Alteration of Growth and Morphogenesis by Endogenous Ethylene and Carbon Dioxide in Conifer Tissue Cultures

Somatic embryo maturation, germination, and soil establishment of plants of black and white spruce (<i>Picea mariana</i> and <i>Picea glauca</i>)

Variation in Results of Three Biology‐Focused Search Engines: A Case Study Using North American Tree Species

Morphological variation in white and black spruce: investigation of natural hybridization between <i>Picea glauca</i> and <i>P. mariana</i>

Eastern dwarf mistletoe (Arceuthobium pusillum Peck) is a hemiparasitic angiosperm that infects white spruce (Picea glauca (Moench) Voss) and red spruce (P. rubens Sarg.) in northeastern North America. The effects of mistletoe infection differ substantially between white and red spruce, with white spruce suffering greater infection-induced mortality. In the present study, we sought to determine the role that species-specific differences in needle-scale responses to parasitism may play in the observed differences in the effect of infection on host tree health. Based on the measurements made, the most apparent effect of parasitism was a reduction in needle size distal to infections. The magnitude of this reduction was greater in white spruce than in red spruce. Eastern dwarf mistletoe was a sink for host photosynthate in red spruce and white spruce; however, there were no adjustments in needle photosynthetic capacities in either host to accommodate the added sink demands of the parasite. Needle total nonstructural carbohydrate concentrations (TNC) were also unaltered by infection. Red spruce needles had higher TNC concentrations despite having lower overall photosynthetic capacities, suggesting that red spruce may be more sink limited and therefore better able to satisfy the added sink demands of parasitic infection. However, if carbon availability limits the growth of the mistletoe, one may expect that the extent of the parasitic infection would be greater in red spruce. Yet in the field, the extent of infection is generally greater in white spruce. Taken together, these results suggest that dwarf mistletoe may not substantially perturb the carbon balance of either host spruce species and that species-specific differences in needle-scale responses to the parasite cannot explain the contrasting effects of infection on white spruce and red spruce.

The developmental process of lily flower bud differentiation has been studied in morphology thoroughly, but the mechanism in molecular biology is still ambiguous and few studies on genetic expression have been carried out. Little is known about the physiological responses of flower bud differentiation in Oriental hybrid lily ‘Sorbonne’ ( Lilium spp.) during the stages of flower bud differentiation and the genes involved in these responses. In this study, the differences in gene expression between two stages of lily bud differentiation: the stage before bud differentiation (SB) and the stage of bud differentiation (SD) were studied. The suppression subtractive hybridization (SSH) method conducted to generate large-scale expressed sequence tags (EST) was designed to identify gene candidates related to the morphological and physiological differences between the stage before bud differentiation and the stage of bud differentiation of lily. The results showed that the SD could induce differential expression of the genes related to lily flower bud differentiation. EST were isolated, cloned, sequenced and identified using BlastN and BlastX, and indicated that at the stage of the flower bud differentiation, there is an activation of a floral development response at a molecular level, mainly related to low temperature and post-transcriptional regulation of nucleic acids. 24.1% of the isolated sequences are not yet described which showed the lack of genomic information currently available for lily. Sequence analysis revealed that most of the differentially expressed genes are related to metabolism and regulation such as protein synthesis and catabolism of carbohydrate related to flower formation. Some genes also encoded transcription factors. These genes showed high mRNA transcript levels in the stage of flower bud differentiation. This study revealed that unknown genes are putatively involved in the stage of lily flower bud differentiation, which serve as a starting point for understanding the differentiation of lily flower bud. Keywords: Lily flower bud differentiation, gene expression, suppression subtractive hybridization (SSH)

Changes of purine and pyrimidine nucleotide biosynthesis during shoot initiation from epicotyl explants of white spruce (Picea glauca)

The production of ethylene and carbon dioxide by Pinus radiata D. Don cotyledons cultured on shoot‐forming medium in sealed Erlenmeyer flasks was studied. To establish the role of these gases on morphogenesis three experimental approaches were used: (1) capping the flasks with serum caps on various days, and removing the serum caps at different stages of morphogenesis, (2) absorbing the gases by setting up traps singly and in combination during the various stages of differentiation and (3) incubating the cultures under continuous flow of constant gas mixtures. The results indicate that both ethylene and carbon dioxide, which build up during the first 10 to 15 days of culture, promote morphogenesis. Excessive accumulation after the initiation of buds causes some degree of dedifferentiation. When both the gases were eliminated from the flasks, bud formation and growth were inhibited. In the absence of oxygen, ethylene and carbon dioxide fail to influence growth and morphogenesis.

