Tentoxin does not cause chlorosis in greening mung bean leaves by inhibiting photophosphorylation

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Abstract
Effects of the fungal toxin, tentotoxin, on development and chlorophyll accumulation of plastids of primary leaves of mung bean [Vigna radiata (L.) Wilczek cv. Berken] were studied using spectrophotometric, electrophoretic, and microscopic procedures. In etioplasts of control tissues both prolamellar bodies and prothylakoids occurred, whereas small vesicles were associated with structurally distinct prolamellar bodies in tentoxin‐affected etioplasts. As determined by in vivo spectrophotometry, tentoxin‐affected etioplasts had 25% less phototransformable protochlorophyll(ide) and 35% less non‐phototransformable protochlorophyll(ide) than had control etioplasts after 5 days of dark seedling growth. Tentoxin had no effect on the rate of the Shibita shift. Protochlorophyll(ide) resynthesis in the dark immediately after protochlorophyll(ide) phototransformation was five to six times slower in tentoxintreated than in control tissues. Effects on chlorophyll(ide) content were observed within 30 min of the beginning of continuous white light exposure. In vivo measurement of cytochrome f redox activity revealed that this cytochrome was linked to light‐driven electron flow in control tissues within 20 min of the beginning of continuous white light, whereas in the tentoxin‐treated tissues there was no linkage (despite the presence of cytochromef) at any time. Coupling factor 1 was present and had potential ATPase activity in both control and tentoxin‐affected plastids. There was about sixteen times more chlorophyll in control than in tentoxin‐treated tissues in continuous as well as in intermittent (2 min light/118 min dark) light. These data are consistent with the view that tentoxin disrupts normal etioplast and chloroplast development through a mechanism unrelated to photophosphorylation.

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