Yeast gene expression during growth at low temperature

Gene expression during growth at low temperature in the yeast Saccharomyces cerevisiae was investigated by means of DNA microarray analysis. A large number of genes showed an increase or decrease in expression at 4 degrees C relative to 25 degrees C. Although a temperature shift was not performed, differential expression of the cold shock genes TIP1, TIR1, TIR2, and NSR1 was observed. These genes may be necessary for growth at temperatures as low as 4 degrees C as well as for adapting to rapid drops in temperature. A new class of genes, many with unknown functions, was found to be induced during growth at low temperature. We propose to call these genes "low temperature growth genes."     

弱光下长期亚适温和短期低温对黄瓜生长及光合作用的影响

弱光下长期亚适温(T1)和短期低温(T2)对黄瓜幼苗的生长及光合作用有重要影响,表现为生长速度、Pn、CE、AQY、ФPSⅡ等均显著降低,最大光化学效率PsⅡ(Fv／Fm)也有所下降．两个处理相比,T1的Pn、CE、AQY降低幅度较小,但恢复速度慢;而T2降低幅度大,但短期内即可恢复正常．Fv／Fm和ФPSⅡ则是T1降低幅度小且恢复快;而T2降低幅度大,恢复速度也较慢．处理后T1的Chla、Chlb和Car含量均显著增加,而T2的含量则明显降低,T1、T2的Chla／b均显著下降．随着恢复时间的延长,Tl的色素含量多有下降趋势。T2逐渐增加,恢复3d时,含量均高于CK,而Chla／b在恢复期间没有显著变化,仍明显低于CK。     

Effect of low temperature on growth and ultra-structure of Staphylococcus spp

The effect of temperature fluctuation is an important factor in bacterial growth especially for pathogens such as the staphylococci that have to remain viable during potentially harsh and prolonged transfer conditions between hosts. The aim of this study was to investigate the response of S. aureus, S. epidermidis, and S. lugdunensis when exposed to low temperature (4°C) for prolonged periods, and how this factor affected their subsequent growth, colony morphology, cellular ultra-structure, and amino acid composition in the non-cytoplasmic hydrolysate fraction. Clinical isolates were grown under optimal conditions and then subjected to 4°C conditions for a period of 8 wks. Cold-stressed and reference control samples were assessed under transmission electron microscopy (TEM) to identify potential ultra-structural changes. To determine changes in amino acid composition, cells were fractured to remove the lipid and cytoplasmic components and the remaining structural components were hydrolysed. Amino acid profiles for the hydrolysis fraction were then analysed for changes by using principal component analysis (PCA). Exposure of the three staphylococci to prolonged low temperature stress resulted in the formation of increasing proportions of small colony variant (SCV) phenotypes. TEM revealed that SCV cells had significantly thicker and more diffuse cell-walls than their corresponding WT samples for both S. aureus and S. epidermidis, but the changes were not significant for S. lugdunensis. Substantial species-specific alterations in the amino acid composition of the structural hydrolysate fraction were also observed in the cold-treated cells. The data indicated that the staphylococci responded over prolonged periods of cold-stress treatment by transforming into SCV populations. The observed ultra-structural and amino acid changes were proposed to represent response mechanisms for staphylococcal survival amidst hostile conditions, thus maintaining the viability of the species until favourable conditions arise again.     

