Figure 6. Schematic model of possible mechanism underlying different leaves symptoms between wild type and anthocyanin deficient mutant in A. thaliana.

Phytoplasma infections cause phloem necrosis in both wild type and anthocyanin deficient mutant (ii). In those leaves, sucrose concentration is increased at high level by impaired phloem loading (iii). Sucrose accumulation activates the anthocyanin biosynthesis pathway in wild type, resulting in purple top symptoms (iv-left column). In anthocyanin deficient mutant, the leaf shows yellowing symptom and dies earlier than wild type (iv-right column). (Drawings by Misako Himeno).