Effect of CaCl2 priming on starch decomposition during sorghum germination under salt stress
Salt stress reduced the starch decomposition rate and sugar accumulation during sorghum germination, alleviated by CaCl2 priming (Fig. 4A, B). When compared to NPN treatment, no significant difference was seen in the starch content at 0 h and 6 h of germination under salt stress. In comparison, a significant increase was seen at 12 h (16.97%), 24 h (27.15%), and 48 h (44.5%). Compared with NPS treatment, HPS treatment significantly decreased the starch content at 0 h (12.06%), 6 h (5.92%), 12 h (7.86%), and 24 h (14.59%), but no significant difference was seen at 48 h. Compared with NPS treatment, the CaPS treatment significantly reduced starch content at 6 h (9.6%), 12 h (12.87%), 24 h (19.57%), and 48 h (27.36%) but not at 0 h (Fig. 4A).
Salt stress significantly decreased the sugar content at 12 h (37.55%), 24 h (39.83%), and 48 h (44.56%) when compared with NPN treatment, while no significant difference was seen at 0 h and 6 h. However, HPS and CaPS treatments significantly increased the sugar content at 0 h (17.94% and 26.27%), 6 h (32.21% and 92.01%, respectively), 12 h (12.05% and 40.21%, respectively), 24 h (20.88% and 37.10%, respectively), and 48 h (23.63% and 44.48%, respectively) compared to NPS treatment (Fig. 4B).
Effects of CaCl2 priming on glucose metabolism enzyme activities during sorghum germination under salt stress
Salt stress significantly decreased the pyruvate kinase activity at 6 h (25.69%), 12 h (30.72%), 24 h (38.85%), and 48 h (36.51%) compared to NPN treatment (Fig. 5A). In contrast, the HPS and CaPS treatments significantly increased the pyruvate kinase activity at 0 h (94.19% and 106.12%, respectively), 6 h (84% and 100.72%, respectively), 12 h (46.92% and 65.17%, respectively), 24 h (24.18% and 54.35%, respectively), and 48 h (30.07% and 42.74%, respectively) compared to NPS treatment.
While no significant difference in phosphofructokinase activity was seen under salt stress at 0 h and 6 h, a significant decrease was seen at 12 h (31.91%), 24 h (31.61%), and 48 h (26%) (Fig. 5B). Compared to NPS treatment, HPS treatment significantly increased phosphofructokinase activity at 0 h (101.26%), 6 h (101.62%), and 24 h (29.41%), while there was no significant difference at 12 h and 48 h. CaPS treatment significantly increased phosphofructokinase activity at 0 h (139.21%), 6 h (142.6%), 12 h (42.91%), 24 h (43.07%), and 48 h (32.71%) compared with NPS treatment.
Salt stress significantly reduced hexokinase activity at 6 h (66.68%), 12 h (52.34%), 24 h (46.73%), and 48 h (39.23%) compared to NPN treatment (Fig. 5C). Compared with NPS treatment, HPS and CaPS treatments significantly increased hexokinase activity at 0 h (514.48% and 457.84%, respectively), 6 h (179.31% and 282.17%, respectively), 12 h (67.13% and 93.66%, respectively), and 24 h (46.41% and 65.19%, respectively), while at 48 h only CaPS treatment significantly increased (41.41%) the hexokinase activity.
Under salt stress, α -ketoglutarate dehydrogenase activity was significantly decreased at 12 h (41.64%), 24 h (50.15%), and 48 h (58.89%) (Fig. 5D). In comparison, no significant difference was seen at 6 h (Fig. 5). Compared with NPS treatment, HPS and CaPS treatments significantly increased α-ketoglutarate dehydrogenase activity at 0 h (172.34% and 174.52%, respectively), 6 h, (78.91% and 127.74%, respectively), 12 h (33.66% and 65.99%, respectively), and 48 h (30.36% and 95.22%, respectively) but not at 24 h. The α-ketoglutarate dehydrogenase activity at all germination times was comparable for HPS and CaPS treatments, but at 48 h, it was 49.75% higher for the CaPS treatment.
NPS treatment significantly reduced the 6-phosphoglucose dehydrogenase activity at 6 h (41.96%), 12 h (46.63%), 24 h (59.53%), and 48 h (62.02%) of sorghum germination compared to NPN treatment, (Fig. 5E). Compared with NPS treatment, HPS treatment significantly increased 6-phosphoglucose dehydrogenase activity at 0 h, 6 h, 12 h, 24 h, and 48 h by 627.12%, 49.10%, 49.65%, 44.53%, and 24.57%, respectively. Similarly, CaPS treatment significantly increased 6-phosphate glucose dehydrogenase activity at 0 h (1000%), 6 h (136.74%), 12 h (76.74), 24 h (101.50%), and 48 h (107.19%). Compared to HPS treatment, CaPS treatment significantly increased the 6-phosphate glucose dehydrogenase activity at 0 h, 6 h, 24 h, and 48 h by 48.02%, 58.78%, 39.42%, and 66.33%, respectively, but not at 12 h.
Effects of CaCl 2 priming on gene expression of sugar-metabolizing enzymes in sorghum germination under salt stress
Salt stress significantly inhibited the expression of phosphofructokinase (PFK2, PFK6), 6-phosphoglucose dehydrogenase (G6PDH1, G6PDH2), and α-ketoglutarate dehydrogenase (KGDH1, KGDH2) genes in germinating sorghum seeds, by 64.52%, 58.60%, 73.86%, 65.45%, 45.46%, 52.11%, respectively (Fig. 6A-F). In contrast, under salt stress, the expression of PFK2, G6PDH1, KGDH1, and KGDH2 genes were significantly up-regulated by water priming, by 43.01%, 86.37%, 46.03%, and 78.13%, respectively. CaCl2 priming significantly increased the expression of PFK2, PFK6, G6PDH1, G6PDH2, KGDH1, and KGDH2 genes in seeds under salt stress by 97.20%, 84.41%, 110.00%, 72.31%, 79.89%, and 65.09%, respectively.