HEDTA - Nitrilotriacetic acid chelator-buffered nutrient solution for zinc deficiency evaluation in rice

Chelator-buffering methods with N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid (HEDTA) are used to elucidate Poaceae growth response to micronutrient metal activities including (Zn2+), but reliable hydroponic methods that maintain stable (Zn2+) for evaluating Zn deficiency in rice (Oryza sativa L,) have not been reported. The objective was to develop a chelator-buffered method that gauges rice growth response to (Zn2+) in an otherwise chemically stable environment. Using GEOCHEM-PC to estimate solution activities, an aero-bic HEDTA-nitrilotriacetic acid (NTA) dual-chelator method was developed that imposed five (Zn2+ levels on cv, IR-36 seedlings for 21 d after transplanting (DAT) in a growth chamber. Control of pH 550 +/- 0.05 using 3.0 mM 2-(4-morpholino)-ethanesulfonic acid (MES) combined with periodic adjustment was critical to preserving target (Zn2+). Solution treatments ranged from Zn deficient, where (Zn2+) = 10(-10.0) M (0.25 muM total chelated Zn), to fully Zn sufficient where (Zn2+) = 10(-8.8) M (4.00 muM total chelated Zn). Using 200.0 muM total chelated Fe(III), adequate Fe was maintained at (Fe3+) = 10(- 14.3) M, Phosphorous supply was controlled to prevent toxic P accumulation at low (Zn2+). With increasing (Zn2+), total biomass at 21 d ranged from 0.94 to 1.90 g plant(-1). Shoot Zn responded to (Zn2+), not total chelated Zn2+, and roots responded similarly. Critical (Zn2+) for normal growth was 10(-9.1) M, and leaf Zn-deficiency symptoms were observed at (Zn2+) less than or equal to 10(-9.4) M (less than or equal to 28 mg Zn kg(-1) shoot). The HEDTANTA method provides a rapid and reliable means for evaluating Zn deficiency tolerance in IR-36 via diagnostic visual and physical symptoms in response to a range of (Zn2+) levels.