Long- and short-term freezing induce different types of injury in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> leaf cells

In nature, intact plant cells are subjected to freezing and can remain frozen for prolonged periods. We assayed the survival of Arabidopsis thaliana leaf cells following freezing and found that short- and long-term exposures produced different types of cellular injury. To identify the cause of these injuries, we examined the ultrastructure of the cell plasma membranes. Our results demonstrate that ultrastructural changes in the plasma membrane due to short-term freezing are associated with interbilayer events, including close apposition of the membranes. In both acclimated and non-acclimated leaf cells, these interbilayer events resulted in “fracture-jump lesions” in the plasma membrane. On the other hand, long-term freezing was associated with the development of extensive protein-free areas caused by the aggregation of intramembrane proteins with consequent vesiculation of the affected membrane regions; this effect was clearly different from the ultrastructural changes induced by interbilayer events. We also found that prolonged exposure of non-acclimated leaf cells to a concentrated electrolyte solution produced effects that were similar to those caused by long-term freezing, suggesting that the ultrastructural changes observed in the plasma membrane following long-term freezing are produced by exposure of the leaf cells to a concentrated electrolyte solution. This study illustrates multiple causes of freezing-induced injury in plant cells and may provide useful information regarding the functional role of the diverse changes that occur during cold acclimation.     

Mass spectrometric approach for identifying putative plasma membrane proteins of Arabidopsis leaves associated with cold acclimation

Although enhancement of freezing tolerance in plants during cold acclimation is closely associated with an increase in the cryostability of plasma membrane, the molecular mechanism for the increased cryostability of plasma membrane is still to be elucidated. In Arabidopsis, enhanced freezing tolerance was detectable after cold acclimation at 2 degrees C for as short as 1 day, and maximum freezing tolerance was attained after 1 week. To identify the plasma membrane proteins that change in quantity in response to cold acclimation, a highly purified plasma membrane fraction was isolated from leaves before and during cold acclimation, and the proteins in the fraction were separated with gel electrophoresis. We found that there were substantial changes in the protein profiles after as short as 1 day of cold acclimation. Subsequently, using matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS), we identified 38 proteins that changed in quantity during cold acclimation. The proteins that changed in quantity during the first day of cold acclimation include those that are associated with membrane repair by membrane fusion, protection of the membrane against osmotic stress, enhancement of CO2 fixation, and proteolysis.     

Arabidopsis dynamin‐related protein 1E in sphingolipid‐enriched plasma membrane domains is associated with the development of freezing tolerance

The freezing tolerance of Arabidopsis thaliana is enhanced by cold acclimation, resulting in changes in the compositions and function of the plasma membrane. Here, we show that a dynamin‐related protein 1E (DRP1E), which is thought to function in the vesicle trafficking pathway in cells, is related to an increase in freezing tolerance during cold acclimation. DRP1E accumulated in sphingolipid and sterol‐enriched plasma membrane domains after cold acclimation. Analysis of drp1e mutants clearly showed that DRP1E is required for full development of freezing tolerance after cold acclimation. DRP1E fused with green fluorescent protein was visible as small foci that overlapped with fluorescent dye‐labelled plasma membrane, providing evidence that DRP1E localizes non‐uniformly in specific areas of the plasma membrane. These results suggest that DRP1E accumulates in sphingolipid and sterol‐enriched plasma membrane domains and plays a role in freezing tolerance development during cold acclimation.     

