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A model of drought was created on pigweed and the effects of drought stress on the activity of acid phosphatase and its protective enzymes were examined. The pot-cultured pigweeds were divided into 4 groups (ten plants per group) when they reached 6 leaves. (1) In the control group, the culture media contained 70 -85% of field moisture capacity, (2) In the second group, the mild drought stress group, the culture media contained 50 -60% of field moisture capacity, (3) The moderate drought stress group had a culture media that contained 40 -50% of field moisture capacity; (4) The severe drought stress group culture media contained 30 -40% of field moisture capacity. All through the process of the present study, the pigweed plants were cultured under natural conditions on the rooftop of the laboratory building; though transferred indoor in rainy days to avoid the influence of natural precipitation. The plants were sampled and detected every five days after the administration of drought stress. The results clearly demonstrated that the drought stress significantly enhanced the activity of acid phosphatase, membrane permeability and MDA contents; though the activity of acid phosphatase declined after a certain time of drought stress, the extent of membrane permeability and MDA contents still increased with the time. The membrane permeability and MDA contents were correlated with a correlation coefficient of 0.963, 0.971 and 0.939 under mild, moderate and severe drought stress, respectively. The activity of superoxide dismutase (SOD), peroxide dismutase (POD) and hydrogen peroxidase (CAT) was also enhanced with increase in the intensity of drought stress or the prolongation of drought stress at first and then decreased some time afterwards. It was concluded that drought stress enhanced the activity of acid phosphatase, membrane permeability and MDA in the pigweed plants, which was able to resist a certain drought stress by enhancing the activity of protective enzymes. However, excessive drought stress markedly affected the metabolic systems of enzyme and decreased the activity of enzyme.

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Core Ideas The dynamics of cellulose accumulation in colored cotton fiber increased in an S‐shaped curve, which was not asymmetric and could be simulated with Richards’ model (R2 > 0.999). Chlorophyll concentrations (estimated by SPAD values) for colored cotton were lower, compared to white cotton, and the degradation rate was relatively faster. This resulted in lower contents of soluble sugar in the boll shell and the subtending leaf. In the boll shell and the fiber, colored cotton had lower ATPase, sucrose invertase, and UDPG‐PPase activities. At 40 DPA, the SS activity for colored cotton was lower than for white cotton. Naturally colored cotton (Gossypium hirsutum L.) fibers are commercially valuable, but low fiber quality limits their use. This study investigates changes in enzymes’ activities and substance contents involved in carbohydrate synthesis to provide a theoretical basis for improving colored cotton fiber quality. Brown cotton Xiangcaimian 2, green cotton Wanmian 39, and white cotton Sumian 9 (control) were used. Fiber cellulose accumulation for Xiangcaimian 2 and Wanmian 39 were lower than the control. Cellulose content was simulated by Richards’ equation (R2 > 0.999) and follows an “S” pattern—initial slow accumulation 0–10 d post anthesis (DPA), then rapid 10–40 DPA, then slow 40–50 DPA. Maximum accumulation, the cumulative rate parameter, and maximum cumulative rate for cellulose of colored cotton were all lower for control. Further analysis showed SPAD chlorophyll meter readings, soluble sugar content, leaf sucrose invertase activity, adenosine triphosphatase, sucrose synthase, and uridine diphosphate glucose pyrophosphorylase (UDPG‐PPase) activities in colored fiber were lower than control. Results suggest insufficient nutrients for boll and fiber development, resulting in lower fiber quality and boll dry weight in colored cotton. Sucrose synthase and UDPG‐PPase activities in colored fiber were significantly correlated with fiber maturation (r = 0.884*, r = 0.914*) and fiber strength (r = 0.895*, r = 0.935*), indicating lower metabolite and enzyme activities in colored cotton reduced fiber quality. Therefore, it appears improving colored cotton fiber quality may require selection efforts to increase photosynthetic capacity in leaves and transportation capacity of carbohydrates in the boll to supply more nutrient during fiber development.

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