Action of Phytochrome During Prechilling of Amaranthus retroflexus L. Seeds

Dark germination of Amaranthus retroflexus L. seeds at 35° increased after several days of prechilling at 20° or lower. Irradiation with far-red light for short periods during the early hours of a prechilling period at 10° inhibited subsequent dark germination at 35°. The inhibition was completely reversible with red light. Far-red irradiation in the latter part of the prechilling period was less effective. Increased dark germination of A. retroflexus seeds following a prechilling period at 20° or less is attributed to action of preexistent P_FR, the far-red absorbing form of phytochrome, within the seeds. Inactivation of P_FR was found to proceed ca. 4 times more rapidly at 25° than at 20°. Failure of imbibition temperatures above 20° to increase dark germination of A. retroflexus seeds is attributed to the rapid thermal reversion of pre-existent P_FR. We suggest that the action of prechilling (layering) on many other seed kinds arises in a similar way.     

Studies of photosynthesis and diffusion resistance in paper birch (Betula papyrifera Marsh.) with synthesis through computer simulation

Summary Canopy structure and physiology of paper birch are examined in the field during two growing seasons. Leaves are found to be steeply inclined in the upper canopy levels and foliage mass is located higher in the canopy than frequently observed in more shade tolerant species. Functional relationships between the controlling environmental factors and the physiological processes of leaf resistance to water vapor diffusion and gross photosynthesis are used in a computer simulation model to examine production and water use aspects of paper birch.     

Phytochrome Control of Germination of Rumex crispus L. Seeds Induced by Temperature Shifts

High germination of curly dock (Rumex crispus L.) seeds is evident after suitable imbibition and temperature shift treatment, but germination at constant temperatures fails without an input of far red-absorbing form of phytochrome. Preliminary imbibitions at high temperatures (30 C) sharply reduce germination induced by temperature shifts. High germination may be restored by low energies of red radiation, or by brief far red adequate for the photosteady state. Prolonged far red during imbibition also nullifies temperature shift-induced germination. After prolonged far red, high germination may be restored by red radiation of an energy dependent upon the duration of the far red treatment. The evidence supports the conclusion that dark germination induced by temperature shifts arises from the interaction of pre-existent far red-absorbing form of phytochrome in the mature seeds with the temperature shift.     

Further studies in flood tolerance of Betula papyrifera seedlings

Flooding of soil for 60 days drastically reduced height growth, cambial growth, dry weight increment, and relative growth rate of 150-day-old Betula papyrifera Marsh. seedlings. Comparisons of responses to flooding of 150-day-old and 230-day-old seedlings indicated important differences between the two age classes. Whereas the younger seedlings produced abundant adventitious roots on submerged portions of stems, the older seedlings did not. Flooding also induced much more leaf abscission in the older seedlings. Flooding generally reduced root-shoot ratios of both age classes, largely as a result of inhibition of growth and decay of root systems. However, root-shoot ratios were altered appreciably by formation of adventitious roots in the younger seedlings and by extensive leaf abscission in the older seedlings.     

Phytochrome and Seed Germination. III. Action of Prolonged Far Red Irradiation on the Germination of Tomato and Cucumber Seeds

Prolonged irradiation with continuous or intermittent far red prevents the germination of tomato and cucumber seeds. The inhibitory efficiency of intermittent far red decreases with the lengthening of the interval between successive irradiations, and with the increase of temperature. If each far red irradiation is followed by red, germination is restored. Intermittent far red is less inhibitory than intermittent red-far red when red is given immediately before each far red. This effect is more evident when the interval between successive irradiation becomes longer.     

Anticancer diarylheptanoid glycosides from the inner bark of Betula papyrifera

Phytochemical investigations of the MeOH extract of Betula papyrifera inner bark led to the isolation of ten phenolic compounds of the following types: diarylheptanoid glycosides (1-4), a diarylheptanoid (5), a lignan (6), flavonoids (7-8) and chavicol glycosides (9-10). Among them, the diarylheptanoid glycoside, (S)-1,7-bis-(4-hydroxyphenyl)-heptan-3-one-5-O-alpha-L-arabinofuranosyl-(1-->6)-beta-D-glucopyranoside, papyriferoside A (1), was isolated and its structure was determined on the basis of 1D and 2D NMR, HPLC-MS, as well as high resolution mass spectroscopic data. Platyphylloside (4) exerted the strongest cytotoxic activity of all isolated compounds with IC(50) values ranging from 10.3 to 13.8 microM.     

