Photosynthesis and stomatal characteristics of Striga hermonthica in relation to its parasitic habit

Photosynthesis and stomatal characteristics of the angiosperm parasite Striga her-monthica (Del.) Benth. have been compared with those of Antirrhinum majus L. cv. Suttons Yellow Rust Resistant, a related, non-parasitic species. The concentration of photosynthetic pigments in S. hermonthica leaves was less than 40% of those of A. majus leaves. Light saturated CO₂ assimilation rate of S. hermonthica was less than 40% that of A. majus on a chlorophyll basis and under 20% than of A. majus on a leaf area basis.
Stomata of Striga showed only partial closure in darkness, remained open in water stressed leaves and showed little response to exogenously applied abscisic acid. Stomatal conductance and transpiration were considerably higher in Striga compared with Antirrhinum . The high transpiration and low photosynthetic rates of S. hermonthica resulted in a low water use efficiency. The water relations of Striga leaves, while seemingly inappropriate for growth in drought prone environments, do appear to maximise nutrient and water acquisition from the host and as such may be an adaptation to the parasitic habit.