Showing papers in "Botanical Review in 1996"

Forest damage and recovery from catastrophic wind

Abstract: The literature on the effects of catastrophic wind disturbance (windstorms, gales, cyclones, hurricanes, tornadoes) on forest vegetation is reviewed to examine factors controlling the severity of damage and the dynamics of recovery. Wind damage has been quantified in a variety of ways that lead to differing conclusions regarding severity of disturbance. Measuring damage as structural loss (percent stems damaged) and as compositional loss (percent stems dead) is suggested as a standard for quantifying severity. Catastrophic wind produces a range of gaps from the size caused by individual treefalls to much larger areas. The spatial pattern of damage is influenced by both biotic and abiotic factors. Biotic factors that influence severity of damage include stem size, species, stand conditions (canopy structure, density), and the presence of pathogens. Abiotic factors that influence severity of damage include the intensity of the wind, previous disturbance, topography, and soil characteristics. Recovery from catastrophic wind disturbance follows one of four paths: regrowth, recruitment, release, or repression. The path of recovery for a given site is controlled both by the severity of disturbance and by environmental gradients of resources. Recovery is influenced also by frequency of wind disturbance, which varies across geographical regions. To develop robust theories regarding catastrophic wind disturbance, the relative roles of different abiotic and biotic factors in controlling the patterns of severity of damage must be determined. These patterns of severity and environmental gradients must then be tied to long-term dynamics of recovery.

Plant phenolics in allelopathy

Abstract: Phenolics are one of the many secondary metabolites implicated in allelopathy To establish that allelopathy functions in a natural ecosystem, the allelopathic bioassay must be ecologically realistic so that responses of appropriate bioassay species are determined at relevant concentrations It is important to isolate, identify, and characterize phenolic compounds from the soil However, since it is essentially impossible to simulate exact field conditions, experiments must be designed with conditions resembling those found in natural systems It is argued that allelopathic potential of phenolics can be appreciated only when we have a good understanding of 1) species responses to phenolic allelochemicals, 2) methods for extraction and isolation of phenolic allelochemicals, and 3) how abiotic and biotic factors affect phenolic toxicity

Root hairs: Specialized tubular cells extending root surfaces

Abstract: Root hairs are tubular extensions of epidermal cells that have their origin either in any protoderm cell or in specialized protoderm cells called trichoblasts. These latter cells are the result of an asymmetric cytokinesis determined by the positioning of a pre-prophase band of microtubules. The smaller sibling cell is the trichoblast and specializes physiologically and structurally prior to root hair outgrowth. Several genes are involved in the initiation and outgrowth of root hairs. Elongation of root hairs is by tip growth, and, correlated with this, cytoplasmic organelles and cytoskeletal elements show a polarized distribution; the apical dome consists of numerous vesicles, many associated with cell wall synthesis. The relationship between cellulose microfibril deposition and the pattern of cortical microtubules has received considerable attention, as has the role of the cytoskeleton and calcium in controlling cytoplasmic streaming. Root hairs extend the absorbing surface of the root and therefore have been studied in terms both of physiological characteristics of the plasma membrane and uptake of water and of various ions in the soil solution. Many plant species develop soil sheaths (rhizosheaths) which protect the root surface from desiccation and harbour various microorganisms; root hairs are intimately involved in these sheaths. Various growth regulators have been studied in terms of their effect on the structure and function of root hairs. Root hairs play a significant role in the interaction between plants and nitrogen-fixing microorganisms (e.g.,Rhizobium, Frankia) and symbiotic mycorrhizal fungi.

Plant extracts as modulators of genotoxic effects

Abstract: Higher plants used extensively in traditional medicines are increasingly being screened for their role in modulating the activity of environmental genotoxicants. The property of preventing carcinogenesis has been reported in many plant extracts. The observation of a close association between carcinogenesis and mutagenesis has extended the survey to include plant extracts and plant products able to modify the process of mutagenesis, which involves alteration in the genetic material. Natural plant products may, apart from inducing mutations, modify the action of other known mutagens on the living organisms by 1) activating the existing mutagens within the cell, 2) inhibiting the production of mutagens in the cell, 3) synergising the activity of existing mutagens, or 4) activating the promutagens within the cell into mutagens. This review deals with data obtained in the course of research on the modulatory effects of plant extracts on mutagenesis and clastogenesis, two genotoxic phenomena associated with carcinogenesis.

Sandstone rockhouses of the eastern United States, with particular reference to the ecology and evolution of the endemic plant taxa

Abstract: Rockhouses are semicircular recesses extending far back under cliff overhangs that are large enough to provide shelter for humans. The largest sandstone rockhouses in the eastern United States are at the heads of gorges, and they are in stream valleys cut during the Pleistocene; most are formed in Mississippian and Pennsylvanian-age rocks. Compared to the surrounding environment, the interior of rockhouses is shaded, is warmer during winter and cooler during summer, and has lower evaporation rates and higher humidities. Water enters rockhouses primarily by groundwater seepage and by dripping from the ceiling. Soil consists mostly of sand with low pH, but high levels of some nutrients are associated with saltpeter earth and with ecofactual and artifactual remains left by human occupants during prehistoric time. Most plant taxa in sandstone rockhouses in eastern United States are native C3 phanerophytes or hemicryptophytes, and similarities in species composition among rockhouses are low. Eleven plant taxa belonging to eight families of flowering plants and ferns are endemic or nearly endemic to sandstone rockhouses in eastern United States. Three endemics are restricted to the gorges of a single river, and only one taxon ranges far north of the Wisconsinan Glacial Boundary. The endemic ferns are Tertiary relicts derived from tropical taxa. The majority of endemic flowering plants are derived from temperate taxa that grow in habitats in the vicinity of rockhouses; their relative age ranges from Late Tertiary to the Recent. All the endemic taxa are perennial; two ferns occur as independent gametophytes. The endemic taxa of rockhouses are threatened primarily by disturbances associated with recreation.

