THE PRESENCE OF PROTEASE‐DIGESTIBLE MATERIAL IN GOLGI VESICLES DURING ENDOSPERM DEVELOPMENT OF SELECTED CEREALS

The presence of dictyosomes secreting densely stained vesicles throughout endosperm protein body formation was confirmed for four cereals (rice, Oryza sativa L.; hard red winter wheat, Triticum aestivum L.; winter feed barley and spring malting barley, Hordeum vulgare L.; oats, Avena sativa L.). The contents of the Golgi vesicles and protein bodies were digested with proteases for all cereals except rice. It was found in the case of rice that OsO4 altered the proteins in the Golgi apparatus and protein bodies making them resistant to protease digestion. These results imply that the Golgi apparatus plays an important role in the concentration and transport of storage proteins into vacuoles. SYNTHESIS OF STORAGE PROTEINS in cereal starchy endosperm involves the rough endoplasmic reticulum (RER) (Cameron-Mills and Ingversen, 1978; Cameron-Mills, Ingversen and Brandt, 1978; Larkins and Hurkman, 1978). The RER in some cereal endosperms may serve not only as the site of protein synthesis, but also function as the storage organelle (protein body; Larkins and Hurkman, 1978; Bechtel and Juliano, 1980). Cereals studied to date, however, have had at least some of the endosperm protein shown to be deposited into vacuoles (see Bechtel and Juliano, 1980, for a review). The mechanism of protein deposition into vacuoles has been under debate. Buttrose (1963) suggested that the Golgi apparatus participated in protein secretion into vacuoles in wheat endosperm. Khoo and Wolf (1970) thought that dictyosomes of corn proliferated protein granule vesicles. These suggestions were challenged by Barlow, Lee and Vesk (1974) and Briarty (1978), however. Vacuolar protein in rice endosperm was thought to occur via a direct connection between the RER and vacuoles (Ivanova, 1974). Wu and Chen (1978) concluded that Golgi secretory vesicles in rice endosperm could not be involved in protein transport because the vesicles lacked protein; yet their fig. 5 and 6 depict pepsin digestion -of secretory vesicles. Re1 Received for publication 13 July 1981; revision accepted 17 September 1981. 2 Contribution No. 81-459j, Division of Biology, Kansas Agricultural Experiment Station, Manhattan, KS 66506. Reference to a company or product does not imply approval or recommendation of the product by the U.S. Department of Agriculture to the exclusion of others that may be suitable. cently the Golgi apparatus has been again implicated in protein secretion in starchy endosperm of rice (Bechtel and Juliano, 1980). We chose to study protein body formation in four cereals (rice, Oryza sativa L.; hard red winter wheat, Triticum aestivum L.; winter feed barley and spring malting barley, Hordeum vulgare L.; oats, Avena sativa L.) because of the lack of agreement as to how deposition of protein into vacuoles occurs, whether the Golgi apparatus is present during protein secretion, and whether Golgi vesicles contain protein. This paper is a preliminary report on the occurrence of the Golgi apparatus in endosperm during protein synthesis and the enzymatic digestion of thin sections containing dictyosomes. Complete developmental studies of these cereals have either been reported or will be presented shortly (Bechtel and Juliano, 1980; Bechtel, Gaines and Pomeranz, 1980). MATERIALS AND METHODS-Rice, experimental high protein cultivar IR 480, was sectioned from samples used in a previous study (Bechtel and Juliano, 1980). Barley cultivars 'Larker' (spring malting barley) and 'Kanby' (winter feed barley), wheat cultivar 'Eagle', and Illinois 73-21-86 oats were all grown during the 1978 and 1980 seasons on experimental maturity plots near Manhattan, KS. Caryopses were sampled at day of flowering (DOF), 2, 4, 6, 7, 8, 10, 12, 14, 17, 21, 24, and 27 days after flowering (DAF) and fixed in a combination of 3% glutaraldehyde (v/v) and 3% paraformaldehyde (w/v) in 0.05 M phosphate buffer (Lillie, 1954) at pH 6.7, postfixed in buffered OSO4 and embedded as previously described (Bechtel