Proteomic profiles and leaf antioxidative metabolism in cacao juvenile plants subjected to Pb and Pb+Fe doses and to soil flooding

Abstract

Under natural conditions, plants can be affected by several types of abiotic stresses, such as flooding and the accumulation of toxic metals in the soil. Pb is a non-essential metallic element for plants and is highly toxic for living beings. Fe, as an essential micronutrient, is involved in fundamental plant processes, such as photosynthesis. The main objective of this work was to evaluate the proteomic profiles and the activity of key enzymes of leaf antioxidant metabolism in juvenile plants of the CCN 51 cacao genotype, grown in flooding soil and subjected to a dose of Pb and to different equimolar doses of Pb+Fe. Doses of Pb and Pb+Fe did not interfere with the predawn leaf water potential (ΨWL) of plants, but soil flooding was a key factor for the decline of ΨWL. There was a differential accumulation of Pb and Fe in the roots and leaves, both in flooded soil and non-flooded. Most of Fe and Pb uptake by the root system predominantly accumulated in the roots and only a small fraction was translocated to the shoot, regardless of the water content in the soil. Flooding and the variation of Pb+Fe doses in the soil did not change the transport of Pb to the plant shoot since there were no major alterations in the levels of Pb in the leaves. Leaf enzymatic antioxidant metabolism was altered, mainly by flooding, in relation to Pb or Pb+Fe doses applied in soil. The time of exposure of plants to stressor factors was important for the changes in the activity of key enzymes of the leaf antioxidant metabolism. Soil flooding, with doses of 2 mmol Pb kg−1 soil + 0.5 mmol Fe kg−1 soil, at 6 and 24 h after treatment application, had a greater influence on ΨWL, antioxidant enzymatic metabolism and leaf proteome, and affected proteins related to photosynthesis, DNA, antioxidative system and carbohydrate metabolism, whose abundance was overexpressed or repressed compared to the control.