Dynamic compositional changes of detergent-resistant plasma membrane microdomains during plant cold acclimation

Plants increase their freezing tolerance upon exposure to low, non-freezing temperatures, which is known as cold acclimation. Cold acclimation results in a decrease in the proportion of sphingolipids in the plasma membrane in many plants including Arabidopsis thaliana. The decrease in sphingolipids has been considered to contribute to the increase in the cryostability of the plasma membrane through regulating membrane fluidity. Recently we have proposed a possibility of another important sphingolipid function associated with cold acclimation.¹ In animal cells, it has been known that the plasma membrane contains microdomains due to the characteristics of sphingolipids and sterols, and the sphingolipid- and sterol-enriched microdomains are thought to function as platforms for cell signaling, membrane trafficking and pathogen response. In our research on characterization of microdomain-associated lipids and proteins in Arabidopsis, a cold-acclimation-induced decrease in sphingolipids resulted in a decrease of microdomains in the plasma membrane and there were considerable changes in membrane transport-, cytoskeleton- and endocytosis-related proteins in the microdomains during cold acclimation. Based on these results, we discuss a functional relationship between the changes in microdomain components and plant cold acclimation.Key words: Arabidopsis, cold acclimation, detergent-resistant plasma membrane, plasma membrane lipid, plasma membrane protein, microdomain, proteome analysisIn fall or early winter, plants recognize the decrease in temperature and change cellular metabolism to survive against freezing stress. This phenomenon is termed as cold acclimation.² Because the plasma membrane is the critical site in cell survival during freezing, diverse cold-acclimation-induced changes are believed to ultimately protect the plasma membrane from the irreversible damage under freezing stress.³ One of the notable changes during cold acclimation is a decrease in sphingolipids, a characteristic plasma membrane lipid.⁴ Sphingolipids have melting temperatures higher than do phosphsolipids, major plasma membrane lipids. Thus, quantitative decreases in sphonglipids are considered to increase in membrane fluidity at low temperatures.⁴ Some 20 years ago, however, experimental results that sphinglipids form lipid microdomains in the plasma membrane were reported in mammalian and yeast cells.^5–7 Sphingolipids are heterogeneously distributed and self-associated with sterols and specific proteins in the plasma membrane. The sphingolipid/sterol-enriched microdomains in the plasma membrane are sometime called “membrane (lipid) raft” or “caveolae” in mammalian cells, and similar domains have been proposed later in plant cells.^8–11 The microdomains are biochemically isolated as low-density detergent-resistant plasma membrane (DRM) fractions and contain specific proteins associated with membrane trafficking, signal transduction, membrane transport, cytoskeleton interaction and pathogen infection.¹² Consequently, the microdomains are suspected to function as platform for assembly of these functional protein complexes and temporal interaction between protein-protein or protein-lipid.⁷ The microdomains change not only in domain size by coalescence of individual domains but also in protein and lipid compositions by physiological stimulus.^12–15We hypothesized that a decrease of sphingolipids in the plant plasma membrane during cold acclimation might not only increase membrane fluidity but also change microdomain formation and/or function. Our recent paper characterized cold-responsiveness of lipid and protein components in plant DRMs.¹ Arabidopsis thaliana is able to increase in freezing tolerance after few days of cold treatment [the temperature of 50% survival is −7°C before cold treatment at 2°C and decreases to −15°C after 7-d-treatment]. We first isolated plasma membrane-enriched fractions using aqueous two-phase partition system from Arabidopsis seedlings before and after cold acclimation. Next, plasma membrane fractions were subjected to 1% (w/v) Triton X-100 on ice for 30 min and then sucrose density gradient centrifugation. DRM fractions appeared as two white bands at about 40% (w/w) sucrose. DRMs in plants are generally recovered as heavier fractions than those in animals.^16–18 This is probably because the ratio of protein to lipid is greater in plants than in animals. Arabidopsis DRM fractions were enriched in sphingolipids (glucocerebrosides) and sterols (free sterols, acylated sterylglucosides and sterylglucosides).