Susan E. Eichhorn

P-protein distribution in mature sieve elements of Cucurbita maxima

SummaryPortions of the hypocotyls of 16-day-old Cucurbita maxima plants, from which the cotyledons and first foliage leaves had been removed 2 days earlier, were fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. In well over 90% of the mature sieve elements examined the P-protein was entirely parietal in distribution in both the lumina and sieve-plate pores. In addition to the parietal P-protein, the unoccluded sieve-plate pores were lined by narrow callose cylinders and the plasmalemma. Segments of endoplasmic reticulum also occurred along the margins of the pores.

Observations on penetration of Barley leaves by the aphidRhopalosiphum maidis (Fitch)

SummaryPenetration of leaves of barley,Hordeum vulgare L., by the corn leaf aphid,Rhopalosiphum maidis (Fitch), was studied with light, phase, and electron microscopes. Penetration of epidermis and mesophyll was largely intercellular, that of vascular bundles or veins largely intracellular. Like other aphids,R. maidis secretes a salivary sheath which surrounds the stylets. When mesophyll cells and parenchymatous elements of the veins were penetrated by stylets, their protoplasts were pushed to one side by intruding sheath material; hence, the protoplasts were not punctured by the stylets, although sometimes the plasmalemma of penetrated cells was ruptured by sheath material. The salivary sheaths ended more or less abruptly outside the walls of sieve elements being fed upon, the maxillary stylets projecting beyond the sheaths and into the sieve elements. Before penetrating a functional sieve element the aphid apparently flushes its stylets in order to clear them for ingestion of food. Salivary and food canals merge near the tips of the maxillary stylets to form a single canal, which ends short of the tips.

Sieve-plate pores in leaf veins of Hordeum vulgare

SummaryThe sieve-plate pores of sieve elements in leaf veins of Hordeum vulgare, fixed in glutaraldehyde with postfixation in osmium tetroxide, were lined by the plasmalemma and variable amounts of callose. All pores were filled with endoplasmic reticulum, which was continuous from cell to cell. Mature sieve elements lacked P-protein.

Sieve-element ultrastructure in Platycerium bifurcatum and some other polypodiaceous ferns: The nucleus.

SummarySieve elements of various ages were examined in Platycerium bifurcatum (Cav.) C. Chr. and Phlebodium aureum (L.) J. Sm., only older ones in Polypodium schraderi Mett. and Microgramma lycopodioides (L.) Copel. Early in sieve-element differentiation small crystalloids arise in the matrix of the sieve-element nuclei in Platycerium. As differentiation continues, the crystalloids increase in size and eventually may occupy up to a third of the cross-sectional area of the nucleus and extend almost its entire length. At the time of nuclear degeneration the crystalloids are liberated into the cytoplasm. Nuclear degeneration during sieve-element development in Phlebodium is essentially similar to that in Platycerium, with the exception that no nuclear inclusions exist in the sieve-element nuclei in Phlebodium. Stacking of endoplasmic reticulum against the nuclear envelope occurs in both Platycerium and Phlebodium. In the final stages of degeneration, the nuclear envelope ruptures and the contents of the nucleus mix with the cytoplasm. At maturity the sieve elements of all four species are devoid of nuclei, although occasional remnants of chromatin persist along the walls of some mature cells.

Sieve-element ultrastructure in Platycerium bifurcatum and some other polypodiaceous ferns: The refractive spherules.

SummarySieve elements of various ages of Platycerium bifurcatum (Cav.) C. Chr. and Phlebodium aureum (L.) J. Sm. and older ones of Polypodium schraderi Mett. and Microgramma lycopodioides (L.) Copel. were examined with the electron microscope. Evidence was obtained which implicated the Golgi apparatus with the formation of refractive spherules in Platycerium and Phlebodium. In all four species the delimiting membranes of the refractive spherules eventually fuse with the plasmalemma in mature sieve elements, and the material comprising the spherules is liberated into the region of the wall.

Tubular extensions of the plasmalemma in leaf cells of Zea mays L.

Leaf tissues of Zea mays were examined with a transmission electron microscope and a high-voltage electron microscope. Tubular extensions (invaginations) of the plasmalemma were found in vascular parenchyma cells and thick-walled, lateformed sieve elements of intermediate and small veins, and in epidermal, mesophyll, and sheath cells of all leaves examined. No continuity seems to exist between the tubules and other cellular membranes.

Plant Nutrition and Soils

Soil composition Soil is made up of three main things: clay, humus and sand. There are also many small organisms that live in the soil, and most of these are useful to the plants. Clay Clay is made from the breakdown and recombination of silicate rocks. It is made up of alternating layers of silicon oxides then aluminium oxides, with various cations such as Ca loosely bound in between the layers. Anions adsorb onto the oxide surfaces, with doubly and triply charged cations sticking better than singly charged ones. Clays are the main source of nutrients in the soil. Humus This is any organic matter in the soil i.e. the products of the decay of plants and animals. It is mostly made up of aromatic compounds. Over time it breaks down to carbon dioxide and water so it needs to be continually replaced. Humus is important in regulating the amount of water in the soil. Sand This is solid particles of ground up rock. A small amount of sand is necessary to ensure the correct water content in the soil.