To roll or not to roll: nyctinastic behavior in young leaves of sacred lotus, Nelumbo nucifera

Abstract

Foliar nyctinasty refers to the daily rhythm in leaf orientation that occurs in evolutionarily diverse taxa. Traditionally, two mechanisms have been identified for the sleep movement of leaves, namely pulvinar and non-pulvinar. Here, we report upon some novel aspects of the nyctinastic behavior of leaves of the sacred lotus (Nelumbo nucifera Gaertn., Nelumbonaceae). We discovered that expanding leaves underwent daily oscillations in leaf orientation with a more vertical position at night, which is similar to many nyctinastic species. Additionally, however, the immature leaves were observed to exhibit a second type of nyctinasty that involved nocturnal rolling of leaf blades, which has not previously been reported. These two distinct mechanisms acted synergistically to make the young leaves more compact at night during a brief period (6 days) of leaf ontogenesis, during which petiole and blade showed substantial growth. We propose that the nyctinastic behavior of immature N. nucifera leaves is an adaptation that facilitates leaf growth at night by reducing mechanical interference with other leaves and plants.