Aris Jansons

Stress-induced transcriptional activation of retrotransposon-like sequences in the Scots pine (Pinus sylvestris L.) genome

Transposition of mobile elements has been implicated in genome instability, rearrangements and therefore also adaptation to changing environmental conditions. Transposons could influence gene activity directly by transposition inside or close to coding regions by their disruption or by addition of regulative sequences. Further, class I transposable elements, which are the most abundant in plant genomes, utilize a RNA intermediate in their life cycle, therefore retrotransposons could act by producing non-coding RNAs that could affect other transcripts by RNA interference. Transposition activity is suppressed by chromatin modifications, and both classes of transposons have been shown to be activated in plants under various stress conditions and developmental stages. Using a nonspecific amplification approach, we demonstrate the differential transcriptional activation of sequences with homology to transposable elements and other associated sequences in the complex genome of Scots pine (Pinus sylvestris L.) after exposure to heat stress, infestation with pine woolly aphids, and salicylic acid and abscisic acid treatment. Sequences with homology to several retrotransposon classes and families were identified, as well as several chimeric transcript types. Some of them represent chloroplast sequence insertions into the pine nuclear genome and these sequences are highly represented in EST databases of a wide range of species. In this study, we identified several retrotransposon classes and families with differing levels of similarity with known transposable elements from other plant species, and which are differentially expressed under various stress conditions in Scots pine.

Pruning effect on Norway spruce (Picea abies (L.) Karst.) growth and quality

Abstract Pruning requires significant investment, therefore, the aim of the study was to characterize occlusion of branch wounds and changes in radial increment as well as frequency of browsing damages after pruning of Norway spruce (Picea abies (L.) Karst.) in order to provide data for financial calculations and recommendations for practical forestry. Altogether 1,614 pruned and 4,368 unpruned trees from 45 Norway spruce stands were measured and cored. Degree of wound occlusion and browsing damages were assessed, and additional volume increment estimated in each stand. Pruning resulted in significant increase of length of branch-free section: for unpruned trees it was 0.3 ± 0.07 m, but for pruned 3.4 ± 0.10 m. Branch wounds for most of the trees (68%) were filled with resin (occluded), for lower share of trees (31%) – still open, but for some trees (1%) completely occluded. Branch wound occlusion rate was not affected by differences in stand density, but was significantly affected by stand age: proportion of trees with occluded branch scars increased with age. Trees with occluded branch wounds had a significantly higher increase in tree ring width after the pruning in comparison to the period before pruning than trees with open branch wounds, emphasizing the importance of radial increment in development of branch-free layer of wood. Pruning resulted in minor (−7% or −0.28 ± 0.05 m3 ha−1) reduction of annual increment that was statistically significant only up to 3 years after this forest management activity for stands younger than 17 years and with mean height up to 10.5 m. Pruned trees were significantly more browsed than unpruned (6.1% and 2.7%, respectively).

Chemistry and kraft pulping of seven hybrid aspen clones. Dimension measurements on the vessels and UMSP of the cell walls

Abstract Micropropagated hybrid aspen clones (Populus tremuloides Michx.×Populus tremula L.) and a plus-tree (superior phenotypes selected) aspen (Populus tremula L.) were grown under similar conditions in the central part of Latvia. After cutting at the age of 12 years, 64 sample trees were examined. The dimensions of the vessels and the content of cellulose, lignin, extractives and ash were determined. The cell walls were characterised by UV microspectrophotometry (UMSP) in the UV range. The dimensions of fibres obtained by kraft pulping were determined such as length, width, and their shape factors. Coarseness measurements were performed, and strength properties of the handsheets were tested. One of the clones (no. 44) had a significantly higher stem volume of 208 dm3 and stem diameter of 17 cm at a height of 1.3 m. This clone had otherwise no notable differences to the other clones concerning the chemical composition, except a slightly higher lignin content (20.0% as compared with the mean value of 19.3% for other clones). Kraft cooking of hybrid aspen chips gave pulp yields in the range of 48.6–52.4%. Slightly higher strength properties (10–15%) were found for the handsheets prepared from a common aspen pulp (reference) as compared with those from hybrid aspen fibres.

Stem damages caused by heart rot and large poplar borer on hybrid and European aspen

Abstract Solid wood production of hybrid aspen requires relative longer rotation periods, thus increasing risk of wood damages by pests and diseases. We compared damages by heart rot and poplar borer of 48 years old hybrid (Populus tremuloides Michx. × P. tremula L.) and European aspen in a progeny trial located in Eastern part of Latvia. Trees were harvested and rot patches and galleries were recorded and measured at a stump level. The number of galleries had positive relation on number of patches and total area of rot. The susceptibility of the rot and poplar borer was similar for both hybrid and European aspen. Yet, some differences among families were detected. No effect of pathogens damage was observed on the tree growth. Larger trees had smaller proportion and incidence of rot and galleries per unit of area as well as wider outer rot-free wood layer.

