Variations in glutelin and high molecular weight endosperm proteins among subspecies of rice (Oryza sativa L.) detected by two-dimensional gel electrophoresis

Abstract

Variations in endosperm polypeptides among 16 cultivars of rice were analyzed by two-dimensional gel electrophoresis. One glutelin α-subunit (α₈) with a molecular mass of 32.5 kDa was exclusively present in indica cultivars. By contrast, the glutelin α₃ subunit, with a molecular mass of 32 kDa, was present only in japonica and javanica cultivars. Glutelin α-subunits α_5a and α_5b, which have a molecular mass of 32 kDa and slightly different isoelectric points, differed among rice subspecies, i.e. the former was detected in japonica cultivars and the latter was detected in indica cultivars, Internal amino acid sequences of the indica-specific glutelin α-subunits α_5b and α₈, were analyzed with a gas-phase protein sequencer. Of 46 amino acid residues determined, only two residues differed, and they corresponded with the sequences deduced from type I and type II cDNAs of glutelin sub family A, respectively. Nine polypeptides of higher molecular mass (35-90 kDa) also differed. In particular, two of these polypeptides designated B and C which were identical to Wx proteins with molecular masses of 58 kDa were strongly expressed in indica endosperms, but only weakly expressed in japonica and javanica. F₁ seeds obtained from a cross between japonica and indica cultivars showed an intermediate intensity of Wx proteins and contained all nine glutelin α-subunits including both the japonica and indica types. In this experiment, Wx proteins designated B and C and glutelin α-subunits could be used to identify differences between japonica and indica cultivars.