The Changes in the Tapetum of Pinus banksiana Accompanying Formation and Maturation of the Pollen

As meiosis is completed, and following the synthesis of lipidduring meiotic prophase, the tapetum begins to form precursorsof sporopollenin. These accumulate in cisternae of the endoplasmicreticulum, resembling large dictyosome vesicles. They are releasedfrom the tapetal protoplasts intact, but rupture in the loculus.The liberated precursors polymerize either on lipid dropletsin the expanded tapetal walls, forming the orbicules, or onthe lipid layer surrounding the loculus, forming the secondcomponent of the peritapetal membrane. On rupture of the callosewall condensation also proceeds on the walls of the meiospores,already coated with a thin layer of sporopollenin synthesizedby the spore itself. The tapetal protoplasts expand considerablyduring synthesis of the precursors. Wide channels also formbetween the protoplasts, and the nuclei undergo irregular divisions. Ribosomes are conspicuous in the tapetal cytoplasm during thesporopollenin synthesis, but protein levels are low. It is proposedthat protein is exported to the loculus and untimately incorporatedinto the developing microspores. In the final phase of microsporogenesis the tapetum fragments,and parts move into the loculus.Protein levels in the tapetumare now high, possible indicating the massive synthesis of hydrolaseswhich accomplish the dissolution of the tissue. Removal of thelipid component of the peritapetal membrane precedes the desiccationof the anther. The surfaces of the mature pollen lack organizedor irregular deposits of tapetal debris.     

Patterns of inter-annual variation in the size asymmetry of growth in Pinus banksiana

A large body of literature suggests that asymmetric competition, where large individuals suppress the growth of smaller individuals by intercepting a disproportionate share of incoming light, is a dominant process in tree population development. This has not been examined extensively for long-lived tree species that accumulate growth over many years under varying growing conditions. Using dendrochronological techniques, we reconstructed annual growth and mortality rates at ten stands of jack pine (Pinus banksiana Lamb.) in Western Canada. We used these data to calculate an annual index of the size asymmetry of growth for each stand for the last 50 years. Jack pine is a shade-intolerant species found in even-aged monoculture stands, so the simple hypothesis is that large trees should consistently perform relatively better than small trees. Inter-annual variation in the index of size-asymmetric growth was positively associated with interannual variation in stand productivity at eight of ten sites. The size asymmetry of growth also showed a positive trend with age at eight of ten sites, even though all sites were in a period of declining leaf area. This should have reduced the intensity of asymmetric competition for light and reduced the size asymmetry of growth over time. Alternate hypotheses for this trend are (1) that physical collisions between crowns result in asymmetric competition for growing space because they are more damaging to small trees, or (2) that a differential build up of diseases in susceptible trees suppresses their growth, even in the absence of competition.     

The original basal stem section influences rooting in Pinus banksiana cuttings

Photosystem II (PSII) from Cu-deficient pea plants ( Pisum sativum L., cv. Lincoln) has been investigated for electron transport activity, Cu content, and changes in some lipid components. Total fatty acid content was lower that in control plants, with an additional shift in the C₁₈ fatty acid patterns. Less α-linolenic and more linoleic and oleic acids were found. PSII preparations from Cu-depleted plants showed a decreased carotenoid content in light harvesting chlorophyll a/b complex of photosystem II (LHCII) and additional variations in pigment composition of pigment-protein complexes. In the green alga Dunaliella the effect of Cu deficiency on fatty acid composition was similar to that in pea plants, but the influence on the carotenoid pattern was much less pronounced.     

Acclimation of respiratory temperature responses in northern and southern populations of Pinus banksiana

Temperature acclimation of respiration may contribute to climatic adaptation and thus differ among populations from contrasting climates. Short-term temperature responses of foliar dark respiration were measured in 33-yr-old trees of jack pine (Pinus banksiana) in eight populations of wide-ranging origin (44-55 degrees N) grown in a common garden at 46.7 degrees N. It was tested whether seasonal adjustments in respiration and population differences in this regard resulted from changes in base respiration rate at 5 degrees C (R(5)) or Q(10) (temperature sensitivity) and covaried with nitrogen and soluble sugars. In all populations, acclimation was manifest primarily through shifts in R(5) rather than altered Q(10). R(5) was higher in cooler periods in late autumn and winter and lower in spring and summer, inversely tracking variation in ambient air temperature. Overall, R(5) covaried with sugars and not with nitrogen. Although acclimation was comparable among all populations, the observed seasonal ranges in R(5) and Q(10) were greater in populations originating from warmer than from colder sites. Population differences in respiratory traits appeared associated with autumnal cold hardening. Common patterns of respiratory temperature acclimation among biogeographically diverse populations provide a basis for predicting respiratory carbon fluxes in a wide-ranging species.     

