Starch granules of the sugar-pathway were eliminated under the stress of PEG-drought compared with Soil-drought

As an important cash crop, cotton is often affected by Soil-drought stress. Soil-drought is a common abiotic stress that seriously affects the growth and development of crops. Since soil moisture is not easy to control and prolonged treatment is required to cause water stress, polyethylene glycol (PEG) is often used to simulate drought stress and cause dehydration in plants. However, whether there is a difference in the effects of these two types of drought stresses on cotton remains unclear. In this study, cotton seedlings with the same water potential under two stresses were used as research materials, and the differences in molecular mechanisms of cotton resistance to the different drought stresses were explored through physiological and biochemical detection, chloroplast ultrastructure observations and transcriptomic sequencing. The results showed that both Soil-drought and PEG-drought can cause water stress effects on cotton seedlings, causing them to dehydrate and wilt. The contents of soluble protein (SP), Proline (Pro), and malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) showed similar changes under the two stresses. However, by observing the chloroplast ultrastructure, we found that starch accumulated in chloroplasts under Soil-drought, but was not obvious under PEG-drought. Stress-induced differentially expressed genes (DEGs) under both types of drought showed similar changes in Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, but Soil-drought induced more DEGs. The differential expression of sugar-related (sugar synthesis, sugar metabolism, sugar transport, etc.) genes in cotton seedlings under Soil-drought stress was higher than that under PEG-drought. In the case of consistent dehydration, there are clear differences in the sugar-pathway when cotton experiences Soil-drought and PEG-drought. PEG drought can simulate Soil drought in terms of the physiological effects of dehydration on cotton, but it is not applicable in terms of the effects of drought stress on the sugar pathway. This study enables us to better understand the response of cotton to different drought stress and provides a certain research basis for exploring cotton resistance to drought stress.