Absence of phosphoenolpyruvate carboxylase AtPPC3 increases sensitivity of Arabidopsis thaliana to cadmium

Phosphoenolpyruvate carboxylase (PEPC) and PEPC kinase (PPCK) catalyze a reaction feeding into the tricarboxylic acid (TCA) cycle, increasing the production of metal-chelating organic acids. Little research has been conducted on PEPC isoenzymes in Cd-stressed plants. Arabidopsis (Arabidopsis thaliana) wild-type and AtPPC1 – AtPPC3 mutants, each lacking one of three PEPC isoenzymes, grown in 0, 1, or 5 µM CdCl2 were smaller and had increased AtPPC1 – AtPPC3 and AtPPCK1 – AtPPCK2 transcript abundance, relative phosphorylation, and PEPC activity, more so in roots than shoots. Concentrations of oxaloacetate, citrate and total organic acids increased with greater CdCl2 concentrations. The absence of AtPPC3, and to a lesser extent AtPPC2, resulted in greater oxaloacetate concentrations and smaller plants in comparison with wild-type. My results indicate that AtPPC3 plays an integral role in Arabidopsis’ ability to cope with Cd. This information can be used to better understand Cd tolerance and stress in other plants, including crops

The mechanism of freezing resistance in cold-acclimated winter wheat and rye crowns

The ability of cold-acclimated crowns to survive freezing is an important environmental factor limiting winter wheat (Triticum aestivum L.) expansion in Western Canada. Coldacclimation refers to the physiological and biochemical processes by which plants acquire freezing resistance. Cold-acclimation establishes an ice segregation freezing survival mechanism. The shoot apical meristem (SAM) cold-acclimates through the accumulation of dehydrins, vernalization-responsive and cold shock proteins. Modifications to the vascular transition zone (VTZ), are centered on increases in pathogenesis-related, antifreeze proteins, sugar hydrolyzing enzymes and increased cell wall glucuronoarabinoxylans. In cold-acclimated winter wheat and rye (Seacale cereale L.), magnetic resonance microimaging revealed a desiccative intermediate zone between the SAM and VTZ with reduced water mobility. Slow cooling rates (≤ 2°C h-1) are required to establish freezing injury in the VTZ prior to injury in the SAM. Infrared thermography was used to observe in the absence of an extrinsic ice nucleator that freezing initiated from the base of the crown. The first freezing event (-3°C to -5°C) corresponded with warm ice nucleation temperatures (-3.5°C) and ice formation in the leaf sheath. Removal of the leaf sheath prior to cooling reduced cold hardiness and resulted in injury to the SAM prior to the VTZ. The second freezing event (-8°C to -12°C) corresponded with non-lethal injury to the VTZ. The third freezing event (-21°C in Norstar, -27°C in Hazlet and -30°C in Puma rye) corresponded with injury to the SAM and the plant’s killing temperature based on whole plant survival tests. It is hypothesized that cold-acclimated crowns survive sub-zero temperatures through the following mechanism. The leaf sheath is established as an ice sink relative to the SAM. An intermediate zone acts as a barrier to ice propagation, allowing the SAM to supercool and avoid freezing. The VTZ acts as an ice sink within the crown. Possible differences in SAM freezing survival between rye and wheat could explain their contrasting cold hardiness

Cross‐disciplinary insights into the mechanisms of plant cold hardiness: From molecules to ecosystems

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Effect of latitude on narrow-leaved purple coneflower (Echinacea angustifolia DC.) yield and phytochemical quality

The worldwide increase in demand for plant-derived drugs has increased interest in medicinal plants as alternative cash crops across western Canada. The objective of this research was to determine if the Northern Vigor® phenomenon, expressed as a combination of elevated crop yield and phytomedicinal quality in crops grown in northern latitudes, exists in narrow-leaved purple coneflower (Echinacea angustifolia DC.). In a 2-yr study, narrow-leaved purple coneflower was grown in three field sites in Saskatchewan, Canada (SK; Saskatoon, La Ronge, and Outlook) and one field site in Oregon, United States (Madras), to test the effects of latitude on root yield, phenolic, and alkylamide phytochemical markers. Roots harvested in 1999 (all three SK sites) and 2000 (two SK sites) had higher root biomass compared with roots harvested in Oregon. Root echinacoside and cynarin content were significantly higher in both years in the three Saskatchewan sites compared with Madras, whereas root chlorogenic acid content and total alkylamides were significantly higher in all three Saskatchewan sites in 1999. In 2000, root chlorogenic acid content and total alkylamides were higher in two of the three Saskatchewan sites compared with Madras. While Aster Yellows were prevalent in Echinacea in Saskatchewan, this disease did not significantly decrease root yield phenolic or phytochemical content. These data suggest that Saskatchewan has a competitive advantage in producing premium-quality narrow-leaved purple coneflower root in North America.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Arabidopsis Ubiquitin-Conjugating Enzymes UBC4, UBC5, and UBC6 Have Major Functions in Sugar Metabolism and Leaf Senescence

