We investigated the effects of agents known to affect cellular glutathione (reduced form, GSH) levels on the growth of rice seedlings treated with Cd. CdClz was more effective than CdS04 in inhibiting root growth. However, CdCl2 had no effect on shoot growth. GSH, a substrate for phytochelatin synthesis, was effective in counteracting growth inhibition of roots by CdC12. Root growth in the CdCl2 medium was found also to be enhanced by the addition of L-glutamic acid and L-cysteine, both of which are substrates for GSH formation. Buthionine sulfoximine, an inhibitor of GSH synthesis, rendered the roots susceptible to growth inhibition by Cd. Our results suggest that GSH level may play a role in regulating Cd-inhibited growth of rice roots.Abbreviations: BSO = buthionine sulfoximine; GSH = reduced form glutathione

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The effects of Cd on changes in proline level and peroxidase activity in roots of rice seedlings were investigated. CdClz was effective in inhibiting root growth and in accumulating proline in roots. The inhibition of root growth by Cd is reversible. The reduction of root growth induced by Cd is closely associated with accumulation of proline in roots. External application of proline markedly inhibited root growth of rice seedlings in the absence of Cd. Ionically bound, but not soluble, peroxidase activity in roots was increased by CdClz. Proline treatment also resulted in an increase in ionically bound peroxidase activity in roots. The relationship between growth inhibition of roots induced by Cd and changes of proline level and peroxidase activity is discussed.

This investigation was designed to examine whether or not deionized water could be acidified by roots of intact rice seedlings. Roots of intact rice seedlings caused significant acidification of the deionized water in which they were immersed and this acidification could be repeated after replacement of acidified water with fresh deionized water. The addition of K + , Na + , and Mg* + to the deionized water significantly increased the rate and extent of acidification. However, no such increase was found when Ca 2+ was present in the water. The inhibition of acidification by vanadate and its promotion by fusicoccin indicated that the acidification of water by roots of intact rice seedlings originated from an ATP-driven proton pump located in the plasmalemma. Ferricyanide was effectively reduced by the roots of intact rice seedlings. This reduction was associated with the acidification of the bathing solution. 8-Hydroxyquinoline and p-nitrophenylacetate inhibited both the reduction of ferricyanide and ferricyanide-induced acidification. Vanadate, although it slightly inhibited the reduction of ferricyanide, did not inhibit the ferricyanide-stimulated decrease in pH. It seems that the involvement of redox activity associated with the plasmalemma in the acidification of deionized water cannot be excluded.

The effects of polyamines (putrescine, spermidine, spermine and diaminopropane) on the production of ethylene in detached rice leaves were investigated. Polyamines effectively promoted the production of ethylene in detached rice leaves under both light and dark conditions. Putrescine stimulated the production of ethylene within 4 hours of its application, a result suggests that putrescine enhances the production of ethylene directly. Putrescine also stimulated the production of ethylene in detached leaves that had been aged for 2 and 4 days. The stimulatory effect of putrescine resulted from the enhancement of the synthesis of 1-aminocyclopropane-lcarboxylic acid (ACC) and the conversion of ACC to ethylene. • The activity of S-adenosylmethionine decarboxylase in segments of rice leaves was inhibited by the application of putrescine. Thus, the enhancement of the synthesis of ACC by putrescine seems to be mediated by increases in the activity of ACC synthase and in the level of the substrate (S-adenosylmethionine) for ACC synthase.