¹ Figure 1 shows the protein and lipid amounts in DRM during cold acclimation. DRM protein recovery rate from the plasma membrane was less than 10% and cold treatment resulted in a gradual decrease of the recovery: the recovery rate of DRM lipids from the plasma membrane rapidly decreased by half only after 2 days of cold acclimation. These data suggest a decrease in the proportion of microdomains in the plasma membrane and temporal changes in proteins and lipids in DRM during cold acclimation.Open in a separate windowFigure 1Changes in the protein and lipid amount in DRM recovered from plasma membrane fractions during cold acclimation. NA, non-acclimated; CA 2, CA 4 and CA 7, cold-acclimated for 2, 4 and 7 days, respectively. (Modified from Minami et al.)We found that there were significant differences in lipid alterations in plasma membrane and DRM fractions in cold acclimation (Fig. 2). The amount of total lipids (per mg of protein) in the plasma membrane fraction greatly increased after cold acclimation but not in the DRM fraction. In the plasma membrane fraction, cold acclimation for 2 days resulted in an increase in the proportions of phospholipids and free sterols and a decrease in the proportion of sphingolipids. In contrast, in the DRM fractions, free sterols increased after 2 days of cold acclimation but the proportion of phospholipids and sphingolipids did not change significantly. These results suggest that the changes in lipid classes in DRM differ from the changes in the whole plasma membrane. Our lipid analysis suggests that the decrease in sphingolipids in the plasma membrane affects the quantitative decrease of microdomains in the plasma membrane during cold acclimation (see Fig. 1). However, the lipid changes in the whole plasma membrane are unlikely to affect proportional changes in DRM-localized lipids except for free sterols.Open in a separate windowFigure 2Lipid changes in DRM and plasma membrane fractions during cold acclimation. NA, non-acclimated; CA 2, CA 4 and CA 7, cold-acclimated for 2, 4 and 7 days, respectively. FS, free sterols; ASG, acylated sterylglucosides; SG, sterylglucosides; GlcCer, glucocerebrosides; PL, phospholipids. (Modified from Minami et al.¹)We demonstrated quantitative changes of DRM-localized proteins during cold acclimation using two-dimensional differential gel electrophoresis (2D-DIGE) and western blot analyses.¹ 2D-DIGE analysis showed that one-third of the DRM-localized proteins quantitatively changed during cold acclimation. Subsequent mass spectrometric analysis of DRM proteins revealed significant changes in various proteins including increases in aquaporin, P-type H⁺-ATPase and endocytosis-related proteins and decreases in cytoskeletal proteins (tubulins and actins) and V-type H⁺-ATPase subunits during cold acclimation. The changes were first detected after 2 days of cold acclimation. Based on these results of protein analyses, Figure 3 illustrates changes in distribution patterns of DRM-localized proteins in the plasma membrane during cold acclimation. Cold acclimation induces the decrease in the amount of DRM proteins and lipids in the plasma membrane (Fig. 1), suggesting that component in microdomains decreases in the plasma membrane during cold acclimation. Furthermore, the proportion of some functional proteins changes in DRM during cold acclimation. Qualitative and quantitative changes of DRM proteins during cold acclimation are possibly associated with the plasma membrane functions. Plant cells at low temperature suffer from changes in membrane fluidity and cytoplasmic pH.^19–21 Upon freezing occurs, plant cells are subjected to severe dehydration and deformation stresses induced by extracellular ice formation.²² To avoid the occurrence of damages from these stresses, plants change plasma membrane components during cold acclimation.²³ H⁺-ATPase or aquaporins are thought to function in regulation of cytoplasmic pH or water transfer across the plasma membrane, respectively.^24,25 Cytoskeleton regulates cell structure and intracellular vesicle-trafficking processes reconstruct plasma membrane itself. Thus, the quantitative changes of these proteins in microdomains are likely associated with protective functions against freezing stress in cold acclimation.Open in a separate windowFigure 3Our hypothesis on changes in microdomains during plant cold acclimation. Cold acclimation results in a decrease in microdomains in the plasma membrane (see Fig. 1) and differential changes in various protein compositions in microdomains. We categorized DRM proteins as (1) membrane transport, (2) vesicle trafficking, (3) cytoskeleton, (4) microdomain-associated proteins and (5) others (e.g., plasma membrane and cell-wall reconstruction). Aquaporin, P-type H⁺-ATPase (1) and endocytosis-related proteins (2) increased and cytoskeletal proteins (3) and V-type H⁺-ATPase subunits (1) decreased in DRM during cold acclimation.We clearly demonstrated that cold acclimation decreased the amount of DRM and changed both lipid and protein compositions in plant DRM. Our study represents a first step towards elucidation of functions of plant microdomains in cold acclimation, strongly suggesting that microdomains, which function as a platform of membrane transport, membrane trafficking and cytoskeleton interaction, are associated with plant cold acclimation. Changes in microdomain lipids may also affect the protein activities during cold acclimation because sterols or sphingolipids are known to regulate activities of membrane transport or endocytosis. Thus, we suspect that the quantitative changes in microdomain lipids and proteins may correlate with development of freezing tolerance during cold acclimation. The hypothesis that the changes in microdomain components are functionally associated with plant cold acclimation should be reinforced by various approaches such as genetics, biochemistry or physical chemistry.     