Local distributions of black spruce (Picea mariana) and white spruce (Picea glauca) are largely determined by edaphic and topographic factors in the interior of Alaska, with black spruce dominant on moist permafrost sites and white spruce dominant on drier upland sites. Given the recent evidence for climate warming and permafrost degradation, the distribution of white spruce is expected to expand, but the transition from black to white spruce may be dispersal limited: unlike the semi‐serotinous black spruce, postfire regeneration of white spruce relies on seed dispersal from unburned areas. To determine the relative roles of dispersal, establishment, and growth in recruitment of white and black spruce, we studied postfire spruce regeneration in a 21‐year‐old burn across a white spruce–black spruce transition in the interior of Alaska. Although prefire spatial distributions of adults of the two species were well separated along the topographic sequence from upland to floodplain sites, the spatial distributions of recruits overlapped considerably. Even &gt;700 m away from its seed source, white spruce sapling density on typical black spruce sites was high enough to form fully stocked stands. In contrast, black spruce regeneration was sparse on typical white spruce upland sites. Establishment rates of both species, estimated from a statistical model, were highest in mossy, wet depressions, which tended to have a thick residual postfire organic layer (∼10 cm). On all site types, height growth rates inferred from age–height relationships were comparable for recruits of both species. On typical black spruce sites ≥300 m into the burn, white spruce was younger (and, therefore, shorter) than black spruce due to the timing of masting events following the fire. There was no indication that dispersal, establishment, or edaphic constraints on juvenile growth limit white spruce's capacity to invade typical black spruce stands during the recruitment stage in our study area. It is unlikely that white spruce recruits would persist to the adult stage if the permafrost returned to the original prefire levels during future postfire succession. However, if permafrost continues to degrade under climate warming, transition to a white spruce‐dominated landscape could be rapid.

Population genetic variation, structure, and evolution in Engelmann spruce, white spruce, and their natural hybrid complex in Alberta

Observations over a two and a half year period in the Northeast United States and adjacent Canada indicate that White—winged Crossbills (Loxia leucoptera) and Red Crossbills (L. curvirostra) shift their diets among the seeds of various conifer species in a seasonal pattern. Both crossbill species forage on white spruce (Picea glauca) in late summer. White—winged Crossbills continue foraging on white spruce or tamarack (Larix laricina) until late autumn or winter, when they switch to black spruce (P. mariana). Red Crossbills switch to white pine (Pinus strobus) in early autumn and to red pine (P. resinosa) or other pines in winter or spring. This pattern of diet shifts is consistent with the hypothesis that crossbills forage to maximize food intake rate. Profitability (milligrams of kernel ingested per second) was measured for crossbills foraging on each of these conifers by observing rates of seed ingestion in the field, and subsequently measuring dry seed kernel masses. Profitability for a given conifer increases as cones and seeds mature, then declines as seeds are shed from the cones. Because conifers differ in the timing of cone ripening, crossbills experience sequential peaks in profitability. Both crossbill species usually foraged predominately on the most profitable conifer species, with switches in conifer use coinciding with shifts in relative profitabilities. However, crossbills often forage on more than one conifer species at a time, even though intake rates might be maximized by foraging on only the most profitable conifer. Predation does not appear to influence diet selection and large—scale patterns of conifer use. Crossbill movements and patterns of abundance, both on local and continent—wide scales, are correlated with patterns of profitability. Dietary overlap between crossbill species is greatest, often approaching 100%, in late summer when seed is most abundant. Overlap then declines rapidly when white pine cones open, and usually remains negligible most of the remainder of the year. Patterns of dietary overlap are a result of differences in profitability for each crossbill species that are largely inherent in the ripening phenology of conifer cones and seed accessibility, not seed depletion by crossbills. Interspecific competition is most likely between White—winged Crossbills and either the smallest form of the Red Crossbill or redpolls (Carduelis sp.) during the late winter of "invasion" years, which occur every 3—4 yr. Intraspecific competition is also likely to be most intense at these times.

