provides evidence that cold induced physiological responses coincide with distinct ultrastructural alterations. Three plants from different evolutionary levels and habitats were investigated: The freshwater alga Micrasterias denticulata, the aquatic plant Lemna sp., and the nival plant Ranunculus glacialis. Ultrastructural alterations during low temperature stress were determined by the employment of 2-D transmission electron microscopy and 3-D reconstructions from focused ion beam–scanning electron microscopic series. With decreasing temperatures, increasing numbers of organelle contacts and particularly the fusion of mitochondria to 3-dimensional networks were observed. We assume that the increase or at least maintenance of respiration during low temperature stress is likely to be based on these mitochondrial interconnections. Moreover, it is shown that autophagy and degeneration processes accompany freezing stress in Lemna and R. glacialis. This might be an essential mechanism to recycle damaged cytoplasmic constituents to maintain the cellular metabolism during freezing stress.

scholarly journals iTRAQ-Based Comparative Proteomic Analysis of the Roots of TWO Winter Turnip Rapes (Brassica rapa L.) with Different Freezing-Tolerance

2018 ◽  
Vol 19 (12) ◽  
pp. 4077 ◽  
Author(s):  
Xiucun Zeng ◽  
Yaozhao Xu ◽  
Jinjin Jiang ◽  
Fenqin Zhang ◽  
Li Ma ◽  
...  
Keyword(s):  
Cold Acclimation ◽  
Linolenic Acid ◽  
Brassica Rapa ◽  
Freezing Tolerance ◽  
Stress Responses ◽  
Molecular Mechanisms ◽  
Carbon Fixation ◽  
Freezing Stress ◽  
Turnip Rape ◽  
Mannose Metabolism

The freezing tolerance of roots is crucial for winter turnip rape (Brassica rapa L.) survival in the winter in Northwest China. Cold acclimation (CA) can alleviate the root damage caused by freezing stress. To acknowledge the molecular mechanisms of freezing tolerance in winter turnip rape, two Brassica rapa genotypes, freezing stressed after the induction of cold acclimation, were used to compare the proteomic profiles of roots by isobaric tags for relative and absolute quantification (iTRAQ). Under freezing stress (−4 °C) for 8 h, 139 and 96 differentially abundant proteins (DAPs) were identified in the roots of “Longyou7” (freezing-tolerant) and “Tianyou4” (freezing-sensitive), respectively. Among these DAPs, 91 and 48 proteins were up- and down-accumulated in “Longyou7”, respectively, and 46 and 50 proteins were up- and down-accumulated in “Tianyou4”, respectively. Under freezing stress, 174 DAPs of two varieties were identified, including 9 proteins related to ribosome, 19 DAPs related to the biosynthesis of secondary metabolites (e.g., phenylpropanoid and the lignin pathway), and 22 down-accumulated DAPs enriched in oxidative phosphorylation, the pentose phosphate pathway, fructose and mannose metabolism, alpha-linolenic acid metabolism, carbon fixation in photosynthetic organisms, ascorbate and aldarate metabolism. The expressional pattern of the genes encoding the 15 significant DAPs were consistent with the iTRAQ data. This work indicates that protein biosynthesis, lignin synthesis, the reduction of energy consumption and a higher linolenic acid content contribute to the freezing tolerance of winter turnip rape. Functional analyses of these DAPs would be helpful in dissecting the molecular mechanisms of the stress responses in B. rapa.

scholarly journals Salt stress-induced cell death in the unicellular green alga Micrasterias denticulata

2009 ◽  
Vol 60 (3) ◽  
pp. 939-954 ◽  
Author(s):  
M. J. Affenzeller ◽  
A. Darehshouri ◽  
A. Andosch ◽  
C. Lutz ◽  
U. Lutz-Meindl
Keyword(s):  
Cell Death ◽  
Salt Stress ◽  
Green Alga ◽  
Unicellular Green Alga ◽  
Micrasterias Denticulata

scholarly journals Saussurea involucrata (Snow Lotus) ICE1 and ICE2 Orthologues Involved in Regulating Cold Stress Tolerance in Transgenic Arabidopsis

2021 ◽  
Vol 22 (19) ◽  
pp. 10850
Author(s):  
Chia-Ling Wu ◽  
Lee-Fong Lin ◽  
Hsiao-Chun Hsu ◽  
Li-Fen Huang ◽  
Chung-Der Hsiao ◽  
...  
Keyword(s):  
Amino Acids ◽  
Cold Stress ◽  
Cold Acclimation ◽  
Transgenic Arabidopsis ◽  
Expression Patterns ◽  
Chinese Herb ◽  
Freezing Stress ◽  
Saussurea Involucrata ◽  
Act Domain ◽  
Snow Lotus

As with other environmental stresses, cold stress limits plant growth, geographical distribution, and agricultural productivity. CBF/DREB (CRT-binding factors/DRE-binding proteins) regulate tolerance to cold/freezing stress across plant species. ICE (inducer of CBF expression) is regarded as the upstream inducer of CBF expression and plays a crucial role as a main regulator of cold acclimation. Snow lotus (Saussurea involucrata) is a well-known traditional Chinese herb. This herb is known to have greater tolerance to cold/freezing stress compared to other plants. According to transcriptome datasets, two putative ICE homologous genes, SiICE1 and SiICE2, were identified in snow lotus. The predicted SiICE1 cDNA contains an ORF of 1506 bp, encoding a protein of 501 amino acids, whereas SiICE2 cDNA has an ORF of 1482 bp, coding for a protein of 493 amino acids. Sequence alignment and structure analysis show SiICE1 and SiICE2 possess a S-rich motif at the N-terminal region, while the conserved ZIP-bHLH domain and ACT domain are at the C-terminus. Both SiICE1 and SiICE2 transcripts were cold-inducible. Subcellular localization and yeast one-hybrid assays revealed that SiICE1 and SiICE2 are transcriptional regulators. Overexpression of SiICE1 (35S::SiICE1) and SiICE2 (35S::SiICE2) in transgenic Arabidopsis increased the cold tolerance. In addition, the expression patterns of downstream stress-related genes, CBF1, CBF2, CBF3, COR15A, COR47, and KIN1, were up-regulated when compared to the wild type. These results thus provide evidence that SiICE1 and SiICE2 function in cold acclimation and this cold/freezing tolerance may be regulated through a CBF-controlling pathway.

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