Chemical composition and fiber properties of fast-growing species in Latvia and its potential for forest bioindustry

Abstract Bioenergy, including energy from wood, currently provides about 9–13% of the total global energy supply. Every fibre of fast-growing wood has a value for its potential use as a material in both pulp and paper and wood chemical industries. The aim of this study was to assess the chemical composition and fibre’s properties of fast-growing species in Latvia – aspen, hybrid aspen, lodgepole pine, poplar and willow. Results showed a variation of cellulose, lignin, extractives and ash contents among the species. Kraft pulp yield and amount of residual lignin were measured and properties of pulp fibres determined. Form factor and fine content in pulp were measured. Poplar and aspen wood had the highest content of cellulose, while lodgepole pine had the highest lignin content in wood and the longest kraft pulp fibres. Willow had 20% of fines in pulp. Individual results suggest the most suitable application of each species.

Proportion of knotty wood in stems of 28-year old lodgepole and Scots pine in experimental plantation in Zvirgzde, Latvia

Abstract In forestry, alien tree species are planted to maximize yield from a stand by increasing productivity and decreasing environmental risks. In Eastern Europe, lodgepole pine (Pinus contorta var. latifolia) might be used as a source of biomass and industrial wood; however, before any recommendations are given, possible gains of the novel species should be scrupulously evaluated. In this study, we compared volume and proportion of knotty stemwood (VKN) of native Scots pine (Pinus sylvestris) from first generation seed orchards and provenances of alien lodgepole pine [Fort Nelson (58°38’ N, 122°41’ W) and Summit Lake (54°24› N, 122°37› W)] at the age of 27 years growing in central Latvia. We also assessed the relationships between VKN and several morphometric parameters. Stem diameter of both species was similar; however, Summit Lake provenance of lodgepole pine exceeded Scots pine in height, while Fort Nelson provenance was lower than Scots pine. Although Scots pine produced nearly two times less whorls than lodgepole pine, volume of knotless stemwood did not differ significantly between the species; though it was higher for Summit Lake provenance of lodgepole pine compared to Scots pine. In contrast, the proportion of VKN differed significantly between both the species and the provenances. Scots pine showed the lowest proportion of VKN (~ 9%) and Fort Nelson provenances of lodgepole pine showed the highest proportion of VKN (~ 14%). Thus, Summit Lake appears more suitable for the production of industrial wood amongst the provenances of lodgepole pine; nevertheless, higher quantity of leftover material is expected. Some morphometric parameters correlated with VKN and the proportion of VKN, but these relationships differed between species and provenances. The total cross-section of branches was the best predictors of VKN for Scots pine and Fort Nelson provenance of lodgepole pine, while stem diameter showed the strongest correlation for Summit Lake provenance. Number of whorls and mean diameter of living branches were the best predictors of the proportion of VKN for lodgepole pine and Scots pine, respectively. Accordingly, morphometric parameters might be useful for the selection of the best trees of lodgepole pine.

Expression of three phenylpropanoid pathway genes in Scots pine (Pinus sylvestris L.) in open-pollinated families with differing relative wood densities during early and late wood formation

Abstract Wood volume and quality are the most important aspects of commercial forestry production, and studies of wood formation are important in order to increase the value and efficiency of forestry production. The phenylpropanoid pathway produces various compounds with diverse functions both for plant defence against biotic and abiotic stress as well as structural development. One of the main roles is monolignol production for lignin biosynthesis, which is a crucial aspect of wood formation. For this study three candidate genes involved in lignin biosynthesis were selected: phenylalanine ammonialyase (PAL1), cinnamyl alcohol dehydrogenase (CAD) and cinnamoyl-CoA reductase (CCR). Candidate gene expression was analysed in selected individuals with high and low wood density from open-pollinated Scots pine families during early wood (EW) and late wood (LW) formation and correlation between expression of these genes, total lignin content, and wood density was determined. Wood density values for analysed trees were similar within tree families but differed significantly between families with high and low wood density (p=1,06E-20). Wood density was slightly negatively correlated with lignin content (r=-0.36, p=0.038), but only in individuals in the high density wood group. In trees with low wood density, expression of the CAD gene was significantly lower in late wood formation compared to early wood (p=0.00179). In trees with high wood density, expression of the PAL1 gene was five times higher during early wood formation compared to late wood formation. A positive correlation was detected between PAL1 and CCR gene expression during early wood formation (r=0.804) and late wood formation (r=0.466).