Abscisic acid (ABA)-mediated inhibition of seed germination involves a positive feedback regulation of ABA biosynthesis in Arachis hypogaea L.

Abscisic acid (ABA) plays an important role in seed dormancy, embryo development and adaptation to environmental stresses. We found that imbibition of exogenous ABA by peanut seeds led to a significant increase in the levels of bothAhNCED1 gene [a key gene encoding nine-cis-epoxycarotenoid dioxygenase (NCED) involved in ABA biosynthesis in peanut] transcript and endogenous ABA in germinating seeds, and also led to a marked decrease in α-amylase activity, germination rate and viability index of germinating seeds. This was associated morphogenetically with inhibited plumule apex growth and reduced leaf primordium elongation, a decreased number and length of axial and lateral buds, and shorter length of compound leaves during germination. Imbibition by peanut seeds of naproxen (a potent ABA biosynthesis inhibitor specifically targeting to NCED) significantly decreased the levels of endogenous ABA and AhNCED1 gene transcript in germinating seeds, and markedly increased α-amylase activity, germination rate and viability index of germinating seeds. This was associated morphogenetically with increased plumule apex growth and leaf primordium elongation as well as increased number and length of axial and lateral buds, but without a significant change in the length of compound leaves during seed germination. These observations suggest the involvement of a positive feedback regulation of ABA biosynthesis in ABA-mediated inhibition of seed germination in peanut.   Key words: Abscisic acid, AhNCED1 gene, biosynthesis, feedback regulation, peanut (Arachis hypogaea L.), seed germination.