Leaf nutrient homeostasis and maintenance of photosynthesis integrity contribute to adaptation of the pea mutant SGECd<sup>t</sup> to cadmium

Abstract

Cadmium (Cd) is a highly toxic and widespread soil pollutant, which negatively affects various aspects of plant growth and physiology. Here, the role of photosynthesis in response to Cd was investigated in the Cd-tolerant pea (Pisum sativum L.) mutant SGECdt. The wild type SGE and the mutant SGECdt were grown in a hydroponic solution supplemented with 1, 3, or 4 µM CdCl2 for 12 d. Root and shoot biomasses of the Cd-treated SGECdt were significantly higher than of SGE. Cadmium had little effect on the quantum yield of photosystem II (φPSII) and chlorophyll content of intact leaves of both pea genotypes. However, when leaf slices were taken from Cd-exposed plants and incubated with high Cd concentrations, the SGECdt mutant showed 1.5-2 times higher φPSII values than SGE, with genotypic differences maximal at 0.1 and 1 mM CdCl2. In contrast, when leaf slices were taken from plants previously unexposed to Cd, both pea genotypes exhibited similar φPSII values. Cadmium content in leaves and mesophyll protoplasts of Cd-treated SGECdt were about 2-3 times higher than in SGE ones. The mutant leaves and mesophyll protoplasts had also higher Ca, Mg, Mn, and Zn content. Thus, SGECdt acclimated to Cd during growth in the Cd-supplemented nutrient solution by developing a molecular mechanism related to photosynthetic integrity. A higher foliar nutrient content likely allows enhanced photosynthesis by counteracting the damage of leaves caused by Cd.