Sucrose metabolism in spring and winter wheat in response to high irradiance, cold stress and cold acclimation

Effects of low‐temperature stress, cold acclimation and growth at high irradiance in a spring (Triticum aestivum L. cv. Katepwa) and a winter wheat (Triticum aestivum L. cv. Monopol) were examined in leaves and crowns with respect to the sucrose utilisation and carbon allocation. Light‐saturated and carbon dioxide (CO₂)‐saturated rates of CO₂ assimilation were decreased by 50% in cold‐stressed spring and winter wheat cultivars. Cold‐ or high light‐acclimated Katepwa spring wheat maintained light‐saturated rates of CO₂ assimilation comparable to those of control spring wheat. In contrast, cold‐ or high light‐acclimated winter wheat maintained higher light and CO₂‐saturated rates of CO₂ assimilation than non‐acclimated controls. In leaves, during either cold stress, cold acclimation or acclimation to high irradiance, the sucrose/starch ratio increased by 5‐ to 10‐fold and neutral invertase activity increased by 2‐ to 2.5‐fold in both the spring and the winter wheat. In contrast, Monopol winter wheat, but not Katepwa spring wheat, exhibited a 3‐fold increase in leaf sucrose phosphate synthase (SPS) activity, a 4‐fold increase in sucrose:sucrose fructosyl transferase activity and a 6.6‐fold increase in acid invertase upon cold acclimation. Although leaves of cold‐stressed and high light‐grown spring and winter wheat showed 2.3‐ to 7‐fold higher sucrose levels than controls, these plants exhibited a limited capacity to adjust either sucrose phosphate synthase or sucrose synthase activity (SS[s]). In addition, the acclimation to high light resulted in a 23–31% lower starch abundance and no changes at the level of fructan accumulation in leaves of either winter or spring wheat when compared with controls. However, high light‐acclimated winter wheat exhibited a 1.8‐fold higher neutral invertase activity and high light‐acclimated spring wheat exhibited an induction of SS(d) activity when compared with controls. Crowns of Monopol showed higher fructan accumulation than Katepwa upon cold and high light acclimation. We suggest that the differential adjustment of CO₂‐saturated rates of CO₂ assimilation upon cold acclimation in Monopol winter wheat, as compared with Katepwa spring wheat, is associated with the increased capacity of Monopol for sucrose utilisation through the biosynthesis of fructans in the leaves and subsequent export to the crowns. In contrast, the differential adjustment of CO₂‐saturated rates of CO₂ assimilation upon high light acclimation of Monopol appears to be associated with both increased fructan and starch accumulation in the crowns.     

Chromosomal control of the tolerance of gradually and suddenly imposed salt stress in the Lophopyrum elongatum and wheat,Triticum aestivum L. genomes

The facultatively halophytic Lophopyrum elongatum, closely related wheat, Triticum aestivum, and their amphiploid tolerate salt stress better if they are gradually exposed to it than if they are suddenly stressed. Lophopyrum elongatum has greater tolerance of both forms of salt stress than wheat, and its genome partially confers this tolerance on their amphiploid. Chromosomal control of the tolerance of both stress regimes in the L. elongatum and wheat genomes was investigated with disomic and ditelosomic addition lines and disomic substitution lines of L. elongatum chromosomes in wheat and with wheat tetrasomics. The tolerance of the sudden salt stress is principally controlled by L. elongatum chromosomes 3E and 5E and less by 1E, 2E, 6E, and 7E and the tolerance of gradually imposed salt stress principally by chromosomes 3E, 4E, and 5E, and less by chromosome 1E and 7E. Ditelosomic analysis indicated that genes conferring the tolerance of sudden stress are on chromosome arms 1EL, 5ES, 5EL, 6EL, 7ES and 7EL and those controlling the gradual stress regime are on 1ES, 1EL, 5ES, 5EL, 6ES, 7ES, and 7EL. In wheat, chromosomes in homoeologous groups 1, 3, and 7 and chromosomes in homoeologous groups 1, 4, and 6 were shown to enhance the tolerance of suddenly and gradually imposed stress, respectively. The arms of chromosome 3E individually conferred tolerance to neither stress regime. Chromosome 2E and wheat chromosomes 2B and 2D reduce the tolerance of both stress regimes in a hyperploid state. In 2E this effect was associated with arm 2EL. A potential relationship between the tolerance of these stress regimes and the expression of the early-salt induced genes is examined.     

