Carbon partitioning and export in transgenic Arabidopsis thaliana with altered capacity for sucrose synthesis grown at low temperature: a role for metabolite transporters

We investigated the role of metabolite transporters in cold acclimation by comparing the responses of wild-type (WT) Arabidopsis thaliana (Heynh.) with that of transgenic plants over-expressing sucrose-phosphate synthase (SPSox) or with that of antisense repression of cytosolic fructose-1,6-bisphosphatase (FBPas). Plants were grown at 23 degrees C and then shifted to 5 degrees C. We compared the leaves shifted to 5 degrees C for 3 and 10 d with new leaves that developed at 5 degrees C with control leaves on plants at 23 degrees C. At 23 degrees C, ectopic expression of SPS resulted in 30% more carbon being fixed per day and an increase in sucrose export from source leaves. This increase in fixation and export was supported by increased expression of the plastidic triose-phosphate transporter AtTPT and, to a lesser extent, the high-affinity Suc transporter AtSUC1. The improved photosynthetic performance of the SPSox plants was maintained after they were shifted to 5 degrees C and this was associated with further increases in AtSUC1 expression but with a strong repression of AtTPT mRNA abundance. Similar responses were shown by WT plants during acclimation to low temperature and this response was attenuated in the low sucrose producing FBPas plants. These data suggest that a key element in recovering flux through carbohydrate metabolism in the cold is to control the partitioning of metabolites between the chloroplast and the cytosol, and Arabidopsis modulates the expression of AtTPT to maintain balanced carbon flow. Arabidopsis also up-regulates the expression of AtSUC1, and to lesser extent AtSUC2, as down-stream components facilitate sucrose transport in leaves that develop at low temperatures.info:eu-repo/semantics/publishedVersio

Characterisation Of The Photosynthetic Responses Of Spring And Winter Wheat To Growth At Cold-hardening Temperatures

In vivo room temperature chlorophyll a fluorescence coupled with CO{dollar}\sb2{dollar} and O{dollar}\sb2{dollar} exchange are measured to determine the effect of cold-hardening on the photosynthetic capacity and the susceptibility to photoinhibition of six cultivars of wheat (Triticum aestivum L.), covering a range of freezing tolerance. The role of the photosystem II (PSII) repair cycle in resistance to, and recovery from, photoinhibition is assessed at both low temperatures (5{dollar}\sp\circ{dollar}C & {dollar}-3\sp\circ{dollar}C) and in the presence of the 70S protein synthesis inhibitor, chloramphenicol. The effect of long-term, repeated photoinhibitory events and sustained reduction in PSII efficiency on net carbon gained is also assessed.;Winter wheat cultivars grown at 5{dollar}\sp\circ{dollar}C show light-saturated rates of CO{dollar}\sb2{dollar} exchange and apparent photon yields for CO{dollar}\sb2{dollar} exchange and O{dollar}\sb2{dollar} evolution that are equal to or greater than those of winter cultivars grown at 20{dollar}\sp\circ{dollar}C. In contrast, spring wheat cultivars grown at 5{dollar}\sp\circ{dollar}C show 35% lower apparent photon yields for CO{dollar}\sb2{dollar} exchange and 25% lower light-saturated rates of CO{dollar}\sb2{dollar} exchange compared to 20{dollar}\sp\circ{dollar}C grown controls. The lower CO{dollar}\sb2{dollar} exchange capacity is not associated with a lower efficiency of PSII activity measured as either the apparent photon yield for O{dollar}\sb2{dollar} evolution or the variable to maximal fluorescence ratio, and is most likely associated with carbon metabolism. In addition, cold-hardened spring wheat cultivars are more sensitive to short-term photoinhibition at low temperatures than cold-hardened winter cultivars. This greater resistance of the winter cultivars is associated with the winter phenotype rather than freezing tolerance per se and is due to an increase in the capacity of cold-hardened winter wheat to keep the primary electron acceptor for PSII, Q{dollar}\sb{lcub}\rm A{rcub},{dollar} oxidised at high irradiance (Oquist et al, 1991a).;Repeated photoinhibition (daily reductions in {dollar}F\sb{lcub}\rm V{rcub}/F\sb{lcub}\rm M{rcub}{dollar} of up to 40%) and sustained depression of PSII efficiency are shown to have no negative effects of net carbon accumulation in both cold-hardened winter and spring wheat. This is related to the finding that up to 50% of the loss in photon yield during photoinhibition is not due to irreversible damage to PSII. It is due instead to a rapidly reversible form on photoinhibition that recovers at temperatures as low as {dollar}-3\sp\circ{dollar}C and without de novo protein synthesis. It is suggested that this rapidly reversible form of photoinhibition is evidence of PSII quenching centres resulting from light induced, reversible modifications to the PSII reaction centre. It is proposed that these rapidly reversible quenching centres act as a regulatory mechanism, adjusting the yield of electron transport to match utilisation by photosynthetic carbon reduction. Thus, in situations where photosynthesis may be limited by factors other than light availability. PSII efficiency can be regulated by these wheat cultivars such that the photosynthetic apparatus is protected from over excitation

Sourcing a Stone Paver from the Colonial St. Inigoes Manor, Maryland

The objective of this study is to determine the source of a limestone paver recovered from the colonial era Old Chapel Field archaeological site (18ST329-183) in St. Inigoes, Maryland. The site is in the Coastal Plain physiographic province, where there are no viable local sources of rock. As the site was a Jesuit manor, the primary hypothesis is that the stone came from England, the emigration origin point for the Maryland colonists. The secondary objective is to determine whether the stone paver was from the Jesuit Brick Chapel at St. Mary’s City (18ST1-103), reused after the chapel was torn down by 1705. Based on paleontological, lithological, and chemical analysis of the paver, sources in the Florida Platform (U.S.), Hampshire Basin (UK), Paris Basin (France), and the Belgian Basin were ruled out. The most likely source is the Aquitaine Basin in southwest France. Comparison with limestone fragments from the chapel supports reuse of the paver from the St. Mary’s City Brick Chapel

Low temperature maximizes growth of Crocus vernus (L.) Hill via changes in carbon partitioning and corm development

In Crocus vernus, a spring bulbous species, prolonged growth at low temperatures results in the development of larger perennial organs and delayed foliar senescence. Because corm growth is known to stop before the first visual sign of leaf senescence, it is clear that factors other than leaf duration alone determine final corm size. The aim of this study was to determine whether reduced growth at higher temperatures was due to decreased carbon import to the corm or to changes in the partitioning of this carbon once it had reached the corm. Plants were grown under two temperature regimes and the amount of carbon fixed, transported, and converted into a storable form in the corm, as well as the partitioning into soluble carbohydrates, starch, and the cell wall, were monitored during the growth cycle. The reduced growth at higher temperature could not be explained by a restriction in carbon supply or by a reduced ability to convert the carbon into starch. However, under the higher temperature regime, the plant allocated more carbon to cell wall material, and the amount of glucose within the corm declined earlier in the season. Hexose to sucrose ratios might control the duration of corm growth in C. vernus by influencing the timing of the cell division, elongation, and maturation phases. It is suggested that it is this shift in carbon partitioning, not limited carbon supply or leaf duration, which is responsible for the smaller final biomass of the corm at higher temperatures