Abstract:

Sweet sorghum （Sorghum bicolor） is a vital forage crop， and cutting effectively improves its production potential. To investigate the regeneration of sweet sorghum and the distribution of carbohydrates after cutting， sweet sorghum plants were grown hydroponically for 42 days until they reached about 100 cm height in an artificially controlled climate chamber， and were then cut to a stubble height of 8 cm. Plant height， fresh weight， number of leaves， growth rate， photosynthesis， root architecture， and structural and non-structural carbohydrate contents were determined before cutting and at 7， 21， and 35 days after cutting. It was found that plant height， number of leaves， and stems and leaves fresh weight of sweet sorghum quickly recovered after cutting， reaching their pre-cutting values by 35 days after cutting. The fresh weight of roots， total root length， root surface area， and number of root tips were significantly greater at 35 days after cutting than before cutting. The growth rate at 7 days after cutting was remarkably enhanced， but the growth rates at 21 and 35 days after cutting were lower than that before cutting. The net photosynthesis rate （A） and intercellular carbon dioxide concentration （C_i） of leaves were not significantly affected by cutting， whereas the transpiration rate （E） and stomatal conductance （G_s） were significantly increased at 21 days after cutting. The sucrose and glucose contents in stems and the sucrose contents in leaves of sweet sorghum were significantly decreased at 7 days after cutting， and then increased at 21 days after cutting. By contrast， starch contents in leaves were significantly increased at 7 days after cutting， and then decreased at 21 days after cutting. The soluble carbohydrate contents of sweet sorghum at 35 days after cutting had recovered to pre-cutting levels. The sucrose contents in roots and starch contents in stems were higher at 35 days after cutting than before cutting. Cutting did not significantly affect the hemicellulose and lignin contents in roots， stems， and leaves of sweet sorghum， but resulted in significantly decreased cellulose contents in roots， stems， and leaves at 7 and 21 days after cutting. The cellulose contents in stems and leaves recovered to pre-cutting levels by 35 days after cutting. Taken together， cutting sweet sorghum promotes starch accumulation in leaves， followed by an increase of sucrose accumulation in leaves and roots， and simultaneously decreases cellulose contents. Through these dynamic regulatory mechanism， cutting stimulates growth rate to ensure regeneration of shoots， and then restores root growth and development， thereby synergistically promoting the rapid regeneration of sweet sorghum.

Key words: sweet sorghum, cutting, regeneration, carbohydrate