Photosynthetic acclimation to elevated atmospheric carbon dioxide and UV irradiation in Pinus banksiana

Pinus banksiana seedlings were grown for 9 months in enclosures in greenhouses at CO₂ concentrations of 350 or 750 μmol mol⁻¹ with either low (0.005 to 0. 3 W m⁻²) or high (0.25 to 0. 90 W m⁻²) ultraviolet-B (UV-B) irradiances. Total seedling dry weight decreased with high UV treatment but was unaffected by CO₂ enrichment. High UV treatment also shifted biomass partitioning in favor of leaf production. Both CO₂ and UV treatments decreased the dark respiration rate and light compensation point. High UV light inhibited photosynthesis at 350 but not at 750 μmol mol⁻¹ CO₂ due to a UV induced increase in ribulose-1, 5-bisphosphate carboxylase/oxygenase efficiency and ribulose-1, 5-bisphosphate regeneration. Stomatal density was increased by high UV irradiance but was unchanged by CO₂ enrichment.     

Proteolytic activity in relation to seasonal cambial growth and xylogenesis in Pinus banksiana.

Proteolytic activity in the cambial zone and developing xylem of Pinus banksiana Lamb. was investigated over an annual cycle of growth and dormancy. Highest proteolytic activity was associated with the most active period of primary-wall radial expansion of cambial derivatives, in early spring, before protoplasmic autolysis was initiated in developing earlywood. Three pH maxima of proteolytic activity, near pH 3.0, 6.5 and 9.5, were observed at that time. In general, activities measured at pH values below 7.0 were greater than those determined above pH 7.0 at all stages in the annual cycle, in both cambial zone and developing xylem, although elevated activity at alkaline pH was also observed during springtime growth. Polyvinylpolypyrollidone (PVP) treatment markedly enhanced pH 7.5 but not pH 4.0 proteolytic activity in the cambial zone, but not in developing xylem, indicating the presence of PVP-binding proteinase regulators in the cambium. By fractionation and effector studies total proteolysis was determined to comprise interactions between serine, cystine, aspartate and metallo-proteases having MWs, by gel chromatography, between 10 and 100 kDa. The observations point to a complex regulatory mechanism controlling the presence and catalytic rates of the distinct types of proteases in the cambial region throughout an annual cycle of growth and dormancy.     

Impact of fire on Picea mariana and Pinus banksiana seedlings in subarctic lichen woodlands

Abstract. The demography of Picea mariana (black spruce) and Pinus banksiana (jack pine) seedlings was monitored through five censuses over 13 months in four different seed bed types after fire of four severity levels in lichen woodland. Most seeds germinated just before early frost in late summer 1990 or immediately after snow thaw in early spring 1991; the germination rate subsequently decreased. For both species, germination rate decreased along a gradient of fire severity. The proportion of Pinus seeds that produced a seedling surviving 13 months after sowing was 4.3 % and 0.4 % respectively in the intact lichen mat and in the mineral soil seed bed type. For Picea these values are 3.2 % and 0.2 % respectively. The low germination rate in a severely burned seed bed type appeared to be associated with the formation of a water-repellent crust at the soil surface following the fire. Seedlings were contagiously distributed and were more frequent in flat and hollow microsites, where there is probably more water available than on bumps or among pebbles. Properties of experimentally burned seed bed types may differ from those under natural fires where regeneration by seed generally occurs following dispersal. However, the high germination rate observed in the intact lichen mat suggests that scattered lichen woodland patches may respond to increased seed input by a higher frequency of seedling establishment.     

Removal of the stem terminal and application of auxin change carbohydrates in Pinus banksiana cuttings during propagation

