EPIDERMAL FOCUSING AND EFFECTS ON LIGHT UTILIZATION IN OXALIS-ACETOSELLA

Image analysis was used to quantify the lateral heterogeneity of the r adiation field within the palisade of Oxalis acetosella L. leaves. Oxa lis acetosella epidermal cells focus light up to four times incident i rradiance, resulting in regions of high and low internal fluence rate within the palisade. Chlorophyll fluorescence from leaves irradiated w ith directional light was found to originate primarily from palisade c ell chloroplasts located within focal zones. When the internal radiati on field was made more homogeneous by using diffuse light or by coatin g the leaf with a layer of mineral oil to eliminate epidermal focussin g, the characteristics of the chlorophyll fluorescence signal were alt ered: non-photochemical quenching (qN) increased, while relaxation of qN was slowed. This indicates that upper palisade chloroplasts may fin e-tune their light utilization to the intra-leaf light microenvironmen t.