Studies on Seeds

Abstract

Glyoxysomes, a form of microbody, are present in castor bean endosperm during the first 8 days of seed germination.They have a "typical" microbody form and are shown histochemically to contain catalase. The catalase label is distributed throughout the microbody and is not an exclusive feature of the crystalline or amorphous core.Castor bean endosperm contain a second cytosome, only slightly larger than the glyoxysomes, which is bound by a rough-surfaced membrane and which does not label for catalase. We have not observed these cytosomes in other tissues, suggesting that they may have a specific cellular function characteristic of castor bean endosperm.Glyoxysomes are a morphologically and biochemically unique component of many cells (3,4,12,13). They are a form of microbody containing enzymes of the glyoxylate cycle. Like peroxisomes and other types of microbodies, they also contain catalase and glycolic acid oxidase (4).Microbodies are present in castor bean endosperm throughout seed development, dormancy, and germination, but enzymes of the glyoxylate cycle do not reach maximal activity until the 4th or 5th day of seed germination (5, 12). There is no indication from ultrastructural studies that microbodies disappear, reform, or change significantly in number, in relation to the appearance of enzymes of the glyoxylate cycle. It is assumed, therefore, that glyoxysomes are somehow evolved from microbodies by enzyme activation or by gradual replacement of existing microbodies with those of the glyoxysome type.We have isolated microbodies, as well as glyoxysomes, from a number of seeds and have found that the glyoxysome fractions from castor bean endosperm sometimes contain a contaminating particle that is similar in size to glyoxysomes. Studies in vivo of germinating castor bean confirm that a microbody-like particle does exist in the endosperm and is most easily recognized when enzymes of the glyoxylate cycle are active. We thought initially that these new particles might be related, or equivalent, to glyoxysomes and, therefore, initiated these studies. This report describes these new particles and compares them structurally and histochemically with microbodies. 2"Studies on Seeds, I through IV" will appear in the Journal of Cell Biology. MATERIALS AND METHODSCastor bean (Hale variety and Baker variety 296 obtained from The Baker Castor Oil Co., La Mesa, Calif.) seeds were scarified and the seeds were soaked in water for 2 to 24 hr. The seeds were germinated for 3 to 8 days in the dark at 28 C in vermiculite moistened with distilled water.Slices of endosperm were prefixed in a mixture of 2% glutaraldehyde-2 % paraformaldehyde in 0.05 M collidine buffer containing 0.06 M sucrose, pH 7.3 to 7.4 for 2 hr, cold. After prefixation, the tissues were rinsed in six 5-to 10-min changes of buffer. Unless otherwise indicated, the buffer used was 0.05 M collidine with 0.06 M sucrose, pH 7.3 to 7.4. The tissues were either postfixed (see below) or allowed to warm to room temperature in the last buffer rinse and then ...

Endoplasmic Reticulum as the Site of Lecithin Formation in Castor Bean Endosperm

“…The elongated vesicular nature of the membranes and dense association of ribosomes is quite similar to that seen in the electron micrographs prepared from intact endosperm tissue (29,42) .…”

“…The fact that inclusion of Mg++ in the gradients yielded enzymatically active fractions of higher density comprised of rough endoplasmic reticulum, and the prevalence of similar structures in sections of living cells (29,42) strongly suggest that this is the location of the enzyme in vivo. Membranes of mitochondria and glyoxysomes from castor bean endosperm contain lecithin as a major structural phospholipid (23,25) .…”

“…12 g/cm 3 provided evidence that the membranes in this fraction were derived from endoplasmic reticulum and thus that this cellular component is the site of lecithin synthesis in vivo . Electron micrographs of cells of castor bean endosperm have shown that the endoplasmic reticulum is richly endowed with ribosomes and is predominantly "rough" in character (29,42) . Studies on cell-free preparations from rat liver have shown that the controlled use of EDTA results in dissociation of the ribosomes from the membranes and further that the attachment can be maintained by appropriate concentrations of Mg++ (38) .…”

The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum

“…In castor bean, daylily, and mung bean, the KDEL-tailed propeptidase is stored in a special organelle, called ricinosome (5,6) or KDEL-tailed cysteine proteinaseaccumulating vesicles (KV) (7). Ricinosomes were first described and ultrastructurally characterized in the endosperm of R. communis (8,9), whereas KV were described as cytoplasmic ''foci'' in Vigna radiata (10). The mature CysEP was originally purified from germinating castor bean endosperm (11).…”

Glycoprotein fucosyl transferase in the endoplasmic reticulum of castor bean endosperm cells

“…Studies with mammalian tissues have established that whereas core sugars such as N-acetylglucosamine and mannose are added to nascent polypeptides by enzymes located in the rough ER membrane [S ,6] peripheral sugars such as fucose are added by enzymes located in the Golgi apparatus [7]. During the early post-germinative development of castor bean seedlings, the gluconeogenie endosperm cells do not divide [8 ] and the Golgi apparatus is not well developed in such cells [9,10].…”