Figure 3.

Role of MTs in response to abiotic stresses. Under salt stress, high osmolality and Na⁺/H⁺ imbalance detected by plant receptors, which activate ABA and Ca²⁺-driven pathways that further regulate the SOS system to maintain Na⁺/H⁺ balance in plants cells. Under drought stress, osmotic stress increases the amount of ABA, different ions and osmolytes in order to maintain osmotic balance and triggers various molecular and metabolic pathways including Ca²⁺, which regulates stomatal openings. PYR/PYL receptors activate the AKS system, which regulates K⁺/H⁺ ion flux across the cell membrane. Various ABA-dependent and ABA-independent pathways regulate the stress-related transcriptional factor (TF) pathways. Under heat stress, ABC transporters and overproduction of ROS activate defense mechanisms in the presence of Ca²⁺, and then both CDPKs and ROS regulate the MAPK system, which upregulates heat shock factors including HSRs, HSPs, WRKYs and DREBs. These pathways maintain ROS and antioxidant (CAT) balance. Under cold stress, COLD1, Ca²⁺ and ABA act as stress receptors and trigger CDPK-driven systems and other TFs systems. Under heavy metal stress, after signal transduction, various hormones, miRNA and Ca²⁺ activate the MAPKs system in order to regulate TFs, which maintain heavy metals/toxic agents and anti-oxidants. In addition to the text, for further details about the model, readers can also refer to [85,124,125,126,127,128,129].