Manganese Deficiency Suppresses Growth and Photosynthetic Processes but Causes an Increase in the Expression of Photosynthetic Genes in Scots Pine Seedlings

Manganese deficiency is a serious plant nutritional disorder, resulting in the loss of crop productivity in many parts of the world. Despite the progress made in the study of angiosperms, the demand for Mn in gymnosperms and the physiological responses to Mn deficiency remain unexplored. We studied the influence of Mn deficiency for 24 weeks on Pinus sylvestris L. seedling growth, ion homeostasis, pigment contents, lipid peroxidation, chlorophyll fluorescence indices and the transcript levels of photosynthetic genes and genes involved in chlorophyll biosynthesis. It was shown that Mn-deficient plants demonstrated suppressed growth when the Mn content in the needles decreased below 0.34 µmol/g DW. The contents of photosynthetic pigments decreased when the Mn content in the needles reached 0.10 µmol/g DW. Mn deficiency per se did not lead to a decrease in the nutrient content in the organs of seedlings. Photoinhibition of PSII was observed in Mn-deficient plants, although this was not accompanied by the development of oxidative stress. Mn-deficient plants had an increased transcript abundance of genes (psbO, psbP, psbQ, psbA and psbC), encoding proteins directly associated with the Mn cluster also as other proteins involved in photosynthesis, whose activities do not depend on Mn directly. Furthermore, the transcript levels of the genes encoding the large subunit of Rubisco, light-dependent NADPH-protochlorophyllide oxidoreductase and subunits of light-independent protochlorophyllide reductase were also increased in Mn-deficient plants.