“Characterizing Tank Bromeliads: Origins and Influences of Tank Acidity”
Authors:John Dawson, Franklin Maharaj
Mentor:Gretchen North, Professor of Biology, Occidental College
Acidic environments can inhibit aquaporins, which are water channel proteins that are critical for transporting water into a plant. The tank water of tank bromeliads, a species of tropical epiphyte that captures water within a leaf rosette, is quite acidic. We have recorded pH as low as 3 in the field and within the greenhouse. We attempt to reconcile what could at first appear to be contradiction by studying tank bromeliad physiology and manipulating environmental conditions through experimentation. In doing so, we delineated the contributions of the apoplastic and symplastic pathways of water, where apoplastic transport is through the open portions within the plant and symplastic flow through the aquaporins of cells. Working with Aechmea nudicaulis, Guzmania lingulata, and Guzmania monostacia, we observed that pH in the symplast is higher than the apoplast by approximately 2 percent. In addition, we measured if pH varies as their tanks dry out, and found no significant relationship between pH and height of tank water. The mechanism through which the bromeliads account for tank acidity remains unclear. We now understand that the apoplastic and sympastic pH differs, but only slightly. Further experimentation is needed to correlate internal pH to external pH. The next step in our research is to employ a fluorescent stain capable of visualizing acidity at the cellular level. Using this dye, we will examine leaf sections, focusing on trichomes and other structures associated with water uptake to determine if acidity can be localized. Furthermore, We suspect that diurnal fluctuations in pH are not reflected in our dry-down results. Ongoing work using data-logging capable probes has proven to be more reliable. In addition to the experiments presented, we provide information regarding tank bromeliad physiology helpful for understanding our lab’s ongoing projects, with examples of microscopy demonstrating the apoplastic and symplastic pathways.