Substrate Availability in Relation to Daylength Effects on Tracheid Development in Picea sitchensis (Bong) Carr

Changes in assimilation and growth were studied in Picea sitchensis(Bong) Carr. seedlings initially grown in long days and subsequentlytransferred to short days. These results, and some from a supplementarystudy involving transfer to reduced light quantity alone, wereexamined in relation to tracheid development. Increases in photosynthesis conditioned by reduced daylengthwere greater in magnitude than those resulting from a reductionin light quantity alone. Possible reasons for this as well asthe apparent absence of such photoperiodic effects in the fieldare discussed. Following a reduction in daylength, ¹⁴C incorporation into reservesand new growth generally decreased while turnover materialsincreased in prominence. Some local changes in this generalpattern were apparent, these changes being consistent with growthchanges in the organs under consideration. Initial changes in tracheid wall thickness and diameter aftershort-day transfer appear to be correlated with expected andobserved changes in endogenous substrate, the results for tracheiddiameter confirming a previous observation that substrate levelexerts an important modifying influence on tracheid radial expansion.     

Effects of Light Intensity on Tracheid Dimensions in Picea sitchensis

In seedlings of Picea sitchensis grown in constant conditions,or within older trees in the field, light intensity had no neteffect on the wall thickness of tracheids produced at the samepoint in time. This appears to be due to a balanced regulatorysystem, effects of light intensity on rate of accumulation ofwall volume per leaf being offset by differences in rate ofxylem increment, and differences in wall material per tracheidbeing nullified in their effects on wall thickness by effectson tracheid diameter. Mean tracheid wall thickness across the growth ring increasedwith light intensity, due to increase in proportion of late-woodassociated with the longer duration of cambial activity at higherlight intensity, duration of wall thickening increasing duringthe season. Duration of wall thickening did not vary with lightintensity. The rate of increase in wall volume was limited by light intensity(and hence possibly by substrate availability) at all lightintensities in the field, but in seedlings in controlled conditionsthe rate of wall production was no greater at 20 000 lx thanat 6700 lx.     

Adaptations to Environmental Change in Picea sitchensis Seedling-changes in Photosynthesis, Growth and Substrate Availability

Effects of a change in night temperature with or without reductionin the duration of photosyntheticallyuseful light were studiedon assimilation and growth of Picea sitchensis seedlings. An increase in night temperature resulted in a rapid, but temporary,increase in photosynthesis while lowering the night temperaturedecreased photosynthetic rate. For the lowest night temperaturetreatments, reduction in light quantity resulted in increasedphotosynthetic efficiency while for the highest night temperaturetreatment, reduction in light quantity apparently checked thefinal decline in photosynthetic rate noted above. These changestended to minimize treatment effects on absolute growth andnet assimilation rates. The results are discussed in relationto the hypothesis or photosynthetic control by substrate level. Short-term redistribution of ¹⁴C labelled assimilate was examinedin control plants and those in the most and least adverse environments.In the most unfavourable environment, total ^l4C transport andincorporation into turnover materials increased while labellingof reserves and new growth decreased. Paradoxically, labellingpatterns for plants in the most favourable environment weresimilar although total ¹⁴C transport was much reduced. It issuggested that this indicates a substrate excess resulting fromoverloading of transport and utilization systems. Growth pattern was markedly affected in the case of developingbranch initials and established branches only. The possibilitythat the observed changes represent adaptive responses is discussed.     

Daylength Effects on Growth, Tracheid Development, and Photosynthesis in Seedlings of Picea sitchensis and Pinus sylvestris

Effects of change in daylength on tracheid expansion and tracheidwall thickening are considered in relation to shoot and rootgrowth, assimilation rate, and starch content, in seedlingsof Picea sitchensis and Pinus sylvestris grown in controlledenviroments. Rates of wall thickening decreased in the first tracheids tobegin wall thickening after decrease in daylength. A sharp decreasein starch-grain size at the same time supports previous suggestionsthat wall thickness is related to available substrate; however,rates of assimilation were found to be far greater in shortdays than in long, suggesting that a surplus of carbohydratemay be produced in long days. It is pointed out that if availablesubstrate does limit wall thickening it is likely to determineto al accumulation of wall material; wall material per tracheidwould follow logistically from this depending on the numberof tracheids around the xylem, and wall thickness would dependalso on the radial tracheid diameter. Unexpectedly, rate of shoot growth accelerated after transferto short days before its final cessation with terminal-bud formation.Root growth declined in short days, but later increased againafter terminal bud formation. Rate of root growth did not appearto be associated with tracheid development in the shoot.     

