Chlorophyll Fluorescence Quenching During Photosynthetic Induction in Leaves ofAbutilon striatumDicks. Infected with Abutilon Mosaic Virus, Observed with a Field-Portable Imaging System

A portable Chi fluorescence imaging system was used to characterise nonuniform Chi fluorescence quenching in Abutilon striatum leaves infected with phloem-localised abutilon mosaic virus. The instrument was used to observe fluorescence emission at intervals during induction transients, and to map nonphotochemical quenching during saturating pulses applied in the course of these transients. Two symptom types were distinguished: yellow vein-associated motifs that showed lower maximum Chi fluorescence than nearby green tissues, but virtually zero nonphotochemical quenching, and vein-defined mosaics (pale green) that initially showed normal maximum Chi fluorescence but strongly impaired nonphotochemical quenching. Mature vein-defined mosaics (yellow to white areas) resembled vein-associated symptoms with zero nonphotochemical quenching. Islands of apparently healthy green tissue enclosed by mosaic symptoms showed slower nonphotochemical quenching than controls. Possible effects of localised carbohydrate accumulation, thought to follow from infection by the phloem-limited virus, on photosynthetic processes as well as the synthesis and stability of chloroplast protein complexes, are discussed in the context of symptom development.