Physiological effects of exogenous auxin on regulating the leaf growth and delaying senescence of viviparous and non-viviparous waterlilies

To investigate the effects of different concentrations of exogenous IAA on the growth and senescence of leaves in water lily, tropical viviparous Nymphaea 'Black Beauty' and non-viviparous Nymphaea 'Colorata' were used as materials, different concentrations of IAA and an equal amount of water (CK) were evenly sprayed on the upper and lower surfaces of leaves of the same age and size, respectively. It is aimed to provide a theoretical basis for delaying the leaf senescence of water lily and promoting robust seedlings and breeding of epiphyllous buds. The results showed that all IAA concentrations treatment increased the leaf length and width, leaf area, and had a promoting effect on the accumulation of chlorophyll content in the viviparous water lily N. 'Black Beauty'. Among them, a better effect was 200 μ mol/L IAA treatment. On the contrary, a lower IAA concentration (50 μ mol/L) was more beneficial for the leaf growth and chlorophyll synthesis of non-viviparous N. 'Colorata'. With the increase in IAA concentration, the content of soluble protein, starch, and soluble sugar in both viviparous and non-viviparous leaves increased and then decreased. At the same time, the reducing sugar content continued to decline, indicating that there were significant differences between different IAA concentrations. In addition, the SOD and POD activities of two types of water lilies reached their maximum at an IAA concentration of 200 μ mol/L, but the POD activity of non-viviparous N. 'Colorata' leaf treated with different IAA concentrations did not show significant differences at different stages. Combined with correlation analysis and principal component analysis, there is a highly significant positive correlation between the morphology, chlorophyll content, and soluble sugar content of viviparous leaves, reflecting the photosynthetic and osmotic regulation abilities of leaves during the growth and development of epiphyllous buds. However, there is also an important synergistic effect between different indicators of non-viviparous leaves, indicating that the leaf development of both types of water lilies was regulated by IAA, and appropriate hormone concentrations can affect leaf morphology, and physiology and delay leaf senescence.