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.

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.