CHLOROPHYLL FLUORESCENCE QUENCHING DURING PHOTOSYNTHETIC INDUCTION INLEAVES OF ABUTILON STRIATUM DICKS - INFECTED WITH ABUTILON MOSAIC-VIRUS, OBSERVED WITH A FIELD-PORTABLE IMAGING-SYSTEM

A portable Chl fluorescence imaging system was used to characterise no nuniform Chl fluorescence quenching in Abutilon strictum leaves infect ed with phloem-localised abutilon mosaic virus. The instrument was use d to observe fluorescence emission at intervals during induction trans ients, and to map nonphotochemical quenching during saturating pulses applied in the course of these transients. Two symptom types were dist inguished: yellow vein-associated motifs that showed lower maximum Chl fluorescence than nearby green tissues, but virtually zero nonphotoch emical quenching, and vein-defined mosaics (pale green) that initially showed normal maximum Chl fluorescence but strongly impaired nonphoto chemical quenching. Mature vein-defined mosaics (yellow to white areas ) resembled vein-associated symptoms with zero nonphotochemical quench ing. Islands of apparently healthy green tissue enclosed by mosaic sym ptoms showed slower nonphotochemical quenching than controls. Possible effects of localised carbohydrate accumulation, thought to follow fro m infection by the phloem-limited virus, on photosynthetic processes a s well as the synthesis and stability of chloroplast protein complexes , are discussed in the context of symptom development.