Epidermal focussing and effects on light utilization in Oxalis acetosella

Abstract

lmage analysis was used to quantify the lateral heterogeneity of the radiation field within the palisade of Oxialis acetosella L. leaves. Oxalis acetosella epidermal cells focus light up to four times incident irradiance, resulting in regions of high and low internal fluenec rate within the palisade. Chlorophyll fluorescence from leaves irradiated with directional light was found to originate primarily from palisade cell chloroplasts located within focal zones. When the internal radiation field was made more homogeneous by using diffuse light or by coating the leaf with a layer of mineral oil to eliminate epidermal focussing, the characteristics of the chlorophyll fluorescence signal were altered: non‐photochemical quenching (qN) increased, while relaxation of qN was slowed. This indicates that upper palisade chloroplasts may fine‐tune their light utilization to the intra leaf light microenvironment.