Cytological study of palisade development in the seed coat of Candle canola

摘要: The differentiation of the palisade layer in the developing seed of Brassica campestris L. cv. Candle canola was studied from pollination to maturity. The palisade was derived from the innermost cell layer of the outer integument and was sandwiched between several layers of crushed parenchyma. The secondary thickening of the radial and inner tangential walls of all palisade cells was initiated about 5 days after pollination and continued for about 20 days. Vesicles and similar-sized invaginations of the plasmalemma were present in the cytoplasm. An increased number of dictyosomes and endoplasmic reticulum associated with paracrystalline bodies were also observed. The palisade cytoplasm appeared normal in unfertilized ovules and seeds 5 days after pollination but degenerated as seeds neared maturity. Outer portions of the radial walls had no secondary thickening and collapsed to form characteristic folds when seen in radial section. Lamellations were visible in areas where secondary thickening was heavily deposited. Remnants of plasmodesmata were present in the lamellations and traversed the primary walls, but were not present in areas of most recent secondary wall deposition. Cross sections showed these remnants were filled with an electron-dense material. The inner tangential wall of the palisade and the outer tangential wall of the parenchymal cell directly below appeared to fuse forming a single continuous layer.