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Endosperm Structural Changes in Wheat During Drying of Maturing Caryopses

¹U. S. Grain Marketing Research Laboratory, USDA, Agricultural Research Service, 1515 College Avenue, Manhattan, KS 66502. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author.

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, and 96 hr and until completely air-dried (7 days). Fresh samples of Karl and Clark were also harvested and prepared immediately for microscopy. Both wheat cultivars underwent similar changes during drying. Few changes were observed during the first 8 hr of drying. By 12 hr after the start of drying, the rough endoplasmic reticulum (RER) was distended and circularized. Protein bodies were 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 hr of drying. RER was typically associated with those regions. Endosperm tissue looked nearly mature after 48 hr 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 with wheat that was not prematurely harvested. This 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.