Just how much of the trunk of a moringa consists of living cells is an important key to understanding how they can resist drought so well. Looking at the swollen trunk of one of the fat bottle tree moringas, like M. drouhardii or M. stenopetala, it’s easy to think that all that water storing trunk tissue is drawn upon to keep the plant going through drought. But the only way really to tell is by seeing whether the cells are alive and functioning or not.
This is exactly what UNAM master’s student Matiss Castorena’s project involves. He is carrying out a comparative study to see how the amount of living tissue in trunks varies across species. To complement this study, he is looking in detail at how living tissue is distributed within a single large M. stenopetala tree. He has taken cores all around and the length of two trunks of the tree. He then takes these cores and incubates them in a solution of triphenyl tetrazolium chloride (TTC). The enzymes involved in metabolism reduce TTC to triphenyl formazan (TPF). The neat thing about this is that TTC is soluble but TPF is not only insoluble but is a deep red color. This means that very active living cells become markedly red, sluggishly metabolically active cells various shades of pink, and dead cells don’t change color at all. This means that along a core sample from the outside to the inside of the trunk, Matiss can map the distribution of metabolically active cells. This is important because only the living areas are involved in conducting water, and in storing and mobilizing photosynthetic products, both factors that are very important in plant functional aspects like supporting the leaves and resisting drought.
What Matiss is finding is very interesting. It turns out that very little of the trunk is alive. Moringas seem to be just a thin layer of live wood overlain on a central core of dead or very metabolically sluggish cells. So those fat trunks, that would seem to be giant water tanks, might not be serving in storage as much as we think. Soon Matiss will be sampling our large Moringa drouhardii from our sap flow experiment, and this will help us to understand the data that those sensors gather. Keep up the good work Matiss!