Transcriptional profiles of primary metabolism and signal transduction-related genes in response to water stress in field-grown sunflower genotypes using a thematic cDNA microarray

A sunflower cDNA microarray containing about 800 clones covering major metabolic and signal transduction pathways was used to study gene expression profiles in leaves and embryos of drought-tolerant and -sensitive genotypes subjected to water-deficit stress under field conditions. Using two-step ANOVA normalization and analysis models, we identified 409 differentially expressed genes among genotypes, water treatment and organs. The majority of the cDNA clones differentially expressed under water stress was found to display opposite gene expression profiles in drought-tolerant genotype compared to drought-sensitive genotype. These dissimilarities suggest that the difference between tolerant and non-tolerant plants seems to be associated with changes in qualitative but not quantitative mRNA expression. Comparing leaves and embryos, 82 cDNA clones showing organ-specific variation in gene expression levels were identified in response to water stress across genotypes. Genes related to amino acids and carbohydrates metabolisms, and signal transduction were induced in embryos and repressed in leaves; suggesting that vegetative and reproductive organs respond differentially to water stress. Adaptive mechanisms controlling water deficit tolerance are proposed and discussed.     

Changes in Photosynthesis in Inbred Maize Lines with Different Degrees of Chilling Tolerance Grown at Optimum and Suboptimum Temperatures

The effects of growth temperature on changes in net photosynthetic rate (PN) and the chlorophyll fluorescence induction parameter Fv/Fm were investigated after cold stress in inbred maize lines with different degrees of cold tolerance. There was no significant difference between lines grown at optimum temperatures of 25/23 and 20/18 °C as regards PN and Fv/Fm determined at the growth temperature, but these parameters were lower for plants grown at a suboptimum temperature of 15/13 °C. After cold treatment, the decrease in PN was more pronounced in chilling-sensitive lines. The higher the growth temperature was, the more pronounced decrease occurred in PN and Fv/Fm. Thus at low growth temperature both damaging and adaptive processes occur.     

Low growth temperature-induced changes to pigment composition and photosynthesis in Zea mays genotypes differing in chilling sensitivity

The effects on pigment composition and photosynthesis of low temperature during growth were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of Zea mays L. The plants were grown under a controlled environment at 24 or 14 °C at a photon flux density (PFD) of 200 or 600 μ mol m^–2 s^–1. At 24 °C, the two classes of genotypes showed little differences in their photosynthetic activity and their composition of pigments. At 14 °C, photosynthetic activity was considerably reduced but the chilling-tolerant genotypes displayed higher photosynthetic rates than the chilling-sensitive ones. Plants grown at 14 °C showed a reduced chlorophyll (Chl) a + b content and a reduced Chl a / b ratio but an increased ratio of total carotenoids to Chl a + b . These changes in pigment composition in plants grown at low temperature were generally more pronounced in the chilling-sensitive genotypes than in the tolerant ones, particularly at high PFD. Furthermore, at 14 °C, all the genotypes showed increased ratios of lutein, neoxanthin and xanthophyll-cycle carotenoids to Chl a + b but a reduced ratio of β -carotene to Chl a + b , especially at high PFD. At 14 °C, the chilling-tolerant genotypes, when compared with the sensitive ones, were characterized by higher contents of β -carotene and neoxanthin, a lower content of xanthophyll-cycle carotenoids, a lower ratio of xanthophylls to β -carotene, and less of their xanthophyll-cycle carotenoid pool in the form of zeaxanthin. These differences between the two classes of genotypes were more pronounced at high PFD than at low PFD. The results are discussed in terms of the relationship that may exist in maize between pigment composition and the capacity to form an efficient photosynthetic apparatus at low growth temperature.     

The effect of temperature on the velocity of exogenous auxin transport in intact chilling-sensitive and chilling-resistant plants

The velocity of exogenous indol-3yl-acetic acid ([1-¹⁴C]IAA) transport from the apical buds of intact pea, sunflower and cotton plants was determined from 0.5° C to 47° C. The minimum temperature at which transport occurred varied from 2° C (pea and sunflower) to 7° C (cotton). Above these temperatures the velocity of transport increased steadily to maxima near 44° C in all three species. Further increase in temperature resulted in a complete cessation of transport, suggesting a sudden high-temperature breakdown of the auxin transport system. Temperature coefficients (Q₁₀) for transport velocity calculated from Arrhenius plots were low (1.36 to 1.41 between 15° C and 30° C).Arrhenius plots for the chilling-sensitive cotton and sunflower plants exhibited abrupt discontinuities at 14.6° C and 8.7° C respectively. An Arrhenius plot for the chilling-resistant pea exhibited no such discontinuity over the whole temperature range at which transport occurred.Abbreviation IAA indol-3yl-acetic acid     

The electron partitioning between the cytochrome and alternative respiratory pathways during chilling recovery in two cultivars of maize differing in chilling sensitivity