Stilbene glucosides in the bark of Picea sitchensis

The fresh bark of Picea sitchensis contains astringin as the major stilbene; isorhapontin and piceid are present in minor amounts. The aglycones astringenin, isorhaponhgenin and resveratrol are absent in samples of fresh bark. Prenylation reactions on 5,3′,4′-tri-O-methylastringenin are described.     

The Kinetics of Tracheid Development in Tsuga canadensis Carr. and its Relation to Tree Vigour

Cell counts from samples taken at weekly intervals, from 14May to 22 October 1969, in a T. canadensis stand in Massachusetts,U.S.A., showed that the width of the annual ring was correlatedwith the rate of cell production and that only the least vigoroustrees (c. 20 tracheids year^–1) had a shorter growing season.The time required for completion of a cell-division cycle inthe cambial zone decreased during the course of the season,from 35 to 20 days for the less vigorous trees (25–45tracheids year^–1) and from 28 to 10 days for the morevigorous trees (45–100 tracheids year^–1). The timerequired for the completion of radial growth of the tracheidsdecreased from 18 to 9 days, with no evidence of any changeswith tree vigour. The actual radial growth-rate of the tracheidswas constant within the range 1.5–3 um day^–1. Thetime required for deposition of the secondary cell wall increasedfrom 10 to 50 days, with little evidence of any changes withtree vigour. The actual rate of deposition of cell wall materialwas about 0.15 µ² µ^–1 day^–1 and seemedto show little change during the course of the season. The timeperiod required for lysis of the cytoplasm was about 4 days,with no evidence of any changes with tree vigour and littleevidence of any changes during the course of the season.     

Adaptive gradients and isolation-by-distance with postglacial migration in Picea sitchensis

Fossil pollen records suggest rapid migration of tree species in response to Quaternary climate warming. Long-distance dispersal and high gene flow would facilitate rapid migration, but would initially homogenize variation among populations. However, contemporary clinal variation in adaptive traits along environmental gradients shown in many tree species suggests that local adaptation can occur during rapid migration over just a few generations in interglacial periods. In this study, we compared growth performance and pollen genetic structure among populations to investigate how populations of Sitka spruce (Picea sitchensis) have responded to local selection along the historical migration route. The results suggest strong adaptive divergence among populations (average Q(ST)=0.61), corresponding to climatic gradients. The population genetic structure, determined by microsatellite markers (R(ST)=0.09; F(ST)=0.11), was higher than previous estimates from less polymorphic genetic markers. The significant correlation between geographic and pollen haplotype genetic (R(ST)) distances (r=0.73, P<0.01) indicates that the current genetic structure has been shaped by isolation-by-distance, and has developed in relatively few generations. This suggests relatively limited gene flow among populations on a recent timescale. Gene flow from neighboring populations may have provided genetic diversity to founder populations during rapid migration in the early stages of range expansion. Increased genetic diversity subsequently enhanced the efficiency of local selection, limiting gene flow primarily to among similar environments and facilitating the evolution of adaptive clinal variation along environmental gradients.     

Competition Within Stands of Picea sitchensis and Pinus contorta

Competition was analysed in plots of Picea sitchensis and Pinuscontorta grown in 50 x 50 hexagonal arrays at 14 cm spacingto ages 7 and 5 years, respectively. Relative growth rates in height (RHGR) became positively relatedto tree heights during the year before harvest. Frequency distributionsof tree heights became negatively kurtotic with tendencies towardsleft-skew ness. By the time of harvest, dead trees were evenlydispersed over the plots. Trees with many taller neighbourshad lower RHGRs than trees with few taller neighbours, and theRHGRs of intermediate-sized trees were correlated with their‘competitive status’. Competition was confined mostlyto first-order neighbours. Large trees depressed the RHGRs ofsmaller neighbours and not vice versa; a simple test for this‘one-sided’ competition is described. Neighboursdid not need to greatly overtop a tree to depress its RHGR,they needed only to be at least as tall. Systematic trends inRHGR across the plots, attributed to site heterogeneity, decreasedwith time, and accounted for only about 10 per cent of the variationin RHGR at harvest. Competitive status accounted for 25 and38 per cent of the variation in RHGR in the Picea sitchensisand Pinus contorta plots, respectively. Picea sitchensis, Pinus contorta, competition, monoculture, self-thinning, relative growth rate, growth model     

Development and Structure of Unusual Xylem Elements During Graft Union Formation in Picea sitchensis L.

