Effects of Different Media and Water Level Treatments on the Growth and Development of the Hypocotyl Roots of Kandelia obovata
The mature hypocotyl of Kandelia obovata quickly establishes root growth within a few hours after being embedded in muddy sediments.However,if carried away by water drift,the hypocotyl will not sprout for a long time.This phenomenon suggests that the mechanical stimulation from the mud may induce root development.To investigate the effects of mechanical stimulation on the growth and development of K.obovata's hypocotyl roots,the hypocotyls from Wenzhou,Zhejiang,were subjected to different media(water,tissue paper,and river sand)and water levels(0 cm,4 cm,and 7 cm)to simulate various mechanical stimulation conditions.The study observed the development of hypocotyl roots,stem and leaf growth,and survival rate under different treatments.Additionally,the modified paraffin section technique was used to observe the anatomical structure characteristics of the roots at different developmental stages.The results showed that there were significant differences in the number of root points,rooting numbers,rooting rate,stem elongation and leaf numbers of hypocotyls under different treatments after 70 days of cultivation.The hypocytol roots exhibited the fastest development when cultivated in river sand at a depth of 7 cm,while those placed horizontally(0 cm)in water showed the slowest development.Furthermore,the lateral roots of K.obovata originate from the pericycle,and we can observe prominent biological macromolecules such as starch grains,tannins,and crystals in the root cells.The root structure of K.obovata was found to be unique,characterized by a central pith displaying a transitional structure between a typical root and stem at the anatomical level.In conclusion,this study confirmed that the germination of K.obovata's hypocotyl roots is influenced by the type of growth medium,and it was found that mechanical stimulation may promote the transformation of the growth and development of the roots from the root points to the lateral roots by observing the root anatomical structure.
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