Studies on the Ripening of Wheat Grain : 6. Development of the furrow side tissues.

Abstract

The furrow side tissue of wheat grain consist of thin pericarp, raphe (conducting strand) and inside nucellar parenchyma. In this report the developmental morphology of these tissues was dealt. At the time of anthesis, the vessels and sieve tubes were not yet found except of some strongly stained ceells layer in the furrow side of the ovary. Immediately after the fertilization, the formation of the conducting strand started at the base of funiculus and it continued until 25∼30 days after anthesis. Thus four groups of the conducting cells which were parallel to the dorsal surface of the endosperm were formed in the raphe. A few of the conducting cells extended to the level of the distal end of endosperm, however, others terminated at several elevations, and their ends were not joined directly to the endosperm even at the distal end of the raphe. Therefore, the number of conducting cells was less in higher portion of the raphe. The fromation of sieve tubes seemed to precede that of vessels, although the typical sieve plate could not be found. Nucellus inside the raphe was dissimilar in character to that in flank and abdominal side, for the former did not show degeneration until full maturation stage. In 5-6 cells layer parallel with the raphe, yellow-coloured substance similar to that in the integument of abdominal side was deposited during 9th to 25th days. But in this side seed cooat and hyaline layer which were formed from integument and outer layer of nucellus respectively in the abdominal and flank side were never formed. Nucellar cells increased in number in early developmental stage and thereafter, all of them elongated toward the center of the dorsal surface of endosperm. The space surrounded by nucellus and endosperm was filled with sap and became narrower in the last stage of development and disappeared at full maturation. From the above mentioned observations, we may assume the following hypothesis regarding the terminal course of translocation of the reserve materials into endosperm. Carbohydrates and other reserve materials enter the conducting cells from the base of ovary, and then transfer into nucellar tissue from several elevations of the conducting tissue. The materials go across the cells layer accumulating the yellow-coloured substance, subsequently they are sent along the elongated nucellar parenchyma in sequence, and lastly flow into the cavity surrrounded by the nucellus and endosperm. Surface area of the endosperm facing to the cavity where the cells are of a peculiar shape plays a role of intaking the reserve substances from the cavity. This hypothesis is showing some points of disagreement with Percival and other researchers. In their explanations, the reserve substances traverse the raphe and diffuse into endosperm from a point in the upper part of it.