Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2005
Publication Date: 7/1/2005
Citation: Bechtel, D.B., Wilson, J.D. 2005. Endosperm structural changes in wheat during drying of maturing caryopses. Cereal Chemistry. 82:385-389. Interpretive Summary: Wheat harvested prior to being ripe and then allowed to air-dry exhibits breadmaking potential that is better than wheat left to mature naturally. Fresh endosperm from preripe grain also exhibits higher bread loaf volume potential than does preripe wheat that is allowed to air-dry. We investigated the sequences of events involved in the drying of preripe starchy endosperm using transmission electron microscopy. Field-grown hard (Karl) and soft (Clark) red winter wheats were harvested preripe at 21 days after flowering and air-dried in the spike at 20 C for 0, 2, 4, 8, 12, 24, 48, 96 h and 7 d. Both wheat varieties underwent similar changes during drying. Harvesting wheat plants prematurely and air-drying them caused endosperm tissue to undergo a number of ultrastructural changes that resulted in the endosperm tissue resembling that of normal mature tissue. The results showed how cellular components degrade and interact during endosperm senescence and provides insight into how wheat may be improved via breeding and improved cultural and grain handling practices.
Technical Abstract: A transmission electron microscopic (TEM) study was conducted on maturing wheat to determine the sequences of events involved during the drying of preripe starchy endosperm. Field-grown hard red winter wheat Karl and soft red winter wheat Clark were harvested at 21 days after flowering (DAF) and air-dried in the spike at 20 C for 2, 4, 8, 12, 24, 48, 96 h and until completely air-dried (one week). Fresh samples of Karl and Clark were also harvested and prepared immediately for microscopy. Both wheat varieties underwent similar changes during drying. Few changes were observed during the first 8 h of drying. By 12 h after the start of drying, the rough endoplasmic reticulum (RER) had become distended and circularized. Protein bodies became irregular in shape and small autophagic vacuoles were found in the cytoplasm. An amorphous material was first observed in areas of the cytoplasm after 24 h of drying. Rough ER was typically associated with those regions. Endosperm tissue looked nearly mature after 48 h of drying. Artificially induced senescence caused by harvesting wheat spikes prematurely caused the endosperm tissue to undergo a number of changes that resulted in the tissue looking normal when compared to wheat that was not prematurely harvested. That suggests that the wheat plant has great capacity to develop normally when subjected to environmental stresses. The methods used in this study can be used to investigate endosperm structural changes caused by adverse environmental stress.