Question

What is the role played by the hypocotyl in epigeal germination?

Answer 1

plantphysiol.org

A role for brassinosteroids in germination in Arabidopsis

Camille M Steber, Peter McCourt

Plant physiology 125 (2), 763-769, 2001

This paper presents evidence that plant brassinosteroid (BR) hormones play a role in promoting germination. It has long been recognized that seed dormancy and germination are regulated by the plant hormones abscisic acid (ABA) and gibberellin (GA). These two hormones act antagonistically with each other. ABA induces seed dormancy in maturing embryos and inhibits germination of seeds. GA breaks seed dormancy and promotes germination. Severe mutations in GA biosynthetic genes in Arabidopsis, such as ga1-3, result in a requirement for GA application to germinate. Whereas previous work has shown that BRs play a critical role in controlling cell elongation, cell division, and skotomorphogenesis, no germination phenotypes have been reported in BR mutants. We show that BR rescues the germination phenotype of severe GA biosynthetic mutants and of the GA-insensitive mutant sleepy1. This result shows that BR stimulates germination and raises the possibility that BR is needed for normal germination. If true, we would expect to detect a germination phenotype in BR mutants. We found that BR mutants exhibit a germination phenotype in the presence of ABA. Germination of both the BR biosynthetic mutantdet2-1 and the BR-insensitive mutantbri1-1 is more strongly inhibited by ABA than is germination of wild type. Thus, the BR signal is needed to overcome inhibition of germination by ABA. Taken together, these results point to a role for BRs in stimulating germination.

Answer 2

Answer:

Epigeal germination is the germination of a seed occurring above the ground level. In this type of germination, the hypocotyl develops to grow for the formation of a loop above the soil. It then clongates thereby pushing the cotyledons through the ground upwards.

Explanation:

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