PHYSIOL, PLAJMT, S6: 387-398. Copenhagen 1982 Tentoxin does not cause chlorosis in greening mung bean leaves by inbibiting pbotopbospliorylation Stephen O. Duke, James L, WickUff, Kevin C. Vaughn and Rex N. Paul Duke, S. O., Wicicliff, J. L., Vaugiin, K. C. and Paul, R. N. 1982. Tentoxin does not cause ciilorosis in greening mung bean ieaves by inhiibiting photophosphoryiation. — Physioi. Piant. 56: 387-398. Effects of the fungal toxin, tentotoxin, on deveiopment and ciiioropliyii accumuiation of plastids of primary leaves of mung bean [Vigna radiata (L.) Wiiczeii cv, Berken] were studied using spectrophotometric, electropiioretic, and microscopic procedures. In etioptasts of control tissues botii protameliar bodies and prottiytakoids occurred, whereas smatt vesicles were assodated witii structurally distinct prolatneliar bodies in tentoxin-affected etiopiasts. As detennined by in vivo spectropliotometry,, ten- toxin-affected etioplasts iiad 25% less phototransformabie protochloiophyii(ide) and 35% less non-phototransformabte protochlorophyll(ide) than had controt etiopiasts after 5 days of dark seedting growtli. Tentoxin had no eff^ect on the rate of the Siiibita shift. Protochlorophyii(ide) resynthesis in the dark immediateiy after pro- tochiorophyil(ide) phototransformation was five to six times slower in tentoxin- treated than in control tissues. Effects on chtorophyll(ide) content were observed within 30' min of the beginnitjg of continuous white iight exposure. In vivo measure- ment of cytochrome / redox activity reveaied that this cytochrome was linked to iigiit-driven eiectron flow in eontrol tissues within 20 min of the beginning of con- tinuous white tight, whereas in the tentoxin-treated tissues there was no hnkage (despite the presence of cytochrome/) at any time. Coupling factor 1 was present and had potential ATPase activity in both controi and tentoxin-affected piastids. There was about sixteen times more chiorophyil in controi than ia tentoxin-treated tissues in continuous as weil as in intermittent (2 min tight/118 min dark) light. These data are consistent with the view that tentoxin disrupts normal etiopiast and chioroptast deveiopment through a mechanism unrelated to photophosphoryiation. Additional key words - Chiorophylt, chtoroplast, coupiing factor, cytochrome /, etiopiast, protochlorophyiiide, Vigna radiata. S. O. Duke (reprint requests), K. C. Vaughn and R. N. Paul, USDA-ARS, Southern Weed Seience Lab., Stoneville, MS 38776, USA; J. L. WickUff, Dept. of Botany & Bacteriology, Univ. of Arkansas, Fayetteville, AR 72701, USA. ,, this hypothesis (Steele et al. 1976). Despite these find- n ro u on .^^^^ coupled electron transport (that is, electron trans- The tnechanism by which the fungal toxin, tentoxin, port stimulated by ADP plus phosphate) is inhibited by causes chlorosis has been hypothesized to be through tetitoxiti in several insensitive species, including radish inhibition of photophosphoryiation (Arntzen 1972, and maize (Arntzen 1972, Steele et al. 1976). Bennett 1976, Sfeele et al. 1976). The finding that ten- The inheritance pattern of tentoxin sensitivity is con- toxin binds to and inhibits the ATPase function of iso- sistent with the photophosphoryiation theory of the lated chloroplast coupling factor one (CF,) from mature mechanism of tentoxin action. In several Nicotiana chloroplasts of a sensitive species (lettuce), but does not species tentoxin sensitivity, determined by chlorosis, is inhibit the ATPase function of CFj of an insensitive cytoplasmically inherited (Durbin and Uchytil 1977, species (radish) has provided the strongest support for Burk and Durbin 1978, Aviv et al. 1980). Three of the Received 10 May, 1982; revised 9 August, 1982 26 Phvsiol. Haul 56,1982 00319317/82/120387-12 $03.00/0 © 1982 Physiologia Piantarum 387