Studies of the Mechanism of Enhancement of Phytochrome-dependent Lettuce Seed Germination by Prechilling

Temperature and kinetic studies were performed to examine the mechanism by which prechilling stimulates phytochrome-dependent seed germination in lettuce, Lactuca sativa, L. cv. Grand Rapids. Imbibed seeds were given a short far red irradiation and one day of dark incubation at 20 C to establish very low levels of the far red-absorbing form of phytochrome—(Pfr). Germination was greatly stimulated by subsequent prechilling treatments when they were followed by a second short far red irradiation. Prechilling therefore increased germination sensitivity to the low, normally inhibitory Pfr levels established by far red irradiation. This sensitivity increased with lowered prechilling temperature to a maximum near 4 C. It was linearly dependent upon duration of prechilling at 4 C up to a near maximal response at 10 hours, and it decayed in a converse manner when seeds were returned to 20 C after 10 hours at 4 C. Prechilling also increased germination responses to subsequent periods of high levels of Pfr which were initiated by red and terminated by far red irradiations. High Pfr periods adequate to promote the germination of unchilled seeds produced sharp inflections at 18 C in the dependence of germination on prechilling temperature. Rates of phytochrome potentiation of germination were not affected by prechilling. The response to prechilling fit a mechanism involving homeoviscous adaptation of membrane lipids to temperature.     

Phytochrome E Controls Light-Induced Germination of Arabidopsis

Germination of Arabidopsis seeds is light dependent and under phytochrome control. Previously, phytochromes A and B and at least one additional, unspecified phytochrome were shown to be involved in this process. Here, we used a set of photoreceptor mutants to test whether phytochrome D and/or phytochrome E can control germination of Arabidopsis. The results show that only phytochromes B and E, but not phytochrome D, participate directly in red/far-red light (FR)-reversible germination. Unlike phytochromes B and D, phytochrome E did not inhibit phytochrome A-mediated germination. Surprisingly, phytochrome E was required for germination of Arabidopsis seeds in continuous FR. However, inhibition of hypocotyl elongation by FR, induction of cotyledon unfolding, and induction of agravitropic growth were not affected by loss of phytochrome E. Therefore, phytochrome E is not required per se for phytochrome A-mediated very low fluence responses and the high irradiance response. Immunoblotting revealed that the need of phytochrome E for germination in FR was not caused by altered phytochrome A levels. These results uncover a novel role of phytochrome E in plant development and demonstrate the considerable functional diversification of the closely related phytochromes B, D, and E.     

Phytochrome and Seed Germination: VI. Phytochrome and Temperature Interaction in the Control of Cucumber Seed Germination

Phytochrome control of cucumber seed germination is temperature-dependent. A prolonged exposure to radiation from broad spectrum far red sources (Pfr/P = 0.05 to 0.07) prevents germination at temperatures below 20 C. Above 20 C there is no inhibition and it appears as if there is an escape from phytochrome control. However, radiation from a monochromatic, narrow band 730 nanometer source (Pfr/P < 0.02) inhibits germination at temperatures above 20 C. This result supports the idea that, even at high temperatures, Pfr is responsible for the activation of germination. After 4 days of exposure to far red, a short red irradiation is quite effective in promoting germination if temperatures during the dark incubation periods are maintained below 20 C; red becomes effective at temperatures above 20 C. Promotion of germination will take place at a temperature of 25 C or higher without red irradiation. Again, we have an apparent escape from phytochrome control at high temperatures. However, if higher temperatures are used for only short periods, 2 to 6 hours, in combination with short red irradiation, one can demonstrate that activation of germination at high temperatures is still dependent on phytochrome. Phytochrome is probably destroyed during prolonged exposure to far red. Thus, the subsequent short red irradiation establishes levels of Pfr which may not be sufficient to promote germination at low temperatures but are probably adequate at high temperatures.     

Phytochrome and Seed Germination. IV. Action of Light Sources With Different Spectral Energy Distribution on the Germination of Tomato Seeds

Germination of tomato seeds exposed to a single, saturating irradiation from light sources of different spectral energy distribution seems to be dependent upon the photostationary P_FR/P_R ratio established by the irradiation. Germination of tomato seeds exposed to prolonged irradiations from the same light sources does not seem to be controlled solely by the P_FR/P_R ratio induced and maintained by the irradiation.     

