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Summary Freeze-fracture electron microscopy was used to study changes in the endomembrane system of barley (Hordeum vulgare L. cv. Himalaya) aleurone protoplasts. Protoplasts were used for this study because their response to calcium and the plant hormone gibberellic acid (Ga3) can be monitored prior to rapid freezing of cells for electron microscopy. Protoplasts incubated in Ga3 plus Ca2+ secrete elevated levels of a-amylase relative to cells incubated in Ga3 or Ca2+ alone. The endoplasmic reticulum (ER) and Golgi apparatus of protoplasts incubated in Ga3 plus Ca2+ undergo changes that are well correlated with the synthesis and secretion of a-amylase. The ER, which appears as short, single sheets of membrane in Ca2+-and Ga3-treated protoplasts, exists as a series of long fenestrated stacks of membranes following incubation in Ga3 plus Ca2+. The Golgi apparatus is also more highly developed in protoplasts treated with Ga3 plus Ca2+. This organelle is larger and has more vesicles associated with its periphery in protoplasts that actively secrete a-amylase. Evidence that the Golgi apparatus participates in a-amylase secretion is also provided by experiments with the ionophore monensin, which causes pronounced swelling of Golgi cisternae and inhibits the secretion of a-amylase. We interpret these observations as showing that the ER and Golgi apparatus of barley aleurone participate in the intracellular transport and secretion of a-amylase. The plasmalemma (PF face) of barley aleurone protoplasts shows a high density of intramembranous particles (IMPs) which, in general, are evenly distributed. Occasionally, ordered arrays of IMPs are observed, possibly resulting fro m osmotic stress. after 48 hours the plasmalemma of some Ga3-treated protoplasts show particle-free areas considered to be indications of senescence.abbreviations ER
endoplasmic reticulum
- Ga3
gibberellic acid
- IEF
isoelectric focusing
- IMP
intramembranous particle
- PF
protoplasmic fracture
- PL
plasmalemma 相似文献
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A procedure for dissolving and handling replicas of cutinized leaves and other plant tissues is described. This technique yields comparatively large replicas which can include vascular tissue, epidermal cells and the cuticle. Dissolution of the tissue involves the sequential use of alcoholic KOH, sulfuric acid and chromic acid. The use of clean, uncoated grids for transfer of the tissue and replicas results in rapid, easy handling with a minimum of breakage or loss. The procedure is more efficient than previous methods and produces large replicas. This allows tissue orientation and more positive identification of cell types for better correlation of freeze fracture results with thin sections of similar material. 相似文献
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