植物抗寒及其基因表达研究进展

植物经过逐渐降低的温度从而提高抗寒能力 ,这个过程被人们称为低温驯化。植物低温驯化过程是一个复杂的生理、生化和能量代谢变化过程 ,这些变化主要包括膜系统的稳定性、可溶性蛋白的积累和小分子渗透物质 ,比如脯氨酸、糖等 ,这些变化中的一些是植物抗寒必需的 ,而另外一些变化不是必需的。主要对冷害和低温生理生化变化、低温诱导表达基因的功能和作用、低温驯化的调节机制及其信号转导方面进行了综述。通过差别筛选 c DNA文库的方法已经鉴定了许多低温诱导表达、进而提高植物抗寒能力的基因 ,其中有脱水素、COR基因和 CBF1转录因子等。低温信号的感受、转导和调节表达是低温驯化的关键环节 ,低温信号的转导过程与干旱胁迫之间具有一定的交叉 ,这为利用 ABA等来提高植物抗寒能力成为可能 ,相信不久的将来人们可以通过提高植物抗寒能力从而增加经济产量成为现实。     

Changes in leaf ultrastructure and carbohydrates inArabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation

Summary We studied cell ultrastructure and carbohydrate levels in the leaf tissue ofArabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation. Freezing tolerance of the leaves from 26 day old plants was determined after 48 h and 10 days at 4°C. Acclimation treatment of 48 h decreased the lethal freezing temperature from –5.7°C to –9.4°C. Freezing tolerance was not altered further by acclimation at 4 °C for 10 days. Ultrastructural changes in the parenchyma cells were evident after 6 to 24 h of cold acclimation. The plasma membrane showed signs of extensive turnover. Evidence of membrane invaginations and sequestering of membrane material was observed. In addition, numerous microvesicles, paramural bodies, and fragments of endoplasmic reticulum were noticed in the vicinity of plasma membrane. Modifications in the structure of cell membranes were evident after 5 days of exposure to low temperature. Small, darkly stained globules were seen on the plasma membrane, tonoplast, chloroplast envelope membrane, mitochondrion outer membrane, dictyosome cisternae membrane, and microvesicle membrane. As far as we are aware, this type of membrane modification has not been described previously in plant cells exposed to low temperature. We propose to call these structures membraglobuli. Acclimation treatment also increased the concentrations of soluble sugars and starch. These observations suggest that cold acclimation inA. thaliana induces changes in both plasma membrane properties and carbohydrate composition.     

Low temperature-induced modifications in cell ultrastructure and localization of phenolics in winter oilseed rape (Brassica napus L. var. oleifera L.) leaves

