Photosynthetic electron transport in pitcher plants (Nepenthes mirabilis).

Abstract

Pitcher plants (Nepenthes sp.) are insectivorous angiosperm plants with modified leaves known as pitchers best known as acting as traps for insects. Pitcher plants are typically found under boggy conditions under both forest cover and open areas with very poor nutrient status, particularly N-status. The pitchers have low photosynthetic activity. The Chl a content of the pitcher tissue of both Nepenthes mirabilis (green and red) varieties was very low. Chl b/a ratios of the green variety phyllodes (lamina) and pitchers were ≈ 0.24 to 0.29. In the red variety, the mature phyllodes had a Chl b/a ratio ≈ 0.28 but both the pitchers and the young phyllodes had Chl b/a ratios of nearly 0.5. Photosynthetic electron transport (ETR) was measured using PAM technology. Phyllodes of both varieties showed photoinhibition at supra-optimal irradiances [Nepenthes mirabilis (green variety), Eopt ≈ 200-250µmol photon m-2s-1; red variety, Eopt ≈ 100-150µmol photon m-2s-1]. Pitchers had low optimum irradiances (Eopt ≈ 40-90µmol photon m-2s-1). Maximum ETR (ETRmax) of phyllodes of both varieties was low (ETRmax ≈ 50µmol e- g-1 Chl a s-1); ETRmax was higher for pitchers on a Chl a basis (ETRmax ≈ 80-100µmol e- g-1 Chl a s-1); a consequence of their low Chl a content on a surface area basis. ETRmax of cut disks of phyllodes did not respond strongly to incubation in NH4+, glutamate or aspartate as N-sources but did respond positively to added urea.