Storage Proteins in Zea mays (L.): Interrelationship of Albumins, Globulins and Zeins in the Opaque‐2 Mutation

Abstract

Mature endosperms from opaque-2 mutant seeds with various genetic backgrounds (B 37, W 64A, R 802A and Oh 43) contained twice as much globulin than the corresponding normals, reduced amounts of zein and an increased amount of albumin. The latter is caused by a diminished disappearance of albumins in mutant endosperms during the final phases of development as compared to normal endosperms. Albumins from the opaque-2 endosperms appeared on gel electrophoresis as a similar but heterogenous polypeptide population comparable to that of normal endosperms except that in all opaque-2 forms a 70-kDa polypeptide was increased. Similarly, one to three specific globulin polypeptides (47 kDa, 52 kDa and 58 kDa) were, depending on the genotype, increased in the mutant lines. The accumulation of albumins, globulins and zeins, studied in developing W 64.4 opaque-2 mutant and corresponding normal maize kernels from 10 days after pollination until maturity, demonstrated two-phasic accumulation patterns for all proteins in the mutant, the first phase extending to about 30 days post pollination and the second one from there on until maturity. The transition time-point from first to second phase was characterized in mutant endosperm by a sudden reduction in accumulating albumins (also seen in normal endosperm), by an enhanced accumulation of globulins and the cessation of further accumulation of zein. Preferential accumulation of certain globulins has been found in the mutant during the second phase of globulin formation. The increased accumulation of globulins in the opaque-2 mutant endosperm is considered a response to the arrest in zein synthesis.Since the discovery of the high lysine mutant in Zea mays (L.) opaque-2 [l] and the finding that the main storage protein, zein, was quantitatively [2] and qualitatively [3 -51 reduced, most investigations have focused on elucidating the characteristics of this protein in terms of physical properties [4,6,7], site and mode of deposition in the endosperm in vivo and in vitro [5,8,9] and most recently on the genes of zein themselves [lo-121. Other storage proteins, such as albumins, globulins or glutelins have not received nearly as much attention as zeins. Few and mostly earlier reports, however, dealt with these non-zein proteins. Glutelins, next to zein the major group of endosperm proteins, are said to form a cytoplasmic matrix in the cells [13]; they require strong alkali and detergents for solubilization and this complicates physicochemical studies [14]. Albumins and globulins, on the other hand, are soluble in salt solutions and therefore easier to study. Hence, proteins of salt-solution extracts of corn grains were shown to be heterogenous as to charge in electrophoretic studies by Foster et al. [IS] and Mertz and coworkers [16] and they could be resolved into a large number of constituents by starch gel electrophoresis [17]. An actual separation of albumins from globulins was done the first time by Paulis and Wall [IS] who analyzed them subsequently on starch gel electrophores...

Quantification of dominance for proteins pleiotropically affected by opaque-2 in maize

“…documented for ribonuclease activity (Cagampang & Dalby, 1972), amounts of albumins, globulins, glutelins (Misra & Mertz, 1975;Dierks-Ventling, 1981) and zeins (Soave eta!., 1976). The amounts of 14 'acidic' polypeptides (or clusters of polypeptides) and 12 'basic' polypeptides were affected by the gene substitution in both F2 and W64A…”

“…Other storage proteins, globulins, albumins and glutelins are more abundant in o2 mutants (Christianson et at., 1974;Misra & Mertz, 1975;Lee et a!., 1976;Di Fonzo et a!., 1977;Dierks-Ventling, 1981). The net photosynthetic assimilation rate of seedlings (MorotGaudry et a!., 1979), yield (Lambert et a!., 1969) and disease resistance (Loesch eta!., 1976) are reduced, as the duration of protandry (Gupta, 1979).…”

Immunochemical crossreactivity between zein, hordein and gliadin

“…Wheat (Triticum aestirum cv. Diplomat) seeds were ground to a flour and gliadins were extracted from 1 g flour using the same conditions as for zeins [ 11 ]; the pooled ethanol extracts were lyophilized to dryness. Hordein from barley (Hordeum vulgate cv.…”

“…Zeins (50 gg protein), hordeins and gliadins (100/ag protein) were loaded onto each track. Fixing and staining was as in [ 11 ].…”

“…Zeins, hordeins and gliadins were dissolved at 2/ag/gl in Laemmli's sample buffer [13] containing 6 M urea and electrophoresed in 15% polyacrylamide-1% SDS gels as in [ 11 ]. Zeins (50 gg protein), hordeins and gliadins (100/ag protein) were loaded onto each track.…”