Gene expression from Arabidopsis under high light conditions

We have investigated the genomic response of Arabidopsis cell suspension culture under high light. Our main goal has been twofold: first, to establish whether chloroplasts in Arabidopsis cell suspension culture are functional and, as such, can act as sensors of adverse external stimuli leading to the activation of genomic defence responses in a manner similar to that described in whole plants exposed to a wide range of environmental stresses and; second, to distinguish which of the ROS that would be probably generated in the chloroplasts is predominant. Our functional genomic analysis has led us to conclude that singlet oxygen is the major ROS in Arabidopsis cell suspension culture under high light stress and that singlet oxygen production is responsible for a genomic activation associated with the biosynthesis and signalling pathway of several phytohormones that ultimately triggers accelerated cell death. After the ninth day of growth, a volume of 200 mL of Arabidopsis cell suspension culture with a cell density of approximately 150-200 mg/mL was placed in a glass vessel surrounded by a water bath to maintain constant temperature during the light treatment. Nine microarray experiments were designed and classified as follows: control 1–3 (50 microE/m2/s), 1-h dark 1–3 and high light 1–3 (1800 microE/m2/s); where 1–3 stands for the number of biological replicates. After each treatment, sample RNA was extracted and its quality evaluated. The transcriptomic analysis was performed using Affymetrix GeneChip Arabidopsis genome ATH1 arrays.