Chilling effects on respiration during the recovery period were studied in two maize (Zea mays L.) cultivars differing in their tolerance to chilling: Penjalinan, a chilling-sensitive cultivar, and Z7, a chilling-tolerant cultivar. Both cultivars were exposed to 5 degrees C for 5 d, after which measurements were taken at 25 degrees C. Chlorophyll fluorescence analysis in dark-adapted leaves showed less damage in cv Z7 than in cv Penjalinan during recovery from the chilling treatment. Studies of the electron partitioning between the cytochrome and the alternative respiratory pathways during chilling recovery using the oxygen isotope fractionation technique showed that, although total leaf respiration was not affected by the chilling treatment in either of the two cultivars, electron partitioning to the alternative pathway was significantly increased in the more stressed chilling-sensitive cv Penjalinan, suggesting that increased activity of the alternative pathway is not related to the plant tolerance to chilling. These results suggest a possible role of the alternative pathway in plants under stress rather than specifically contributing to plant resistance to chilling.     

Overexpression of the rice Osmyb4 gene increases chilling and freezing tolerance of Arabidopsis thaliana plants

The expression of the gene Osmyb4, detected at low level in rice (Oryza sativa) coleoptiles grown for 3 days at 29 degrees C, is strongly induced by treatments at 4 degrees C. At sublethal temperatures of 10 and 15 degrees C, its expression in rice seedlings is already evident, but this effect cannot be vicariated by other stresses or ABA treatment. We demonstrate by transient expression that Myb4 transactivates the PAL2, ScD9 SAD and COR15a cold-inducible promoters. The Osmyb4 function in vivo is demonstrated overexpressing its cDNA in Arabidopsis thaliana plants (ecotype Wassilewskija) under the control of the constitutive CaMV 35S promoter. Myb4 overexpressing plants show a significant increased cold and freezing tolerance, measured as membrane or Photosystem II (PSII) stability and as whole plant tolerance. Finally, in Osmyb4 transgenic plants, the expression of genes participating in different cold-induced pathways is affected, suggesting that Myb4 represents a master switch in cold tolerance.     

How do changes in temperature during growth affect leaf pigment composition and photosynthesis in Zea mays genotypes differing in sensitivity to low temperature?

The changes in photosynthetic activity and composition of pigments induced by changes in temperature were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of maize (Zea mays L.). The plants were grown under a controlled environment at a photon flux density of 550 mol m^-2 s^-1, a 12 h photoperiod and at a suboptimal temperature of 14/12 C (day/night) until the full expansion of the third leaf. After this treatment, the chilling-tolerant genotypes, when compared with the sensitive ones, displayed a higher photosynthetic activity, a higher content of chlorophyll (Chl) a+b, a higher Chl a/b ratio, a larger total carotenoid pool size as well as a different carotenoid composition. When temperature was subsequently increased to 24/22 C for 3 d the composition of the pigments changed, but the chilling-sensitive genotypes, while adjusting their lower Chl a/b ratio and their different carotenoid composition, were unable to adjust their lower content of chlorophyll, their smaller total carotenoid pool size or their lower photosynthetic performance. Moreover, while the chilling-tolerant genotypes converted the most part of zeaxanthin to violaxanthin in the xanthophyll cycle, the chilling-sensitive genotypes retained high amounts of zeaxanthin. The changes in pigment composition that occurred over the 3 d at 24/22 °C were largely conserved when the plants were returned to 14/12 °C, but photosynthetic activity decreased and zeaxanthin accumulated again. The results suggest that the capability of the chilling-tolerant genotypes, when compared with the sensitive ones, to retain high amounts of pigments and to form a competent photosynthetic apparatus at low temperature is the basis for their more vigorous growth in cool climates.     

Differential expression of genes important for adaptation in Capsella bursa-pastoris (Brassicaceae)

Understanding the genetic basis of natural variation is of primary interest for evolutionary studies of adaptation. In Capsella bursa-pastoris, a close relative of Arabidopsis (Arabidopsis thaliana), variation in flowering time is correlated with latitude, suggestive of an adaptation to photoperiod. To identify pathways regulating natural flowering time variation in C. bursa-pastoris, we have studied gene expression differences between two pairs of early- and late-flowering C. bursa-pastoris accessions and compared their response to vernalization. Using Arabidopsis microarrays, we found a large number of significant differences in gene expression between flowering ecotypes. The key flowering time gene FLOWERING LOCUS C (FLC) was not differentially expressed prior to vernalization. This result is in contrast to those in Arabidopsis, where most natural flowering time variation acts through FLC. However, the gibberellin and photoperiodic flowering pathways were significantly enriched for gene expression differences between early- and late-flowering C. bursa-pastoris. Gibberellin biosynthesis genes were down-regulated in late-flowering accessions, whereas circadian core genes in the photoperiodic pathway were differentially expressed between early- and late-flowering accessions. Detailed time-series experiments clearly demonstrated that the diurnal rhythm of CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) and TIMING OF CAB EXPRESSION1 (TOC1) expression differed between flowering ecotypes, both under constant light and long-day conditions. Differential expression of flowering time genes was biologically validated in an independent pair of flowering ecotypes, suggesting a shared genetic basis or parallel evolution of similar regulatory differences. We conclude that genes involved in regulation of the circadian clock, such as CCA1 and TOC1, are strong candidates for the evolution of adaptive flowering time variation in C. bursa-pastoris.     

