Striga hermonthicadecreases photosynthesis inZea maysthrough effects on leaf cell structure

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Abstract
Maize seedlings were grown in pots either with or without preconditioned seeds of the parasitic weed, Striga hermonthica. After between 4 and 8 weeks, net photosynthesis in the leaves of maize plants infected with Striga decreased compared to leaves of uninfected control plants. The activities of four enzymes of photosynthetic metabolism were, however, little affected by infection. A pulse-chase experiment using 14CO2 showed that C4 acids were the main early products of assimilation even when the rate of photosynthesis was much decreased by infection, but more radio-activity appeared in glycine and serine than in leaves of healthy maize plants. Leaves of infected maize required longer to reach a steady rate of photosynthesis upon enclosure in a leaf chamber than leaves of uninfected plants after similar treatment. Electron microscopy of transverse sections of the leaves of infected maize indicated that the cell walls in the bundle sheath and vascular tissue were less robust than in leaves of healthy plants. The results suggest that infection with Striga causes an increase in the permeability of cell walls in the bundle sheath, leakage of CO2 from the bundle sheath cells and decreased effectiveness of C4 photosynthesis in host leaves.

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