Studies on the phytotoxic effects of some organotin(IV) compounds on the germination of the mung bean seed,Phaseolus aureus

A selected range of organotin(IV) compounds of formula R_xSnX_4-x (x = 2 or 3; R = alkyl, cycloalkyl or aryl), as well as the adducts, (p-ZC₆H₄)₃SnCl. Ph₃PO (Z = H, Me) were examined in vivo for their phytotoxic effects relative to the more powerful s-triazine herbicides against the mung bean seed, Phaseolus aureus. Phytotoxicity was assessed in terms of changes in (a) weights of primary leaves, (b) weights of cotyledons, (c) seedling heights and (d) root morphology. The triorganotin compounds were more phytotoxic than the diorganotins, and within the R₃Sn structural class, inhibitory potency was greater for alkyltins than for aryltins. Decreasing the alkyl chain lengths or placing electrondonating substituents on the aromatic rings increased the phytotoxicity. A significant phytotoxic effect, comparable with that of Ph₃SnCl, was manifested by tricyclohexyltin chloride, in marked contrast to the well-known low phytotoxicity of tricyclohexyltin hydroxide. Using Ph₃SnCl as the model compound, it was further demonstrated that the total chlorophyll content decreased with increasing concentration of Ph₃SnCl, but the ration of chlorophyll a to chlorophyll b was constant. It was also found that tin uptake in the seedlings was directly proportional to Ph₃SnCl test concentrations; the magnesium and iron levels in the treated seedlings, however, were unchanged relative to the control.