Low temperature-induced changes in the distribution of H2O2 and antioxidants between the bundle sheath and mesophyll cells of maize leaves

The distribution of antioxidants between bundle sheath and mesophyll cells of maize leaves was analysed in plants grown at 20 degrees C, 18 degrees C and 15 degrees C. The purity of the isolated bundle sheath and mesophyll fractions was determined using compartment-specific marker enzymes. In plants grown at 15 degrees C, ascorbate peroxidase, CuZn-superoxide dismutase (CuZn-SOD) and monodehydroascorbate reductase activities were increased in the bundle sheath cells, and glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase activities were enhanced in the mesophyll cells. SOD was absent from the mesophyll of plants grown at 20 degrees C but an Fe-SOD activity was found in the mesophyll of plants grown at 15 degrees C. Foliar Mn-SOD activities were decreased at 15 degrees C compared to 20 degrees C. Catalase was undetectable in the mesophyll extracts of plants grown at 15 degrees C. Ascorbate and glutathione contents were considerably higher in the mesophyll than the bundle sheath fractions of plants grown at 20 degrees C. The ratios of reduced to oxidized forms of these antioxidants were significantly decreased in the bundle sheath, but increased in the mesophyll of leaves grown at 15 degrees C. Foliar H2O2 accumulated at 15 degrees C compared to 20 degrees C. Most of the foliar H2O2 was localized in the mesophyll tissues at all growth temperatures. The differential distribution of antioxidants between leaf bundle sheath and mesophyll tissues, observed at 20 degrees C, is even more pronounced when plants are grown at 15 degrees C and may contribute to the extreme sensitivity of maize to low temperatures.     

草菇耐低温突变菌株Vtlt-1和原始菌株V23转录组差异的研究

为了培育草菇耐低温菌株与解析其耐低温的分子机制,采用紫外诱变的方法,选育出耐低温草菇菌株Vtlt-1,并利用表达谱芯片技术,比较突变菌株Vtlt-1与原始菌株V23的表达差异基因,筛选差异显著基因后利用GO（gene ontology）功能注释和KEGG（kyoto encyclopedia of genes and genomes）通路富集等方法分析,结果发现与V23相比Vtlt-1表达显著差异基因共有1 600个,其中704个基因上调表达,896个基因下调表达。针对差异基因的GO功能分类结果发现：生物学过程方面,差异基因主要分布在金属离子结合、氧化还原过程、碳水化合物的代谢与核酸的结合。细胞组分方面主要与细胞核相关;分子功能中,氧化还原活性以及解旋酶活性,依赖于ATP 的解旋酶活性、DNA指导的RNA聚合酶活性。KEGG注释结果发现差异表达基因主要富集在氨基酸与氮类物质的代谢、脂肪酸与生物碱的合成这两方面,此外还富集到核糖体的生物合成、细胞色素P450、RNA聚合酶、硫和氨基酸的代谢、核酸的修复等通路。这些结果为解析草菇耐低温机制提供分子依据和理论基础。     

Molecular,Physiological and Biochemical Responses of Theobroma cacao L. Genotypes to Soil Water Deficit

Six months-old seminal plants of 36 cacao genotypes grown under greenhouse conditions were subjected to two soil water regimes (control and drought) to assess, the effects of water deficit on growth, chemical composition and oxidative stress. In the control, soil moisture was maintained near field capacity with leaf water potentials (ΨWL) ranging from −0.1 to −0.5 MPa. In the drought treatment, the soil moisture was reduced gradually by withholding additional water until ΨWL reached values of between −2.0 to −2.5 MPa. The tolerant genotypes PS-1319, MO-20 and MA-15 recorded significant increases in guaiacol peroxidase activity reflecting a more efficient antioxidant metabolism. In relation to drought tolerance, the most important variables in the distinguishing contrasting groups were: total leaf area per plant; leaf, stem and total dry biomass; relative growth rate; plant shoot biomass and leaf content of N, Ca, and Mg. From the results of these analyses, six genotypes were selected with contrasting characteristics for tolerance to soil water deficit [CC-40, C. SUL-4 and SIC-2 (non-tolerant) and MA-15, MO-20, and PA-13 (tolerant)] for further assessment of the expression of genes NCED5, PP2C, psbA and psbO to water deficit. Increased expression of NCED5, PP2C, psbA and psbO genes were found for non-tolerant genotypes, while in the majority of tolerant genotypes there was repression of these genes, with the exception of PA-13 that showed an increased expression of psbA. Mutivariate analysis showed that growth variables, leaf and total dry biomass, relative growth rate as well as Mg content of the leaves were the most important factor in the classification of the genotypes as tolerant, moderately tolerant and sensitive to water deficit. Therefore these variables are reliable plant traits in the selection of plants tolerant to drought.