Long-Term Exposure to Combined Treatment of Elevated CO 2 and Salt Induces Iron Deficiency Responses in Porteresia coarctata

Plants with rising atmospheric carbon dioxide (CO₂) level in the environment may change their nutrient demands to sustain growth. The mechanisms concerning iron dynamics in plants under the interactive effect of salinity and elevated CO₂ are poorly understood. This study examines the effects of long-term as well as short-term growth at elevated CO₂ and salt on iron deficiency-associated molecular responses of Porteresia coarctata through analysing the transcript expression of iron deficiency-responsive genes in the leaf tissue. Plants were grown in hydroponic media at ambient or elevated atmospheric CO₂ (500 μl l^-1), with or without salt, and samples were analysed at three time points, on the 15th, 45th and 90th day. The semiquantitative RT-PCR analysis showed an induced expression of iron deficiency-responsive transcription factor PcIDEF1 and its putative targets OsIRO2-like gene, OsNAAT1-like gene, OsNAS1-like gene, OsYSL2- like gene and PcIRT1 at elevated CO₂ with NaCl. Furthermore, a positive correlation in gene expression was observed between PcIDEF1 and its putative targets in the 15th and 45th day samples. By contrast, in the 90th day sample, correlation in gene expression was less evident. Our findings suggest that the interactive effect of elevated CO₂ and NaCl can induce a set of molecular responses in P. coarctata for enhanced iron uptake and utilization, thereby reflecting an iron deficiency like stress under such conditions.