JIA-2018-09

1994 ZHANG Xiang et al. Journal of Integrative Agriculture 2018, 17(9): 1991–1998 3. Results 3.1. Boll Cry1Ac protein concentration in response to high temperatures at peak boll development stage The boll insecticidal protein contents decreased with increased temperature after 24 h treatment for SK-1 and SK-3 both in 2011 and 2012 (Fig. 1). However, the effects varied under different high temperature treatments. Greater decreases were detected when the temperature was above 36°C. In 2011, the insecticidal protein contents decreased by 46.2% for SK-1 and by 6.7% for SK-3 when the temperature increased from 36 to 38°C, and decreased by 35.0% for SK-1 and by 58.9% for SK-3 when temperature increased from 38 to 40°C, respectively. Similar results were found in 2012. 3.2. Boll shell Cry1Ac protein levels in response to DH/NN stress In contrast to the results in 2011 and 2012 (Fig. 1), there were no significant temperature effects on Cry1Ac protein concentration after exposure to the DH/NN stress for 4 d (96 h) in 2012 and 2013. After the DH/NN stress treatment applied for 7 d, significant temperature effects on the boll shell Cry1Ac protein content level were detected, with DH/NN treatment decreasing Cry1Ac protein content by 19.1 and 17.5% for SK-1 and by 15.3 and 13.7% for SK-3 in 2012 and 2013, respectively, compared to the control (Table 1). After 10 d under the stress treatment, Cry1Ac protein concentration levels declined by 44.5 and 44.7% for SK-1 and by 33.2 and 32.7% for SK-3 in 2012 and 2013, respectively. These results indicated that Cry1Ac protein concentrations in Bt cotton boll shells began to decline markedly after only 4 d of exposure to the stress treatment. As the stress time increased, we observed a greater decline in Cry1Ac protein content. We also observed a significant difference in Cry1Ac protein content levels in response to the DH/NN stress between the two cultivars. The decline in protein concentration levels was greater for SK-1 than that for SK-3. Table 1 Effect of the 38/27°C day/night temperature regime stress on the expression of Cry1Ac protein in the boll shell of Bt cotton at boll stage (ng g –1 fresh weight (FW)) Stress time (d) SK-1 1) SK-3 1) Treatment CK1 Treatment CK2 2012 2013 2012 2013 2012 2013 2012 2013 0 330.8 a 315.6 a 330.8 a 315.6 a 373.0 a 362.1 a 373.0 a 362.1 a 4 325.1 a 302.3 a 334.6 a 318.5 a 369.5 a 355.6 a 378.0 a 360.3 a 7 268.9 b 260.2 b 332.2 a 320.3 a 321.1 b 312.3 b 378.9 a 370.1 a 10 183.7 c 174.5 c 330.8 a 321.1 a 250.6 c 241.3 c 375.3 a 358.9 a Significance ( P ) <0.001 <0.001 0.890 0.883 <0.001 <0.001 0.908 0.912 1) CK1 and CK2 are the controls for Sikang 1 (SK-1, a conventional cultivar) and Sikang 3 (SK-3, a hybrid cultivar), respectively. The values are means ( n =3). Means followed by the same letter within each column are not significantly different according to LSD ( P =0.05). a ab b c d a ab bc c d 50 100 150 200 250 300 350 400 32 34 36 38 40 SK-1 SK-3 Bt insecticidal proein content (ng g –1 FW) 2011 a ab b c d a ab bc c d 50 100 150 200 250 300 32 34 36 38 40 Temperature (°C) Temperature (°C) Bt insecticidal proein content (ng g –1 FW) 2012 Fig. 1 The boll shell insecticidal protein contents of cotton cultivars exposed to 32, 34, 36, 38, and 40°C for 24 h in 2011 and 2012. Sikang 1 (SK-1, a conventional cultivar) and Sikang 3 (SK-3, a hybrid cultivar) represent the names of the two Bt cultivars. Vertical bars represent SE of the mean ( n =3). The same letter within each cultivar represents non-significant difference according to Duncan multiple range tests ( P =0.05).