Stomata actively regulate internal aeration of the sacred lotus Nelumbo nucifera

• Published in: Plant, cell and environment cell and environment, 2014-02, Vol.37 (2), p.402-413
• Main Authors: MATTHEWS, PHILIP G. D., SEYMOUR, ROGER S.
• Format: Article
• Language: English
• Subjects: Air Pressure; Biological and medical sciences; Carbon Dioxide - metabolism; Cell Respiration; convective airflow; flooding; Fundamental and applied biological sciences. Psychology; gas canal; Models, Biological; Nelumbo - anatomy & histology; Nelumbo - metabolism; Nelumbo - physiology; Periodicity; Photosynthesis; Plant Leaves - anatomy & histology; Plant Leaves - metabolism; Plant Leaves - physiology; Plant Stomata - physiology; pressurization
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12163

The sacred lotus Nelumbo nucifera (Gaertn.) possesses a complex system of gas canals that channel pressurized air from its leaves, down through its petioles and rhizomes, before venting this air back to the atmosphere through large stomata found in the centre of every lotus leaf. These central plate stomata (CPS) lie over a gas canal junction that connects with two‐thirds of the gas canals within the leaf blade and with the larger of two discrete pairs of gas canals within the petiole that join with those in the rhizome. It is hypothesized that the lotus actively regulates the pressure, direction and rate of airflow within its gas canals by opening and closing these stomata. Impression casting the CPS reveal that they are open in the morning, close at midday and reopen in the afternoon. The periodic closure of the CPS during the day coincides with a temporary reversal in airflow direction within the petiolar gas canals. Experiments show that the conductance of the CPS decreases in response to increasing light level. This behaviour ventilates the rhizome and possibly directs benthic CO2 towards photosynthesis in the leaves. These results demonstrate a novel function for stomata: the active regulation of convective airflow. The sacred lotus Nelumbo nucifera possesses a complex system of gas canals that channel pressurised air from its leaves, down through its petioles and rhizomes, before venting this air back to the atmosphere through large stomata found in the centre of every lotus leaf. We show that these central plate stomata have evolved to perform a unique function: actively regulating the direction and rate of convective airflow through the gas canal system. Our experiments show that these stomata act as exhaust valves, closing fully by midday in response to increasing light levels before reopening during the afternoon.