Biochemical composition and photosynthetic activity of chloroplasts from Striga hermonthica and Striga aspera, root parasites of field‐grown cereals

Abstract

Striga hermonthica(Del.) Benth. and Striga aspera (Willd.) Benth. are root parasites causing dramatic losses in field‐grown cereals in semi‐and tropics. Being achlorophyllous and obligate parasites during their underground development, upon emergence from the soil, they become green leafy plants; but, despite the presence of chlorophyll, they exhibit only low rates of photosynthesis. To investigate if deficiency in the photosynthetic apparatus could account for the low rates of photosynthesis, chloroplasts were isolated from S. hermonthica parasitizing sorghum [Sorghum bicolor (L.) Moench cv. Tiemarifing] and from S. aspera parasitizing maize (Zea mays L. cv. Tiémantié) grown under greenhouse conditions or in their natural surroundings. Isolated chloroplasts exhibited the characteristics of chloroplasts from C3 plants but displayed low levels of chlorophyll and polar lipids, while the protein content was less reduced. Main changes occurred in polar lipid composition, with decreases in monogalactosyldiacylglycerol and digalactosyldiacylglycerol. All polar lipids showed a decrease in the degree of unsaturation of fatly acids. All these changes were particularly pronounced in chloroplasts from plants that experienced heavy drought in Africa. On a chlorophyll basis, chloroplasts did not display a dramatic decrease in photosynthetic activities. These results are discussed in relation to parasitism and drought adaptation.