Influence of copper on hormone content and selected morphological, physiological and biochemical parameters of hydroponically grown Zea mays plants

The impact of copper on hydroponically grown Zea mays L. has been characterized at the level of morphological changes and phytohormones. Maize plants were grown in Hoagland nutrient solution for 14 days with the addition of 50 µM or100 µM CuSO4. Both the height and the fresh weight of plants were reduced. The hormone analysis, performed by mass spectrometry, revealed elevation of abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA) and indole-3-acetic acid (IAA) in directly exposed roots, only content of active cytokinins (CKs) did not change. In leaves, the content of ABA, JA, IAA and CKs was increased, while the content SA did not change. The content of Ca, Mg, K and Zn decreased in leaves and roots with increasing concentration of Cu in nutrient medium. Leaf Cu concentration decreased at 100 µM CuSO4 in medium compared to the control (by 48%). Endogenous Cu content highly increased in roots exposed to 50 µM CuSO4 (by 690%), while only moderate elevation was observed at 100 µM CuSO4. The content of phenolic substances and flavonoids increased in both roots and leaves, while protein content increased in leaves, not changing in roots. In conclusion, the increase in content of ABA, SA, JA, CKs and IAA in response to elevated Cu concentration in the medium indicated their participation in maize responses to Cu stress. Negative correlation revealed between endogenous Cu and JA or CKs content in leaves suggested their role in reduction of Cu uptake.