Cinnamic acid is a known allelochemical that affects seed germination and plant root growth and therefore influences several metabolic processes. In the present work, we evaluated its effects on growth, indole-3-acetic acid (IAA) oxidase and cinnamate 4-hydroxylase (C4H) activities and lignin monomer composition in soybean (Glycine max) roots. The results revealed that exogenously applied cinnamic acid inhibited root growth and increased IAA oxidase and C4H activities. The allelochemical increased the total lignin content, thus altering the sum and ratios of the p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) lignin monomers. When applied alone or with cinnamic acid, piperonylic acid (PIP, a quasi-irreversible inhibitor of C4H) reduced C4H activity, lignin and the H, G, S monomer content compared to the cinnamic acid treatment. Taken together, these results indicate that exogenously applied cinnamic acid can be channeled into the phenylpropanoid pathway via the C4H reaction, resulting in an increase in H lignin. In conjunction with enhanced IAA oxidase activity, these metabolic responses lead to the stiffening of the cell wall and are followed by a reduction in soybean root growth.
The changes in activities of soluble and cell wall-bound peroxidases and lignin contents in juglone-stressed soybean (Glycine max) seedlings and their relationships with root growth were investigated. Soybean seedlings (3-d-old) were cultivated in nutrient solution supplemented with 0.5 to 25 μM juglone for 24 h. Length and dry mass of roots decreased after 5 to 25 μM juglone treatments. Low juglone concentrations (≤ 1 μM) increased soluble peroxidase activity, while high concentrations (≥ 10 μM) inhibited activities of soluble and cell wall-bound peroxidases. Juglone (≤ 1 μM) did not affect lignin content but highly increased lignification after 5 to 25 μM treatments. Results indicate that lignification may be an important step in root growth reduction of juglone-stressed soybean.
L-3,4-Dihydroxyphenylalanine (L-DOPA) is an allelochemical released by roots of velvet bean (Mucuna pruriens) that affects the growth of several plant species. However, its mechanism of action is inconclusive. In this work, we compared the effects of L-DOPA (0.01-1.0 mmol L -1 ) and of aqueous extracts (300, 1200, and 3000 mg L -1 ) of velvet bean on growth and photosynthesis (gas exchange and chlorophyll a fluorescence) of soybean (Glycine max). Overall, the results showed that both L-DOPA and aqueous extracts of velvet bean reduced the growth, leaf area, photosynthetic rate (A), stomatal conductance (g s ), transpiration (E), and quantum yield of electron flow through photosystem II (PSII) in vivo (U F ). In addition, L-DOPA and aqueous extracts increased the internal CO 2 concentration (Ci) and the leaf wax and trichome density on the leaf surface, while the maximum quantum yield of PSII (F v /F m ) was not changed. These results suggest that the reduction of A should not be related exclusively to the stomatal closure, but also to limitations of the carbon metabolism, as indicated by the increase of Ci and decrease of U F . Briefly, we concluded that soybean growth inhibition by L-DOPA and aqueous extracts of velvet bean is due to the combination of damage in the root meristem and reduction in A.
Emergência e crescimento de alface (Lactuca sativa L.) submetida a substratos orgânicosAbstract: Organic agriculture stands out as a mode of production consisting of a sustainable system. One of the challenges of this method of cultivation is the production of sufficient quality food in sufficient quantities without compromising the environment. The objective of this study was to analyze the effect of organic substrates on germination and initial lettuce growth. The experiment was conducted in a completely randomized design with four treatments (substrates) and two replicates. The substrates were tested: Sibipiruna compound, commercial substrate, Sibipiruna compound with slurry and commercial slurry substrate. The manure was obtained exclusively from the decomposition of vegetables. The effect of the substrates was evaluated by percentage of germination, fresh mass, dry mass and radicular length. It was possible to consider that there was a significant difference between treatments. The seeds, when germinated in substrate of Sibipiruna with slurry, presented higher dry mass and radicle length. Regarding the fresh mass, the values obtained were higher when the slurry was added to both substrates. The slurry obtained from the decomposition of plants increased the germination and the initial growth of the seedlings.
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