Lysine-containing proteins in maize endosperm: a major contribution from cytoskeleton-associated carbohydrate-metabolizing enzymes.
We measured fresh weight, dry weight, total protein, and the amounts of several individual proteins during endosperm development in three varieties of maize ( Zea mays L.): W64A wild-type (WT) and opaque-2 (o2), and sweet corn (SW). By 28 days after pollination (DAP), fresh weight was much higher in WT and SW than in o2, but o2 had a higher dry weight and thus a much lower water content. By 28 DAP, protein concentration [mg (g tissue(-1))] was highest in o2 and lowest in WT, while the protein content (microg seed(-1)) was lowest in o2. The storage proteins, alpha- and gamma-zeins, were low initially, but by 28 DAP they comprised over 50% of the total protein in WT and SW, but only about 30% in o2. In all varieties, the cytoskeleton proteins, actin, tubulin and eEF1alpha, sedimented with the protein bodies at 30 g to 27,000 g in tissue homogenized in cytoskeleton-stabilizing buffer. Other cytoskeleton-associated proteins increased during development, including UDP-glucose starch glucosyltransferase (UDP-GSGT, EC 2.4.1.11), sucrose synthase 1 (SuSy-1, EC 2.4.1.13) and fructose-1,6 bisphosphate aldolase (FBA, EC 4.1.2.13). At 28 DAP, these cytoskeleton-associated proteins combined make up 27% (WT), 23% (SW) and 33% (o2) of the total protein. These proteins are all rather high (5-11%) in lysine, and so they contribute about 75% (WT), 67% (o2), and 51% (SW) of the total endosperm lysine. We conclude that efforts to elevate the levels of these proteins could make a significant contribution to the nutritional value of corn.
Azama
Kishu
K
Laboratory of Molecular Cell Biology, Faculty of Agriculture, Ehime University, 790-8566 Matsuyama, Japan.
Abe
Shunnosuke
S
Sugimoto
Hideki
H
Davies
Eric
E
D000199:Actins / Q000378:metabolism; D050260:Carbohydrate Metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism*; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D008239:Lysine / Q000378:metabolism*; D020648:Peptide Elongation Factor 1 / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D012639:Seeds / Q000201:enzymology* / Q000254:growth & development; D014404:Tubulin / Q000378:metabolism; D003313:Zea mays / Q000201:enzymology* / Q000254:growth & development; D015028:Zein / Q000378:metabolism
D000199:Actins; D004798:Enzymes; D020648:Peptide Elongation Factor 1; D010940:Plant Proteins; D014404:Tubulin; D015028:Zein; D005964:Glucosyltransferases; D006006:Glycogen Synthase; C022699:sucrose synthase; D005634:Fructose-Bisphosphate Aldolase; D008239:Lysine