The content of hormones in the embryos of inbreds competent and incompetent for morphogenesis
--Dolgykh, YI, Zhdanova, NE, Pustovoitova, TN

Maize genotypes are known to differ in their capacity for morphogenesis in vitro. The degree of competence for morphogenesis can depend on the concentration of endogenous phytohormones in the cells of explants. The contents of free auxin (IAA), cytokinins (Z and ZR) and abscisic acid (ABA) were compared by immunoenzyme assay in (1) immature embryos of regenerable (A188) and recalcitrant (Gk26) lines isolated at the developmental stage, which was optimal for callus induction, and (2) mature and immature A188 embryos, which differed in their morphogenetic capacities. The analysis showed that the frequency of embryogenic callus formation was related to the concentration of hormones in the explant cells (Table1). Lower level of auxin and cytokinins and higher concentration of abscisic acid characterized the tissues with a competence for somatic embryogenesis. To temporarily decrease the auxin content in the isolated immature Gk26 embryos, one batch of the embryos was incubated with IAA-oxidase co-factors p-coumaric acid and 2,4-dichlorophenol. The second batch of Gk26 embryos was treated with exogenous ABA to elevate the concentration of the endogenous hormone. The effect of the treatment depended on the concentration of reagents. The artificial change in the balance of endogenous hormones resulted in a 3-10-times higher frequency of embryogenic callus formation by the explants (Table 2).

Table 1. The content of endogenous hormones in maize embryos (ng/g fresh weight)
Frequency of embryonic callus induction, %
A188, immature embryos
A188, mature embryos
Gk26, immature embryos
3000.0 ±451.8

Table 2. The frequency of explants forming embryogenic callus.
Untreated p-Coumaric acid, 5 x 10-4 M 2,4-dichlorophenol, 10-5 M ABA, 2 x 10-5 M 
2.4+1.4 12.2±3.4 13.9±3.2 20.9±4.4

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

Return to the MNL 73 On-Line Index
Return to the Maize Newsletter Index
Return to the MaizeGDB Homepage