This study determined how surgical removal of the stem terminal, with indole-3-butyric acid (IBA) treatment, influenced concentrations and partitioning of carbohydrates in Pinus banksiana Lamb, cuttings during propagation. Seedlings and cuttings that originated from 90-day-old stock plants were untreated or treated by removing the stem terminal, followed by application of IBA to the severed apical or basal (cuttings only) stem. Fresh and dry weights of the basal 1-cm stems of cuttings were determined daily for the first 10 days of propagation (i.e., before roots were visible). In addition, basal 1-cm stems, upper (ca 9-cm) stems and needles of seedlings and cuttings were analyzed for sucrose, soluble reducing sugar and total non-structural carbohydrate. Net concentrations of each carbohydrate in cuttings were obtained by subtracting corresponding concentrations for similarly treated seedlings, yielding data directly related to only the physiology of rooting. Data for cuttings indicated that presence of the stem terminal combined with applied IBA positively influenced rooting through processes that increased basal stem fresh and dry weights before root emergence. Removal of the stem terminal influenced accumulation of net total carbohydrate in cuttings, but the major effect was on carbohydrate partitioning. Either type of IBA treatment after removal of the stem terminal usually resulted in different net carbohydrate concentrations in each tissue source of cuttings, compared with only removal of the terminal. Neither basal nor apical IBA treatment of cuttings without stem terminals yielded results for carbohydrate accumulation and partitioning like those obtained with intact cuttings. Removal of the stem terminal, even if followed by IBA treatment, may have lessened rooting potential of cuttings because it resulted in greater reducing sugarstarch concentration ratios in basal stems compared with those in intact cuttings.     

Morphometric analysis of Pinus banksiana Lamb. root anatomy during a 3-month field study

Tree roots are variable in their growth rates, alternating between periods of elongation and dormancy. This variability may have a strong influence on root anatomy. In the present study, field-grown Pinus banksiana Lamb. roots were divided into four distinct anatomical regions (i.e. white without mycorrhizae, white with mycorrhizae, condensed tannin, and cork). Changes in root growth, the proportions of the root system occupied by the various regions, and cortical plasmalemma surface area (CPSA) were determined for 6- to 9-month-old ectomycorrhizal P. banksiana seedlings during a 3-month period (August through October) in northern Ontario. The region in which the greatest change in length occurred was the condensed tannin zone, which was also the dominant contributor to root length (up to 74% of total). The roots of seedlings grown under artificial conditions had the same zones but in different proportions compared to roots in the field. A correlation was noted between increased root growth, low metacutization, and high soil water availability. The CPSA data were assumed to be a factor influencing ion uptake capacity in a positive manner. Interestingly, increases in CPSA were not directly correlated with changes in root length for field-grown seedlings. The primary contributor to CPSA in the field-grown roots was the ectomycorrhizal zone (approximately 80%). In comparison, the bulk (85%) of the CPSA in the chamber-grown roots was found in the white root region. The conditions under which the seedlings were grown strongly influenced the anatomy of their roots. Received: 27 April 1999 / Accepted: 6 December 1999     

Effects of nitrogen limitation on water relations of jack pine (Pinus banksiana Lamb.) seedlings

The water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure-volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g^?1 dry mass and a 10-fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor-loss point, however, declined as N concentrations decreased, indicating an increased ability of N-deficient jack pine plants to maintain turgor. The increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g^?1 and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross-linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to N limitation.     

Inequality of size and size increment in Pinus banksiana in relation to stand dynamics and annual growth rate

BACKGROUND AND AIMS: Changes in size inequality in tree populations are often attributed to changes in the mode of competition over time. The mode of competition may also fluctuate annually in response to variation in growing conditions. Factors causing growth rate to vary can also influence competition processes, and thus influence how size hierarchies develop. METHODS: Detailed data obtained by tree-ring reconstruction were used to study annual changes in size and size increment inequality in several even-aged, fire-origin jack pine (Pinus banksiana) stands in the boreal shield and boreal plains ecozones in Saskatchewan and Manitoba, Canada, by using the Gini and Lorenz asymmetry coefficients. KEY RESULTS: The inequality of size was related to variables reflecting long-term stand dynamics (e.g. stand density, mean tree size and average competition, as quantified using a distance-weighted absolute size index). The inequality of size increment was greater and more variable than the inequality of size. Inequality of size increment was significantly related to annual growth rate at the stand level, and was higher when growth rate was low. Inequality of size increment was usually due primarily to large numbers of trees with low growth rates, except during years with low growth rate when it was often due to small numbers of trees with high growth rates. The amount of competition to which individual trees were subject was not strongly related to the inequality of size increment. CONCLUSIONS: Differences in growth rate among trees during years of poor growth may form the basis for development of size hierarchies on which asymmetric competition can act. A complete understanding of the dynamics of these forests requires further evaluation of the way in which factors that influence variation in annual growth rate also affect the mode of competition and the development of size hierarchies.     

