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In an attempt to comprehensively study the dynamics of non-structural carbon compounds (NCCs), we measured the seasonal changes of soluble sugars, starch, lipids and sugar alcohols in the leaves, branches, stem and roots of the fast-growing Pinus contorta (Loudon) (pine) and slow-growing Picea glauca (Moench) Voss (spruce) trees growing in a boreal climate. In addition to measuring the seasonal concentrations of these compounds, the relative contribution of these compounds to the total NCC pool within the organs of trees (~8 m tall) was estimated and compared across different phenological and growth stages. Both species showed large seasonal shifts from starch to sugars from spring to fall in nearly all organs and tissues; most likely an adaptation to the cold winters. For both species, the total fluctuation of sugar + starch across the year (i.e. the difference between the minimum and maximum observed across collection times) was estimated to be between 1.6 and 1.8 kg for all NCCs. The fluctuation, however, was 1.40 times greater than the minimum reserves in pine, while only 0.72 times the minimum reserves in spruce. By tissue type, NCC fluctuations were greatest in the roots of both species. Roots showed a large build-up of reserves in late spring, but these reserves were depleted over summer and fall. Storage reserves in needles and branches declined over the summer, and this decline may be linked to the sink strength of the stem during diameter growth. Some notable highlights of this holistic study: a late winter build-up of sugars in the stem xylem of both species, but especially spruce; and an increase in sugar alcohols in the bark of spruce in very late winter, which could indicate mobilization to support early growth in spring and high lipid reserves in the bark of pine, which appeared not to be impacted by seasonal changes between summer and winter. Collectively, these observations point toward a more conservative NCC reserve strategy in spruce compared with pine, which is consistent with its stress tolerance and greater longevity. [ABSTRACT FROM AUTHOR]

A new member of the Argonaute (AGO) family of proteins was isolated from conifers and designated as PgAGO (Gene Bank Accession No. DQ068741; protein ID AAY67884). The complete coding sequence of PgAGO was obtained through screening cDNA libraries generated from white spruce (Picea glauca (Moench) Voss) somatic embryos. The PgAGO gene has an open reading frame of 2880 bp and encodes a protein of 960 amino acids. The predicted protein has an isolectric point of 9.17, a molecular mass of 107 kD and lacks prominent hydrophobic domains, which makes its cellular location inconclusive. The PgAGO protein contains the two conserved regions (the PAZ and PIWI domains) typically found in all members of the AGO family. The PAZ domain of PgAGO comprises 117 amino acid residues and shares a low degree of homology with similar domains in other species. The C-terminal PIWI domain contains 86 amino acids and is more conserved. Localization and transformation studies suggest that PgAGO is required for embryo development, specifically for proper shoot and root apical meristem differentiation. Based on RNA-in situ hybridization, the PgAGO transcripts are preferentially localized in cells of the shoot and root apical meristems from the early phases of embryo development. The RNA-mediated suppression of PgAGO results in severe abnormalities during embryo development, including the formation of poorly organized apical meristems. The root meristems lack the group of large central cells that separate the procambial region from the root cap, whereas the shoot meristem fails to differentiate apical initials. These abnormalities result in poor post-embryonic performance, leading to meristem abortion and growth cessation. [ABSTRACT FROM AUTHOR]

Effects of drying and cryopreservation on survival of spruce (Picea glauca (Moench) Voss and Picea glauca × engelmannii complex) somatic embryos (SEs) were investigated with the aim of developing simple and robust protocols for embryo storage. Somatic embryos dried over salt solutions of known water potential (Ψ) survived removal of virtually all free water, to a relative water content (RWC) of approximately 0.13, a value similar to that for spruce zygotic embryos from dry seed. Desiccated SEs also survived subsequent freezing in liquid nitrogen, without the addition of cryoprotectant or pre-culture steps. Highest survival (> 80%) after freezing in liquid nitrogen was in embryos pre-dried to Ψ of –15 to –20 MPa, which yielded RWC close to predicted bound (apoplastic) water values. Low (< 35%) or no survival after freezing was observed in embryos pretreated at higher Ψ (above –5 MPa) or at very low Ψ (–540 MPa, using silica gel), respectively. [ABSTRACT FROM PUBLISHER]

It has previously been shown that exogenous applications of ascorbic acid (AA) increase the conversion frequency of somatic embryos of white spruce (Picea glauca (Moench) Voss). To determine whether ascorbic acid alters purine metabolism during the early phases of embryo germination, the relative rates of purine salvage and degradation were investigated by following the metabolic fates of exogenously applied [8-14C]adenine, [8-14C]adenosine, and [8-14C]inosine, and the activities of several key enzymes. We demonstrated that both the salvage and the degradation pathways operate during germination. Specifically, adenine and adenosine were mainly salvaged to nucleotides and nucleic acids, whereas an appreciable amount of inosine was degraded to CO2 and ureides. Comparisons of purine metabolism between control and AA-treated embryos showed that exogenous applications of ascorbic acid enhanced the ability of the embryos to take up adenine and adenosine throughout the germination period. Furthermore, the higher enzymatic activities of adenosine kinase and adenine phosphoribosyltransferase were responsible for the larger proportion of adenine and adenosine being salvaged in AA-treated embryos compared with control embryos. Thus, there was a positive correlation between the ability to anabolize purine precursors and successful embryo conversion. [ABSTRACT FROM AUTHOR]

Significant reductions in needle water content were observed in white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill) B.S.P.), and jack pine (Pinus banksiana Lamb.) seedlings in response to a 10-day drought, although turgor was apparently maintained. When the seedlings were re-watered after the drought, jack pine needles regained their original saturated volume, whereas white spruce and black spruce needles did not. Significant drought-induced reductions in turgor-loss volume (i.e., tissue volume at the point of turgor loss) were observed in shoots of all three species, especially jack pine. Repeated exposure to 7 days of drought or treatment with the cytochrome P450 inhibitor, paclobutrazol ((2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol), reduced seedling height relative to that of untreated controls in all three species. The reductions in saturated and turgor-loss needle volumes in the paclobutrazol-treated seedlings were comparable with those of seedlings subjected to a 10-day drought. The treatment-induced reductions in shoot and needle water contents enabled seedlings to maintain turgor with tissue volumes close to, or below, the turgor-loss volume of untreated seedlings. Paclobutrazol-treated seedlings subsequently survived drought treatments that were lethal to untreated seedlings. [ABSTRACT FROM AUTHOR]