Plastid and seedling development in SAN-9789 [4-chloro-5-(methylamine)-2-(α,α,α-trifluoro-m-tolyl)-3-(2H)-pyridasinone]-treated etiolated bean seedlings

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Abstract
SAN 9789 [4-chloro-5-(methylamine)-2-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-3-(2H)-pyridasinone] inhibits carotenoid synthesis at the level of phytoene in P. vulgaris L. Although carotenoids are greatly reduced in the primary leaves, prolamellar bodies and thylakoid membranes are formed containing phototransformable protochlorophyll(ide). SAN 9789 also produces developmental effects similar to those of red light since seedlings treated in darkness are short, show plumular unhooking, formation of adventitious roots, expansion of primary leaves and full expansion of the 1st trifoliate leaf and 1st internode. The effect is not directly on phytochrome since far red light does not reverse the effect of SAN. If abscisic acid (ABA) is indeed formed from carotenoids, these may be the consequences of reduced levels of ABA leading to reduced ethylene production as occurs with red light. The 1st trifoliate leaf of SAN-treated plants contains practically no carotenoids (0.2%) compared with untreated 7 day old, etiolated primary leaves yet shows normal development of etioplasts, prolamellar bodies, thylakoid membranes and phototransformable protochlorophyll(ide). In Euglena, lack of carotenoids stops synthesis and assembly of other membrane components; in higher plants this type of regulation does not appear to operate.