Localization of flavonoid enzymes in Arabidopsis roots

Saslowsky, D Winkel-Shirley, B

D. Saslowsky et B. Winkel-shirley, Localization of flavonoid enzymes in Arabidopsis roots, PLANT J, 27(1), 2001, pp. 37-48

46

INGLESE

Article

Plant Sciences","Animal & Plant Sciences

PLANT JOURNAL

0960-7412 → ACNP

27

1

2001

37 - 48

ISI

0960-7412(200107)27:1<37:LOFEIA>2.0.ZU;2-F

Immunofluorescence and immuno-electron microscopy have been used to test th e hypothesis that flavonoid metabolism is organized as a membrane-associate d enzyme complex. The cellular and subcellular locations of chalcone syntha se (CHS) and chalcone isomerase (CHI), the first two enzymes of this pathwa y, were examined in Arabidopsis roots. High levels of both enzymes were fou nd in the epidermal and cortex cells of the elongation zone and the root ti p, consistent with the accumulation of flavonoid endproducts at these sites . Co-localization of CHS and CHI was observed at the endoplasmic reticulum and tonoplast in these cells, and also in electron-dense regions that are, as yet, unidentified. In addition, a striking asymmetric distribution was o bserved for these enzymes in cortex cells of the elongation zone, which may provide clues about the physiological function of flavonoids in roots. The accumulation of CHS and CHI was also examined in tt7(88), a mutant in the gene for flavonoid 3'-hydroxylase (F3'H), which has been postulated to serv e as a membrane anchor for the flavonoid enzyme complex. CHS and CHI accumu lated to lower levels in cortex cells and higher levels in epidermal cells in the roots of this mutant as compared with wild-type plants. Moreover, th e electron-dense regions containing these two enzymes were not observed. Ho wever, localization of CHS and CHI to the ER and tonoplast did not appear t o be affected, suggesting that other proteins may function in recruiting th e 'soluble' flavonoid enzymes to membranes. Staining of flavonoid endproduc ts with DPBA was consistent with expression of CHS and CHI in these seedlin gs.