Long-term chilling of young tomato plants under low light

The properties of two Calvin-cycle key enzymes, i.e. stromal fructose-1,6-bisphosphatase (sFBPase) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were studied in the cultivated tomato (Lycopersicon esculentum Mill.) and in four lines of a wild tomato (L. peruvianum Mill.) from different altitudes. During chilling for 14 d at 10°C and low light, the activation energy (E_A) of the reaction catalyzed by sFBPase decreased by 5–10 kJ·mol^–1 inL. esculentum and the threeL. peruvianum lines from high altitudes. InL. peruvianum, no loss or only small losses of enzyme activity were observed during the chilling. Together with the change in E_A, this indicates that the latter species is able to acclimate its Calvin-cycle enzymes to low temperatures. InL. esculentum, the chilling stress resulted in the irreversible loss of 57% of the initial sFBPase activity. Under moderately photoinhibiting chilling conditions for 3 d, theL. peruvianum line from an intermediate altitude showed the largest decreases in both the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m) and the in-vivo activation state of sFBPase, while the otherL. peruvianum lines showed no inhibition of sFBPase activation. Ribulose-1,5-bisphosphate carboxylase/oxygenase was isolated by differential ammonium-sulfate precipitation and gel filtration and characterized by two-dimensional electrophoresis. The enzyme fromL. esculentum had three isoforms of the small subunit of Rubisco, each with different isoelectric points. Of these, theL. peruvianum enzyme contained only the two more-acidic isoforms. Arrhenius plots of the specific activity of purified Rubisco showed breakpoints at approx. 17°C. Upon chilling, the specific activity of the enzyme fromL. esculentum decreased by 51%, while E_A below the breakpoint temperature increased from 129 to 189 kJ·mol^–1. In contrast, Rubisco from theL. peruvianum lines from high altitudes was unaffected by chilling. We tested several possibile explanations for Rubisco inactivation, using two-dimensional electrophoresis, analytical ultracentrifugation, gel filtration and inhibitor tests. No indications were found for differential expression of the subunit isoforms, proteolysis, aggregation, subunit disassembly, or inhibitor accumulation in the enzyme from chilledL. esculentum. We suggest that the activity loss in theL. esculentum enzyme upon chilling is the result of a modification of sulfhydryl groups or other sidechains of the protein.Abbreviations a.s.l. above sea level - Chl chlorophyll - DTT dithiothreitol - E_A activation energy - FBP fructose-1,6-bisphosphate - F_v/F_m ratio of variable to maximum chlorophyll fluorescence - HL high light (500 mol photons·m^–2·s^–1) - LSU large subunit of Rubisco - ME 2-mercaptoethanol - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate - sFBPase stromal fructose-1,6-bisphosphatase - SSU small subunit of Rubisco     

Transcript profiling in Vitis riparia during chilling requirement fulfillment reveals coordination of gene expression patterns with optimized bud break

Endodormant grapevine buds require a period of chilling before they break and begin to grow. Custom Vitis bud cDNA microarrays (9,216 features) were used to examine gene expression patterns in overwintering Vitis riparia buds during 2,000 h of 4°C chilling. Three-node cuttings collected concurrently with buds were monitored to determine dormancy status. Chilling requirement was fulfilled after 1,500 h of chilling; however, 2,000 h of chilling significantly increased the rate of bud break. Microarray analysis identified 1,469 significantly differentially expressed (p value < 0.05) array features when 1,000, 1,500, and 2,000 h of chilling were compared to 500 h of chilling. Functional classification revealed that the majority of genes were involved in metabolism, cell defense/stress response, and genetic information processing. The number of significantly differentially expressed genes increased with chilling hour accumulation. The expression of a group of 130 genes constantly decreased during the chilling period. Up-regulated genes were not detected until the later stages of chilling accumulation. Hierarchical clustering of non-redundant expressed sequence tags revealed inhibition of genes involved in carbohydrate and energy metabolism and activation of genes involved in signaling and cell growth. Clusters with expression patterns associated with increased chilling and bud break were identified, indicating several candidate genes that may serve as indicators of bud chilling requirement fulfillment. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Long-term chilling of young tomato plants under low light and subsequent recovery

The influence of unfavourable climatic conditions at the onset of the growth period on chilling-sensitive tomato (Lycopersicon esculentum Mill., cv. Abunda) was studied by exposing young plants to combinations of low temperature and low light (60–100 mol quanta · m^–2 · s^–1) for several weeks. When the temperature did not decrease below a critical point (8 ° C) no loss of developmental capacity of the plants was detected. However, while new leaves were readily formed upon return to normal growth conditions (22/18 °C, day/night, in a greenhouse), net accumulation of biomass showed a lag phase of approximately one week. This delay was accompanied by a strong, irreversible inhibition of photosynthesis in the fully expanded leaves which had been exposed to the chilling treatment. When plants were subjected to temperatures below 8 ° C, survival rates decreased after three weeks at 6 ° C and irreversible damage of apical meristematic tissue occurred. Drought-hardening prior to chilling ensured survival at 6 ° C and protected the plants against meristem loss.Abreviation Chl chlorophyll Thanks are due to G.P. Telkamp for technical assistance. This research is financially supported by the Netherlands Technology Foundation (STW, Utrecht, The Netherlands), and is coordinated by the Foundation for Biological Research (BION, 's-Gravenhage, The Netherlands).     