Occurrence and taxonomic significance of ruminate endosperm

Abstract: Ruminate endosperm is characterized by its uneven and enlarged surface. A list of 58 angiosperm families in which this trait is known to occur is presented. The simultaneous presence of different rumination types in angiosperms and even within single families leads to the conclusion that ruminate endosperm has originated several times in parallel. Therefore, the mere occurrence of rumination does not provide evidence for phylogenetic hypotheses. Nevertheless, rumination features can provide valuable characters for taxonomic purposes, if structural and ontogenetic evidence is considered.

Strategies for "minimal growth maintenance" of cell cultures: a perspective on management for extended duration experimentation in the microgravity environment of a Space station

Abstract: How cells manage without gravity and how they change in the absence of gravity are basic questions that only prolonged life on a Space station will enable us to answer. We know from investigations carried out on various kinds of Space vehicles and stations that profound physiological effects can and often to occur. We need to know more of the basic biochemistry and biophysics both of cells and of whole organisms in conditions of reduced gravity. The unique environment of Space affords plant scientists an unusual opportunity to carry out experiments in microgravity, but some major challenges must be faced before this can be done with confidence. Various laboratory activities that are routine on Earth take on special significance and offer problems that need imaginative resolution before even a relatively simple experiment can be reliably executed on a Space station. For example, scientists might wish to investigate whether adaptive or other changes that have occurred in the environment of Space are retained after return to Earth-normal conditions. Investigators seeking to carry out experiments in the low-gravity environment of Space using cultured cells will need to solve the problem of keeping cultures quiescent for protracted periods before an experiment is initiated, after periodic sampling is carried out, and after the experiment is completed. This review gives an evaluation of a range of strategies that can enable one to manipulate cell physiology and curtail growth dramatically toward this end. These strategies include cryopreservation, chilling, reduced oxygen, gel entrapment strategies, osmotic adjustment, nutrient starvation, pH manipulation, and the use of mitotic inhibitors and growth-retarding chemicals. Cells not only need to be rendered quiescent for protracted periods but they also must be recoverable and further grown if it is so desired. Elaboration of satisfactory procedures for management of cells and tissues at "near zero or minimal growth" will have great value and practical consequences for experimentation on Earth as well as in Space. All of the parameters and conditions and procedural details needed to meet all the specific objectives will be the basis of the design and fabrication of cell culture units for use in the Space environment. It is expected that this will be an evolutionary process.

Floristic summary ofManual of Vascular Plants of Northeastern United States and Adjacent Canada, second edition

Abstract: The second edition of theManual of Vascular Plants of Northeastern United States and Adjacent Canada by Gleason and Cronquist (1991) is the most recent and up-to-date taxonomic treatment of the flora of that region. Since no floristic summary of theManual was included in the publication, a computer analysis of the taxonomic data of theManual was performed in order to generate a floristic summary. Totals of 4285 species, 1091 genera, and 191 families were tabulated. The largest genus wasCarex, with 230 species; the largest family was the Asteraceae, with 528 species. Comparisons made with earlier floras of the same region indicated small declines on the order of 10% for these taxonomic groups.

Profiles of Pioneer Women Scientists: Katherine Esau

Abstract: “Profiles of Pioneer Women Scientists: Katherine Esau” tells the story of a noted botanist, plant anatomist, and electron microscopist who was born in the Russian Ukraine (in 1898), forced to flee the Bolshevik Revolution with her family—her father a mayor of Ekaterinoslav under the Czar—to Germany, where she received a bachelor’s degree in agriculture, education she put to good use in America. Beginning in a sugarbeet field in Salinas, California, she progressed through the doctoral degree at the University of California at Davis (UC Davis) and there began her exceptional research on plant anatomy and plant viral diseases. Her textbookPlant Anatomy became known among college students as “Aunt Kitty’s Bible,” and all of her textbooks have gone into second, and some to third, editions. Transferring to the University of California at Santa Barbara (with its new Chancellor, V. I. Cheadle) only two years before retirement, she blossomed anew, producing some of her best work there and obtaining National Science Foundation support for a new electron microscope and other research funds through her 89th year. Katherine Esau started accruing awards and honors at a relatively early age (Faculty Research Lecturer at age 50, election to the National Academy of Sciences at 59) and has never stopped (the President’s Medal of Science at age 91, a UC Santa Barbara building named for her at age 93). It has been her good fortune to live to enjoy these honors. The short autobiography of her father, a truly enterprising engineer, is included here, as are the recollections of Celeste Turner Wright. Celeste, who arrived at UC Davis the same year as Katherine Esau, became an acclaimed poet, and chaired the English Department for many years. She has added a lively reminiscence of the days she and Katherine spent at UC Davis. The introduction to the book by one of Esau’s former graduate students, Ray Franklin Evert, himself a renowned plant pathologist, provides a heartfelt tribute to his greatly admired professor.