Water deficit is considered the main abiotic stress that limits agricultural production worldwide. Brassinosteroids (BRs) are natural substances that play roles in plant tolerance against abiotic stresses, including water deficit. This research aims to determine whether BRs can mitigate the negative effects caused by water deficiency, revealing how BRs act and their possible contribution to increased tolerance of cowpea plants to water deficit. The experiment was a factorial design with the factors completely randomised, with two water conditions (control and water deficit) and three levels of brassinosteroids (0, 50 and 100 nM 24-epibrassinolide; EBR is an active BRs). Plants sprayed with 100 nM EBR under the water deficit presented significant increases in U PSII , q P and ETR compared with plants subjected to the water deficit without EBR. With respect to gas exchange, P N , E and g s exhibited significant reductions after water deficit, but application of 100 nM EBR caused increases in these variables of 96, 24 and 33%, respectively, compared to the water deficit ? 0 nM EBR treatment. To antioxidant enzymes, EBR resulted in increases in SOD, CAT, APX and POX, indicating that EBR acts on the antioxidant system, reducing cell damage. The water deficit caused significant reductions in Chl a, Chl b and total Chl, while plants sprayed with 100 nM EBR showed significant increases of 26, 58 and 33% in Chl a, Chl b and total Chl, respectively. This study revealed that EBR improves photosystem II efficiency, inducing increases in U PSII , q P and ETR. This substance also mitigated the negative effects on gas exchange and growth induced by the water deficit. Increases in SOD, CAT, APX and POX of plants treated with EBR indicate that this steroid clearly increased the tolerance to the water deficit, reducing reactive oxygen species, cell damage, and maintaining the photosynthetic pigments. Additionally, 100 nM EBR resulted in a better dose-response of cowpea plants exposed to the water deficit.

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RESUMO:O presente estudo tem por objetivo avaliar o efeito da omissão de macro e micronutrientes no crescimento de plantas de arroz em Latossolos de textura média e argilosa. O experimento foi conduzido na casa de vegetação da Universidade Federal Rural da Amazônia (UFRA), no município de Belém-PA. O delineamento experimental utilizado foi o inteiramente casualizado com 11 tratamentos e dois substratos com diferentes texturas (média e argilosa), com três repetições. Os tratamentos avaliados foram: T1) Controle; T2) Completo (Calagem + macronutrientes + B, Zn, Cu, Si, Ni); T3) NPK + B, Zn, Cu, Mn + Si (sem calagem); T4) Omissão de N; T5) Omissão de P; T6) Omissão de K; T7) Omissão de Ca; T8) Omissão de Mg; T9) Omissão de B, Zn, Cu, Si e Ni; T10) Omissão de Si; e T11) Omissão de Ni. As variáveis avaliadas foram: massa seca das folhas, massa seca dos colmos e massa seca das panículas. As omissões de K, P e N influenciaram diretamente na produção da cultura do arroz. A deficiência de nitrogênio e potássio afetou a produção da cultura, por restringir o crescimento inicial da planta. PALAVRAS-CHAVE: crescimento, nutrição de plantas, Oryza sativa. EFFECTS OF OMISSION NUTRIENTS IN COMPONENTS OF RICE PRODUCTIVITY IN NORTHEASTERN PARAENSE LATOSOLSABSTRACT: The present study aims to evaluate the effect of the omission of macro and micronutrients in the growth of rice plants in sandy loam Oxisols and clayey. The experiment was conducted in a greenhouse at the Federal Rural University of Amazonia (UFRA) in the city of Belem-PA. The experimental design was a completely randomized design with 11 treatments and two substrates with different textures (clayey and silty) with three replications. The treatments were: T1) Control; T2) Complete (Liming + macronutrients + B, Zn, Cu, Si, Ni); T3) NPK + B, Zn, Cu, Mn + Si (without lime); T4) N omission; T5) P omission; T6) K omission; T7) Ca omission; T8) Mg omission; T9) Omission of B, Zn, Cu, Si, Ni; T10) Si omission; and T11) Ni omission. The variables evaluated were: leaf dry weight, dry weight of stem and panicle dry mass. The omission of K, P and N directly influenced the production of rice. The deficiency of nitrogen and potassium affect crop production, by restricting the initial growth of the plant.