Cercidium Floridum Seed Coat, Light and Electron Microscopic Study

Abstract

Scott, Flora Murray, B. G. Bystrom, and E. Bowler. (U. California, Los Angeles.) Cercidium floridum seed coat, light and electron microscopic study. Amer. Jour. Bot. 49(8): 821–833. Illus. 1962.—The structure of the seed coat of the desert tree Cercidium is typical of the family Leguminosae, but the inner integument is mucilaginous. The characteristic palisade cells of the epidermis and the many‐armed cells of the mucilaginous zone are discussed in detail. The minute wax rodlets on the surface of the young seed fuse later into a film of wax. The epidermal palisade cells are polygonal in transection and the walls are strengthened by cellulose flanges. The palisade cells are enclosed in a thin suberin‐like sheath which connects with the film which lines all air‐filled intercellular spaces in the outer integument. Plasmodesmata extend from the protoplast through the subcuticular zone to the cuticle and also interconnect with adjacent cells through numerous pits in the interflange areas of the main wall. The cells of the inner integument are many‐armed. Intercellular spaces at all stages of growth observed are occluded with mucilage; nevertheless, they are lined with a suberin‐like film similar in reaction to that of the air‐filled intercellular spaces of the outer integument. The distribution of wall materials and ergastic substances was determined by microchemical tests. For electron microscopic study, the epidermis and the mucilaginous zone were fragmented ultrasonically, after chemical treatment when necessary. Cuticular fragments, frequently polygonal in outline, are dense to the electron beam at photographic illumination. When exposed to the electron beam, full‐strength, volatile components are driven off and condense on other wall fragments or on substrate. Unique structures occur in the subcuticular zone, termed here, collar, cone and paddle structure. The basic material of the cell wall as a whole is cellulose impregnated with matrix materials, mainly non‐cellulosic polysaccharides. In addition, lipid‐like substances are conspicuous particularly in the flanges of the palisade cells. Under the electron beam, full‐strength, these substances volatilize and leave the flanges with a blistered outline except in the region of the light line. The volatile substances may be absent from this zone or the microfibrillar structure may prevent distortion. The microfibrillar pattern throughout the length of the flanges is dominantly parallel, but a change to reticulate arrangement occurs in the light‐line region. Numerous pits mark the paths of the plasmodesmata in the subcuticular zone and also through flange and interflange areas of the wall. The dominant microfibrillar pattern in the mucilage cells is reticulate in young and old cells, except for helical orientation in extending arms. Pits occur on arm ends but are infrequent elsewhere. The loose microfibrillar structure presumably allows continuous secretion of mucilage.

Cracks in the Palisade Cuticle of Soybean Seed Coats Correlate with their Permeability to Water

“…M. alba; Hamly, 1932Hamly, , 1935. It was also suggested that the light line is a region where the microfibrils changed from a longitudinal to a transverse orientation (Scott et al, 1962;Werker, 1980/81) but this was not the case in soybean (Fig. 10J).…”

The Ultrastructure and Development of the Light Line in the Geraniaceae Seed Coat

“…There is obviously another kind of amorphous substance forming the light line. Other SEM descriptions concerning changes in the anticlinal direction of the cell wall fibrils (Scott et al, 1962 [15] ) or differences between more or less thick parts of the cell wall (Manning and Van Staden, 1985 [8] ) cannot be confirmed for the Geraniaceae seed coat.…”

“…One amazing feature of the palisade cells in the Geraniaceae is the so-called light line running in a periclinal direction through the secondary cell wall material. The structure and function of the light line, which was so named for its bright character in the light microscope, has been discussed for different plant families, such as the Fabaceae and the Malvaceae (Hamly, 1935 [6] ; Scott et al, 1962 [15] ; Manning and Van Staden, 1985 [8] ; Christiansen and Moore, 1958 [3] ). The light line was often interpreted as an optical phenomenon without any chemical significance (Hamly, 1935 [6] ; Tran and Cavanagh, 1984 [20] ; Rangaswamy and Nandakumar, 1985 [12] ) and was thought to be generated by changes in the fibrillar pattern of the cellulose molecules (Scott et al, 1962 [15] ) or by differences in the cell wall thickness (Manning and Van Staden, 1985 [8] ).…”