A comparison of low temperature growth vs low temperature shifts to induce resistance to photoinhibition in spinach (Spinacia oleracea)

Plants of Spinacia oleracea L. cv. Savoy grown under cold-hardening (5°C) and nonhardening (16°C) conditions were exposed to a photoinhibitory irradiance of 1300 μmol rrr^: m-² S-¹ 5°C for 12 h. Plants grown at 5°C exhibited a greater resistance to photoinhibition at low temperature in comparison to plants grown at 16°C as measured by the photochemical efficiency of photosyslem II. In contrast, tuily expanded leaves of plants grown at 16°C and then shifted to 5°C for 10 days did not exhibit increased resistance to photoinhibition. This was observed irrespective of the phoioperiod experienced during the shift to a lower temperature. Furthermore, spinach grown at 16°C and subsequently exposed to a stepped, daily decrease in temperature from 16 to 1°C over 10 days w ith a concomitant reduction in photoperiod. also did not exhibit any change in susceptibility to photoinhibition. Thus, a decrease in photoperiod accompanied by either an abrupt or stepped low temperature shift cannot induce increased resistance to photoinhibition. This confirms the hypothesis that growth and development at cold-hardening temperature are absolute requirements for the acquisition of resistance to photoinhibition at low temperature.     

'P' solubilization potential of plant growth promoting Pseudomonas mutants at low temperature

Pseudomonas fluorescens strain GRS₁, PRS₉ and their cold tolerant mutants were examined for their tricalcium phosphate (TCP) solubilizing activity in NBRIP (broth) media at 10°C and 25°C. Invariably, all the cold tolerant mutants of GRS₁ and PRS₉ were found more efficient than their respective wild type counterparts for ‘P’ solubilization activity at 10°C as compared to 25°C. ‘P’ solubilization potential of CRM was found maximum among all the strains followed by CRPF₆ and CRPF₄. To the best of out knowledge, this is the first report regarding low temperature ‘P’ solubilization activity.     

硅对低温胁迫下黄瓜幼苗生长的影响

采用砂基培养的方法,研究硅对低温胁迫下黄瓜幼苗生长的影响.结果表明加硅处理能使低温胁迫下的黄瓜幼苗超氧化物歧化酶(SOD)、过氧化物酶(POD)活性显著升高:丙二醛(MDA)含量和超氧阴离子自由基(O₂^-)产生速率显著下降,叶片质膜透性降低;硅提高了低温胁迫下黄瓜幼苗的可溶性蛋白质和叶绿素含量、叶绿素a/b比值及植株生物量.因此,硅可以减弱低温胁迫对黄瓜幼苗的伤害.     

Effect of hymexazol on growth and reproduction of low temperature Phytophthora species

The effect of hymexazol (3-hydroxy-5-methylisoxazole or HMI) on growth and reproduction of low temperature Phytophthora species with growth maxima under 30 °C, was studied on clarified V-8 juice agar medium at 50 g/ml and 5 g/ml. HMI severely inhibited growth of P. infestons, P. phaseoli, P. porri and P. syringae, retarded the growth of P. hibernalis and P. lateralis but enhanced the growth of P. fragariae and P. ilicis. Phytophthora cactorum and P. pseudotsugae with a maximal temperature of 30 °C were moderately inhibited.HMI reduced or prevented sporangial production on agar medium by P. cactorum, P. hibernalis, P. ilicis, P. infestons, P. lateralis, P. phaseoli, P. porri and P. primulae, and suppressed chlamydospore formation in P. porri and to a lesser extent, P. lateralis. The production of sex organs was prevented by HMI in P. phaseoli, P. porri, and P. syringae, reduced in P. hibernalis and P. ilicis but unaffected in P. cactorum, P. primulae and P. psuedotsugae.     

Recovery of maize seedling growth, development and photosynthetic efficiency after initial growth at low temperature

