2.1 Experimental design
The
experiment was conducted in the greenhouse at Hebei Agricultural
University (38°85’N, 115°30’E) in Baoding Hebei Province, China. Two
cotton varieties, the drought-tolerant type ”Guoxin 02” (DT type) and
the drought-sensitive type ”Ji 228” (DS type), were selected for this
study (Guo et al., 2022). After
sterilization with 75% ethanol, the seeds were rinsed 5-8 times
repeatedly with distilled water, then soaked in distilled water for 8
hours and placed on a towel to germinate. The radicle was transferred to
a hydroponic pot at 2 cm. Once the cotyledons were fully expanded, the
samples were transferred to an incubator (485*355*245 mm) for continued
hydroponic growth in the Hoagland nutrient solution. Each incubator
contained 24 seedlings and 50 L of Hoagland’s nutrient solution.
Cotton plants were grown to the two true leaf stages, at which point
water treatments were initiated. The treatments included no-stress (NS,
0% PEG6000) and drought stress (DS, 8% PEG6000) for 15 days, and each
treatment had 24 replications. The pH of the nutrient solution was
adjusted to 6.0 ± 0.1, and the solution was replaced every 3 days. The
growth parameters included an average daily temperature of approximately
(28 ± 2) / (25 ± 2) °C (day/night), a photoperiod of 14/10 hours of
light/darkness, relative humidity of 40%-50%, and a light intensity of
600 µM. Oxygen was supplied twice daily, with each session lasting 30
minutes.