The ubiquitin-conjugating enzyme (E2) is required for protein ubiquitination. Arabidopsis has 37 E2s grouped into 14 subfamilies and the functions for many of them are unknown. We utilized genetic and biochemical methods to study the roles of Arabidopsis UBC4, UBC5, and UBC6 of the E2 subfamily IV. The Arabidopsis ubc4/5/6 triple mutant plants had higher levels of glucose, sucrose, and starch than the control plants, as well as a higher protein level of a key gluconeogenic enzyme, cytosolic fructose 1,6-bisphosphatase 1 (cyFBP). In an in vitro assay, the proteasome inhibitor MG132 inhibited the degradation of recombinant cyFBP whereas ATP promoted cyFBP degradation. In the quadruple mutant ubc4/5/6 cyfbp, the sugar levels returned to normal, suggesting that the increased sugar levels in the ubc4/5/6 mutant were due to an increased cyFBPase level. In addition, the ubc4/5/6 mutant plants showed early leaf senescence at late stages of plant development as well as accelerated leaf senescence using detached leaves. Further, the leaf senescence phenotype remained in the quadruple ubc4/5/6 cyfbp mutant. Our results suggest that UBC4/5/6 have two lines of important functions, in sugar metabolism through regulating the cyFBP protein level and in leaf senescence likely through a cyFBP-independent mechanism

Data from: Tissue-specific changes in apoplastic proteins and cell wall structure during cold acclimation of winter wheat crowns

The wheat (Triticum aestivum L.) crown is the critical organ of low temperature stress survival over winter. In cold-acclimated crowns, ice formation in the apoplast causes severe tissue disruption as it grows at the expense of intracellular water. While previous crown studies have shown the vascular transition zone (VTZ) to have a higher freezing sensitivity than the shoot apical meristem (SAM), the mechanism behind the differential freezing response is not fully understood. Cooling cold-acclimated crowns to –10 °C resulted in an absence of VTZ tetrazolium chloride staining, whereas the temperatures at which 50% of the SAM stained positive and 50% of plants recovered (LT50) were similar after cold acclimation for 21 (–16 °C) and 42 d (–20 °C) at 4 °C. Proteomic analysis of the apoplastic fluids identified dehydrins, vernalization-responsive proteins, and cold shock proteins preferentially accumulated in the SAM. In contrast, modifications to the VTZ centered on increases in pathogenesis-related proteins, anti-freeze proteins, and sugar hydrolyzing enzymes. Fourier transform infrared spectroscopy focal plane array analysis identified the biochemical modification of the cell wall to enhance methyl-esterified cross-linking of glucuronoarabinoxylans in the VTZ. These findings indicate that the SAM and VTZ express two distinct tissue-specific apoplastic responses during cold acclimation

Supplementary Table S1

List of identified and quantified apoplast proteins collected from the apical meristem and vascular transition zone of winter wheat cv. Norstar crowns. Plants were treated for 0, 21, or 42 d at four degrees Celsius to induce a cold acclimation response

Supplementary Table S2

Apoplastic fluid malate dehydrogenase (MDH) specific activity in ‘Norstar’ shoot apical meristem (SAM) and vascular transition zone (VTZ) following 0, 21, or 42 d of cold acclimation. Means followed by the same letter within each column are not significantly different based on Fisher’s Least Significant Difference test (P < 0.05)

Effect of location on dwarf French bean (Phaseolus vulgaris L.) seed production and seedling vigour

This study examined if dwarf French bean (Phaseolus vulgaris L.) grown at northern latitudes develop seeds with superior yielding potential compared with plants grown at more southern latitudes. Two lines (BND3085 and BND3106) were grown at four sites across latitudes ranging from 52°N to 3°S. BND3085 and BND3106 seeds from Saskatoon grown plants (52°N) had the least damaged seed coats but the highest degree of electrolyte leakage from the seed and the lowest maximum germination rates. The Saskatoon (BND3085 and BND3106) and Nunhem (BND3106) seed lots had the lowest maximum germination rates when germinated at 28°C, 12°C, or when exposed to saline (100 mM NaCl) conditions. Saskatoon BND3085 seed produced plants with the lowest aboveground vegetative and total seed dry matter as well as the lowest pod number per plant. In contrast, plants grown from Saskatoon BND3106 seed produced 1.5-fold more total pods, 1.3-fold more total pods and 1.4-fold higher seed dry matter per plant as compared to plants grown from the Nunhem (51°N) or Arusha seed sources. This resulted in a 2.4–4.5% higher harvest index. These results suggest cultivar-specific dwarf French bean seed propagation at more northern sites may increase the productivity of the resulting crop