[Effects of exogenous growth regulators on plant elongation and carbohydrate consumption of rice seedlings under submergence.].

This experiment was conducted to evaluate the effects of exogenous regulators on plant elongation and carbohydrate consumption of rice seedlings under submergence. IR64 and IR64-Sub1 with submergence tolerance gene Sub1 were used. Twenty-day-old seedlings were sprayed with 1-aminocyclopropane-1-carboxylic acid (ACC), paclobutrazol (PB), gibberellic acid (GA), or distilled water (as control) two days prior to the submergence. Plants were completely submerged and water depth was maintained for 0, 4, 8, 12, 16 days respectively in tanks. The plants were allowed to recover for seven days after submergence. We investigated the effects of ACC, PB, and GA on the survival percentage, shoot elongation, chlorophyll degradation and recovery, as well as non-structure carbohydrate (NSC) consumption. The results showed that complete submergence resulted in significant elongation of plant shoots, rapid decline of SPAD, and quick depletion of soluble sugars in leaves. However, the initial NSC content in shoots of IR64-Sub1 was higher than that of IR64, and the consumption rate during submergence was lower, and the starch content in shoots maintained after submergence was higher. PB could significantly enhance rice seedling survival by reducing plant elongation, chlorophyll degradation and NSC consumption, and the effect of PB pretreatment on IR64-Sub1 was more pronounced. Conversely, GA increased plant elongation, leaf chlorophyll degradation and depletion of NSC, which resulted in the lowest recovery capability and survival percentage. However, the inhibition of GA on submergence tolerance of IR64-Sub1 was much poorer compared with IR64. Plant elongation treated by ACC was much lower than by GA. In conclusion, PB could restrain plant elongation effectively, retarding chlorophyll degradation, decelerating NSC consumption and retaining more NSC after de-submergence. The results suggested that PB could increase rapid recovery of rice after submergence stress which was of significance in alleviating flood and waterlogging injury in flash-flood-prone areas.