Óxido nítrico como atenuador da toxicidade de cobre na emergência, crescimento inicial, nutricional e parâmetros ecofisiológicos em milho.

Abstract

The work evaluated the effect of nitric oxide (NO) as an attenuator of copper toxicity in emergence, initial growth, nutritional and ecophysiological parameters in corn (Zea mays L.). The first experiment was conducted at the EBPS seed laboratory (UFRA/Belém campus), the design consisted of a completely randomized design in a 4 x 3 factorial, with 12 treatments and 8 repetitions, totaling 96 trays containing 25 seeds per repetition. The seeds of the K9606VIP3 variety were soaked for 48 hours in Germitest paper with a solution containing sodium nitroprusside Na2[Fe (CN)5 NO]2H2O (0, 75 e 150 µM), as NO donor, sodium ferrocyanide Na4Fe(CN)6 (0, 75 and 150 µM) as compensator and deionized water (control). The emergence was negatively influenced by the copper concentrations that promoted an increase in the percentage of abnormal seedlings, a reduction in the emergency speed coefficient and a longer average emergence time. The dosage of 200 µM of copper provided less root dry matter and increased proline in the roots. NO mitigated the effect of copper toxicity in relation to the dry mass of the aerial part. There was an accumulation of copper in the roots, altering the mineral balance and the mobilization of nutrients. Sodium nitroprusside and sodium ferrocyanide caused toxicity and negatively influenced nutrient levels.The second experiment was conducted in a greenhouse. The corn seeds were soaked for 48 hours in Germitest paper with a solution containing sodium nitroprusside Na2[Fe (CN)5 NO]2H2O (0, 200 and 300 µM), sodium ferrocyanide Na4Fe(CN)6 (0, 200 and 300 µM) and deionized water. The seeds were sown in buckets with 15kg of soil containing copper concentrations CuSO4.5H2O (0, 60 and 200 mg kg-1) incubated for 50 days. The design consisted of randomized blocks, with 12 treatments and 4 repetitions, totaling 48 plants. The data were submitted to ANOVA, using the Tukey test at 5% using SISVAR. There was no effect of treatments on height, leaf area, number of leaves, observing an increase in stem diameter in copper treatments. There was no effect of treatments on the chlorophyll content measured by the SPAD index and gas exchange. Copper concentrations did not negatively affect the chlorophyll a fluorescence variables. The chlorophyll a fluorescence variables demonstrated the protective effect of nitric oxide present in sodium nitroprusside and cyanide present in sodium ferrocyanide in corn plants of the K9606VIP3 variety.