Acclimation of winter oilseed plants in the cold (i.e. at temperatures >0 degrees C) followed by short exposure to sub-lethal freezing temperatures resulted in pronounced ultrastructural changes of leaf epidermal and mesophyll cells. The following major changes were observed upon acclimation at 2 degrees C: increased thickness of cell walls; numerous invaginations of plasma membranes; the appearance of many large vesicles localized in the cytoplasm in close proximity to the central vacuole; the occurrence of abundant populations of microvesicles associated with the endoplasmic reticulum (ER) cisternae or located in the vicinity of dictyosomes; and the occurrence of paramural bodies and myelin-like structures. In addition, large phenolic deposits were observed in the vicinity of the plasma membrane and membrane-bound organelles such as chloroplasts, large vesicles or cytoplasm/tonoplast interfaces. Transient freezing (-5 degrees C for 18 h) of the cold-acclimated leaves led to reversible disorganization of the cytoplasm and to pronounced structural changes of the cellular organelles. Chloroplasts were swollen, with the stroma occupying one half of their volume and the thylakoid system being displaced to the other half. Large phenolic aggregates disappeared but distinct layers of phenolic deposits were associated with mitochondrial membranes and with chloroplast envelopes. In frost-thawed cells recovered at 2 degrees C for 24 h, dictyosomes and dictyosome- or ER-derived small vesicles reappeared in the ribosome-rich cytoplasm. Aberrations in the structure of chloroplasts and mitochondria were less pronounced. Few phenolic deposits were seen as small grains associated with chloroplast envelopes and vesicle membranes. These observations demonstrate that plants undergo different changes in cell ultrastructure depending on whether they are subjected to chilling or freezing temperatures. Results are discussed in relation to membrane recycling and the possible role of phenolics during the first and second stages of plant acclimation at low temperature.     

Alterations in Detergent-Resistant Plasma Membrane Microdomains in Arabidopsis thaliana During Cold Acclimation

Microdomains in the plasma membrane (PM) have been proposedto be involved in many important cellular events in plant cells.To understand the role of PM microdomains in plant cold acclimation,we isolated the microdomains as detergent-resistant plasma membranefractions (DRMs) from Arabidopsis seedlings and compared lipidand protein compositions before and after cold acclimation.The DRM was enriched in sterols and glucocerebrosides, and theproportion of free sterols in the DRM increased after cold acclimation.The protein-to-lipid ratio in the DRM was greater than thatin the total PM fraction. The protein amount recovered in DRMsdecreased gradually during cold acclimation. Cold acclimationfurther resulted in quantitative changes in DRM protein profiles.Subsequent mass spectrometry and Western blot analyses revealedthat P-type H⁺-ATPases, aquaporins and endocytosis-related proteinsincreased and, conversely, tubulins, actins and V-type H⁺-ATPasesubunits decreased in DRMs during cold acclimation. Functionalcategorization of cold-responsive proteins in DRMs suggeststhat plant PM microdomains function as platforms of membranetransport, membrane trafficking and cytoskeleton interaction.These comprehensive changes in microdomains may be associatedwith cold acclimation of Arabidopsis.     

Temporal cell wall changes during cold acclimation and deacclimation and their potential involvement in freezing tolerance and growth

Plants adapt to freezing stress through cold acclimation, which is induced by nonfreezing low temperatures and accompanied by growth arrest. A later increase in temperature after cold acclimation leads to rapid loss of freezing tolerance and growth resumption, a process called deacclimation. Appropriate regulation of the trade-off between freezing tolerance and growth is necessary for efficient plant development in a changing environment. The cell wall, which mainly consists of polysaccharide polymers, is involved in both freezing tolerance and growth. Still, it is unclear how the balance between freezing tolerance and growth is affected during cold acclimation and deacclimation by the changes in cell wall structure and what role is played by its monosaccharide composition. Therefore, to elucidate the regulatory mechanisms controlling freezing tolerance and growth during cold acclimation and deacclimation, we investigated cell wall changes in detail by sequential fractionation and monosaccharide composition analysis in the model plant Arabidopsis thaliana, for which a plethora of information and mutant lines are available. We found that arabinogalactan proteins and pectic galactan changed in close coordination with changes in freezing tolerance and growth during cold acclimation and deacclimation. On the other hand, arabinan and xyloglucan did not return to nonacclimation levels after deacclimation but stabilized at cold acclimation levels. This indicates that deacclimation does not completely restore cell wall composition to the nonacclimated state but rather changes it to a specific novel composition that is probably a consequence of the loss of freezing tolerance and provides conditions for growth resumption.     

