Elevated temperature further inhibited cottonseed protein synthesis under severe drought, but promoted cottonseed protein synthesis under mild drought

Cottonseed as the main by-product of cotton has important industrial utilization value due to the high protein content. Although previous studies found that high temperature or drought can affect cottonseed protein yield, reports on the detailed physiological mechanisms are limited. Moreover, the combination of the two stresses on cottonseed protein synthesis has received little attention. To address this, two cotton cultivars, Sumian 15 and PHY370WR, were exposed to two temperature regimes consisting of ambient temperature and elevated temperature (ambient temperature plus 2.5–2.7 °C), and three water treatments including soil relative water content (SRWC)(75 ± 5)% (optimum soil moisture), SRWC(60 ± 5)% (mild drought) and SRWC(45 ± 5)% (severe drought) were established under each temperature regime. Results showed that individual elevated temperature or drought had quite different effects on protein synthesis. Elevated temperature alone improved the kernel protein content by 3.90–8.53% for both cultivars compared with ambient temperature by increasing the maximum rate of protein accumulation (Vm). Moreover, elevated temperature alone enhanced amino acid synthesis by increasing the activity of glutamine synthetase (GS) and glutamate synthase (GOGAT) and the expression of GhGS and GhGOGAT, which was also good for increasing protein content. Mild drought slightly affected the protein accumulation during cottonseed kernel development. Although the duration of protein rapid accumulation increased, severe drought significantly decreased the Vm and the activity of GS and GOGAT as well as the expression of GhGS and GhGOGAT, finally leading to lower protein content. The interaction effect between the two stresses on protein synthesis was significant, since elevated temperature promoted protein synthesis under mild drought by increasing the Vm, the activity of GS and GOGAT, and the expression of GhGS and GhGOGAT; however, elevated temperature further reduced GS and GOGAT activities and GhGS and GhGOGAT expressions to inhibit protein synthesis under severe drought.