cis-Stereoisomers of β-carotene and its congeners in the alga Dunaliella bardawil, and their biogenetic interrelationships

Biosynthesis of Abscisic Acid by the Direct PathwayviaIonylideneethane in a Fungus,Cercospora cruenta

“…The temperature (30 C) for the culture used by Yamamoto et al was higher than the optimum temperature for fungal growth and might affect the biosynthetic rate of ABA. We also observed that all four oxygen atoms of ABA were not always labeled with 18 O from 18 O 2 . When the fungus began to produce ABA at a late period, day 22 after inoculation, two oxygen atoms at C-1 and -1 0 were labeled with 18 O from 18 O 2 , but two oxygen atoms at C-1 and -4 0 were not (data not shown).…”

“…Labeling of 4, 5, and ABA with 18 O 2 18 O-Labeling of the intermediates 4 and 5 in addition to ABA was examined. The period of accumulation and the location were different between compound 4 on the one hand and compound 5 and ABA on the other.…”

“…Our finding is consistent with the direct pathway via ionylideneethane. But incorporation of two 18 O atoms into C-1 of ABA from 18 O 2 might be possible for the carotenoid pathway in which oxidation at C-1 of a putative C 15 -aldehyde intermediate was catalyzed by monooxygenase with molecular oxygen. If the carotenoid pathway occurs in C. cruenta, the fungus could produce the 9Z-carotenoid possessing -ring as well as the C 15 -intermediates 4-6.…”

“…This fungus produces 2Z,4E--ionylideneethanol (4) and 2Z,4E-1 0 ,4 0 -dihydroxy--ionylideneacetic acid (5) as the biosynthetic intermediates of ABA. 7,14) The production of these compounds appears to support the direct pathway, but the fungus produces -carotene and an aldehyde-intermediate, 2Z,4E--ionylideneacetaldehyde (6), and incorporates 18 O from 18 O 2 into C-1, -1 0 , and -4 0 of ABA. 8) These facts suggest that ABA of the fungus is biosynthesized by the carotenoid pathway, although the 9Z-carotenoid possessing -ring that should be a precursor of 6 has not been found in this fungus.…”

“…8) These facts suggest that ABA of the fungus is biosynthesized by the carotenoid pathway, although the 9Z-carotenoid possessing -ring that should be a precursor of 6 has not been found in this fungus. We re-examined the 18 O-labeling of ABA with 18 O 2 , made precise analysis of ABA-related carotenoids and sesquiterpenoids, and did feeding experiments of labeled compounds in C. cruenta to solve the confusion over the biosynthesis of ABA. This paper reports the occurrence of the direct pathway via ionylideneethane in C. cruenta as well as in B. cinerea.…”