Cotton Genomics and Genetics 2025, Vol.16, No.3, 126-136 http://cropscipublisher.com/index.php/cgg 129 signal of drought (Wang et al., 2016). These proteins are like "sensors" that go out in the first place. However, not all reactions occur at the same time. For example, in the roots, when drought just begins, the proteins involved in the synthesis of cutin, suberin, and wax have begun to increase in expression (Xiao et al., 2020). Their role is more like building a line of defense to help cells stabilize their structure while sending the signal that "we are short of water." Looking further down, some proteins are specifically responsible for "messaging" and "regulation." For example, some proteins involved in phosphorylation and post-translational modification are activated during drought and regulate the intensity and direction of signal transduction pathways (Koh et al., 2015; Ghatak et al., 2017). Simply put, this entire reaction chain, from "discovering problems" to "mobilizing responses", is linked together by these proteins. 4.2 Antioxidant and defense proteins Drought can easily cause plants to produce a large amount of reactive oxygen species (ROS), which can damage cells. In order to reduce damage, plants increase the content of some antioxidant and defense proteins. These proteins include various antioxidant enzymes, heat shock proteins, and some enzymes that can participate in detoxification (Wang et al., 2016). In drought-resistant cotton varieties, the content of these proteins is usually higher, which helps to enhance stress resistance (Yahoueian et al., 2021). The increased activity of these proteins is related to root growth, water retention, and survival rate under drought conditions (Zeng et al., 2019). 4.3 Metabolism and structural proteins Not all proteins are silent during drought. Some metabolic and structural proteins become more active, but this "activity" varies in different cotton varieties. Proteins related to sugar, energy, fatty acid, and amino acid metabolism are often regulated under drought conditions. Plants do this to save energy and to regulate water balance in their bodies (Michaletti et al., 2018). However, not all cotton copes so well. Drought-sensitive varieties often have decreased sugar metabolism and nitrogen metabolism-related proteins, and photosynthesis is also slowed down. In contrast, drought-tolerant varieties are more "stable", and the expression of many key proteins has not only not decreased, but sometimes even increased, which allows them to continue to grow (Subramani et al., 2024). In addition, structural proteins cannot be ignored. In particular, proteins involved in cell wall construction and adjustment will also change significantly during drought (Ren et al., 2022). They are a bit like "scaffolds", which stabilize cell morphology on the one hand and prevent rapid water loss on the other. In the final analysis, these proteins are actually helping plants "save water". 5 Key Proteomic Findings in Salt Stress Response 5.1 Ion transport and homeostasis proteins When there is too much salt, the first thing plants feel is often not "salty", but that the ions inside and outside the cells are not right. In the study of cotton, a special type of protein frequently "goes online", such as TIPs on the vacuole membrane and PIPs on the plasma membrane, which become more active (Li et al., 2015). These proteins help water and ions to transport back and forth between cell membranes, just like valves that regulate flow, maintaining electrolyte balance in cells. However, the flow of water and ions alone is not enough. Cotton also needs some proteins that can regulate the sodium-potassium ratio - especially those involved in the calcium signaling pathway, which are often involved. This type of protein can isolate or expel excess sodium ions, which can be regarded as a "clearance mechanism" for cells to fight salt poisoning (Passamani et al., 2017). After all, these seemingly inconspicuous membrane transport proteins are the key role in plants "keeping their ground" under salt stress. 5.2 Osmoprotectant biosynthesis enzymes If cells want to avoid "dehydration" in a high-salt environment, it is not enough to control ions alone. They will also synthesize some "talismans" by themselves - osmotic protectants. These small molecules are not large, but they play a significant role. They can protect protein structures from deformation and stabilize cell membranes (Yan et al., 2005). Studies have found that when cotton faces salt stress, some enzymes related to carbohydrate and amino acid metabolism begin to express more strongly. These enzymes help synthesize small molecules such as proline and soluble sugars. They do not directly "fight salt", but can regulate the turgor pressure of cells so that
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