Even granting our uncertainties about parts of our model of the sulfur cycle, we can draw some conclusions from it: 1) Man is now contributing about one half as much as nature to the total atmospheric burden of sulfur compounds, but by A.D. 2000 he will be contributing about as much, and in the Northern Hemisphere alone he will be more than matching nature. 2) In industrialized regions he is overwhelming natural processes, and the removal processes are slow enough (several days, at least) so that the increased concentration is marked for hundreds to thousands of kilometers downwind. 3) Our main areas of uncertainty, and ones that demand immediate attention because of their importance to the regional air pollution question, are: (i) the rates of conversion of H(2)S and SO(2) to sulfate particles in polluted as well as unpolluted atmospheres; (ii) the efficiency of removal of sulfur compounds by precipitation in polluted air. And for a better understanding of the global model we need to know: (i) the amount of biogenic H(2)S that enters the atmosphere over the continents and coastal areas; (ii) means of distinguishing man-made and biogenic contributions to excess sulfate in air and precipitation; (iii) the volcanic production of sulfur compounds, and their influence on the particle concentration in the stratosphere; (iv) the large-scale atmospheric circulation patterns that exchange air between stratosphere and troposphere (although absolute amounts of sulfate particles involved are small relative to the lower tropospheric burden); (v) the role of the oceans as sources or sinks for SO(2).

https://science.sciencemag.org/content/sci/175/4022/587.full.pdf

The Sulfur Cycle

http://science.sciencemag.org/content/sci/192/4236/218.full.pdf

Surface modulation in cell recognition and cell growth.

This paper reports an electron microscope examination of the cortices of some plant cells engaged in wall formation. Previous studies of similar material fixed in OSO4 alone have disclosed discontinuities in the plasma membrane and other evidence of inadequate fixation. After glutaraldehyde, used as a fixative in this present study, the general preservation of cortical fine structure is greatly improved. This is shown, for example, by the first evidence of slender tubules, 230 to 270 A in diameter and of indeterminate length, in plant cells of this type. They have been found in the cortical regions of cells of two angiosperms and one gymnosperm, representing all the material so far studied following this method of fixation. The tubules are identical in morphology to those also observed here in the mitotic spindles of plant cells, except that the latter have a somewhat smaller diameter. It is noted that the cortical tubules are in a favored position to govern cytoplasmic streaming and to exert an influence over the disposition of cell wall materials. In this regard it may be of some significance that the tubules just beneath the surface of the protoplast mirror the orientation of the cellulose microfibrils of the adjacent cell walls.

/pdf/a-microtubule-in-plant-cell-fine-structure-hg4l28yewb.pdf

A "microtubule" in plant cell fine structure.

Publisher Summary The purification of a specific membrane-bound ATPase is complicated by the presence of several membrane-associated ATPases in plant cells. In situ cytochemical studies have shown ATPase activity to be associated with mitochondria, plastids, plasma membranes, tonoplast, Golgi apparatus, and the endoplasmic reticulum of plant root cells. Using continuous gradient centrifugation and taking advantage of differing pH and ion-sensitivities of the various ATPases, the chapter has distinguished 5 different membrane-associated ATPases in oat root extracts. To facilitate identification of these membranes, a discontinuous gradient was devised, based on the membrane densities found from isopycnic centrifugations, which provided membrane fractions enriched in the various ATPases.

Purification of a plasma membrane-bound adenosine triphosphatase from plant roots.

Alteration of intracellular traffic by monensin; mechanism, specificity and relationship to toxicity

Cytochemical techniques for the electron microscopic localization of inosine diphosphatase, thiamine pyrophosphatase, and acid phosphatase have been applied to the developing root tip of Zea mays . Following formaldehyde fixation the Golgi apparatus of most of the cells showed reaction specificity for IDPase and TPPase. Following glutaraldehyde fixation marked localization of IDPase reactivity in the Golgi apparatus was limited to the root cap, the epidermis, and the phloem. A parallelism was apparent between the sequential morphological development of the apparatus for the secretion of a polysaccharide product, the fairly direct incorporation of tritiated glucose into the apparatus to become a component of this product and the development of the enzyme reactivity. Acid phosphatase, generally accepted as a lysosomal marker, was found in association with the Golgi apparatus in only a few cell types near the apex of the root. The localization was usually in a single cisterna at the face of the apparatus toward which the production of secretory vesicles builds up and associated regions of what may be smooth endoplasmic reticulum. Since the cell types involved were limited regions of the cap and epidermis and some initial cells, no functional correlates of the reactivity were apparent. Despite the presence of this lysosomal marker, no structures clearly identifiable as ‘lysosomes’ were found and the lack of reaction specificity in the vacuoles did not allow them to be so defined.

Phosphatases and differentiation of the Golgi apparatus.

https://science.sciencemag.org/content/sci/175/4022/596.full.pdf

Golgi Apparatus: Influence on Cell Surfaces

The Golgi apparatus and an early stage in cell plate formation.

The Dynamics of Cytoplasmic Membranes During Development

Maize root tips were fixed in potassium permanganate, embedded in epoxy resin, sectioned to show silver interference color, and studied with the electron microscope. All the cells were seen to contain an endoplasmic reticulum and apparently independent Golgi structures. The endoplasmic reticulum is demonstrated as a membrane-bounded, vesicular structure comparable in many aspects to that of several types of animal cells. With the treatment used here the membranes appear smooth surfaced. The endoplasmic reticulum is continuous with the nuclear envelope and, by contact at least, with structures passing through the cell wall. The nuclear envelope is characterized by discontinuities, as previously reported for animal cells. The reticula of adjacent cells seem to be in contact at or through the plasmodesmata. Because of these contacts the endoplasmic reticulum of a given cell appears to be part of an intercellular system. The Golgi structures appear as stacks of platelet-vesicles which apparently may, under certain conditions, produce small vesicles around their edges. Their form changes markedly with development of the cell.

/pdf/the-endoplasmic-reticulum-and-the-golgi-structures-in-maize-1g8ev08foq.pdf

Joyce E. Kephart

Papers

Phosphatases and differentiation of the Golgi apparatus.

Golgi Apparatus: Influence on Cell Surfaces

The Golgi apparatus and an early stage in cell plate formation.

The Dynamics of Cytoplasmic Membranes During Development

The Endoplasmic Reticulum and the Golgi Structures in Maize Root Cells