Differential remodeling of the lipidome during cold acclimation in natural accessions of Arabidopsis thaliana

Freezing injury is a major factor limiting the geographical distribution of plant species and the growth and yield of crop plants. Plants from temperate climates are able to increase their freezing tolerance during exposure to low but non‐freezing temperatures in a process termed cold acclimation. Damage to cellular membranes is the major cause of freezing injury in plants, and membrane lipid composition is strongly modified during cold acclimation. Forward and reverse genetic approaches have been used to probe the role of specific lipid‐modifying enzymes in the freezing tolerance of plants. In the present paper we describe an alternative ecological genomics approach that relies on the natural genetic variation within a species. Arabidopsis thaliana has a wide geographical range throughout the Northern Hemisphere with significant natural variation in freezing tolerance that was used for a comparative analysis of the lipidomes of 15 Arabidopsis accessions using ultra‐performance liquid chromatography coupled to Fourier‐transform mass spectrometry, allowing the detection of 180 lipid species. After 14 days of cold acclimation at 4°C the plants from most accessions had accumulated massive amounts of storage lipids, with most of the changes in long‐chain unsaturated triacylglycerides, while the total amount of membrane lipids was only slightly changed. Nevertheless, major changes in the relative amounts of different membrane lipids were also evident. The relative abundance of several lipid species was highly correlated with the freezing tolerance of the accessions, allowing the identification of possible marker lipids for plant freezing tolerance.     

Cryobehavior of the plasma membrane in protoplasts isolated from cold-acclimated Arabidopsis leaves is related to surface area regulation

Extracellular freezing in plants results in dehydration and mechanical stresses upon the plasma membrane. Plants that acquire enhanced freezing tolerance after cold acclimation can withstand these two physical stresses. To understand the tolerance to freeze-induced physical stresses, the cryobehavior of the plasma membrane was observed using protoplasts isolated from cold-acclimated Arabidopsis thaliana leaves with the combination of a lipophilic fluorescent dye FM 1-43 and cryomicroscopy. We found that many vesicular structures appeared in the cytoplasmic region near the plasma membrane just after extracellular freezing occurred. These structures, referred to as freeze-induced vesicular structures (FIVs), then developed horizontally near the plasma membrane during freezing. There was a strong correlation between the increase in individual FIV size and the decrease in the surface area of the protoplasts during freezing. Some FIVs fused with their neighbors as the temperature decreased. Occasionally, FIVs fused with the plasma membrane, which may be necessary to relax the stress upon the plasma membrane during freezing. Vesicular structures resembling FIVs were also induced when protoplasts were mechanically pressed between a coverslip and slide glass. Fewer FIVs formed when protoplasts were subjected to hyperosmotic solution, suggesting that FIV formation is associated with mechanical stress rather than dehydration. Collectively, these results suggest that cold-acclimated plant cells may balance membrane tension in the plasma membrane by regulating the surface area. This enables plant cells to withstand the direct mechanical stress imposed by extracellular freezing.     

植物寒害和抗寒机制中膜与蛋白质研究的进展

低温对细胞膜体系的损伤是植物寒害的重要机制。膜体系的稳定性与植物的抗寒性成正相关,但不同的细胞膜体系对细胞外结冰的敏感程度是不同的。抗寒锻炼中膜磷脂的生物合成与抗寒力的发展有密切关系,但不是抗寒力发展的前提条件,可能是对发展高水平的抗寒力起作用;而膜脂脂肪酸不饱和度的增加是植物对低温生长的反应,与抗寒性无立直接关系。近年来膜脂 — 膜蛋白相互关系的研究引起研究者们的重视,已在多种植物低温锻炼中观察到抗寒特异蛋白质合成与基因表达均有所改变,并发现抗寒力的诱导主要是在转录水平上的调控。     

Chemical and Biophysical Changes in the Plasma Membrane during Cold Acclimation of Mulberry Bark Cells (Morus bombycis Koidz. cv Goroji)