Responses of ectomycorrhizal Populus tremuloides and Betula papyrifera seedlings to salinity

Roots of trembling aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.) seedlings were inoculated with Hebeloma crustuliniforme or Laccaria bicolor and treated with 25 mM NaCl for 6 weeks. Both tree species appeared to be relatively tolerant of the applied NaCl treatment and did not develop visible leaf symptoms that are characteristic of salt injury. Salt treatment reduced total dry weights in aspen and birch, but did not significantly affect transpiration rates and root hydraulic conductance. Salt-treated ectomycorrhizal aspen maintained higher root hydraulic conductance compared with non-mycorrhizal plants. Na and Cl concentrations increased in shoots and roots of mycorrhizal and non-mycorrhizal aspen and birch in response to NaCl treatment. Roots of NaCl-treated aspen inoculated with H. crustuliniforme had over twofold higher concentrations of Na compared with non-mycorrhizal NaCl-treated plants. Similarly to aspen, Na and Cl concentrations increased in roots and shoots of NaCl-treated birch seedlings. However, in birch, there were no significant differences in Na and Cl concentrations between mycorrhizal and non-mycorrhizal plants. The results suggest that salt exclusion by the ectomycorrhizal associations is host-specific or/and that the processes leading to salt exclusion are activated in ectomycorrhizal plants by a threshold salt level which may vary between plant species.     

Genetic and metal analyses of fragmented populations of Betula papyrifera (Marsh) in a mining reclaimed region: identification of population–diagnostic molecular marker

White birch (Betula papyrifera) is an open pollinate species that is, dominant in the Northern Ontario after land reclamation. In fact, this species represents 65% of all trees in the region. We hypothesized that the exchange of genetic information between fragmented populations by range‐wide paternal introgression is possible in wind‐pollinated species such as B. papyrifera. On the other hand, the effects of heavy metal contamination from the mining activities on plant growth and population dynamics are well documented. The main objectives of this study were (1) to assess the level of genetic variation, gene flow, and population sustainability of B. papyrifera after land reclamation; and (2) to determine the level of phytoavailable metals in soil and their accumulation in trees. We found that B. papyrifera is a Ni and Zn accumulator with a translocation factor of 6.4 and 81, respectively, and an indicator of Cu and Pb. The level of polymorphic loci, Shannon index, Nei's genetic diversity, observed number of alleles, and gene flow were determined for the fragmented populations within the targeted region. The percent of polymorphic loci ranged from 28% to 56%; the gene flow was also low with a value of 0.89, and the population differentiation was very high with a value of 0.36. Two population–diagnostic ISSR markers were identified. They were cloned, sequenced, and converted to SCAR markers. Overall, the fragmented populations of B. papyrifera in Northern Ontario are genetically sustainable based on the moderate level of intrapopulation variability.     

Phytochrome Transformation and Action in Seeds of Rumex crispus L. during Secondary Dormancy

Promotion of germination by red light fails after prolonged dark imbibition of Rumex crispus L. seeds, indicative of a secondary dormancy. The degree and rate of inception of the dormancy increases with increasing temperature. Following establishment of the dormancy, germination response to red light can be restored by either prolonged cold treatment or brief high temperature shifts. Loss of phytochrome was not a factor in the initial establishment of the dormancy. When the seeds are in secondary dormancy, the chromophore of phytochrome can be transformed to the far red-absorbing form, but the far red-absorbing form cannot induce germination. The responses to changes in temperature suggested dependence of germination on order disorder transitions in components of the seeds.     

Diurnal and Seasonal Changes in Water Balance of Acer saccharum and Betula papyrifera

Diurnal and seasonal changes in plant water potential, leaf diffusion resistance, and stem radial changes of Acer saccharum and Betula papyrifera trees were studied in northern Wisconsin during the 1974 and 1975 growing seasons. Water potential decreased during the day, following relatively high values in the morning, and increased in the late afternoon and evening. Diurnal patterns and actual values of water potential varied with species, soil water availability, and factors influencing transpiration (e.g., solar radiation, vapor pressure deficit, and transpiration flux density). When plant water deficits were not severe, leaf resistance of both species was rather stable during the day. During severe droughts, however, leaf resistance increased (stomata closed) during the day when light intensity was high. Leaf resistance at high light intensity was higher in Acer than in Betula. Stomatal closure with decreasing light intensity varied between species and among Acer trees. Tree stems of both species shrank during the day, as internal water deficits developed, and they expanded as trees rehydrated during the night. Stems of Acer shrank more than those of Betula. The amount of daily stem shrinkage increased as the season progressed if the trees were not under severe water deficits. During severe droughts the amount of diurnal stem shrinkage decreased. Shrinkage of stems lagged behind water potential changes by 1 to 2 h in Acer and less than 1 h in Betula. The relationship between stem radius and leaf water potential was not constant throughout the growing season.     

