Fig. 2.

Altering CO₂ or O₂ supply has little effect on the high-light response of the rice bundle sheath. (A) Neither reducing (200 ppm) nor increasing (2,000 ppm) CO₂ had a clear effect on DAB staining at 21% O₂ under high light (750 μmol ⋅ m⁻² ⋅ sec⁻¹ PPFD). The dotted line indicates the boundary between high light (HL) and dark-exposed parts of the leaf. (B) Quantitation of DAB staining of leaves exposed to 200, 400, or 2,000 ppm CO₂. ANOVA indicated no significant statistical difference associated with CO₂ treatment (P = 0.22). (C) Inhibition of photorespiration by reducing O₂ from 21 to 2% at 400 ppm CO₂ did not abolish H₂O₂ accumulation in the bundle sheath under HL (750 μmol ⋅ m⁻² ⋅ sec⁻¹ PPFD). (D) Quantification of DAB staining in leaves exposed to 2 or 21% O₂. ANOVA indicated no significant statistical difference associated with O₂ treatment (P = 0.0933). (E) DAB staining leaves of C₄ G. gynandra, S. italica, Z. mays, and S. bicolor exposed to high light. Although C₄ species have limited photorespiration in the bundle sheath, DAB staining was still detected in this tissue. (Scale bars: 1 mm in A and C and 50 μm in E.)