Responses Of Sweet Sorghum To External Regulation At Germination And Early Seedling Stage Under Saline Conditions

Sweet sorghum is an important energy crop. It is usually grown on marginal lands that can be prone to having medium and high salt concentrations. However, germination rate is often low and seedling establishment often poor when the soils contain high salt concentrations. The studies on the responses of sweet sorghum to external regulation at germination and early seedling stage under saline conditions are of great practical importance to solve the problems of low germination rate and poor seedling establishment. The seeds of two genetically different sweet sorghum varieties (Zaoshu1and Chuntian2) were used to investigate the effects of salinity on seed water uptake and germination. Then, Chuntian2, which was proved to be more salt tolerant, was selected to investigate the effects of the amendment of foreign substances on seed uptake, germination, the growth and physiological parameters of sweet sorghum under saline conditions. The main results were as follows.1. Water uptake and germination of sweet sorghum seeds as influenced by salinityEfficient water uptake is essential for germination. Salinity, however, is a very important environmental stress limiting germination. The seeds of two sweet sorghum varieties (Zaoshu1and Chuntian2) with significant difference in salt tolerance were cultured in water solutions at different salinity levels (0,50and100mM NaCl) to investigate the effects of salinity on seed water uptake and germination. Salinity produced significant effects on water uptake and germination of sweet sorghum seeds. Compared with Zaoshu1, Chuntian2was more salt tolerant. Compared with0mM NaCl, seeds treated with50mM NaCl had higher water uptake percentage, water uptake rate, germination percentage, and germination index. At the salinity level of50mM NaCl, the length of radical and germ of Chuntian2was increased and the length of radical and germ of Zaoshu1was decreased as compared with0mM NaCl salinity level. At the salinity level of100mM NaCl, however, water uptake, germination percentage, germination index, the growth of radical and germ was significantly inhibited as compared with0mM NaCl salinity level. Water absorption and germination of sweet sorghum seeds have a role in promoting under suitable low salinity level, while high salinity level can inhibit the water absorption and germination of sweet sorghum seeds. 2. Effects of external regulation on water uptake and germination of sweet sorghum seeds under saline conditionsThe seeds of Chuntian2were cultured in water solutions at different NaCl levels (0,50, and100mM) and different external levels of GA3(0,144,288, and576μM GA3) and KNO3(0,6,11, and16mM KNO3) to investigate the effects of salinity and external regulation on seed water uptake and germination. As compared with the treatment of0μM GA3at0mM NaCl, the amendment of144or288μM GA3at50mM NaCl had significant improvement on water uptake percentage, water uptake rate, germination percentage, germination index, and the length of germ and radical. At100mM NaCl level, the treatment with576μM GA3had significant negative effects on seeds water uptake percentage, water uptake rate, germination percentage, and germination index, the growth of germ and radical. In conclusion, at low salinity level, external GA3of144μM and288μM can improve seeds water absorption and germination. However the high salinity will inhibit the seeds absorption and germination, and with the increasing level of external GA3, the germination time will delay. The treatment with50mM NaCl and6mM KNO3had certain positive effects on water absorption and germination.3. Effects of salinity and external regulation on growth and physiology of sweet sorghum seedlingsSeedling growth could be affected under salt stress conditions. Reasonable amendment of exogenous hormones could be an effective way to combat the negative effects of salt stress. A study was done to investigate the effects of salinity level (0,0.3, and0.6g NaCl·kg-1dry seedling media) and GA3concentration (0,45,90, and180μg GA3·kg-1dry seedling media) on growth characteristics of sweet sorghum seedlings. With the increase of salinity level in the seedling media, emergence percentage, plant height, leaf length and width, root length, plant dry weight, and SPAD readings were significantly decreased. With the increase of GA3level, emergence percentage, plant height, root length, plant dry weight and SPAD value followed an upward trend first and then a downward trend. With the increase of GA3concentration, leaf length was increased and leaf width was reduced. The amendment of GA3at45and90μg GA3·kg-1dry seedling media generally produced good amending effects on seedling growth.Salt stress and GA3amendment affected physiological parameters at early seedling stage. The result shows that with the increased salinity level, the soluble protein content and the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) followed an upward trend first and then a downward trend. At the salinity level of0.3kg NaCl·kg-1dry seedling media, the soluble protein content and the activity of catalase (CAT). peroxidase (POD), and superoxide dismutase (SOD) was at the highest level as compared with the salinity levels of0and0.6kg NaCl·kg-1dry seedling media. The content of MAD was increased as the increased salinity level. With increased amendment level of GA3, soluble protein content, CAT, POD and SOD activity followed an upward trend first and then a downward trend. The content of MAD was increased as the increased GA3level. The amendment of GA3at45and90μg GA3·kg-1dry seedling media generally produced good amending effects on increasing the content of soluble protein and the activity of CAT, SOD, and POD of sweet sorghum seedlings at early seedling stage.