The nitrogen-induced recovery of alpha-zein gene expression in in vitro cultured opaque2 maize endosperms depends on the genetic background

The effect of nitrogen nutrition on the accumulation of seed storage protei ns has been studied in vitro by cultivating on agar media maize.(Zea mays L .) endosperm explants from seeds at 10 days after pollination. The experime nts were performed on various genetic backgrounds bearing different opaque2 (o2) mutant alleles and on the corresponding wild-type lines, In the seed of the o2 genotypes the high molecular weight alpha -zein polypeptides (zHs ), whose transcription is Opaque2 (O2) regulated, are absent or extremely r educed. The endosperms were incubated on basal agar medium with amino acid supply, In these growth conditions, fresh and dry weights increased in both wild-type and o2 endosperms, irrespective of the genetic background, In 4 out of the 5 o2 mutant genotypes analysed we detected an accumulation of th e zHs similar to the corresponding wild-type explants or seeds, However, in one of these mutants, Mo17o2R, the addition of amino acids to the culture media had no effect on the zH accumulation, We showed that the Mo17o2R beha viour is not due to a negative regulation but to the absence of putative tr anscription factor(s) able to regulate the zH transcription occurring in th e other o2 mutants.