Brassinosteroids mitigate iron deficiency improving nutritional status and photochemical efficiency in Eucalyptus urophylla plants

Iron (Fe) is essential for the biosynthesis of constitutive proteins of chloroplasts, mitochondria and other organelles, and its deficiency triggers negative effects on photochemical efficiency and electron transport. Brassinosteroids are steroids that play beneficial roles related to chlorophyll fluorescence and plant nutrition. The aims of this research were to answer if epibrassinolide (EBR) can mitigate Fe deficiency in Eucalyptus urophylla plants and to evaluate the repercussions on nutritional status and physiological and biochemical behaviours. The experiment followed a completely randomized factorial design with two Fe conditions (Fe deficiency and control) and three levels of 24-epibrassinolide (0, 50 and 100nM EBR). EBR application in E. urophylla plants exposed to Fe deficiency increased Fe contents in root, stem and leaf. EBR reduced the negative effects of Fe deficiency on chlorophyll fluorescence and gas exchange parameters. Fe deficiency caused reductions in Chl a, Chl b and total Chl, while plants sprayed with 100nM EBR showed significant increases in these variables. Our results clearly reveal that EBR attenuated the negative effects caused by Fe deficiency on nutritional status and in the physiological and biochemical behaviours of E. urophylla plants, and these results were connected to increases in the contents of macronutrients and micronutrients, including Fe. EBR also improved the photochemical efficiency of PSII, gas exchange and photosynthetic pigments, inducing minor accumulations of oxidative compounds. Additionally, E. urophylla plants submitted to 100nM of EBR had better nutritional, biochemical, physiological and morphological results.