Temporal synthesis and radiolabelling of the sorghum 3‐deoxyanthocyanidin phytoalexins and the anthocyanin, cyanidin 3‐dimalonyl glucoside

Abstract

Sorghum (Sorghum bicolor) synthesizes a complex mixture of 3-deoxyanthocyanidin phytoalexins in response to inoculation with the non-pathogenic fungus Bipolaris maydis. The anthocyanin cyanidin 3-dimalonyl glucoside, is also synthesized naturally in response to light. To determine the order and time of appearance of these compounds, etiolated sorghum mesocotyls were inoculated with B. maydis and tissue extracts were analysed by photodiode array-HPLC every 2 h for the first 24 h and at 48 h post inoculation (hpi). Uninoculated and inoculated etiolated mesocotyls were also allowed to incorporate L-[U-"%C] phenylalanine. Apigeninidin appeared at 10 hpi, followed by luteolinidin and apigeninidin 5-O-arabinoside at 14 hpi. Luteolinidin 5-methylether was not detected until 18 hpi and apigeninidin 7-methylether not until 20 hpi. The concentrations of the primary phytoalexins, apigeninidin, luteolinidin and apigeninidin 5-O-arabinoside, rose steadily between 12 and 24 hpi, and the levels of apigeninidin and luteolinidin were approximately equivalent by 24 hpi. However, between 24 and 48 hpi luteolinidin and luteolinidin 5-methylether accumulated rapidly so that by 48 hpi the amounts of luteolinidin and luteolinidin 5-methylether had increased approximately twofold. Radiolabelling also showed that "%C was incorporated into the 3-deoxyanthocyanidins and cyanidin 3-dimalonyl glucoside. Several other unidentified phenolic compounds also accumulated radioactivity.

Flavonoid Phytoalexin-Dependent Resistance to Anthracnose Leaf Blight Requires a Functional yellow seed1 in Sorghum bicolor

“…In sorghum leaves, a suite of reddish-brown flavonoid compounds are induced in the epidermal cells at the site of attempted fungal ingress (Snyder and Nicholson 1990). These pigments belong to the 3-deoxyanthocyanidin class, which includes luteolinidin, 5-methoxy-luteolinidin, apigeninidin, caffeic acid ester of arabinosyl 5-O-apigeninidin,and 7-methoxyapigeninidin (Snyder and Nicholson 1990;Lo et al 1996;Wharton and Nicholson 2000).…”

Differential Induction of 3-deoxyanthocyanidin Phytoalexins in Relation to Colletotrichum falcatum Resistance in Sugarcane

“…It was specifically induced upon pathogen inoculation in the cv Baragua. In sorghum, apigeninidin accumulation was found to be the first response upon inoculation of non pathogenic fungus Bipolaris maydis in resistant cultivars, however during course of time (by 24 h) caffeic acid ester of arabinosyl 5-O-apigeninidin and luteolinidin were found to accumulate at higher levels (Wharton and Nicholson, 2000). Luteolinidin and its derivative were found to be more fungitoxic than apigenenidin compounds (Lo et al 1996).…”

An approach on phytoalexins: function, characterization and biosynthesis in plants of the family Poaceae

“…Sorghum produces two distinct 3-deoxyanthocyanidin phytoalexins known as apigeninidin (2-(4-hydroxyphenyl) benzopyrilium chloride) and luteolinidin (2-(3,4-dihydroxyphenyl)-chromenylium 5,7-diol) (Figure 2). Biosynthesis of 3-deoxyanthocyanidin phytoalexins is independent of light, it occurs in the dark, in contrast to the light dependent anthocyanin biosynthesis (flavonoid compounds, which are plant pigments) (WHARTON & NICHOLSON, 2000).…”