Figure legends
FIGURE 1 (a) Partial view of Exp. 1 and Exp. 2 with the drought and heat stress, with a detail on how the system looked like from inside the enclosures. (b) Partial view of Exp.3 with the drought and heat stress, with a detail on how the system looked like from inside the enclosures. (c) The stage exposed to drought, heat and combined drought and heat stress for each treatment. (d) The growth conditions in Exp.1. (e) Processing of maize grains cultivation in vitro in Exp. 2 and Exp. 3. CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 2 (a) Time courses of average soil water potential and temperature in Exp. 1 and Exp. 2. (b) Time courses of soil water content and temperature in Exp. 3. CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 3 Schematic diagram of logistic curve (black color), where W is the kernel weight (mg), K is the final kernel weight (mg), t is the time after pollination. a, b are coefficients determined by regression. Phase I: The slow-increase period (d); Phase Ⅱ: The fast-increase period (d); Phase Ⅲ: The slight-increase period (d).
FIGURE 4 Effects of drought, heat and combined drought and heat stress around flowering on kernel numbers and 1000-kernels weight at physiological maturity. (a) The kernel numbers in Exp. 1. (b) The 1000-kernels weight in Exp.1. (c) The 1000-kernels weight in Exp. 2. Values with the same letter are not significantly different atP <0.05 within the same parameter of each hybrid. Bars denote the standard error of the mean (n=4). CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 5 Effect of drought, heat and combined drought and heat stress around flowering on grain dry matter accumulation. (a) The changes of 1000-kernels weight in superior and inferior grains in Exp. 1. (b) The 1000-kernels weight in superior and inferior grains in Exp. 2. Values with the same letter are not significantly different atP <0.05 within the same parameter of each hybrid. Bars denote the standard error of the mean (n=4). CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 6 Effect of drought, heat and combined drought and heat stress around flowering on leaf area, SPAD and net photosynthesis (Pn; μmol CO2 m-2 s-1). (a) The changes of leaf area in Exp.1. (b) The changes of SPAD in Exp.1. (c) The changes of net photosynthesis in Exp.1. (d) The relationship between 1000-kernel weight and leaf area reduction at maturity. (e) The relationship between 1000-kernel weight and SPAD reduction at maturity. (f) The relationship between 1000-kernel weight and net photosynthesis reduction at maturity. Values with the same letter are not significantly different at P<0.05 within the same parameter of each hybrid. Bars denote the standard error of the mean (n=4). CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 7 The soluble sugar content and starch content in superior and inferior grains under drought, heat and combined drought and heat stress around flowering. (a) The changes of soluble sugar in Exp. 3. (b) The changes of starch content in Exp. 3. Values with the same letter are not significantly different at P<0.05 within the same parameter of each hybrid. Bars denote the standard error of the mean (n=4). CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 8 Enzymes activity related to starch synthesis in superior grains and inferior grains under drought, heat and combined drought and heat stress around flowering in Exp. 3. (a) The sucrose invertase activity in superior and inferior grains. (b) The sucrose synthase activity in superior and inferior grains. (c) The ADP Glc pyrophosphorylase activity in superior and inferior grains. (d) The starch synthase activity in superior and inferior grains. Values with the same letter are not significantly different atP <0.05 within the same parameter of each hybrid. Bars denote the standard error of the mean (n=4). CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 9 Hormone content in superior grains and inferior grains under drought, heat and combined drought and heat stress around flowering in Exp. 3. (a) The ZR content in superior and inferior grains. (b) The IAA content in superior and inferior grains. (c) The GA3 content in superior and inferior grains. (d) The ABA content in superior and inferior grains. Values with the same letter are not significantly different at P<0.05 within the same parameter of each hybrid. Bars denote the standard error of the mean (n=4). CK, control treatment. DS, drought stress treatment. HS, heat stress treatment. DHS, combined drought and heat stress treatment.
FIGURE 10 A schematic diagram of how drought, heat and combined drought and heat stress around flowering reduced kernel weigh. CK: control treatment; DS: drought stress treatment; HS: heat stress treatment; DHS: combined drought and heat stress treatment. Solid line indicated superior grain. Dotted line represented the inferior grain. The three lines from left to right represent DS, HS and DHS stress. The line thickness represents the influence degree of stresses.