EFFECTS OF FUSARIUM-SOLANI NAPHTHAZARIN TOXINS ON THE CYTOLOGY AND ULTRASTRUCTURE OF ROUGH LEMON SEEDLINGS

Two naphthazarin phytotoxins (dihydrofusarubin and isomarticin) produc ed by Fusarium solani were used to determine their effects on the cyto logy of leaves of rough lemon (Citrus jambhiri Lush) seedlings maintai ned in a dilute solution of the toxins. Dihydrofusarubin alone or in c ombination with isomarticin (80:20, v/v) caused cell necrosis above th e midveins and lateral veins, plasmolysis or collapse of spongy mesoph yll cells, collapse of phloem, depletion of starch, swelling of chloro plasts and disruption of cellular organization. At the ultrastructural level, the toxins affected chloroplast membranes by causing swelling, breaks in outer membranes, granal stack disorganization and swelling of intergranal membranes. The interstromal lamellae appeared as vesicl es and sometimes as peripheral reticulum, with an increase in plastogl obuli. The tonoplast was broken or vesiculated. The only membranes not affected by the toxins were those of the nucleus and the mitochondria . This study establishes that the initial toxin effects of these funga l phytotoxins are on organellar membranes, primarily those of the chlo roplasts, plasmalemma and tonoplast.