The lipid and protein composition of the plasma membrane isolated from mulberry (Morus bombycis Koidz.) bark cells was analyzed throughout the cold acclimation period under natural and controlled environment conditions. There was a significant increase in phospholipids and unsaturation of their fatty acids during cold acclimation. The ratio of sterols to phospholipids decreased with hardiness, primarily due to the large increase in phospholipids. The fluidity of the plasma membrane, as determined by fluorescent polarization technique, increased with hardiness. Electrophoresis of plasma membrane proteins including glycoproteins revealed change in banding pattern during the early fall to winter period. Some of the protein changes could be related to growth cessation and defoliation. However, minor changes in proteins also occurred during the most active period of hardening. Changes in glycoproteins were coincident both with changes in growth stages and with the development of cold hardiness.     

The role of raffinose in the cold acclimation response of Arabidopsis thaliana

In many plants raffinose family oligosaccharides are accumulated during cold acclimation. The contribution of raffinose accumulation to freezing tolerance is not clear. Here, we investigated whether synthesis of raffinose is an essential component for acquiring frost tolerance. We created transgenic lines of Arabidopsis thaliana accessions Columbia-0 and Cape Verde Islands constitutively overexpressing a galactinol synthase (GS) gene from cucumber. GS overexpressing lines contained up to 20 times as much raffinose as the respective wild-type under non-acclimated conditions and up to 2.3 times more after 14 days of cold acclimation at 4 degrees C. Furthermore, we used a mutant carrying a knockout of the endogenous raffinose synthase (RS) gene. Raffinose was completely absent in this mutant. However, neither the freezing tolerance of non-acclimated leaves, nor their ability to cold acclimate were influenced in the RS mutant or in the GS overexpressing lines. We conclude that raffinose is not essential for basic freezing tolerance or for cold acclimation of A. thaliana.     

A global survey of gene regulation during cold acclimation in Arabidopsis thaliana

Many temperate plant species such as Arabidopsis thaliana are able to increase their freezing tolerance when exposed to low, nonfreezing temperatures in a process called cold acclimation. This process is accompanied by complex changes in gene expression. Previous studies have investigated these changes but have mainly focused on individual or small groups of genes. We present a comprehensive statistical analysis of the genome-wide changes of gene expression in response to 14 d of cold acclimation in Arabidopsis, and provide a large-scale validation of these data by comparing datasets obtained for the Affymetrix ATH1 Genechip and MWG 50-mer oligonucleotide whole-genome microarrays. We combine these datasets with existing published and publicly available data investigating Arabidopsis gene expression in response to low temperature. All data are integrated into a database detailing the cold responsiveness of 22,043 genes as a function of time of exposure at low temperature. We concentrate our functional analysis on global changes marking relevant pathways or functional groups of genes. These analyses provide a statistical basis for many previously reported changes, identify so far unreported changes, and show which processes predominate during different times of cold acclimation. This approach offers the fullest characterization of global changes in gene expression in response to low temperature available to date.     

Effects of MPK3 and MPK6 kinases on the chloroplast architecture and function induced by cold acclimation in Arabidopsis

Photosynthesis Research - Exposure to low, non-freezing temperatures develops freezing tolerance in many plant species. Such process is called cold acclimation. Molecular changes undergone during...     

植物寒害和抗寒机制中膜与蛋白质研究的进展

低温对细胞膜体系的损伤是植物寒害的重要机制。膜体系的稳定性与植物的抗寒性成正相关,但不同的细胞膜体系对细胞外结冰的敏感程度是不同的。抗寒锻炼中膜磷脂的生物合成与抗寒力的发展有密切关系,但不是抗寒力发展的前提条件,可能是对发展高水平的抗寒力起作用;而膜脂脂肪酸不饱和度的增加是植物对低温生长的反应,与抗寒性无直接关系。近年来膜脂-膜蛋白相互关系的研究引起研究者们的重视,已在多种植物低温锻炼中观察到抗寒特异蛋白质合成与基因表达均有所改变,并发现抗寒力的诱导主要是在转录水平上的调控。