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Effects of Urea and Ammonium Nitrate on Penetration of NAA Through Enzymatically Isolated Tomato Fruit Cuticular Membranes Pages: 17 Published: Jan 2003
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View License Agreement Source: STP1449-EB Abstract The effects of ammonium nitrate (AMN) on penetration of foliar-applied (1-L droplets) 1-naphthylacetic acid (NAA) through enzymatically isolated tomato ( Mill cv. Pik Red) fruit cuticular membranes (CM) were studied using a finite dose diffusion system. The maximum rate of penetration (R) and the total amount penetrated after 120 h (P) were used to measure the treatment effects. AMN (8 mM) increased NAA penetration significantly at pH values (5.2, 6.2) above the pK (4.2), but had no effect at pH 3.2. Ammonium sulfate and ammonium dihydrogen phosphate were equally effective as AMN at pH 5.2, but potassium and calcium nitrate reduced NAA penetration compared to NAA alone. Alkylamine hydrochlorides were equally effective as AMN. On a relative basis, AMN had a greater effect on NAA penetration through native, nondewaxed CM (P 172 vs. 500pmol) than through dewaxed CM (P 503 vs. 671 pmol). The AMN effect was dependent on relative humidity (RH); both the R and P were greater at lower (<63 %) than at higher (>64 %) RH. Droplet drying and the presence of AMN and NAA together in the donor (droplet/residue) were required for AMN enhancement of NAA penetration. We suggest that the presence of AMN in the drying droplets/residues results in protonation of the NAA anion, yielding free NAA (nondissociated), which penetrates readily. The volatilization of the ammonia produced and penetration of the nondissociated NAA into the CM favor continued formation of free NAA as long as NAA and AMN are available and the conditions in the deposit support these reactions.
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