SEED AND HORMONAL-REGULATION OF GIBBERELLIN 20-OXIDASE EXPRESSION IN PEA PERICARP

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.