Histopathology of Seed-Borne Infections - Applied Research Center ...

28 Histopathology of Seed-Borne InfectionssctcolpcotfflsaepbsamesrarcrarccolrABCFIGURE 2.10 Diagrams of dicot A, monocot B, and grass C, embryos to show the relativeposition of cotyledons and plumule, and additional structures, coleoptile, coleorhiza, andepiblast in grass embryo. (Abbreviations: colp, coleoptile; colr, coleorhiza; cot, cotyledon;epb, epiblast; ffl, first foliage leaf; mes, mesocotyl; ra, radicle; rc, root cap; sa, shoot apex;sct, scutellum.)Jensen, 1969; Newcomb and Fowke, 1974; Yeung and Clutter, 1979). The suspensorin Phaseolus coccineus comprises nearly 200 cells. Experimental studies inP. coccineus after administration of 14 C-sucrose to excised pods and seeds haveprovided direct evidence that the suspensor is the preferred major site of uptake ofmetabolites for the embryo, particularly at the globular-heart shaped stages (Yeung,1980).Plasmodesmata have been reported in the cell walls between the suspensor andendosperm (Figure 2.12C). They are also abundant between individual suspensorcells (Figure 2.12B) and between suspensor cells and the embryo proper in fababean (Johansson and Walles, 1993). The distribution of wall ingrowths and plasmodesmatashows the occurrence of apoplastic as well as symplastic pathways fortransport of nutrients from the endosperm to the embryo through the suspensor.2.8.3 CHANGES IN NUCELLUSThe nucellus in tenuinucellar ovules is absorbed during the prefertilization stages,and the developing female gametophyte comes in direct contact with the innerepidermis of the inner integument or that of the single integument. In crassinucellarovules, the nucellar cells are polygonal and rich in cytoplasmic contents in unfertilizedovules. After fertilization, as the endosperm and the embryo grow, and the