Glyphosate and nickel differently affect photosynthesis and ethylene in glyphosate-resistant soybean plants infected by Phakopsora pachyrhizi.

Nickel (Ni) and glyphosate (Gl) are able to reduce the symptoms of Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, in soybean. However, their combined effects on the energy balance and ethylene metabolism of soybean plants infected with this fungus has not been elucidated. Therefore, the effects of Ni, Gl, and the combination of Ni + Gl on ASR development, photosynthetic capacity, sugar concentrations, and ethylene concentrations in plants of a Gl-resistant cultivar, uninfected or infected with P. pachyrhizi, were investigated. Inoculated plants supplied with Ni had the highest foliar Ni concentration in all the treatments. Gl had a negative effect on the foliar Ni concentration in Ni-sprayed plants. The ASR severity was reduced in plants sprayed with Ni and Gl. Carotenoid and chlorophyll concentrations were higher in inoculated Ni, Gl, and Ni + Gl plants than in control plants. Based on the chlorophyll a fluorescence parameters, the photosynthetic apparatus of the control inoculated plants was damaged, and the least amount of energy was directed to the photochemistry process in these plants. The reduced capacity of the photosynthetic mechanism to capture light and use the energy absorbed by photosystem II in inoculated plants was reflected in their reduced capacity to process CO2 , as indicated by the high internal CO2 concentrations and low rates of net carbon assimilation. The low sugar concentrations in inoculated plants from the control treatment were linked to their reduced photosynthetic capacity due to the high ASR severity. In uninfected plants, the ethylene concentration was not affected by Ni or Gl, while the ethylene concentration decreased in inoculated plants; this decrease was more pronounced in plants from the control treatment than in treated inoculated plants. In conclusion, this study sheds light on the role played by both Ni and Gl in ASR control from a physiological perspective. Soybean plants exposed to Ni and Gl were able to maintain high ethylene concentrations and photosynthetic capacity during the P. pachyrhizi infection process; as a result, these plants consumed less of their reserves than inoculated plants not treated with Ni or Gl.

Pigment production and growth of Alternanthera plants cultured in vitro in the presence of tyrosine

The aim of the present study was to investigate the influence of tyrosine on the in vitro growth and the production of the betacyanin pigment in Alternanthera philoxeroides and A. tenella. Nodal segments were inoculated in MS medium containing different concentrations of tyrosine (0, 25, 50 and 75 μM), and the number of sprouts and buds, height, root length, fresh matter of shoots and roots and betacyanin content were evaluated. In A. philoxeroides , the highest production of betacyanin (51.30 mg 100 g-1 FM) was in the stems with the addition of approximately 45 μM tyrosine, while the increase in the leaves was proportional to the tyrosine concentration, and the best average was obtained with a tyrosine concentration of 75 μM (15.32 mg 100 g-1 FM). Higher tyrosine concentrations were deleterious to the growth of A. tenella plants, and a concentration of 75 μM was considered toxic. However, a tyrosine concentration of 50 μM benefitted betacyanin production, which reached 36.5 mg 100 g-1 FM in the plant shoots. These results showed the positive effect of tyrosine on the production of betacyanin in both species; however, application at high concentrations hampered the growth of Alternanthera plants.