Gene expression profiling reveals unique pathways associated with differential severity of lyme arthritis

The murine model of Lyme disease provides a unique opportunity to study the localized host response to similar stimulus, Borrelia burgdorferi, in the joints of mice destined to develop severe arthritis (C3H) or mild disease (C57BL/6). Pathways associated with the response to infection and the development of Lyme arthritis were identified by global gene expression patterns using oligonucleotide microarrays. A robust induction of IFN-responsive genes was observed in severely arthritic C3H mice at 1 wk of infection, which was absent from mildly arthritic C57BL/6 mice. In contrast, infected C57BL/6 mice displayed a novel expression profile characterized by genes involved in epidermal differentiation and wound repair, which were decreased in the joints of C3H mice. These expression patterns were associated with disease state rather than inherent differences between C3H and C57BL/6 mice, because C57BL/6-IL-10(-/-) mice infected with B. burgdorferi develop more severe arthritis than C57BL/6 mice and displayed an early gene expression profile similar to C3H mice. Gene expression profiles at 2 and 4 wk postinfection revealed a common response of all strains that was likely to be important for the host defense to B. burgdorferi and mediated by NF-kappaB-dependent signaling. The gene expression profiles identified in this study add to the current understanding of the host response to B. burgdorferi and identify two novel pathways that may be involved in regulating the severity of Lyme arthritis.     

Gene expression profiling in prostate cancer cells with Akt activation reveals Fra-1 as an Akt-inducible gene

To determine which genes may be regulated by Akt and participate in the transformation of cells, we have examined by microarray analyses genes turned on in the prostate cancer cell line, PC3, when Akt activity was induced. PC3 cells, which lack the lipid phosphatase PTEN, were treated overnight with a reversible inhibitor of the phosphatidylinositol 3-kinase, LY294002 (a treatment which was found to reversibly decrease Akt enzymatic activity). The inhibitor was then washed out and mRNA collected 2, 6, and 10 h later and compared by microarray analyses with mRNAs present immediately after removal of the inhibitor. One of the identified induced mRNAs, Fra-1, was further studied by transient transfections of a reporter construct containing its 5' regulatory region. This construct was found to be directly induced 4- to 5-fold by co-transfection with constitutively active Akt3 but not kinase dead Akt. The regulation by Akt3 was found to be due to two specific regions in the Fra-1 regulatory sequence which match Sp1 consensus sites. Finally, gel shift studies showed that the binding of Sp1 to one of these sites was dependent on the PI 3-kinase pathway. These results indicate that LY294002 treatment and washout is a useful method to study the activation of Akt in the context of a tumor cell. Moreover, the identification of Fra-1 as an Akt-regulated gene may have implications for the ability of Akt to transform cells since Fra-1 has been implicated in cell growth and the aggressiveness of tumors.     

Effects of phosphorus and chilling under low irradiance on photosynthesis and growth of tomato plants

To determine the effects of phosphorus nutrition on chilling tolerance of photosynthetic apparatus, tomato (Lycopersicon esculentum Mill. cv. Kenfengxin 2002) plants were raised under different P contents and subjected to 7 d of chilling at 9/7 °C. After chilling (2 h or 7 d) plant growth, P content in tissue, gas exchange and chlorophyll fluorescence were measured. Decreasing P concentration [P] in the nutrient solution markedly reduced plant growth and the chilled plants exhibiting higher optimum [P] than the unchilled plants. Decreasing [P] significantly decreased light saturated net photosynthetic rate (P_Nsat), maximum carboxylation velocity of Rubisco (V_cmax), maximum potential rate of electron transport contributed to Rubisco regeneration (J_max), quantum efficiency of photosystem (PS) 2 (ΠPS2) and O₂ sensitivity of P_Nsat (PS_O2) and this trend was especially apparent in chilled plants.     

Enhanced sensitivity and characterization of photosystem II in transgenic tobacco plants with decreased chloroplast glutathione reductase under chilling stress

Chloroplast glutathione reductase (GR) plays an important role in protecting photosynthesis against oxidative stress. We used transgenic tobacco (Nicotiana tabacum) plants with severely decreased GR activities by using a gene encoding tobacco chloroplast GR for the RNAi construct to investigate the possible mechanisms of chloroplast GR in protecting photosynthesis against chilling stress. Transgenic plants were highly sensitive to chilling stress and accumulated high levels of H?O? in chloroplasts. Spectroscopic analysis and electron transport measurements show that PSII activity was significantly reduced in transgenic plants. Flash-induced fluorescence relaxation and thermoluminescence measurements demonstrate that there was a slow electron transfer between Q(A) and Q(B) and decreased redox potential of Q(B) in transgenic plants, whereas the donor side function of PSII was not affected. Immunoblot and blue native gel analyses illustrate that PSII protein accumulation was decreased greatly in transgenic plants. Our results suggest that chloroplast GR plays an important role in protecting PSII function by maintaining the electron transport in PSII acceptor side and stabilizing PSII complexes under chilling stress. Our results also suggest that the recycling of ascorbate from dehydroascorbate in the ascorbate-glutathione cycle in the chloroplast plays an essential role in protecting PSII against chilling stress.     

Transcriptome analysis reveals dynamic changes in the gene expression of tobacco seedlings under low potassium stress

Journal of Genetics - Potassium plays a key role in plant development and reproduction. In agricultural practice, potassium deficiency is common worldwide, and leads to crop growth inhibition and...