
TY  - JOUR
A1  - Milborrow, B. V. 
A1  - Lee, H-S. 
T1  - Endogenous Biosynthetic Precursors of (+)-Abscisic Acid. IV. Biosynthesis of ABA from [<emph type="7">2</emph>H<emph type="2"><emph tye="8">n</emph></emph>] Carotenoids by a Cell-free System from Avocado
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1998
VL  - 24
IS  - 6
SP  - 715
EP  - 726
KW  - abscisic acid, biosynthesis, carotenoids, cell-free, 9&acute;-cis-neoxanthin, avocado.
UR  - https://doi.org/10.1071/PP96100 
N2  - The supernatant fraction (12 000 g) of a homogenate of avocado mesocarp incorporated 3-R-&#91;2-14C&#93;mevalonate (54 &#181;Ci/&#181;mol, 0.9 &#181;Ci/5mL) into ABA and was used to examine the incorporation of carotenoids into ABA. &#91;2Hn&#93;carotenoids were isolated by HPLC from mustard (Sinapis alba) seedlings that had germinated in closed flasks in 2H2O (55 atom%). The carotenoids were dissolved in Tween 80 and acetone (1:1 v/v; 100 &#181;L) and added to the cell-free system final vol. 5 mL, pH 7.1, together with cofactors. After 16 h incubation in darkness the ABA was isolated by HPLC and converted into the pentafluorobenzyl ester. The samples were analysed by capillary gas&#8211;liquid chromatography and the CH4 chemical ionisation, negative ion mass spectra recorded. Deuterium-labelled ABA was detected when &#91;2H&#93; carotenoids were supplied. &#8216;Cold traps&#8217; of unlabelled carotenoids added to the cell-free system lowered the &#91;14C&#93;mevalonate incorporated into ABA to 33% of the control value (1195 dpm) (trans-viola, 33%; trans-neo, 32%) but with 9&acute; -cis-neoxanthin the value fell to 29%. The addition of naproxen (an inhibitor of lipoxygenases) hardly increased the 14C trapped in trans-viola- or trans-neoxanthin but reduced the 14C in ABA to 17% of the control and raised the 14C trapped by the 9&acute;-cis-neoxanthin by 179%. These changes support earlier suggestions that it is 9&acute;-cis-neoxanthin that is cleaved to give the future ABA residue. Other metabolic inhibitors (bisulfite, AMO 1618, tungstate, CO, piperonyl butoxide) affected the incorporation of &#91;14C&#93;mevalonate into ABA by the cell-free system and the incorporation of &#91;14C&#93;mevalonolactone into ABA formed in slices of avocado fruit in a closely similar way. This provides strong support for ABA&#8217;s being biosynthesised in the cell-free system by the same reactions as those by which it is made in vivo. 
ER  -