In order to investigate the mechanisms of maize adaptation to temperate climate, we studied photosynthetic efficiency, as evaluated by means of phiPSII and chloroplast ultrastructure, as well as growth and development of two inbred lines (the chilling-tolerant KW 1074 and the chilling-sensitive CM 109) under laboratory conditions. Plants were grown from seed to the 3rd leaf stage at a suboptimal temperature (14 degrees C/ 12 degrees C) and then the temperature was increased to 24 degrees C/22 degrees C. To verify the results obtained with the two model lines, twelve inbred lines were tested under both laboratory and field conditions. Initial growth at low temperature affected the chloroplast ultrastructure and photosynthetic efficiency, and this was more pronounced in CM 109 than in KW 1074 plants. The differences between the two lines were particularly pronounced in leaf 5. One week after the onset of favourable conditions, mesophyll chloroplast grana in the CM 109 line were small and thylakoids were developed only poorly. Also, thylakoids in bundle sheath chloroplasts were less frequent in CM 109 than in KW 1074. However, two weeks after the temperature increase, the ultrastructure of chloroplasts of the 5th leaf no longer differed distinctly between the two lines. One should note that in both lines, only the 7th and younger leaves reached a chloroplast ultrastructure and phiPSII indistinguishable from those of control plants. In general, the recovery of photosynthetic efficiency followed the development of leaves. It was delayed in the CM 109 more than in the KW 1074 inbred line relative to control plants grown continuously at the optimal temperature. The growth difference of 2-3 days between the two lines persisted even after the growth temperature was elevated. This suggested that the primary factor responsible for the different chilling-sensitivities of the two model lines was leaf development and the differences in development of the photosynthetic apparatus had only a secondary role. The delay in leaf development appeared as early as the stage of the 1st leaf. The same delay was observed when only the shoot apex was cooled. The importance for further recovery of the early stages of morphogenesis was confirmed by a correlation of Laboratory and field data that were obtained using a set of 12 inbred lines. Our results suggest that early stages of shoot morphogenesis determine the duration of the vegetative phase in cool regions, since the delay in growth at a low temperature cannot be compensated for during later growth at a higher temperature.     

BipA is required for growth of Escherichia coli K12 at low temperature

The bipA gene encodes a ribosome-associated GTPase postulated to be involved in regulatory functions in enteropathogenic Escherichia coli. Previous studies demonstrated that BipA is tyrosine phosphorylated in EPEC strains, but not in E. coli strain K12. Results presented here indicate that BipA function is required at low temperatures in E. coli K12, suggesting a regulatory role independent of phosphorylation and of pathogenicity.     

Identification of Listeria monocytogenes genes expressed in response to growth at low temperature

Listeria monocytogenes is a food-borne bacterial pathogen that is able to grow at refrigeration temperatures. To investigate microbial gene expression associated with cold acclimation, we used a differential cDNA cloning procedure known as selective capture of transcribed sequences (SCOTS) to identify bacterial RNAs that were expressed at elevated levels in bacteria grown at 10 degrees C compared to those grown at 37 degrees C. A total of 24 different cDNA clones corresponding to open reading frames in the L. monocytogenes strain EGD-e genome were obtained by SCOTS. These included cDNAs for L. monocytogenes genes involved in previously described cold-adaptive responses (flaA and flp), regulatory adaptive responses (rpoN, lhkA, yycJ, bglG, adaB, and psr), general microbial stress responses (groEL, clpP, clpB, flp, and trxB), amino acid metabolism (hisJ, trpG, cysS, and aroA), cell surface alterations (fbp, psr, and flaA), and degradative metabolism (eutB, celD, and mleA). Four additional cDNAs were obtained corresponding to genes potentially unique to L. monocytogenes and showing no significant similarity to any other previously described genes. Northern blot analyses confirmed increased steady-state levels of RNA for all members of a subset of genes examined during growth at a low temperature. These results indicated that L. monocytogenes acclimation to growth at 10 degrees C likely involves amino acid starvation, oxidative stress, aberrant protein synthesis, cell surface remodeling, alterations in degradative metabolism, and induction of global regulatory responses.     

