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Biomedical subjects

M S Greenwood

Publications and source records attributed to M S Greenwood.

14 recordsLinked to original sources
PubMed2006

Ultrasonic sensor to characterize wood pulp during refining.

A novel sensor concept has been developed for measuring the degree of refining, the water retention value (WRV), and the weight percentage of wood pulp during the refining process. The measurement time is less than 5 min and the sensor can operate in a slip-stream of the process line or as an at-line instrument. The degree of refining and the WRV are determined from settling measurements. The settling of a pulp suspension (with a weight percentage less than 0.5 wt%) is observed, after the mixer, which keeps the pulp uniformly distributed, is turned off. The attenuation of ultrasound as a function of time is recorded and these data show a peak at a time designated as the "peak time." The peak time T increases with the degree of refining, as demonstrated by measuring pulp samples with known degrees of refining. The WRV can be determined using the relative peak time, defined as the ratio T(2)/T(1), where T(1) is an initial peak time and T(2) is the value after additional refining. This method offers an alternative WRV test for the industry to the current time-consuming method.

Equipment Design↗
PubMed2006

Long-path measurements of ultrasonic attenuation and velocity for very dilute slurries and liquids and detection of contaminates.

The objective was to use multiple paths through the slurry to determine the lowest concentration that provided accurate attenuation measurements and to measure the velocity of sound through an effective long path. Ultrasonic attenuation measurements were obtained for slurries of silica (10 microm diameter) in water for concentrations of 0.1%, 0.25%, 0.5%, 0.75% and 1% silica by weight. Attenuation measurements for concentrations less than 0.1% may prove useful for process control to detect contaminants. A long path is obtained due to multiple reflections occurring within the stainless steel (SS) vessel used; broad-band transducers are affixed on the outside of the thick-walled vessel. The signal in the receive transducer permits the measurement of the attenuation and also the velocity by measuring the time-of-flight. The FFT of the appropriate signal for each echo was obtained and compared with that for water to yield the attenuation as a function of frequency. The attenuation measurements are self-calibrating because they are not affected by changes in the pulser voltage. The data show the feasibility for measuring a concentration of 0.025 wt% silica, which is equivalent to 0.25 g of silica in 1 l of water. Therefore, such measurements can prove useful for detecting contaminants in liquid. The velocity of sound measurements for solutions of hydrogen peroxide in water were obtained and accurate to about 0.3m/s, or 0.02% uncertainty.

Journal Article↗
PubMed2002

Age- and size-related trends in woody plant shoot development: regulatory pathways and evidence for genetic control.

Woody plants exhibit significant and predictable patterns of change in morphology and physiology as they become older and larger. Four models of potential pathways controlling these changes are presented: a stimulus-response model in which fully developed organs respond to changes in environment (defined here as everything external to the organ); an extrinsic model in which the attributes of developing organs are determined by environmental factors; an intrinsic model in which changes are a result of programmed changes in gene expression; and an extrinsic-intrinsic model in which changes in gene expression are induced by environmental factors. We review evidence that a genetic component is involved in controlling age- and size-related changes in foliar morphology and physiology and discuss the possibility of complex interactions among model pathways.

Models, Biological↗
PubMed2001

Age-related changes in foliar morphology and physiology in red spruce and their influence on declining photosynthetic rates and productivity with tree age.

The contribution of changes in meristem behavior to age-related decline in forest productivity is poorly understood. We studied age-related trends in needle morphology and gas exchange in a population of red spruce (Picea rubens Sarg.) growing in a multi-cohort stand where trees ranged from first-year germinants to trees over 150 years old, as well as in grafted scions from these trees. In the field study, age-related trends in foliar morphology were determined in six cohorts ranging in age from 2 to 120 years, and differences in gas exchange characteristics were compared between 60- and 120-year age classes. In a common-rootstock study, scions from trees representing 20-, 60-, and 120-year cohorts were grafted onto juvenile rootstock and maintained for three growing seasons, after which morphological and physiological foliar attributes were evaluated. The field study revealed significant age-related trends in foliar morphology, including decreasing specific leaf area, and increasing needle width, projected area, and width/length ratio. Similar trends were apparent in foliage from the grafted scions. Both in situ foliage and shoots of grafted scions from the oldest cohort showed significantly lower photosynthetic rates than their counterparts from younger trees; however, differences in stomatal conductance and internal CO(2) concentrations were not significant. These results suggest that: (1) foliage of red spruce exhibits age-related trends in both morphology and physiology; (2) age-related decreases in photosynthetic rates contribute to declining productivity in old red spruce; (3) declines in photosynthetic rates result from nonstomatal limitations; and (4) age-related changes in morphology and physiology are inherent in meristems and persist for at least 3 years in scions grafted to juvenile rootstock.

Carbon Dioxide↗
PubMed2001

Maturation, topophysis and other factors in relation to rooting in Larix.

