Relationship between CO₂-limiting stress and high-light stress in a green alga, Chlamydomonas reinhardtii deduced from cDNA array analyses

Abstract

Carbon concentrating mechanism (CCM) is induced by lowering CO₂ in light. To understand whether induction of CCM depends on light intensity or not, the photosynthetic rate and K_1/2(Ci) values were measured in various light intensities with different CO₂ concentration. As light intensities were stronger, the apparent affinities for Ci were higher in the presence of 1.2% CO₂. And by using cDNA macroarrays containing 10,368 ESTs, global gene expression was examined during acclimation to high-light and/or CO₂-limiting conditions. Chlamydomonas cells were cultured under 5% CO₂ with 120μEm^-2s^-1.For high-light treatment, cells were transferred to 1000μEm^-2s^-1, and for CO₂-limiting conditions, cells were transferred to 0.04 % CO₂. After treatments, cells were harvested after 0.3, 1, 2, and 6h. Expression levels of 391 genes were altered, 132 genes were high-light responsive genes and 317 genes were low-CO₂ responsive genes. We discuss the cross-talk between the light-signaling and the CO₂-signaling.