Nitrate uptake and assimilation and chlorate tolerance of wheat

Productivity of nonlegume crops depends partly on nitrate uptake and reduction. To study the nitrate assimilation pathway of plants, the herbicide chlorate has been exploited as an analog of nitrate. Marked variations in visible leaf chlorosis among 15 soft red winter wheat (Triticum aestivum L.) seedlings exposed to 120 μM chlorate were reported by others. From their study, we selected three chlorate- tolerant and three chlorate-sensitive ranked cultivars and measured influx and assimilation of ¹⁵N-nitrate to determine if these traits were related to differences in chlorate sensitivity. Effects of 120 μM chlorate on growth, leaf chlorophyll concentration, and nutrition were also quantified. The growth and chlorophyll levels of main stem oldest leaf blades decreased in the presence of chlorate in all cultivars except for one chlorate-tolerant cultiver. Neither the level of tissue nitrate nor the influx and assimilation of ¹⁵N-nitrate was related to chlorate sensitivities we observed, or those previously reported for the six selected cultivars. Chlorate toxic effects unrelated to nitrate assimilation and interactions between absorbed nitrate and chlorate and their compartmentation may alter the response of these cultivars to chlorate. Inferences that chlorate sensitivity of wheat is related to nitrate uptake and assimilation appeared to be inappropriate.