We examined effects of mist quantity, topophysis (origin of cutting in the crown of 6-year-old trees), maturation state of the donor stock, and time of sticking on rooting and root system quality of cuttings representing five full-sib hybrid larch families obtained with Larix decidua Mill., L. laricina (du Roi) K. Koch, and L. kaempferi (Lamb.) Sarg. (Sieb. and Zucc.) Gord., as parents. Mist frequency, supplemental watering and family all had highly significant effects on percentage of cuttings rooting and root system quality. The high-frequency misting regime yielded both higher rooting percentages and higher quality root systems than the low-frequency regime without supplemental watering. Supplemental watering of the rooting medium in the low-frequency misting regime increased both percent rooting and root system quality to values comparable with those obtained by cuttings in the high-frequency misting regime. Rooting of cuttings from the top, middle and bottom whorls of 5-year-old plantation grown trees tended to decline with increasing height for three of the five families. Overall, height of cutting origin did not significantly affect rooting, but when analyzed separately, two families exhibited a significant decline in rooting toward the top of the trees. Age of donor ortet (ranging from 1 to 7 years) significantly affected both percent rooting and root system quality. Rooting percentages declined linearly with age, and root system quality declined more sharply than percent rooting. The relatively poor root system quality of cuttings from ortets older than 1 year was closely associated with plagiotropic growth. Softwood cuttings (stuck in mid-July) rooted better than hardwood cuttings (stuck in early September) across all families.

Forestry↗
PubMed1999

Expansins are conserved in conifers and expressed in hypocotyls in response to exogenous auxin.

Differential display reverse transcription-polymerase chain reaction was used to detect the induction of gene expression during adventitious root formation in loblolly pine (Pinus taeda) after treatment with the exogenous auxin indole-3-butyric acid. A BLAST search of the GenBank database using one of the clones obtained revealed very strong similarity to the alpha-expansin gene family in angiosperms. A near-full-length loblolly pine alpha-expansin sequence was obtained using 5'- and 3'-rapid amplification of cDNA end cloning, and the deduced amino acid sequence was highly conserved relative to those of angiosperm expansins. Northern analysis indicates that alpha-expansin mRNA expression increases 50- to 100-fold in the base of hypocotyl stem cuttings from loblolly pine seedlings in response to indole-3-butyric acid, with peak expression occurring 24 to 48 h after induction.

Amino Acid Sequence↗
PubMed1997

Effects of cone-induction treatments on black spruce (Picea mariana) current-year needle development and gas exchange properties.

Both drought and root pruning (RP) increased the number of cones induced when black spruce (Picea mariana (Mill.) B.S.P.) grafts were injected with gibberellins A(4/7) (GA), but their effects on predawn shoot water potential and current-year needle development differed. Drought decreased predawn shoot water potential (Psi(pd)), but only during the period when irrigation was withheld, and it had no effect on the growth or gas exchange properties of current-year needles. Conversely, root pruning had little effect on Psi(pd), but it resulted in trees with smaller current-year needles that had lower nitrogen and chlorophyll concentrations and reduced rates of gas exchange up to the later stages of shoot elongation compared with needles of control trees. These findings are discussed in relation to potential effects on the development of induced cones in the following growth cycle.

Journal Article↗
PubMed1995

Genetic variation in rooting ability of loblolly pine cuttings: effects of auxin and family on rooting by hypocotyl cuttings.

After about 20 days, hypocotyl cuttings from 20-day-old loblolly pine (Pinus taeda L.) seedlings rooted easily in the presence of the auxin indole-3-butyric acid (IBA), with roots forming directly from xylem parenchyma. In contrast, woody cuttings from 1-2-year-old hedged seedlings formed roots indirectly from callus tissue in 60-90 days, but IBA had little effect on rooting. Variation in rooting among hypocotyls from both half- and full-sib families was highly significant in response to IBA, and rooting did not occur within 20 days unless IBA was applied. Hypocotyls from poor rooting families tended to produce fewer roots per cutting than hypocotyls from good rooting families. Rooting by woody cuttings and hypocotyl cuttings from the same nine full-sib families was weakly correlated, raising the possibility that at least some common genetically controlled processes were affecting rooting by both types of cutting. The phytotropin N-1-naphthylphthalamic acid (NPA), supplied at 1 micro M with 10 micro M IBA, significantly inhibited rooting by hypocotyl cuttings from both good and poor rooting families, but there was no significant family x treatment interaction. Family variation in rooting ability may be a function of the frequency of occurrence of auxin-responsive cells in the hypocotyls.

Journal Article↗
PubMed1995

Canopy dynamics and the morphological development of Abies balsamea: effects of foliage age on specific leaf area and secondary vascular development.

