Protein-Level Assessment of Aquaporins in Alfalfa Under Salt Stress

Aquaporins (AQPs) are integral membrane proteins that facilitate water and solute transport, playing crucial roles in stress adaptation in both plants and animals. In mammals, aquaglyceroporins such as AQP3 and AQP7 are well characterized, whereas their plant counterparts remain less understood, particularly at the protein level. In this study, alfalfa (Medicago sativa) was grown in Hoagland’s medium supplemented with 0, 50, 100, 200, or 400 mM NaCl for 21 days. Protein extracts were analyzed by SDS-PAGE and Western blotting using antibodies against human - mouse - rat AQP3 and mouse - human AQP7. Two distinct cross-reactive protein bands were identified. Their expression was weak at 200 mM NaCl but strongly induced under severe salt stress at 400 mM NaCl. These results suggest a threshold-dependent regulation of aquaporin-like proteins in alfalfa. Unlike transcriptomic analyses, our protein-level approach highlights stress-specific expression dynamics and points to potential functional similarities with mammalian aquaglyceroporins, particularly in osmolyte transport and osmotic adjustment. This study underscores the importance of direct protein analysis for understanding stress physiology and provides new insights into salt stress adaptation mechanisms in forage legumes.