Effect of light on endogenous levels of gibberellin and abscisic acid in seed germination of photoblastic weedy rice (Oryza sativa L.)

Abstract

The effect of red (R) and R/far-red (FR) lights on endogenous gibberellin (GA) and abscisic acid (ABA) content was first investigated during the germination of photoblastic black-hulled weedy rice (PBWR) seeds. The R light-treated PBWR seeds germinated after 36-48 h and germination was increased to 63% at 72 h. However, the FR light-treated seeds after R light treatment, suppressed the R light effect showing only 11% germination even at 72 h after the light treatment. The PBWR seed treated with R light rapidly increased the endogenous level of GA1 to about 200 times at 12 h before seed germination as compared with R/FR (control) which suppressed the effect of R light. The contents of other GAs like GA12, GA53, GA19, GA20, and GA8 were not affected by the R light irradiation. These results showed that the major biosynthetic pathway of GAs in PBWR seeds is the early 13-hydroxylation pathway leading to GA1, which was suggested to be physiologically active in the PBWR seed germination. The decrease in the level of ABA in the R light-treated seeds was greater than the R/FR light-treated seeds, indicating that the balance of endogenous GA1 and ABA is responsible for the induction of germination in the PBWR seed.

Molecular Mechanisms Underlying Abscisic Acid/Gibberellin Balance in the Control of Seed Dormancy and Germination in Cereals

“…The roles of these two lights in modulating the balance between ABA and GA metabolisms and therefore the transition of seeds between dormant and germinating states have also been investigated in monocot species. For example, the transition from dormant to germinating state of Brachypodium and photoblastic weedy rice seeds appeared to be promoted by red light but repressed by far-red light ( Kim et al, 2009 ; Barrero et al, 2012 ), and these effects of the two lights in weedy rice seeds have been shown to be associated with changes in ABA and GA levels ( Kim et al, 2009 ). Contrary to these observations, red and far-red lights are reported not to have an effect on the expression of ABA biosynthetic genes, the level of ABA and germination in barley seeds ( Gubler et al, 2008 ).…”