| 11986762 |
Yamaguchi S, Kamiya Y: Gibberellins and Light-Stimulated Seed Germination. J Plant Growth Regul. 2001 Dec;20(4):369-376.
Bioactive gibberellins (GAs) promote seed germination in a number of plant species. In dicots, such as tomato and Arabidopsis, de novo GA biosynthesis after seed imbibition is essential for germination. Light is a crucial environmental cue determining seed germination in some species. The red (R) and far-red light photoreceptor phytochrome regulates GA biosynthesis in germinating lettuce and Arabidopsis seeds. This effect of light is, at least in part, targeted to mRNA abundance of GA 3-oxidase, which catalyzes the final biosynthetic step to produce bioactive GAs. The R-inducible GA 3-oxidase genes are predominantly expressed in the hypocotyl of Arabidopsis embryos. This predicted location of GA biosynthesis appears to correlate with the photosensitive site determined by using R micro-beam in lettuce seeds. The GA-deficient non-germinating mutants have been useful for studying how GA stimulates seed germination. In tomato, GA promotes the growth potential of the embryo and weakens the structures surrounding the embryo. Endo-b-mannanase, which is produced specifically in the micropylar endosperm in a GA-dependent manner, may be responsible for breaking down the endosperm cell walls to assist germination. Recently, a role for GA in overcoming the resistance imposed by the seed coat was also suggested in Arabidopsis from work with a range of seed coat mutants. Towards understanding the GA signaling pathway, GA response mutants have been isolated and characterized, some of which are affected in GA-stimulated seed germination. |
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