Electron microscope studies of Sitka spruce have been undertakento observe the sequence of cellular development following grafting.Observations at the graft interface reveal a recovery and regenerationsequence associated with union formation. Xylem elements differentiateddirectly from the vascular cambia of the rootstock and scionare different from elements arising from parenchymatous callusderived from ray parenchyma, which may be produced in an attemptto establish a connecting water conducting system as rapidlyas possible. Failure to form such a system may be a primarycause of graft failure. Grafting, Picea sitchensis, xylen elements     

Two antimicrobial and nematicidal peptides derived from sequences encoded Picea sitchensis

Two antimicrobial peptides (piceain 1 and 2) derived from sequences encoded Picea sitchensis are identified. Their amino acid sequences are KSLRPRCWIKIKFRCKSLKF and RPRCWIKIKFRCKSLKF, respectively. One intra‐molecular disulfide bridge is formed by these two half‐cysteines in both piceain 1 and 2. Antimicrobial activities of synthesized piceains against several kinds of microorganisms were tested. They showed antimicrobial activities against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and fungus Candida albicans but little antimicrobial activity against Bacillus subtilis. The results of nematicidal test showed they exerted strong nematicidal activities against Caenorhabditis elegans, following exposure for 5 h at concentrations as low as 10 µg/ml. They had weak hemolytic abilities against human and rabbit red cells. At the concentration of 250 µg/ml, they induced red cell hemolysis of less than 5%. Circular dichroism spectra of the two antimicrobial peptides were investigated in several solutions. Their main secondary structure components are β‐sheet and random. The current work provides a novel family of antimicrobial and nematicidal peptides with unique disulfided loop containing nine amino acid residues. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Convexity of the Photosynthetic Light-Response Curve in Relation to Intensity and Direction of Light during Growth

Photosynthesis in the intermediate light range is most efficient when the convexity of the photosynthetic light-response curve is high. Factors determining the convexity were examined for intact leaves using Salix sp. and for a plant cell culture using the green microalga Coccomyxa sp. It was found that the leaf had lower convexity than diluted plant cells because the light gradient through the leaf was not fully matched by a corresponding gradient in photosynthetic capacity. The degree to which the leaf gradients were matched was quantified by measuring photosynthesis at both leaf surfaces using modulated fluorescence. Two principal growth conditions were identified as those causing mismatch of leaf gradients and lowering of the convexity relative to cells. The first was growth under low light, where leaves did not develop any noteworthy gradient in photosynthetic capacity. This led to decreased convexity, particularly in old leaves with high chlorophyll content and, hence, steep light gradients. Second and less conspicuous was growth under high light conditions when light was given bilaterally rather than unilaterally, which yielded leaves of high photosynthetic capacity at both surfaces. Two situations were also identified that caused the convexity to decrease at the chloroplast level: (a) increased light during growth, for both leaves and cells, and (b) increased CO2 concentration during measurement of high-light-grown leaves. These changes of the intrinsic convexity were interpreted to indicate that the convexity declines with increased capacity of ribulose-1,5-bisphosphate carboxylase/oxygenase relative to the capacity of electron transport.     

Shoot Apical Meristems of Picea sitchensis Seedlings Accelerate in Growth Following Bud-set

First-year seedlings of Picea sitchensis were induced to setbuds by transferring them from long days (17 h) to short days(10 h at 20 °C, 12 h night at 12 °C). After 20 shortdays, the seedlings stopped growing in height, the shoot apicaldomes began enlarging and the transverse growth rates of theshoot apical dome tissues increased. For about 25 days thereafterprimordia were produced faster within the developing buds thanat the apices of seedlings which had been kept in long daysto prevent bud-set. Accelerated primordia production after bud-setenables the largest possible buds to be formed during the frost-freeperiod before winter. Picea sitchensis, apical meristem, bud-set     

Temperature and Tracheid Development in Pinus sylvestris Seedlings

Seedlings of Pinus sylvestris were grown in long days at day/nighttemperatures of 27.5/20 °C. 22.5/15 °C, and 17.5/10°C to determine effects of temperature on tracheid expansionand wall thickening. Inbuilt regulatory systems make it unlikely that mean temperaturedifferences account for much of the normal seasonal variationin tracheid dimensions, for while an increase in temperatureincreased rates of both tracheid expansion and wall thickening,the duration of both was reduced. Though wall thickness increasedwith decreasing temperature in tracheids at the same distancefrom the pith, this was offset by a slower rate of tracheidproduction at lower temperatures. While rates of wall accumulation increased with increase intemperature, storage starch grain sizes were smaller at highertemperatures. It is suggested that wall thickness is not limitedby available substrates in these conditions.     