Response of the photosynthetic apparatus in maize leaves grown at low temperature on transfer to normal growth temperature

Low temperatures are known to restrict chloroplast development and prevent the attainment of photosynthetic competence in maize leaves. The responses of the photosynthetic apparatus of mature maize leaves grown at 14°C on transfer of the plants to 25°C are examined. The synthesis of thylakoid proteins increased immediately on transfer of leaves from 14 to 25°C, with a dramatic accumulation of thylakoid proteins and chlorophylls occurring after 3 d at 25°C. Thylakoid structure and organization also became similar to those observed in leaves grown at 25°C over this period. However, no comparable development of photosynthetic competence in photosystems I and II or in the rate of CO₂ assimilation was observed on transfer of leaves from 14 to 25°C. Immunocytological analyses demonstrated heterogeneity in the distribution of a range of thylakoid proteins (cy tochrome f, the α and β subunits of the coupling factor, Dl of the photosytem II reaction centre, the 33kDa protein of the extrinsic oxygen-evolving complex of photosystem II, and subunit II of photosystem I between mesophyll cells in leaves grown at 14°C, and in the responses of individual proteins to transfer of the leaves to 25°C. Such heterogeneity between mcsophyll cells would account for the inability of the leaves to develop the expected degree of photosynthetic competence on transfer to 25°C. The effects of low growth temperatures on chloroplast biogenesis are complex, as are the changes induced by the transfer ofleaves grown at low temperatures to optimal growth temperature, and both these factors may limit the canopy development and photosynthetic productivity of crops in temperate regions.     

Is photosynthetic acclimation to low temperature controlled by capacities for storage and growth at low temperature? Results from comparative studies of grasses and trees

The ability of warm-grown leaves to acclimate their photosynthetic machinery to low, non-freezing temperature was compared for contrasting species of grasses and trees. All trees ( Betula pubescens , Salix sp. and Picea abies ), and young plants of one of the grasses ( Hordeum vulgare ) showed acclimation of photosynthesis while the other two grasses ( Phalaris arundinacea and Festuca ovina ) did not. It was those species that maintained leaf sugar concentrations essentially unchanged that showed acclimation. Trees maintained leaf sugar concentrations essentially unchanged by effectively converting leaf sugar surpluses into storage compounds. Grasses were, by comparison, less effective. However, very young plants of Hordeum maintained leaf sugar concentrations unchanged by continued growth rather than by increased storage. This diversity of low-temperature responses are discussed in relation to possible different priorities of trees and grasses: for grasses to undergo cold hardening by allowing sugars to rise, and for trees to store sugars to allow photosynthesis to operate independently of growth as growth varies with growth rhythm and air temperature.     

Chloroplast thylakoid protein changes induced by low growth temperature in maize revealed by immunocytology

Tissue-specific effects of low growth temperature on maize chloroplast thylakoid protein accumulation were analysed using immunocytology. Sections of leaves from plants grown at 25 and 14°C were probed with antibodies to specific chloroplast thylakoid proteins from the four major protein multisubunit complexes of the thylakoid membrane followed by fluorescein-conjugated goat anti-rabbit antibodies. At a normal growth temperature of 25°C, the 32 kDa D1 protein of the photosystem II reaction centre and the 33 kDa protein of the extrinsic oxygen-evolving complex of photosystem II are both accumulated to a greater degree in the mesophyll than in the bundle sheath chloroplasts. In contrast, subunit II of photosystem I, cytochrome f and the α- and β-subunits of ATP synthetase are predominant in the bundle sheath thylakoids at 25°C. A striking difference between the 25°C-grown and the 14°C-grown leaf tissue was the presence in the latter of (20–30%) cells whose chloroplasts apparently completely lack several of the thylakoid proteins. In plants grown at 14°C, the accumulation of the 33 kDa protein of the extrinsic oxygen-evolving complex of photosystem II was apparently unchanged, but other thylakoid proteins showed a significant reduction. The uneven distribution of proteins between the bundle sheath and mesophyll chloroplasts observed at 25°C was also maintained at 14°C. Reduction in the fluorescence at 14°C was manifested either as an overall reduction in the diffuse fluorescence across the chloroplast profiles or less frequently as a reduction to small discrete bodies of intense fluorescence. The significance of these results to low-temperature-induced reduction in the photosynthetic productivity of maize is discussed.     