宁夏枸杞异型绒毡层发育的超微结构特点

采用半薄和超薄切片技术对宁夏枸杞(Lycium barbarum L.)异型绒毡层的来源、结构及发育特点进行了研究,结果表明:(1)枸杞异型绒毡层由药隔绒毡层和药壁绒毡层组成,两种绒毡层除了来源、形态及分布位置不同外,其分化、成熟和降解时间,以及细胞质组成、分泌物成分等均有差异.(2)小孢子母细胞期间,药隔绒毡层细胞电子密度大,具有很强的脂质性质,光滑内质网和脂质小泡很丰富;而药壁绒毡层细胞中的核糖体和粗糙内质网较多.四分体后期,两种绒毡层细胞均含有很丰富的核糖体、粗糙内质网和分泌团.减数分裂前,两种绒毡层的细胞壁出现松散并呈絮状.之后,由于不同发育时期绒毡层细胞的不同分泌物在絮状细胞壁中的分布,致使二者的细胞壁都出现了一系列变化.(3)从小孢子早期开始,两种绒毡层细胞的质膜都发生了局部解体.分析推测,在母细胞期间药隔绒毡层具有较高的糖和脂类合成率,药壁绒毡层具有较高的蛋白质类合成率;在四分体后期,药隔绒毡层具有加强胼胝质酶合成和分泌的功能;而两种绒毡层絮状松散的细胞壁和局部解体的质膜有利于绒毡层的较大颗粒分泌物大量、顺利地分泌出绒毡层细胞.     

Postglacial range expansion and population growth of Picea mariana, Picea glauca and Pinus banksiana in the western interior of Canada

The fossil pollen records from the sediments of thirteen lakes are used to reconstruct the postglacial spread and population expansions of Picea mariana (Mill.) B.S.P., Picea glauca (Moench) Voss and Pinus banksiana Lamb. across the western interior of Canada. The objective of this study was to examine temporal and spatial patterns in the growth of the populations and to determine if intraspecific and interspecific variations exist across a range of latitudes and elevations. Pollen accumulation rates (PARs) are estimated from pollen grain counts and sedimentation rates throughout the early to mid-Holocene and are used to represent the population level at the time of pollen deposition. Exponential equations are used to calculate population growth rates. Three-dimensional diagrams (time, space, abundance) are constructed to illustrate range expansion and population growth.The rates of population growth varied from south to north for all three species. Pinus banksiana , on average, had slower population growth rates, and its expansion across the region began over 4000 years later and lasted approximately 1000 years longer than the two Picea species. All three tree taxa experienced reduced rates of population growth at northern high elevation sites. These variations are examined in light of the physical and biological environmental conditions which existed during postglacial range expansion and population growth.     

Root Browning in Pinus banksiana Lamb. and Eucalyptus pilularis Sm. 2. Anatomy and Permeability of the Cork Zone

The periderm in roots of Pinus banksiana Lamb. and the polyderm in roots of Eucalyptus pilularis Sm. originate from the pericycle. This occurs after the roots have turned brown due to deposition of tannins in the walls of cells external to the endodermis. In both species, cork cells form a continuous sheath around the vascular tissues. The cork cell walls are modified by the presence of suberin, lignin and tannin and it is the latter which imparts a brown colour to the tissue. The first layer of cork cells in both species constitutes an apoplastic barrier which prevents the fluorescent dye, berberine, from entering the vascular tissues, despite the absence of an identifiable Casparian band in the cells. Because the roots are still covered with the cortex and epidermis during early stages of periderm and polyderm formation, it is not possible to tell from the external aspect of the root when it makes a transition from the tannin zone to the cork zone.     

Studies on the Sporogenous Lineage in the Moss Timmiella barbuloides IX. Development of the Tapetum

The ultrastructure of tapetal cells in Timmiela barbuloideswas investigated in relation to events of sporogenesis. Aftertheir establishment both internally and externally to the sporogonialinitials, tapetal cells enlarge and assume a permanently polarizedorganization after completion of meiosis. A large vacuole isformed in the cell region distal to the spore sac, the nucleusbecomes centrally located, and amyloplasts lie in the cytoplasmadjacent to the spore sac. An extensive endomembrane systemdevelops in tapetal cells during the stage of exine depositionin spore tetrads. Sheets of rough endoplasmic reticulum developfirst around the nucleus then also in close proximity to theplasma membrane abutting the spore sac. Concomitantly, interveningdictyosomes produce a variety of vesicles. Unusual structureswith vesicle-like profiles also occur in the inner tapetum cellwalls abutting the spore sac. At the same time most of the starchis lost from the plastids in which grana-fretwork systems develop.A massive secretion of extremely electron-opaque material isassociated with perine deposition onto the free spore surfaces.Degeneration of the tapetal cells during the terminal stagesof spore maturation is marked by distortion of the organelles,increase in vacuolation and the appearance of electron-opaquematerial between the sheets of endoplasmic reticulum.Copyright1994, 1999 Academic Press Bryophytes, endomembrane dynamics, Timmiella, ultrastructure, development, tapetum