In plants, knowledge about linkage disequilibrium (LD) is relevant for the design of efficient single-nucleotide polymorphism arrays in relation to their use in population and association genomics studies. Previous studies of conifer genes have shown LD to decay rapidly within gene limits, but exceptions have been reported. To evaluate the extent of heterogeneity of LD among conifer genes and its potential causes, we examined LD in 105 genes of white spruce (Picea glauca) by sequencing a panel of 48 haploid megagametophytes from natural populations and further compared it with LD in other conifer species. The average pairwise r(2) value was 0.19 (s.d.=0.19), and LD dropped quickly with a half-decay being reached at a distance of 65 nucleotides between sites. However, LD was significantly heterogeneous among genes. A first group of 29 genes had stronger LD (mean r(2)=0.28), and a second group of 38 genes had weaker LD (mean r(2)=0.12). While a strong relationship was found with the recombination rate, there was no obvious relationship between LD and functional classification. The level of nucleotide diversity, which was highly heterogeneous across genes, was also not significantly correlated with LD. A search for selection signatures highlighted significant deviations from the standard neutral model, which could be mostly attributed to recent demographic changes. Little evidence was seen for hitchhiking and clear relationships with LD. When compared among conifer species, on average, levels of LD were similar in genes from white spruce, Norway spruce and Scots pine, whereas loblolly pine and Douglas fir genes exhibited a significantly higher LD.

Stand and landscape level effects of a major outbreak of spruce beetles on forest vegetation in the Copper River Basin, Alaska

FORECAST, an ecosystem simulation model, was calibrated for aspen (Populus tremuloides Michx) and white spruce (Picea glauca (Moench) Voss) stands using data collected in the Boreal White and Black Spruce biogeoclimatic zone in northeastern British Columbia and published data. Simulations were undertaken to examine the effects of initial density of aspen on yield of white spruce in an aspen and spruce mixedwood stand, and to compare the predicted stemwood biomass yields of aspen, white spruce and mixedwood stands. Results of the simulations suggest that mixedwood management regimes on the same medium quality site should have higher stemwood yield compared to pure white spruce stand. Simulated stemwood biomass yield of pure aspen stands over 240 years on medium site varied from 682.5 Mg ha−1 to 239.1 Mg ha−1 for different rotation lengths (30 to 120 years). Repeated rotations of monoculture white spruce produced much less stemwood biomass, simulated yields over 240 years ranging from 877.3 Mg ha−1to 248.4 Mg ha−1 for rotation lengths of 60 to 240 years. Simulated aspen and white spruce mixedwood stands produced higher stemwood biomass yields than the pure white spruce stands, but less than the pure aspen stands; from 217.4 Mg ha−1 to 292.8 Mg ha−1 over 240 years. Variations in initial densities of aspen did not affect spruce stemwood biomass yield over the simulation period. This model shows potential for comparing the relative effects of different management strategies on harvestable volume and variety of other ecosystem variables. A calibrated version of the model should be useful as both a management simulator and a research tool. However, shortcomings in the representation of the canopy architecture of mixed species stands suggested the need to develop an individual tree version of this ecosystem management model for application to mixed species stands.

Population genetic variation, structure, and evolution in Engelmann spruce, white spruce, and their natural hybrid complex in Alberta

Polymerase chain reaction (PCR) primer pairs for 21 simple sequence repeat (SSR) loci in Pinus strobus L. and 6 in Pinus radiata D. Don. were evaluated to determine whether SSR marker amplification could be achieved in 10 other conifer species. Eighty percent of SSR primer pairs for (AC)n loci that were polymorphic in P. strobus also amplified SSR loci in two other soft pines of the subgenus Strobus but not in seven hard pines of the subgenus Pinus, nor in Picea glauca (Moench) Voss or Pseudotsuga menziesii (Mirb.) Franco. The six P. strobus SSR primer pairs that did amplify loci from conifers other than soft pines were those that were specific to loci monomorphic within P. strobus. These six loci were also monomorphic within seven other species tested, but four of the loci were polymorphic among species. A comparison of allelic variation among the three soft pine species found only 25 shared alleles among a total of 122 alleles at eight loci. Primer pairs for dinucleotide SSR loci that were polymorphic in Pinus radiata also specifically amplified loci from various other hard pines but not from the soft pines or from the other conifers tested.