Plastid characteristics

Starch, another of the most abundant polymers of glucose, is stored by most green plants in a semicrystalline form in numerous small granules. These granules, which are usually formed within colorless membrane-bounded plastids, have characteristic shapes and appearances (Fig. 4-6) that vary from plant to plant. One component of starch, amylose, is a linear polymer of many a-D-glucopyranose units in 1,4 linkage (Fig. 4-7) as in maltose. Starch granules always contain a second kind of molecule known as amylopectin.58... 

Chloroplasts contain large 120- to 169-kb circular genomes encoding about 100 proteins (Chapter 23). A characteristic feature of most chloroplast DNA is the presence of long inverted repeat sequences (10,058 bp in the liverwort, 25,339 bp in tobacco).463 464 These are separated by 19,813 and 81,095 bp single copy regions in the liverwort and by similar sized regions in tobacco. Plastid DNA exists as a mixture of monomeric molecules with smaller amounts of dimers, trimers, and tetramers.464... 

Endosperm of ae du wx in a sweet corn background has a major developmental gradient typical of normal and a type-II minor gradient characteristic of du.43 Saussy43 reports that starch granule and plastid development in ae du wx is similar to that of du wx. 

Like chlorophyll, plastoquinone A has a nonpolar terpenoid or isoprenoid tail, which can stabilize the molecule at the proper location in the lamellar membranes of chloroplasts via hydrophobic reactions with other membrane components. When donating or accepting electrons, plastoquinones have characteristic absorption changes in the UV near 250 to 260, 290, and 320 nm that can be monitored to study their electron transfer reactions. (Plastoquinone refers to a quinone found in a plastid such as a chloroplast these quinones have various numbers of isoprenoid residues, such as nine for plastoquinone A, the most common plastoquinone in higher plants see above.) The plastoquinones involved in photosynthetic electron transport are divided into two categories (1) the two plastoquinones that rapidly receive single electrons from Peso (Qa and Qb) and (2) a mobile group or pool of about 10 plastoquinones that subsequently receives two electrons (plus two H+ s) from QB (all of these quinones occur in the lamellar membranes see Table 5-3). From the plastoquinone pool, electrons move to the cytochrome b f complex. 

The order Caryophyllales embraces families which have a characteristic ultrastructure of their sieve-element plastids, namely, the P-III subtype (104). In addition, the widespread occurrence of C4 photosynthesis as well as DNA-RNA hybridization data support this taxonomic treatment (23). Within this order, the occurrence of betalains is restricted to nine of the eleven families of the Caryophyllales. The two exceptions, Caryophyllaceae and Molluginaceae, produce anthocyanins instead. There is controversy regarding the phylogenetic importance of this phenomenon (105). It has been suggested that a division of the Caryophyllales into two phylogenetic lines is possible, the betalain-producing Chenopodiineae and the anthocyanin-producing Caryophyllineae (103) (see Scheme 9). The presence of betalains has been an important criterion in the classification of questionable taxa as demonstrated by various examples (13). 

Elavonoid transport from the sites of biogenesis or from the sites of transitional accumulation takes place by diffusion or active transport across the closely connected membranes of smooth EE and associated organelles (plastids, vacuoles, plasmalemma), and through the EB. During the endoplasmic transfer, the osmiophilic properties of the secretion disappear. This characteristic may be related to the possible bonding of aglycons with proteins, vjith terpenoids or with phenolic acids. 

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