Magnesium Deficiency Results in Damage of Nitrogen and Carbon Cross-talk of Maize and Improvement by Cerium Addition

Magnesium (Mg) deficiency has been reported to affect plant photosynthesis and growth, and cerium (Ce) was considered to be able to improve plant growth. However, the mechanisms of Mg deficiency and Ce on plant growth remain poorly understood. The main aim of this work is to identify whether or not Mg deprivation affects the interdependent nitrogen and carbon assimilations in the maize leaves and whether or not Ce modulates the assimilations in the maize leaves under Mg deficiency. Maize plants were cultivated in Hoagland's solution. They were subjected to Mg deficiency and to cerium chloride administration in the Mg-present Hoagland's media and Mg-deficient Hoagland's media. After 2 weeks, we measured chlorophyll (Chl) a fluorescence and the activities of nitrate reductase (NR), sucrose-phosphate synthase (SPS), and phosphoenolpyruvate carboxylase (PEPCase) in metabolic checkpoints coordinating primary nitrogen and carbon assimilations in the maize leaves. The results showed that Mg deficiency significantly inhibited plant growth and decreased the activities of NR, SPS, and PEPCase and the synthesis of Chl and protein. Mg deprivation in maize also significantly decreased the oxygen evolution, electron transport, and efficiency of photochemical energy conversion by photosystem II (PSII). However, Ce addition may promote nitrogen and carbon assimilations, increase PSII activities, and improve maize growth under Mg deficiency. Moreover, our findings would help promote usage of Mg or Ce fertilizers in maize production.