Root growth and enzymes related to the lignification of maize seedlings exposed to the allelochemical L-DOPA.

L-3,4-Dihydroxyphenylalanine (L-DOPA) is a known allelochemical exuded from the roots of velvet bean (Mucuna pruriens L. Fabaceae). In the current work, we analyzed the effects of L-DOPA on the growth, the activities of phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), and peroxidase (POD), and the contents of phenylalanine, tyrosine, and lignin in maize (Zea mays) roots. Three-day-old seedlings were cultivated in nutrient solution with or without 0.1 to 2.0 mM L-DOPA in a growth chamber (25°C, light/dark photoperiod of 12/12, and photon flux density of 280 µ mol m(-2) s(-1)) for 24 h. The results revealed that the growth (length and weight) of the roots, the PAL, TAL, and soluble and cell wall-bound POD activities decreased, while phenylalanine, tyrosine, and lignin contents increased after L-DOPA exposure. Together, these findings showed the susceptibility of maize to L-DOPA. In brief, these results suggest that the inhibition of PAL and TAL can accumulate phenylalanine and tyrosine, which contribute to enhanced lignin deposition in the cell wall followed by a reduction of maize root growth.

The allelochemical L-DOPA increases melanin production and reduces reactive oxygen species in soybean roots.

The non-protein amino acid, L-3,4-dihydroxyphenylalanine (L-DOPA), is the main allelochemical released from the roots of velvetbean and affects seed germination and root growth of several plant species. In the work presented here, we evaluated, in soybean roots, the effects of L-DOPA on the following: polyphenol oxidase (PPO), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities; superoxide anion (O·-2), hydrogen peroxide (H(2)O(2)), and melanin contents; and lipid peroxidation. To this end, 3-day-old seedlings were cultivated in half-strength Hoagland's solution (pH 6.0), with or without 0.1 to 1.0 mM L-DOPA in a growth chamber (at 25°C, with a light/dark photoperiod of 12/12 hr and a photon flux density of 280 µmol m(-2) s(-1)) for 24 hr. The results showed that L-DOPA increased the PPO activity and, further, the melanin content. The activities of SOD and POD increased, but CAT activity decreased after the chemical exposure. The contents of reactive oxygen species (ROS), such as O·-2 and H(2)O(2), and the levels of lipid peroxidation significantly decreased under all concentrations of L-DOPA tested. These results suggest that L-DOPA was absorbed by the soybean roots and metabolized to melanin. It was concluded that the reduction in the O·-2 and H(2)O(2) contents and lipid peroxidation in soybean roots was due to the enhanced SOD and POD activities and thus a possible antioxidant role of L-DOPA.

Salt stress alters the cell wall polysaccharides and anatomy of coffee (Coffea arabica L.) leaf cells.

Coffea arabica is the most important agricultural commodity in the world, and salinity is a major threat to its sustainable irrigation. Coffee leaf polysaccharides from plants subjected to salt stress were extracted and the leaves visualized through optical and electron microscopy. Alterations were detected in the monosaccharide composition of the pectin and hemicelluloses, with increases in uronic acid in all fractions. Changes in the polysaccharides were confirmed by HPSEC and FTIR. Moreover, the monolignol content was increased in the final residue, which suggests increased lignin content. The cytoplasm was altered, and the chloroplasts appeared irregular in shape. The arrangement of the stroma lamellae was disordered, and no starch granules were present. It was concluded that leaves of C. arabica under salt stress showed alterations in cell wall polysaccharides, increased monolignol content and structural damage to the cells of the mesophyll.

Individual and interactive effects of phenolic acids on peroxidase and lipid peroxidation in soybean, Glycine max (L.) Merr. roots (Leguminosae-Faboidae) / Efeitos individuais e interativos de ácidos fenólicos sobre a peroxidase e peroxidação lipídica em raízes de soja, Glycine max (L.) Merr. (Leguminosae-Faboidae)

The purpose of the present work was to evaluate the individual and simultaneous effects of p-coumaric acid (p-CA) and p-hydroxybenzoic acid (p-HB) on soybean, Glycine max (L.) Merr. (Leguminosae-Faboidae) peroxidase (POD, EC 1.11.1.7), lipid peroxidation (LP) and root growth. Three-day-old seedlings were cultivated in nutrient solution containing p-CA or p-HB (0.5 and 1.0 mM) or equimolar mixtures for 24 hours. Individually, the two allelochemicals decreased root length (RL), root fresh weight (FW), root dry weight (DW), increased soluble POD and cell wall (CW)-bound POD but did not affect LP. The joint effects of these compounds were lower than the sum of the effects of each one tested separately. The results indicate that the mixtures of these allelochemicals can affect growth of soybean roots in an antagonistic manner.

