Growth and differentiation of the Golgi apparatus and wall formation during carposporogenesis in the red alga, Gigartina teedii (Roth) Lamour.

Abstract

ABSTRACTThe fine structure of the Golgi apparatus during development of carposporangia of Gigartina teedii has been studied. Dictyosomes in differentiating carposporangia undergo extraordinary changes in size and morphology.Dictyosomes of gonimoblast cells and the auxiliary cell are composed of a stack of 5–7 straight cistemae and are approximately 0·18μm thick; from the structural and functional viewpoint, these are similar to dictyosomes in most other plants.Hypertrophied Golgi cistemae with fibrillar contents occur in immature and nearly mature carposporangia. Secretory vesicles originate from the ends of cistemae and by complete vésiculation of terminal cistemae; vesicles with a diameter of 0·2–0·6 μm and fibrillar contents are abundant throughout the cytoplasm of immature and nearly mature carposporangia. Some vesicles secrete their contents into the carpospore wall. At this stage the dictyosomes are straight in profile and only some Golgi cistemae and Golgi vesicles show acid phosphatase activity.Mucilage sacs appearing to be derived from either dilating endoplasmic reticulum or membraneous formations with a lysosomal character exist in both the mature gonimoblast cells and the immature carposporangia. These mucilage sacs constitute a considerable portion of the cytoplasmic volume and ultimately migrate to the outside of the cytoplasm. The mucilage sacs disappear completely in the mature carposporangia.Throughout the development of the wall of immature and nearly mature carposporangia, multi-vesicular lomasome-like bodies, showing acid phosphatase activity, are released through the plasmalemma. Apart from any other possible activities, these bodies seem to contribute to the plasticity of the expanding cell wall.The older carposporangia are recognized by having very active dictyosomes with a semicircular profile, producing vesicles with an electron-opaque centre (cored vesicles). These vesicles are likely to contain glycoproteins and to contribute to the formation of vacuoles with fibrous contents, as they are dominant in the carpospores before their liberation.The dictyosomes of older carposporangia are composed of a polarized stack usually composed of 7 to 11 cistemae. They exhibit anomalous, densely staining, laminated mid-regions, which are formed due to close apposition of 6—7 adjacent cistemae from the forming face. The mid-regions of the rest of the cistemae towards the maturing face have large intercistemal spaces, which usually contain darkly staining small vesicles probably originating from the endoplasmic reticulum. The cistemae towards the maturing face contain dense granules.Observations suggest that materials polymerize into fibrils within the Golgi system and the inflated Golgi-derived vesicles participate directly in the formation of the fibrillar network of the carpospore wall in the Gigartina teedii.