Orientador: Paulo Alexandre Monteiro de Figueiredo / Resumo: Diante da iminente escassez de fósforo (P) para utilização agrícola, surge a necessidade de estudos voltados para o melhor entendimento de estratégias de suprimento deste elemento. Estudos recentes demonstram que a atividade hormonal potencializa processos em que o P é vital para ocorrência no metabolismo, destacando os análogos de Brassinoesteróides (BR) pela influência sobre o desenvolvimento vegetal. São escassos os estudos sobre a interação P e BR e sua aplicação em grandes culturas consumidoras de fósforo, como é o caso da cana-de-açúcar. Assim, o objetivo do presente estudo foi avaliar o efeito da aplicação de doses do análogo de BR 24-epibrassinolide (0; 0,5; 1,0; 2,0 mg. L-1), associado à presença ou ausência de fertilização fosfatada sobre os parâmetros de crescimento, fosfatase, micorrização e fotossíntese de plantas jovens de cana-de-açúcar. O experimento foi conduzido em casa de vegetação, em DBC com fatorial 4x2 com seis repetições. A aplicação dos BR proporcionou um incremento nos valores de massa seca radicular até o ponto máximo da curva de 1,27 mg.L-1. A interação P com BR incrementou respectivamente em 30% e 48% os valores de massa seca aérea nas doses 0,5 e 1,0 mg.L-1 do hormônio; e apresentou uma correlação de Pearson positiva das doses de BR com adição de P sobre essa variável. A presença de P estimulou todas as variáveis de crescimento da cana-de-açúcar. O BR desencadeou um pico significativo na atividade da enzima fosfatase ácida na dose de 1,0 mg. L-1 ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In view of the imminent shortage of phosphorus (P) for agricultural use, increase the need for studies aimed at better understanding the supply strategies of this element. Recent studies show that hormonal activity potentiates processes in which it is vital for the occurrence of metabolism, highlighting the analogues of Brassinoesterteroids (BR) for their influence on plant development. There are few studies on P and BR interaction and their application in large phosphorus-consuming crops, such as sugar cane. Thus, the objective of the present study was to evaluate the effect of applying doses of the 24-epibrassinolide dialogue (0; 0.5; 1.0; 2.0 mg. L-1), associated with the presence or absence of phosphate fertilization on the growth, phosphatase, mycorrhization and photosynthesis parameters of young sugarcane plants. The experiment was conducted in the greenhouse, in the DBC with a 4x2 factorial with six replications. The application of BR provides an increase in the values of root dry mass up to the maximum point of the curve of 1.27 mg. L-1. A P interaction with BR increases, respectively, by 30% and 48% the values of air dry mass at doses 0.5 and 1.0 mg.L-1 of the hormone; and showed a positive Pearson correlation of BR doses with the addition of P on this variable. The presence of P stimulates all sugar cane growth variables. BR triggered a significant peak of acid phosphatase enzyme activity at a dose of 1.0 mg. L-1 and did not affect root mycorrhizal colonization. The... (Complete abstract click electronic access below) / Mestre

Brassinosteroids (BRs) have been recognized to alleviate damages caused by drought stress and to enhance tolerance to water deficit. Soaking of maize kernels before the sowing in solution with different 24-epibrassinolide concentrations (especially the 10-8 M) had a positive effect on growth of plants before and after the stress period, although it did not affected relative water content and photosynthetic parameters. After the recovery under optimal conditions there were no differences among the treatments. When compared to spraying, soaking of maize kernels was not proved to have any advantages, though its positive effect on plants germination under water deficit conditions could be possible. Based on the results of the second season experiment it is not possible to deduce the role of exogenous BRs application (spraying with 24-epibrassinolide) or endogenous BRs biosynthesis (spraying with biosynthesis inhibitor - brassinazole) in maize plants subjected to water deficit. However, decrease in relative water content in contrast to chlorophylls content increase during the days following after drought stress onset in both cultivars (contrastive in drought sensitivity) challenges for further investigation of this problem. Understanding the role of BRs in plant drought tolerance and resistance is...

Brassinosteroids and ecdysteroid are naturally occuring chemical compounds in plants. The aim of this study was to show whether the application of exogenous steroids such as brassinosteroids (24-epibrassinolide, 28-homobrassinolide, 24-epicastasterone) and ecdysteroid (20-hydroxyecdysone) can affect the morphological parameters and primary photosyntetic processes of selected monocotyledons that was barley, wheat, maize and sorghum. Non-destructive method for measuring of fast kinetics of chlorophyll fluorescence in investigated plants was used. Analysis of primary photosynthetic processes was realized in five time periods from the application of exogenous steroids on the two different old leaves. The response to the treatment by exogenous steroid was different species by plant species. One week after the application of exogenous steroids plants showed differences in their morphological parameters but most of them were not signifficant. The most steroid-sensitive plant was wheat morphological parameters of were significantly different from untreated control plants. No change in maximum quantum yield of photosystem II to the application of exogenous steroid in plants of Sorghum bicolor L. was detected. In the other examined plant species changes in photosynthesis parameters were detected which...