Effects of Environmental Change on Wood Production and Wood Structure in Picea sitchensis Seedlings

Changes in environment that would be expected to reduce substrateavailability, decrease the rate of xylem increment, tracheiddiameter and wall thickness, in seedlings of Picea sitchensis.But after reaching a minimum about 10 days to 3 weeks afterenvironmental change, xylem increment, tracheid wall thickness,and in some instances tracheid diameter, increase again up toabout 4 to 6 weeks after transfer. This recovery parallels arecovery in net assimilation rate, and is associated with anincrease in photosynthetic efficiency. Although the light intensity and temperature treatments imposedwere more drastic than those that would normally be expectedin the field, they had remarkably little net effect on tracheiddimensions. On the other hand change in photoperiod producedgreater changes in tracheid dimensions, photoperiodic effectsbeing superimposed on effects of change in substrate availability.It is suggested that adaptation to reduced substrate will bufferthe plant against climatic fluctuations during the growing season,while the photoperiodic response will ensure preparation forwinter dormancy. It is concluded that the major seasonal changes in tracheiddimensions are unlikely to be caused by variation in substrateavailability. Changes in light intensity and temperature haveminor effects on wood production and structure through effectson substrate availability, but the major seasonal trends aremore likely to be associated with changes in growth regulationproduction.     

Shoot Extension in Picea sitchensis I. Seasonal Variation Within a Forest Canopy

The seasonal variation of the daily increment of the shootsof 20-year-old Picea sitchensis is described. Data collectedfor leading shoots and those on the five topmost whorls of branchesare compared qualitatively with seasonal trends in weather.Moving averages are used to describe the seasonal trend in dailyextension rate and systematic variation through the canopy isnoted in this trend. The fitting of Richards' growth functionsto cumulative increment is described. The fitted growth curvedescribed the seasonal trend of cumulative increment well onthe basis of residual sums of squares, but systematic variationwith time was noted in the residuals. Relative growth rate didnot decline as a simple mathematical function of increasingsize attained thus suggesting that simple determinate growthcurves may not be appropriate in describing the growth of foresttrees. Picea sitchensis, Sitka spruce, seasonal growth trends, Richards' growth functions, plant growth model     

Somatic embryogenesis in Sitka spruce (Picea sitchensis (Bong.) Carr.)

Embryonal-suspensor masses from immature embryos from cones of Sitka spruce (Picea sitchensis (Bong.) Carr.) proliferated on a modified Murashige & Skoog medium with N⁶-benzyl-aminopurine, kinetin, 2,4-dichlorophenoxyacetic acid and an organic nitrogen source. The slimy white embryonal-suspensor masses with proembryos were maintained on a solid proliferation medium with reduced amounts of growth regulators. Transfer of embryonal-suspensor masses to a non-woven polyester carrier with liquid maturation media containing ±2-cis-4-trans-abscisic acid and a reduced amount of inositol and organic nitrogen resulted in synchronized embryo formation. Further development was achieved on a medium without ±2-cis-4-trans-abscisic acid and organic nitrogen. Somatic embryos were successfully transferred ex vitrum.Abbreviations ABA ±2-cis-4-trans-abscisic acid - BAP N⁶-benzyl-aminopurine - ESM embryonal-suspensor masses - KIN kinetin - 2,4-D 2,4-dichlorophenoxyacetic acid     

The architecture of Picea sitchensis structural root systems on horizontal and sloping terrain

The coarse root systems of 24 Sitka spruce (Picea sitchensis (Bong.) Carr.) trees, from a 40-year-old plantation in west Scotland, were extracted, digitised in three dimensions, and root topology was recorded. Roots were from trees grown on a steep (ca. 30°) north-facing slope, and from an adjacent horizontal area with similar gleyed mineral soil. The prevailing wind was across-slope from the west. Analysis of below-ground parts of the trees in comparison with those above-ground revealed a positive linear relationship between coarse root volume and stem volume. Most non-directional characteristics of the root systems were similar between trees on the slope and on flat terrain. Allocation of root mass around trees was examined in relation to the slope and the prevailing wind direction. Trees on the horizontal area had more root mass in leeward sectors than other sectors, but trees on the slopes had more root mass in the windward sectors than other sectors. Centres of mass of the root systems from the horizontal part of the site were not significantly clustered in any direction, but root systems of trees on the slope had centres of mass significantly clustered across the slope in the windward direction. For trees on the slope, the mean direction of the largest sector without structural roots was 4° from north, i.e. downslope. The results are discussed in relation to soil characteristics and the biomechanical behaviour of trees on slopes.