Sieve–element characters

Abstract

Of all the ultrastructural features recognized within sieve elements their specific plastids provide the most successful characters in seed plant systematics. Sieve–element plastids are classified into subtypes and forms according to their protein and starch contents. Presently 26 different forms grouped into six subtypes within the two basic types (S– and P–) may be discerned. Plastid forms containing protein crystals, protein filaments and starch grains are proposed to be primitive, forms missing any one of these contents held to be derived (a synoptical key is given to ease the identification of the different plastid forms). Based on the quantitative distribution of over 1500 investigated species and the suggested evolution of plastid forms a cladistic diagram is prepared to demonstrate interrelationships between forms of sieve–element plastids and the evolution of seed plant taxa. Correlations exist between subtype PII and Monocotyledons, subtype PHI and Centrospermae, subtype PIV and Fabales. Genuine plastid forms characterize Buxaceae (PVIc), Erythroxylaceae and Rhizophoraceae (both PVc) and Cyrillaceae (PVcf). The Magnoliiflorae are distinct by presence in its families of a great number of forms of subtype PI. Phylogenetic correlations for some of these taxa are discussed. – Crystalline P–protein of sieve–elements provides another character to be used for the delimitation of some families (e.g. Fabaceae), while presently ER–complexes or other organelles of sieve elements do not contribute to seed plant systematics.

Sieve Tubes in Action

“…P plastids are long-established organelles in the SEs of dicotyledons, the substructure of which is strongly species specific (Behnke, 1981). They are composed of a core or subcores of starchy and/or proteinaceous material in a matrix of aggregated proteins surrounded by a membrane (Behnke, 1981).…”

“…They are composed of a core or subcores of starchy and/or proteinaceous material in a matrix of aggregated proteins surrounded by a membrane (Behnke, 1981). It is probably the membrane of the P plastid that is stained by RH-160 ( Figures 4F, 5B, and 6A).…”

“…It is probably the membrane of the P plastid that is stained by RH-160 ( Figures 4F, 5B, and 6A). The P plastids in Fabaceae belong to the PIVcs-or S-type, which implies that the P plastid contains subcores of proteins and several starch grains (Behnke, 1981). In fava bean, one starch grain is much larger than the other ones (Figures 2 and 10; I. Dörr, personal communication).…”

Karyotypes and fluorescent chromosome banding in Pyrrhocactus (Cactaceae)

“…areoles -that bear spines. Cacti are further characterized by the presence of betalains, crassulacean acid metabolism, specialized xylem cells helping in water storage, and sieve-element plastids of the centrospermous type lacking starch inclusions (Behnke 1981, Cronquist 1981, Barthlott and Hunt 1993, Mauseth and Plemons 1995, Mauseth 2006. Their flowers are mostly solitary, hermaphroditic, and actinomorphic, having commonly numerous tepals in a graded series; the ovary is inferior and there are usually numerous stamens (Cronquist 1981, Barthlott and Hunt 1993, Anderson 2001.…”

Enzymes of Jasmonate Biosynthesis Occur in Tomato Sieve Elements

“…2B). Plastids of SE identified for many different species were subdivided into S-type plastids, containing only starch inclusions, and P-type plastids, containing mainly protein inclusions (Behnke 1981). Due to the absence of starch-granules within the SE, we assume a P-type in tomato.…”