Siderophore mediated plant growth promotion at low temperature by mutant of fluorescent pseudomonad⋆

A cold resistant mutant of Pseudomonas fluorescens ATCC 13525 was developed, which could grow equally well at 25 and 10 °C and its effect on plant growth promotion under in vitro and in situ conditions was observed. Siderophore estimation revealed it to be a siderophore-overproducing mutant (17-fold increase) when compared to its wild type counterpart. A gnotobiotic root elongation assay indicated that the mutant (CRPF₉) promoted growth more than its wild type both at 25 and 10 °C, indicating its effectiveness at low temperature. Further, root colonization studies showed that CRPF₉ was an efficient rhizosphere colonizer, inducing a significant increase in root (35%) and shoot length (28%) of mung bean plants in unsterilized soil system. The persistence and stability of the mutant was evident in rhizospheric soil. A sand culture experiment showed that ferric citrate was better than Fe(OH)₃ as an iron source for plant growth, but in the presence of CRPF₉ both salts were comparable. This study demonstrates the potential of chemical mutagenesis for improving the plant growth promoting properties of a P. fluorescens strain and its stimulating impact on plant growth promotion at low temperature both under in vitro and in situ conditions.     

Rice LTG1 is involved in adaptive growth and fitness under low ambient temperature

Low temperature (LT) is one of the most prevalent factors limiting the productivity and geographical distribution of rice (Oryza sativa L.). Although significant progress has been made in elucidating the effect of LT on seed germination and reproductive development in rice, the genetic component affecting vegetative growth under LT remains poorly understood. Here, we report that rice cultivars harboring the dominant LTG1 (Low Temperature Growth 1) allele are more tolerant to LT (15–25°C, a temperature range prevalent in high‐altitude, temperate zones and high‐latitude areas), than those with the ltg1 allele. Using a map‐based cloning strategy, we show that LTG1 encodes a casein kinase I. A functional nucleotide polymorphism was identified in the coding region of LTG1, causing a single amino acid substitution (I357K) that is associated with the growth rate, heading date and yield of rice plants grown at LT. We present evidence that LTG1 affects rice growth at LT via an auxin‐dependent process(es). Furthermore, phylogenetic analysis of this locus suggests that the ltg1 haplotype arose before the domestication of rice in tropical climates. Together, our data demonstrate that LTG1 plays an important role in the adaptive growth and fitness of rice cultivars under conditions of low ambient temperature.     

Selection of RAPD marker for growth of seedlings at low temperature in rice.

We have developed a polymerase chain reaction (PCR)-based assay that could effectively reduce the time period required to screen and select the cold tolerance gene of rice seedlings under field conditions. The two specific random amplified polymorphic DNA (RAPD) fragments for the assay were identified on the basis of quantitative trait loci (QTL) analysis which were found to be tightly linked to cold sensitivity. The two RAPD fragments, OPT8(600) in the cold sensitivity rice cultivar 'Dular (indica)' and OPU20(1200) in the resistance rice cultivar 'Toyohatamochi (japonica)', were identified after screening 11 RAPD fragments using 2 random primers on the genomic DNAs of 'Dular' and 'Toyohatamochi'. These primers, when used in a multiplexed PCR, specifically amplified a 0.6 kb and a 1.2 kb fragment in the sensitive and resistant rice cultivars, respectively. When this assay was performed on the genomic DNAs of 16 japonica, 3 Tongil (indica/ japonica), and 2 indica rice cultivars, the primers amplified a 0.6 kb fragment in all of the cold sensitivity rice cultivars or 1.2 kb fragment in all of the resistance ones. These markers can be of potential use in the marker-assisted selection (MAS) for cold tolerance in rice seedling. As screening for resistance can now be conducted independent of the availability of low temperature, the breeding of cold tolerance cultivars can be hastened.