Expression of SK3-type dehydrin in transporting organs is associated with cold acclimation in Solanum species

The expression of a gene, encoding a dehydrin protein designated as DHN24 was analyzed at the protein level in two groups of Solanum species differing in cold acclimation ability. The DHN24 protein displays consensus amino acid sequences of dehydrins, termed K- and S-segments. The S-segment precedes three K-segments, classifying the protein into SK₃-type dehydrins. A group of Solanum species able to cold acclimation constituted by S. sogarandinum and S. tuberosum, cv. Aster, and a second one composed of a S. sogarandinum line, that lost ability to cold acclimation, and of S. tuberosum, cv. Irga, displaying low ability to cold acclimation were studied. Under control conditions, noticeable levels of the DHN24 protein was observed in stems, tubers, and roots of Solanum species. No protein was detected in leaves. During low temperature treatment the DHN24 protein level substantially increased in tubers, in transporting organs and in apical parts, and only a small increase was observed in leaves. The increase in protein abundance was only observed in the plants able to cold acclimate and was found to parallel the acclimation capacity. Upon drought stress, the DHN24 level decreased in stems and in leaves, but increased in apical parts. These results suggest that Dhn24 expression is regulated by organ specific factors in the absence of stress and by factors related to cold acclimation processes during low temperature treatment in collaboration with organ-specific factors. A putative function of the SK₃-type dehydrin proteins during plant growth and in the tolerance to low temperature is discussed.     

Cold resistance in Antarctic angiosperms

Deschampsia antarctica Desv. (Poaceae) and Colobanthus quitensis (Kunth) Bartl. (Cariophyllaceae) are the only two vascular plants that have colonized the Maritime Antarctic. The primary purpose of the present work was to determine cold resistance mechanisms in these two Antarctic plants. This was achieved by comparing thermal properties of leaves and the lethal freezing temperature to 50% of the tissue (LT50). The grass D. antarctica was able to tolerate freezing to a lower temperature than C. quitensis. The main freezing resistance mechanism for C. quitensis is supercooling. Thus, the grass is mainly a freezing‐tolerant species, while C. quitensis avoids freezing. D. antarctica cold acclimated; thus, reducing its LT50. C. quitensis showed little cold‐acclimation capacity. Because day length is highly variable in the Antarctic, the effect of day length on freezing tolerance, growth, various soluble carbohydrates, starch, and proline contents in leaves of D. antarctica growing in the laboratory under cold‐acclimation conditions was studied. During the cold‐acclimation treatment, the LT50 was lowered more effectively under long day (21/3 h light/dark) and medium day (16/8) light periods than under a short day period (8/16). The longer the day length treatment, the faster the growth rate for both acclimated and non‐acclimated plants. Similarly, the longer the day treatment during cold acclimation, the higher the sucrose content (up to 7‐fold with respect to non‐acclimated control values). Oligo and polyfructans accumulated significantly during cold acclimation only with the medium day length treatment. Oligofructans accounted for more than 80% of total fructans. The degrees of polymerization were mostly between 3 and 10. C. quitensis under cold acclimation accumulated a similar amount of sucrose than D. antarctica, but no fructans were detected. The suggestion that survival of Antarctic plants in the Antarctic could be at least partially explained by accumulation of these substances is discussed.     

Comparison of the genetic organization of the early salt-stress-response gene system in salt-tolerant Lophopyrum elongatum and salt-sensitive wheat

Lophopyrum elongatum is a facultative halophyte related to wheat. Eleven unique clones corresponding to genes showing enhanced mRNA accumulation in the early stages of salt stress were previously isolated from a L. elongatum salt-stressed-root cDNA library. The chromosomal distribution of genes complementary to these clones in several genomes of the tribe Triticeae and their copy number in the L. elongatum and wheat genomes are reported. Genes complementary to clones pESI4, pESI14, pESI15, pESI28, and pESI32 were found in homoeologous group 5, those complementary to pESI18 and pESI35 in homoeologous group 6, and those complementary to pESI47, pESI48, pESI3, and pESI2 in homoeologous groups 1, 3, 4, and 7, respectively. The genes are present in a single copy per genome in L. elongatum with the exception of those complementary to pESI2 and pESI18 which are present in at least two and five copies, respectively. Since similar copy numbers per genome were found in wheat (except for pESI2), the ability of L. elongatum to accumulate higher mRNA levels than wheat in response to salt shock apears to have evolved by changes in the regulation of these genes.     

Long‐term after‐effects of cold exposure in adult Alphitobius diaperinus (Tenebrionidae): the need to link survival ability with subsequent reproductive success