Two Sites of Hormonal Action during Germination of Chenopodium album Seeds

During the overall germination process in the light-requiring seeds of Chenopodium album L. two sites of hormonal action can be distinguished. The start of visible growth is induced in darkness by the gibberellins 4 and 7 (GA₄₊₇) or by ethylene. Added cytokinins are inactive although 8-¹⁴C-kinetin shows rapid penetration into the seed and rapid turnover. The induction of growth by GA₄₊₇ and the uptake of 8-methylene-¹⁴C-GA₃ are enhanced at lower pH values. Prolonged incubation in darkness results in a decreased responsiveness of the seeds towards GA₄₊₇ and ethylene. A second site of hormonal action is located during the progress of growth inside the covering structures. ABA inhibits radicle growth, while GA₄₊₇, GA₃, kinetin, zeatin and ethylene reduce the inhibition.     

Characterization of wound responses of stems of paper birch (Betula papyrifera) and European white birch (Betula pendula)

Plants respond to feeding injury by chewing insects by inducing both a general response to mechanical wounding and a specific response to herbivore-associated elicitors. In both cases, plant response involves complex biochemical and physiological changes. We compared chemical and physical responses of paper birch (B. papyrifera) and European white birch (B. pendula) stems to mechanical injury to determine if aspects of their wound response correspond with the much higher resistance of paper birch to bronze birch borer (Agrilus anxius). We also characterized stem responses to mechanical wounding plus bronze birch borer larval homogenate to determine if larval cues elicited a more specific response than mechanical wounding alone. In both species, wounding decreased concentrations of individual phenolics, total phenolics, and condensed tannins, perhaps because they were diverted to lignin biosynthesis, the concentration of which increased. Nitrogen concentration increased in both species while free amino acid concentrations declined, perhaps because they were utilized to synthesize proteins. Application of larval homogenate did not elicit a response different from that induced by mechanical injury. When comparing wound responses of the two birch species, phenolic profiles differed most conspicuously. However, multivariate analyses revealed no differences between constitutive and wound-induced phenolic profiles within each species, and the rate of wound periderm growth was equivalent between species. These results suggest that components of the wound response we measured may not contribute to interspecific variation in bronze birch borer resistance of paper birch and European white birch.     

Effects of intensive harvesting on forest floor properties in Betula papyrifera stands in Newfoundland

Abstract. Betula papyrifera (White birch) is a common tree throughout the boreal forest of Canada; makes up 12% of the total tree volume in insular Newfoundland. It forms pure stands after harvesting and wildfire disturbance and it is a common component in most softwood stands. Little is known regarding the environmental impact of whole-tree or conventional harvesting of this species and variation in impact related to variation in soil and site conditions. This study investigates litter and organic matter production and related site ecology in nine medium to high quality Betula papyrifera stands in three locations in central Newfoundland on a variety of land form and drainage conditions. Three sites, Badger West (BW), Moose Pond (MP) and Middleton Lake (ML) were selected. The ML site has the highest quality (with the best height/age ratio, 18 m/60 yr, and height/DBH ratio, 18 m/30 cm, followed by MP and BW. Litter depth on well developed moders or mulls was usually 2 - 3 cm and varied from 1 - 15 cm. Forest floor depths (measured in 324 profiles) rarely reached 20 cm and was commonly 5 - 10 cm; it varied with position and site. Total and available nutrients indicate that B. papyrifera produces one of the highest -quality organic matter types of the local forest types and is important in improving site quality. The mean N-concentration in green foliage (2.21%) and trapped litter (1.03%) was highest at the best quality site ML, followed by MP and BW. The concentration of calcium, 0.85%, was highest at the poorest quality site. Four years after harvesting, litter depth significantly decreased in all sites and treatments with the exception of the BW whole-tree harvest treatment. Total forest floor depth significantly decreased at all sites in the stem-only harvest treatment as well as the MP whole-tree harvest treatment. There was a significant decrease in available nitrogen following harvesting in both treatments at both the MP and BW sites. Change in available phosphorus was insignificant, with the exception of an increase in the MP stem-only harvest treatment. There was a significant decrease in available potassium at both the ML and BW whole-tree harvest treatments, but a significant increase in the stem-only harvest treatments at ML and MP. There was a significant decrease in available calcium in both treatments at both the MP and BW sites.