MICROSPECTROPHOTOMETRIC CHARACTERIZATION OF AROMATIC CONSTITUENTS IN CELL-WALLS OF HARD AND SOFT WHEATS

Cell walls of epidermis, hypodermis, nucellar epidermis, aleurone, and endosperm in hard and soft wheat (Triticum aestivum L) kernels were evaluated for aromatic constituents using ultraviolet (UV) absorption microspectrophotometry. Wheat varieties sampled were soft red winter Caldwell, hard red winter varieties Tam 200 and Karl, and hard red spring varieties Len and Yecora rojo. Spectra of cell walls of epidermis and hypodermis (beeswing cells) suggested larger amounts and a greater degree of polymerization of aromatic constituents in these walls compared to those of other cell types. Results also suggested the presence of ester-linked ferulic acid. Nucellar epidermal walls also had polymerized aromatics and ferulic acid, but amounts appeared to be much less than in the walls of the beeswing cells. UV spectra of aleurone walls suggested that the predominant aromatic was ester-linked ferulic acid; anticlinal walls had substantially more aromatic constituents than outer or inner periclinal walls. Endosperm walls lacked any indication of aromatics by this method. Grain hardness did not appear to be related to cell wall aromatics. UV absorption microspectrophotometry indicated significant variations in wall aromatics of different cell types of wheat grains.