McClure, P. R., Omholt, T. E. and Pace, G. M. 1986. Anion uptake in maize roots; Interactions between chlorate and nitrate [107][108][109][110][111][112] Effects of nitrate, chloride and chlorate ions upon nitrate and chlorate uptake by roots of maize {Zea mays L., cv. B73) seedlings were examined. Net nitrate uptake, ''ClOj' influx and *C1" influx (the latter two in a background of 0.5 mM K.NO3) displayed similar pH profiles with optima at pH 5.5 and below. External, non-labeled chloride had little effect on the accumulation of ' "CIO3" (both m 5 h and 20 min uptake assays), while nitrate and chlorate had almost identical, marked inhibitory effects. Nitrate pretreatment caused an apparent induction of both *ClOj and "NO, uptake activities. After 5 h of treatment in nitrate, the uptake activities of chloride-and chlorate-pretreated plants increased to that of nitrate-pretreated ptants. During 6 h exposure to chlorate, "^lOj uptake activity of nitrate-pretreated plants decreased to that of chlorate-and chloride-pretreated plants. The results support the existence of a shared nitrate/chlorate transport system in maize roots which is not inhibited by external chloride, and which is induced by nitrate, but not by chlorate or chloride. The suggestion is made that selection of chlorate-resistant mutants of maize can identify nitrate uptake as well as nitrate reductase mutants.Additional key words -Chloride uptake, nitrate reduction, nitrate uptake mutants, Zea mays. P. R. McClure (reprint requests) and T. E. Omholt,

Nitrate regulation of protein synthesis and RNA translation in maize (Zea mays L. var B73) roots was examined, using in vivo labeling with [5Sjmethionine and in vitro translation. Nitrate enhanced the synthesis ofa 31 kilodalton membrane polypeptide which was localized in a fraction enriched in tonoplast and/or endoplasmic reticulum membrane vesicles. The nitrate-enhanced synthesis was correlated with In the present study, we have searched for nitrate-inducible polypeptides in maize roots, in an attempt to identify nitrate membrane transport proteins. We have examined the profiles of polypeptides synthesized in maize roots incubated with or without nitrate. The spectra of in vitro translation products of nitrateinduced and noninduced total root RNA were also compared.MATERIALS AND METHODS Plant Material. Maize seeds (Zea mays L. var B73) were germinated in darkness at 29'C between germination paper saturated with 0.5 mM CaSO4. After 3 d, the roots ofthe seedlings were transferred to aerated solutions containing 0.5 mM CaSO4, 5 mM K2HPO4, 1 mM MgSO4, 1.25 mM K2SO4, micronutrients (13) and FeEDTA at 1 mM Fe. The seedlings were grown in an incubator at 29°C under fluorescent lights (about 100-200 ,uEm-2 -s) with a light/dark cycle of 16/8 h. During induction periods, typically during the first part of the light period on the 7th d after the beginning ofgermination, the roots ofthe seedlings were transferred to aerated solutions containing, in addition to 10 mm Mes (pH 5.5), either 5 mM Ca(N03)2 (induced) or 5 mM CaCl2 (noninduced). To label root proteins, the roots of 5 to 8 seedlings were bathed in either control or induction solutions (45 ml)

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