Irradiance and Spectral Quality Affect Chlorosis of Barley Primary Leaves During Growth in Elevated Carbon Dioxide

Abstract

The development of chlorosis was studied in primary leaves of barley plants (Hordeum vulgare L. cv. Brant) grown at ambient and twice-ambient CO2 partial pressures. Leaf yellowing was observed 17 d after sowing when plants were grown in controlled environment chambers equipped with high-intensity discharge lamps at an irradiance of 800 μmol quanta m-2 s-1. The extent of leaf yellowing, measured as changes of total chlorophyll, increased when the CO2 partial pressure was raised from 37 to 70 Pa. Chlorosis was increased further by increasing the irradiance from 800 to 1100 μmol quanta m-2 s-1. Rates of photosynthetic O2 evolution by primary leaves, measured 17 d after sowing, were 20% lower for elevated compared with ambient CO2–grown plants. This result agreed with the level of chlorosis. However, soluble protein, Rubisco protein (ribulose, 1,5-bisphosphate carboxylase/oxygenase), and initial and total Rubisco activity 17 d after sowing were unaffected by CO2 enrichment and the extent of chlorosis. Leaf st...