O propósito do presente trabalho foi avaliar os efeitos individuais e simultâneos dos ácidos p-cumárico (p-CA) e p-hidroxibenzóico (p-HB) sobre a peroxidase (POD, EC 1.11.1.7) de soja Glycine max (L.) Merr. (Leguminosae-Faboidae), peroxidação lipídica (LP) e crescimento das raízes. Plântulas de três dias de desenvolvimento foram cultivadas, durante 24 horas, em solução nutritiva contendo p-CA ou p-HB (0,5 e 1,0 mM) ou misturas equimolares. Individualmente, os dois aleloquímicos diminuíram o comprimento das raízes (RL), a biomassa fresca das raízes (FW), a biomassa seca das raízes (DW), aumentaram a POD solúvel e POD ligada à parede celular mas não afetaram a LP. Os efeitos simultâneos desses compostos foram menores que a soma dos efeitos de cada um, testado separadamente. Os resultados indicam que as misturas desses aleloquímicos podem afetar o crescimento das raízes de soja de maneira antagônica.

Individual and interactive effects of phenolic acids on peroxidase and lipid peroxidation in soybean, Glycine max (L.) Merr. roots (Leguminosae-Faboidae) / Efeitos individuais e interativos de ácidos fenólicos sobre a peroxidase e peroxidação lipídica em raízes de soja, Glycine max (L.) Merr. (Leguminosae-Faboidae)

The purpose of the present work was to evaluate the individual and simultaneous effects of p-coumaric acid (p-CA) and p-hydroxybenzoic acid (p-HB) on soybean, Glycine max (L.) Merr. (Leguminosae-Faboidae) peroxidase (POD, EC 1.11.1.7), lipid peroxidation (LP) and root growth. Three-day-old seedlings were cultivated in nutrient solution containing p-CA or p-HB (0.5 and 1.0 mM) or equimolar mixtures for 24 hours. Individually, the two allelochemicals decreased root length (RL), root fresh weight (FW), root dry weight (DW), increased soluble POD and cell wall (CW)-bound POD but did not affect LP. The joint effects of these compounds were lower than the sum of the effects of each one tested separately. The results indicate that the mixtures of these allelochemicals can affect growth of soybean roots in an antagonistic manner.

O propósito do presente trabalho foi avaliar os efeitos individuais e simultâneos dos ácidos p-cumárico (p-CA) e p-hidroxibenzóico (p-HB) sobre a peroxidase (POD, EC 1.11.1.7) de soja Glycine max (L.) Merr. (Leguminosae-Faboidae), peroxidação lipídica (LP) e crescimento das raízes. Plântulas de três dias de desenvolvimento foram cultivadas, durante 24 horas, em solução nutritiva contendo p-CA ou p-HB (0,5 e 1,0 mM) ou misturas equimolares. Individualmente, os dois aleloquímicos diminuíram o comprimento das raízes (RL), a biomassa fresca das raízes (FW), a biomassa seca das raízes (DW), aumentaram a POD solúvel e POD ligada à parede celular mas não afetaram a LP. Os efeitos simultâneos desses compostos foram menores que a soma dos efeitos de cada um, testado separadamente. Os resultados indicam que as misturas desses aleloquímicos podem afetar o crescimento das raízes de soja de maneira antagônica.

Crescimento e lignificação de raízes de soja convencional e resistente ao glifosato, em baixa temperatura / Root growth and lignification of glyphosate susceptible and resistant soybean at low temperatures

O estresse causado pela baixa temperatura, dentre outras implicações, afeta o crescimento do vegetal assim como o seu metabolismo secundário. Pelo fato da soja RR apresentar variante enzimática de uma das principais vias do metabolismo secundário, ligada à síntese de lignina, pode apresentar comportamento diferenciado, sob baixa temperatura, se comparada com sua linhagem parental. O objetivo deste trabalho foi investigar possíveis diferenças no crescimento e nos conteúdos de lignina nas raízes de soja cultivar transgênica resistente ao glifosato e cultivar parental em resposta a redução de temperatura. Após três dias de germinação das sementes, as plântulas foram mantidas em solução nutritiva, a 10, 15, 20 e 25C (±2C), com fotoperíodo de 12 horas. Após 96 horas, foi avaliado o comprimento relativo da raiz primária, biomassa fresca e seca das raízes e os teores de lignina. Os resultados mostram que a baixa temperatura promoveu redução no crescimento das plântulas e raízes. Dentre as cultivares em estudo, a soja transgênica apresentou maior comprimento relativo, biomassas e teores de lignina.

Low temperature stress affects plant growth, including primary and secondary metabolism. Glyphosateresistant soybean contains a modified DNA, which encodes a different type of secondary metabolism enzyme related to lignin synthesis compared to conventional glyphosate-susceptible cultivars. Thus, this soybean cultivar might respond differently to low temperatures, compared to glyphosate-susceptible cultivars. This work aimed to investigate how decreasing temperatures influence the growth and lignin content of the glyphosate-resistant soybean compared to its susceptible parental cultivars. Three-day-old seedlings were cultivated in nutrient solution at 10, 15, 20, and 25C (±2C), using a 12-h photoperiod. After 96 h, taproot growth, fresh and dry biomass, and lignin levels were determined. The results indicate that lower temperatures decreased seedling and root growth in both types of cultivars; however, glyphosate-resistant soybean exhibited greater root length, biomass, and lignin content compared to the glyphosate-susceptible parental cultivar.