Thermal damage to chloroplast envelope membranes

Nuclear magnetic resonance was used to detect thermal injury to chloroplasts in vivo. A lesion occurs in the chloroplast envelope membrane at temperatures between 53°C and 57°C, depending on species, leaf condition, and heating rate. The injury is associated with a sudden loss of water from the chloroplast.     

Water is allocated differently to chloroplasts in sun and shade leaves

Hydrogen-1 nuclear magnetic resonance spectroscopy was used to study water allocation in cell compartments of sun and shade leaves. NMR spectra of Acer platanoides were resolved into two peaks that were assigned to chloroplast and nonchloroplast water. Sun leaves contained 1.7 times more water per unit area of surface than shade leaves, and the water was allocated differently. Chloroplasts in sun leaves contained 17% of the total leaf water versus 47% in shade leaves. Comparing equal leaf surface areas, the chloroplasts in shade leaves contained 60% more water than those in sun leaves.     

Chlorophyll a fluorescence and carbon assimilation in developing leaves of light-grown cucumber

The development of photochemical activity and carbon assimilation in light-grown cucumber (Cucumis sativus L. cv Natsusairaku) leaves was studied to determine the pattern of acquisition and its relationship to leaf growth and expansion. Measurements of chlorophyll a fluorescence showed that leaves acquire photochemical function over a period of 6 or more days, and gas exchange studies showed increases in carbon assimilation over a parallel time period. As leaves expand and mature, they undergo a sequential, three-step series of changes in fluorescence response. The initial kinetics show the absence of wholly functional quenching mechanisms. Dynamic imaging of fluorescence kinetics showed that a temporal series of changes occurred within defined areas of individual developing leaves. The spatial acquisition of photochemical activity in leaves was basipetal as is their directional expansion, development of air spaces and stomata, and the cessation of imported carbon.     

Ultrastructure of potato tubers formed in microgravity under controlled environmental conditions

Previous spaceflight reports attribute changes in plant ultrastructure to microgravity, but it was thought that the changes might result from growth in uncontrolled environments during spaceflight. To test this possibility, potato explants were examined (a leaf, axillary bud, and small stem segment) grown in the ASTROCULTURETM plant growth unit, which provided a controlled environment. During the 16 d flight of space shuttle Columbia (STS-73), the axillary bud of each explant developed into a mature tuber. Upon return to Earth, tuber slices were examined by transmission electron microscopy. Results showed that the cell ultrastructure of flight-grown tubers could not be distinguished from that of tuber cells grown in the same growth unit on the ground. No differences were observed in cellular features such as protein crystals, plastids with starch grains, mitochondria, rough ER, or plasmodesmata. Cell wall structure, including underlying microtubules, was typical of ground-grown plants. Because cell walls of tubers formed in space were not required to provide support against the force due to gravity, it was hypothesized that these walls might exhibit differences in wall components as compared with walls formed in Earth-grown tubers. Wall components were immunolocalized at the TEM level using monoclonal antibodies JIM 5 and JIM 7, which recognize epitopes of pectins, molecules thought to contribute to wall rigidity and cell adhesion. No difference in presence, abundance or distribution of these pectin epitopes was seen between space- and Earth-grown tubers. This evidence indicates that for the parameters studied, microgravity does not affect the cellular structure of plants grown under controlled environmental conditions.     

Patterns of chlorophyll fluorescence kinetics in relation to growth and expansion in cucumber leaves

Photochemical development was studied in developing cucumber (Cucumis sativus L. cv Hokushin) leaves to determine if the spatial pattern coincided with relative growth rates of expanding leaves, intercalary cell division, or position relative to the vascular tissue. Both leaf surfaces undergo a series of similar changes in chlorophyll a fluorescence kinetics, but the upper surface more quickly achieved the characteristic response. Imaging of fluorescence showed an individual developing leaf has four regions differing in kinetics, but these regions do not coincide with areas of increasing relative growth rate. Two of these regions lie at the leaf edge and their divergent kinetics may be related to structural and physiological features present at this position. A third area with different kinetics, in the basal region of the leaf, is spatially consistent with primordial regions that are clonal during development. The correspondence between areas of clonal growth and specific fluorescence kinetics indicates that cells of common ancestry show functional uniformity. No evidence was found that the proximity of the vascular tissue influenced development of photochemical function.     

Stomatal patterning in angiosperms

My thesis is that understanding stomatal patterning requires a holistic perspective. Since stomata are structures critical to the survival of terrestrial plants, they need to be viewed in relation to their function and their interface with other structural components. With this outlook, I begin by discussing pattern types, means of measuring them, advantages of each type of measurement, and then present patterning from evolutionary, physiological, ecological, and organ views. I suggest areas where I believe profitable studies might enable us to better understand stomatal patterning. The final sections of the paper review stomatal patterning on angiosperm leaves and present a theory of patterning. With the abundance of molecular information, and coming genomic sequences and new tools, an opportunity exists to dissect the process of how cells are selected to become different from their neighbors and assume a fate critical to plant survival. Understanding this biological process at the molecular level requires comprehending the broad base on which stomatal patterning rests.     

Stomatal patterning in Tradescantia: an evaluation of the cell lineage theory.

The cell lineage theory, which explains stomatal patterning in monocot leaves as a consequence of orderly divisions, was studied in Tradescantia. Data were collected to test the theory at three levels of organization: the individual stoma; stomata distributed in one dimension, in linear fashion along cell files; and stomata apportioned in two dimensions, across the length and breadth of the leaf. In an attempt to watch the patterning process through regeneration, stomata in all visible stages of development were laser ablated. The results showed that the formation of stomatal initials was highly regular, and measurements of stomatal frequency and spacing showed that pattern was determined near the basal meristem when the stomatal initials arose. Following the origin of initials, the pattern was not readjusted by division of epidermal cells. Stomatal initials were not committed when first present and a small percentage of them arrested. The arrested cells, unlike stomata, were consistently positioned in cell files midway between a developed pair of stomata. At the one-dimensional level of pattern, stomata in longitudinal files were separated by a variable number of epidermal cells and the frequency of these separations was not random. The sequential spacing of stomata also was not random, and stomata separated by single epidermal cells were grouped into more short and long series than expected by chance. The stomatal pattern across the width of the leaf resulted from cell files free of stomata which alternated with cell files containing stomata, but not with a recurring periodicity. Files lacking stomata were found only over longitudinal vascular bundles. Laser ablations of developing stomata did not disrupt the pattern in nearby cells or result in stomatal regeneration. We conclude that the cell lineage theory explains pattern as an individual stomatal initial arises from its immediate precursor and satisfactorily accounts for the minimum spacing of stomata in a cell file, i.e., stoma-epidermal cell-stoma. However, the theory does not explain the collective stomatal pattern along the cell files, at the one-dimensional level of patterning. Nor does the theory account for the for the two-dimensional distribution of stomata in which regions devoid of stomata alternate with regions enriched with stomata, but not in a highly regular nor haphazard manner. We suggest that the grouping of epidermal cells and stomata separated by single epidermal cells in cell files may result from cell lineages at a specific position in the cell cycle as they traverse the zone where stomatal initials form.(ABSTRACT TRUNCATED AT 400 WORDS)