To understand further how seeds, auxin (4-chloroindole-3-acetic acid [
4-Cl-IAA]), and gibberellins (GAs) regulate GA biosynthesis in pea (Pi
som sativum L.) pericarp at the molecular level, we studied the expres
sion of GA 20-oxidase in this tissue using northern-blot analysis. Per
icarp GA 20-oxidase mRNA levels were highest from prepollination (-2 d
after anthesis [DAA]) through anthesis (0 DAA), then decreased 3-fold
by 2 DAA, and remained at these levels through 6 DAA. The effects of
seeds and hormones (4-Cl-IAA and GA(3)) on the expression of GA 20-oxi
dase in pea pericarp were investigated over a 36-h treatment period. G
A 20-oxidase mRNA levels in 2 DAA pericarp with seeds remained relativ
ely stable throughout the treatment period; however, when the seeds we
re removed the pericarp transcript levels declined. When 2 DAA deseede
d pericarps were treated with 4-Cl-IAA, a significant increase in GA 2
0-oxidase mRNA levels was detected within 2 h and transcript levels re
mained elevated for up to 12 h after 4-Cl-IAA application. GA(3) signi
ficantly decreased GA 20-oxidase mRNA levels in deseeded pericarp with
in 2 h of application. These data suggest that the previously reported
conversion of GA(19) to GA(20) in pea pericarp is controlled by seeds
, 4-Cl-IAA, and GA(3) at least in part by regulating GA 20-oxidase mRN
A levels in this tissue.