Development of Zea mays L. caryopses : regulation of embryo dormancy and differences in protein patterns associated with manipulation of ABA levels in intact kernels cultured in vitro

Abstract

Sectors of Zea mays cobs, with and without kernels were cultured in vitro in the presence and absence of fluridone. Kernel sections cultured in the presence of fluridone were transferred to medium containing fluridone and ABA. Cultured kernels, cob tissue and embryos developed similarly to those grown in the field. Abscisic acid (ABA) levels in the embryos were evaluated by enzyme-linked immunosorbant assay. ABA levels in intact embryos cultured in the presence of fluridone were very low at 0.72 ng g^-1 fresh weight (FW). ABA levels in isolated cob tissue indicate that ABA is actively produced by cob tissue. Depletion of preformed carotenoid pools and inhibition of further carotenoid synthesis in cob tissue cultured with fluridone result in progressively lower levels of ABA over time. Addition of ABA to the medium from 13 to 15 days after pollination (DAP) restored dormancy in 67% of the kernels. Addition of ABA after 15 DAP did not result in any dormant kernels. To investigate control of ABA over general and specific protein synthesis, [35]S-methionine was injected into kernel sections cultured with and without fluridone from 12 to 19 DAP. Incorporation of labelled amino acids into protein decreased before 14 DAP in the embryo and endosperm of kernels cultured without fluridone. Embryo electrophoretic protein patterns were not different from 12 to 15 DAP but embryos with normal levels of ABA showed the continued production of 32 and 53 kD proteins from 16 to 19 DAP that were not continued in the ABA-deficient fluridone-treated embryos. The fluridone-treated embryos began producing 33 and 64 kD proteins at 16 DAP that continued to be synthesized to 19 DAP. Endosperm showed no protein differences from 12 to 14 DAP but endosperm with normal ABA levels showed a marked decrease in all bands above 30 kD after 14 DAP with the exception of a 45 kD band. Endosperm treated with fluridone showed continued production of high molecular weight bands. This suggests that ABA induces dormancy by the induction and/or inhibition of synthesis of specific proteins and groups of proteins.