PATTERNS OF DR5::GUS EXPRESSION IN ORGANS OF PEA (PISUM SATIVUM)

The recent availability of DR5 reporter constructs to visualize regions of auxin response allows us to examine the role of auxin in developmental processes. In Arabidopsis, DR5::GUS is sensitive to auxin pools in a dosage-dependent manner and has been used extensively to visualize areas of high auxin concentration. We transformed pea (Pisum sativum) with DR5:: GUS. Several lines, originating from independent events, have shown stable expression through T-5. In pea, GUS expression occurred in embryos, root tips, developing flowers, procambium, and pollen. In root primordia, GUS expression was most abundant in the peripheral root cap cells, protoderm, and protoxylem. In leaf primordia, dark blue staining occurred in the distal tip of the primordium from plastochrons P-0 through P4-5. Lateral tendril primordia and tendril tips stained more intensely blue and for more plastochrons than leaflet primordia and tips. Blue (GUS) staining in floral organs during initiation and development also revealed specific, shifting patterns. Quantitative MUG assays showed that DR5 is differentially responsive to different natural and synthetic auxins, with 4-Cl-IAA giving the strongest response. The DR5:: GUS transgene is being crossed into various mutants, which will allow identification of the role of auxin in different developmental events in pea.