Short-term Physiological Changes In Roots And Leaves Of Sugarcane Varieties Exposed To H2o2 In Root Medium.

The aim of this study was to evaluate the differential sensitivity of sugarcane genotypes to H2O2 in root medium. As a hypothesis, the drought tolerant genotype would be able to minimize the oxidative damage and maintain the water transport from roots to shoots, reducing the negative effects on photosynthesis. The sugarcane genotypes IACSP94-2094 (drought tolerant) and IACSP94-2101 (drought sensitive) were grown in a growth chamber and exposed to three levels of H2O2 in nutrient solution: control; 3mmolL(-1) and 80mmolL(-1). Leaf gas exchange, photochemical activity, root hydraulic conductance (Lr) and antioxidant metabolism in both roots and leaves were evaluated after 15min of treatment with H2O2. Although, root hydraulic conductance, stomatal aperture, apparent electron transport rate and instantaneous carboxylation efficiency have been reduced by H2O2 in both genotypes, IACSP94-2094 presented higher values of those variables as compared to IACSP94-2101. There was a significant genotypic variation in relation to the physiological responses of sugarcane to increasing H2O2 in root tissues, being root changes associated with modifications in plant shoots. IACSP94-2094 presented a root antioxidant system more effective against H2O2 in root medium, regardless H2O2 concentration. Under low H2O2 concentration, water transport and leaf gas exchange of IACSP94-2094 were less affected as compared to IACSP94-2101. Under high H2O2 concentration, the lower sensitivity of IACSP94-2094 was associated with increases in superoxide dismutase activity in roots and leaves and increases in catalase activity in roots. In conclusion, we propose a general model of sugarcane reaction to H2O2, linking root and shoot physiological responses.

Rootstocks induce contrasting photosynthetic responses of orange plants to low night temperature without affecting the antioxidant metabolism

Low temperatures negatively impact the metabolism of orange trees, and the extent of damage can be influenced by the rootstock. We evaluated the effects of low nocturnal temperatures on Valencia orange scions grafted on Rangpur lime or Swingle citrumelo rootstocks. We exposed six-month-old plants to night temperatures of 20ºC and 8ºC under controlled conditions. After decreasing the temperature to 8ºC, there were decreases in leaf CO2 assimilation, stomatal conductance, mesophyll conductance and CO2 concentration in the chloroplasts, in plant hydraulic conductivity and in the maximum electron transport rate driven ribulose-1,5-bisphosphate (RuBP) regeneration in plants grafted on both rootstocks. However, the effects of low night temperature were more severe in plants grafted on Rangpur rootstock, which also presented reduction in the maximum rate of RuBP carboxylation and in the maximum quantum efficiency of the PSII. In general, irreversible damage due to night chilling was found in the photosynthetic apparatus of plants grafted on Rangpur lime. Low night temperatures induced similar changes in the antioxidant metabolism, preventing oxidative damage in citrus leaves on both rootstocks. As photosynthesis is linked to plant growth, our findings indicate that the rootstock may improve the performance of citrus trees in environments with low night temperatures, with Swingle rootstock improving the photosynthetic acclimation in leaves of orange plants.