1. The effects of cold acclimation and cold exposure on the survival and reproductive capabilities of Alphitobius diaperinus (Tenebrionidae) adult beetles are examined. 2. First, the impact of temperature on survival duration was assessed by placing beetles in a range of cool temperature treatments. Second, the importance of acclimation duration was assessed. Third, the impact of thermal stress on subsequent reproductive ability was examined for beetles that had no previous cold exposure, and for beetles that had been subjected to previous cold exposure (i.e. acclimated) at various conditions, including fluctuating temperatures. 3. In all groups, the number of recorded survivors was strongly impacted by recovery period duration (i.e. 2 vs. 10 days). Survival of non‐acclimated and 3‐day acclimated beetles, expressed as lethal time for 50% of the samples, was reduced significantly when the insects were re‐assessed for survival at 10 days after being returned to optimal growth conditions (7.9 ± 0.4 vs. 5.1 ± 0.6 days and 8.8 ± 0.5 vs. 6.8 ± 0.6 days, respectively). 4. Insects that had been subject to cold acclimation expressed better subsequent reproduction success than non‐acclimated beetles. This beneficial impact increased when the acclimation period was prolonged, but some longer acclimation periods had no significant impact on survival. 5. Our results indicate that cold exposure has the capacity to irreversibly damage the reproductive system and that insect survival depends on the duration of the recovery period. Both the survival ability and subsequent reproductive output have to be examined to objectively determine insect cold resistance.     

羊草DHN3基因的克隆及其逆境响应的表达分析

该研究从羊草（Leymus chinensis）中克隆得到1个脱水素（Dehydrin,DHN）编码基因LcDHN3。通过序列分析表明,LcDHN3开放阅读框为501 bp,编码167个氨基酸,分子量为17.01 kD,理论等电点为8.05,为亲水性蛋白。LcDHN3蛋白具有脱水素的保守结构域,含有1个Y 片段、1个S 片段和2个K 片段,属于YSK2型脱水素。亚细胞定位预测LcDHN3蛋白定位在细胞质和细胞核。同源比对分析显示,LcDHN3与大麦（Hordeum vulgare）等6种植物的DHNs整体相似性为84.27%。进化分析显示,LcDHN3和大麦的DHN亲缘关系最近。荧光定量PCR结果显示,LcDHN3基因的表达受干旱、冷、热、NaCl、高pH和机械损伤胁迫诱导,同时受植物激素ABA和JA的诱导。研究表明,LcDHN3参与了羊草响应逆境胁迫的信号途径。     

Receptor‐like kinase OsSIK1 improves drought and salt stress tolerance in rice (Oryza sativa) plants

Receptor‐like kinases (RLKs) play essential roles in plant growth, development and responses to environmental stresses. A putative RLK gene, OsSIK1, with extracellular leucine‐rich repeats was cloned and characterized in rice (Oryza sativa). OsSIK1 exhibits kinase activity in the presence of Mn²⁺, and the OsSIK1 kinase domain has the ability to autophosphorylate and phosphorylate myelin basic protein (MBP). OsSIK1 promoter‐GUS analysis revealed that OsSIK1 is expressed mainly in the stem and spikelet in rice. The expression of OsSIK1 is mainly induced by salt, drought and H₂O₂ treatments. Transgenic rice plants with overexpression of OsSIK1 show higher tolerance to salt and drought stresses than control plants. On the contrary, the knock‐out mutants sik1‐1 and sik1‐2, as well as RNA interference (RNAi) plants, are sensitive to drought and salt stresses. The activities of peroxidase, superoxide dismutase and catalase are enhanced significantly in OsSIK1‐overexpressing plants. Also, the accumulation of H₂O₂ in leaves of OsSIK1‐overexpressing plants is much less than that of the mutants, RNAi plants and control plants, as measured by 3,3′‐diamino benzidine (DAB) staining. We also show that OsSIK1 affects stomatal density in the abaxial and adaxial leaf epidermis of rice. These results indicate that OsSIK1 plays important roles in salt and drought stress tolerance in rice, through the activation of the antioxidative system.     

A cold inducible multidomain cystatin from winter wheat inhibits growth of the snow mold fungus, Microdochium nivale

A novel cold-induced cystatin cDNA clone (TaMDC1) was isolated from cold acclimated winter wheat crown tissue by using a macroarray-based differential screening method. The deduced amino acid sequence consisted of a putative N-terminal secretory signal peptide of 37 amino acids and a mature protein (mTaMDC1) with a molecular mass of 23 kDa. The mTaMDC1 had a highly conserved N-terminal cystatin domain and a long C-terminal extension containing a second region, which exhibited partial similarity to the cystatin domain. The recombinant mTaMDC1 was purified from Escherichia coli and its cysteine proteinase inhibitory activity against papain was analyzed. The calculated Ki value of 5.8×10⁻⁷ M is comparable to those reported for other phytocystatins. Northern and western blot analyses showed elevated expression of TaMDC1 mRNA and protein during cold acclimation of wheat. In addition to cold, accumulation of the TaMDC1 message was induced by other abiotic stresses including drought, salt and ABA treatment. Investigation of in vitro antifungal activity of mTaMDC1 showed strong inhibition on the mycelium growth of the snow mold fungus Microdochium nivale. Hyphae growth was totally inhibited in the presence of 50 μg/ml mTaMDC1 and morphological changes such as swelling, fragmentation and sporulation of the fungus were observed. The mechanisms of the in vitro antifungal effects and the possible involvement of TaMDC1 in cold induced snow mold resistance of winter wheat are discussed.     

