To understand further how seeds, auxin (4-chloroindole-3-acetic acid [4-Cl-IAA]), and gibberellins (GAs) regulate GA biosynthesis in pea (Pisum sativum L.) pericarp at the molecular level, we studied the expression of GA 20-oxidase in this tissue using northern-blot analysis. Pericarp 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 GA3) on the expression of GA 20-oxidase in pea pericarp were investigated over a 36-h treatment period. GA 20-oxidase mRNA levels in 2 DAA pericarp with seeds remained relatively stable throughout the treatment period; however, when the seeds were removed the pericarp transcript levels declined. When 2 DAA deseeded pericarps were treated with 4-Cl-IAA, a significant increase in GA 20-oxidase mRNA levels was detected within 2 h and transcript levels remained elevated for up to 12 h after 4-Cl-IAA application. GA3 significantly decreased GA 20-oxidase mRNA levels in deseeded pericarp within 2 h of application. These data suggest that the previously reported conversion of GA19 to GA20 in pea pericarp is controlled by seeds, 4-Cl-IAA, and GA3 at least in part by regulating GA 20-oxidase mRNA levels in this tissue.
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