To verify this hypothesis we have examined the effect on dry weight, total N content and electrophoretic patterns of total proteins of immature endosperms of IHP and ILP grown for 5, 8, 12 days on a solid medium containing a different ratio of sucrose to asparagine content. Furthermore, these results were compared with those obtained on plants of the same genotypes grown in the field (Fig. 1).

Figure 1. Dry weight and N content of IHP (s-----s) and ILP (*-----*) endosperms grown in vivo and in vitro. All media contained 0.4 mg/l thiamine, 100 ug/l inositol, salts as described in Nitsch and Nitsch (1969) and 8 g/l agar. A, B, C culture media contained various concentrations of sucrose (30, 20 and 10 g/l, respectively) and asparagine (2, 3, 4 g/l, respectively).

The ILP strain cultured in vitro accumulated a greater amount of dry matter per endosperm than the IHP strain, maintaining the same behaviour observed in vivo. The accumulation of total N per endosperm followed a different trend when the in vivo and the in vitro conditions were compared. In vivo IHP endosperms were more efficient than ILP in accumulating N; the reverse was observed in vitro: here the ILP strain, at all stages of development considered and on all culture media, was always capable of accumulating higher amounts of N per endosperm than the IHP strain. IHP endosperms, during development in vivo and in vitro, synthesized both the 22 kDa and the 20 kDa fractions of zeins. While ILP endosperms grown in vivo were not able to accumulate the 22 kDa fraction of zeins, the same endosperms, under in vitro culture, were able to restore the synthesis of the 22 kDa zein fraction. Our data suggest that the expression in endosperm of the IHP and ILP phenotype is controlled by the N metabolites supplied to the developing kernels.

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