Abstract
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.
Highlights
Seed germination is regulated by dormancy and environmental factors such as light, oxygen and temperature, and it is thought that the key to this is the balance of the negative and positive regulative effects of abscisic acid (ABA) and gibberellin (GA). Gonai et al (2004) suggested
We found that imbibition of exogenous Abscisic acid (ABA) by peanut seeds led to a significant increase in the levels of both AhNCED1 gene [a key gene encoding nine-cis-epoxycarotenoid dioxygenase (NCED) involved in ABA biosynthesis in peanut] transcript and endogenous ABA in germinating seeds, and led to a marked decrease in α-amylase activity, germination rate and viability index of germinating seeds
Phytohormones, ABA and GA, are well known to be involved in normal germination control (Tamura et al, 2006) - for example, de novo ABA biosynthesis is required for thermoinhibition of lettuce seeds germination (Yoshioka et al, 1998)
Summary
Seed germination is regulated by dormancy and environmental factors such as light, oxygen and temperature, and it is thought that the key to this is the balance of the negative and positive regulative effects of abscisic acid (ABA) and gibberellin (GA). Gonai et al (2004) suggested. Negative feedback regulation occurs mostly in instances of auxin- or stress-induced ethylene production in various plant organs. We found that ABA inhibited lateral root development of peanut plants by up-regulation of AhNCED1 gene causing accumulation of endogenous ABA (Guo et al, 2009). Szepesi et al (2009) suggested a positive feedback regulation of ABA synthesis by salicylic acidinduced ABA accumulation in tomato plants, and Barrero et al (2006) showed that accumulated ABA levels exerted a positive feedback on its own biosynthetic pathway in Arabidopsis, inspite of some earlier reports where no feedback regulation was found in ABA biosynthesis in cowpea (Iuchi et al, 2000) and tomato (Thompson et al, 2000)
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