Source of nitrogen associated with recovery of relative growth rate in Arabidopsis thaliana acclimated to sustained cold treatment

To determine (1) whether acclimation of carbon metabolism to low temperatures results in recovery of the relative growth rate (RGR) of plants in the cold and (2) the source of N underpinning cold acclimation in Arabidopsis thaliana, we supplied plants with a nutrient solution labelled with ¹⁵N and subjected them to a temperature shift (from 23 to 5 °C). Whole‐plant RGR of cold‐treated plants was initially less than 30% of that of warm‐maintained control plants. After 14 d, new leaves with a cold‐acclimated phenotype emerged, with the RGR of cold‐treated plants increasing by 50%; there was an associated recovery of root RGR and doubling of the net assimilation rate (NAR). The development of new tissues in the cold was supported initially by re‐allocation of internal sources of N. In the longer term, the majority (80%) of N in the new leaves was derived from the external solution. Hence, both the nutrient status of the plant and the current availability of N from external sources are important in determining recovery of growth at low temperature. Collectively, our results reveal that both increased N use efficiency and increases in nitrogen content per se play a role in the recovery of carbon metabolism in the cold.     

Overexpression of a <Emphasis Type="Italic">Panax ginseng</Emphasis> tonoplast aquaporin alters salt tolerance,drought tolerance and cold acclimation ability in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> plants

Water movement across cellular membranes is regulated largely by a family of water channel proteins called aquaporins (AQPs). Since several abiotic stresses such as, drought, salinity and freezing, manifest themselves via altering water status of plant cells and are linked by the fact that they all result in cellular dehydration, we overexpressed an AQP (tonoplast intrinsic protein) from Panax ginseng, PgTIP1, in transgenic Arabidopsis thaliana plants to test its role in plant’s response to drought, salinity and cold acclimation (induced freezing tolerance). Under favorable conditions, PgTIP1 overexpression significantly increased plant growth as determined by the biomass production, and leaf and root morphology. PgTIP1 overexpression had beneficial effect on salt-stress tolerance as indicated by superior growth status and seed germination of transgenic plants under salt stress; shoots of salt-stressed transgenic plants also accumulated greater amounts of Na⁺ compared to wild-type plants. Whereas PgTIP1 overexpression diminished the water-deficit tolerance of plants grown in shallow (10 cm deep) pots, the transgenic plants were significantly more tolerant to water stress when grown in 45 cm deep pots. The rationale for this contrasting response, apparently, comes from the differences in the root morphology and leaf water channel activity (speed of dehydration/rehydration) between the transgenic and wild-type plants. Plants overexpressed with PgTIP1 exhibited lower (relative to wild-type control) cold acclimation ability; however, this response was independent of cold-regulated gene expression. Our results demonstrate a significant function of PgTIP1 in growth and development of plant cells, and suggest that the water movement across tonoplast (via AQP) represents a rate-limiting factor for plant vigor under favorable growth conditions and also significantly affect responses of plant to drought, salt and cold stresses.     

Emergence, basking behaviour, mean selected temperature and critical thermal minimum in high and low altitude subspecies of the tropical lizard Mabuya striata

Emergence, basking behaviour, selected temperature, and critical thermal minimum were studied in warm and cold acclimated groups of two subspecies of the lizard Mabuya striata. The high-altitude M. s. punctatissima emerges earlier than the low-altitude M. s. striata. Under conditions of warm acclimation, M. s. punctatissima has a longer initial bask. The two subspecies do not differ in either mean selected temperature or critical thermal minimum, although in both cases values for cold acclimated lizards are lower than for warm acclimated lizards. I have previously demonstrated differences between the subspecies in the pattern of thermal acclimation of rate of oxygen consumption. I thus consider that M. striata is static in some aspects of its thermal biology but labile in others.     

Differential expression of wheat genes during cold acclimation

Overwintering crops such as winter wheat display significant increase in freezing tolerance during a period of cold acclimation (CA). To gain better understanding of molecular mechanisms of CA, it is important to unravel functions and regulations of CA-associated genes. Differential screening of a cDNA library constructed from cold acclimated crown tissue of winter wheat identified three novel CA-associated cDNA clones. Nucleotide sequence analysis showed that the clones encode a high mobility globular protein (HMGB1), a glycine-rich RNA-binding protein (TaGRP2), and a LEA D-11 dehydrin (DHN14). Accumulation of the three mRNAs during 14 days of CA was differentially regulated. In response to drought, and ABA, DHN14 mRNA rapidly accumulated while HMGB1 and TaGRP2 mRNA levels remained unchanged. The possible functions of each of these genes in cold acclimation are discussed.