Data were collected from two branches from each whorl of nine open-grown Abies balsamea (L.) Miller trees to test the hypothesis that specific leaf area (SLA, m(2) projected fresh leaf area kg(-1) oven-dry foliage) is constant among five foliage age classes (current-year, 1-year-old, 2-year-old, 3-year-old and 4-year-old-plus). Between-tree variation in SLA was greater than within-tree variation. Differences in SLA among the foliage age classes were small, but statistically significant, showing a trend of decreasing SLA with increasing foliage age. Using data from two previous biomass studies, we found that three different methods of calculating SLA of individual trees produced the same projected leaf area estimates. To test the hypothesis that foliage mass increases with foliage age as a result of secondary xylem or phloem development, we examined the secondary vascular development of foliage collected from five age classes and three crown sections in an open-grown A. balsamea. The number of rows of xylem cells was not constant among foliage age classes, but the differences were small and showed no consistent pattern of change with foliage age. Total number of rows of phloem cells increased, number of living rows of phloem cells decreased, and the number of rows of nonliving crushed phloem cells increased with foliage age.

Journal Article↗
PubMed1993

Maturation in larch: age-related changes in xylem development in the long-shoot foliage and the main stem.

As the meristems of eastern larch (Larix laricina (Du Roi) K. Koch) mature, they produce long-shoot foliage with progressively higher chlorophyll content and net photosynthesis and progressively lower specific leaf area (Hutchison et al. 1990). Despite the apparent increase in foliar vigor, both shoot height and diameter growth rates declined during maturation. These changes were associated with changes in xylem morphology of the vascular tissue of both the long-shoot foliage and the main stem. Although the number of xylem cells remained constant in a cross section of the foliage, their diameters increased with age. With increasing maturation, the same number of xylem cells were produced per radial file in the annual rings of the main stem, but their radial diameters decreased, which accounted for the decrease in diameter growth. There was no change in tracheid length during maturation. We conclude that the decrease in growth rate with increased maturation is not due to a decrease in physiological vigor of the foliage, but is a function of reduced sink strength of the growing shoots.

Journal Article↗
PubMed1990

Maturation in Larch : II. Effects of Age on Photosynthesis and Gene Expression in Developing Foliage.

The effect of maturation on the morphological and photosynthetic characteristics, as well as the expression of two genes involved in photosynthesis in the developing, current year foliage of Eastern larch (Larix laricina [Du Roi]) is described. These effects were observed on foliage during the third growing season after grafting of scions from trees of different ages onto 2 year old rootstock. Specific leaf weight (gram dry weight per square meter), leaf cross-sectional area (per square millimeter), and chlorophyll content (milligram per gram dry weight) all increase with increasing age in long shoot foliage from both indoor- and outdoor-grown trees. Net photosynthesis (NPS) (mole of CO(2) per square millimeter per second) increases with age on indoor- but not outdoor-grown trees. NPS also increases with increased chlorophyll content, but outdoor-grown scions of all ages had higher chlorophyll content, and chlorophyll does not appear to be limiting for NPS outdoors. To extend these studies of maturation-related differences in foliar morphology and physiology to the molecular genetic level, sequences were cloned from the cab and rbsS gene families of larch. Both cab and rbcS gene families are expressed in foliage but not in roots, and they are expressed in light-grown seedlings of larch but only at very low levels in dark-grown seedlings (~2% of light-grown seedlings). Steady-state cab mRNA levels are relatively higher (~40%) in newly expanding short shoot foliage from juvenile plants compared to mature plants. Unlike cab, the expression of the rbcS gene family did not seem to vary with age. These data show that the maturation-related changes in morphological and physiological phenotypes are associated with changes in gene expression. No causal relationship has been established, however. Indeed, we conclude that the faster growth of juvenile scions reported previously (MS Greenwood, CA Hopper, KW Hutchison [1989] Plant Physiol 90: 406-412) is not due to increased NPS or cab expression. Long shoot foliage is the dominant foliar type on young trees and its lower specific leaf weight will permit production of more photosynthetic surface area per unit of leaf biomass.

Journal Article↗
PubMed1989

Maturation in larch : I. Effect of age on shoot growth, foliar characteristics, and DNA methylation.

The time course of maturation in eastern larch (Larix laricina [Du Roi] K. Koch) was examined by grafting scions from trees of different ages onto 2-year-old root stock and following scion development for several years. Height, diameter, foliar chlorophyll content, and rooting ability of scion-derived cuttings all varied linearly as a function of log(10) age. Chlorophyll content (milligrams per gram of dry weight) increased while height, diameter, and ability to root decreased with age (P < 0.01). The tendency toward orthotropic growth and branch formation per centimeter of main stem decreased abruptly between age 1 and 5 years (P < 0.01). Total chlorophyll content of both long and short shoot foliage increased by 30 to 50% with increasing age, but the chlorophyll a/b ratio did not change. Also, juvenile long shoot needles were significantly longer than mature (P < 0.01). Surprisingly, the juvenile scions produced more total strobili over two successive years, but the mature scions produced a significantly higher proportion of male strobili (P < 0.001 year 1; P < 0.02 year 2). The age-related changes in foliar traits were not associated with changes in DNA methylation between juvenile and mature scions. Using HPLC, we found that 20% of foliar DNA cytosine residues were methylated in both scion types.

Journal Article↗