Dr Bronwyn Lowe (University of Otago) describes her use of scanning electron microscopy (SEM) to explore harakeke leaves. Bronwyn found that different harakeke varieties have differently patterned waxes on the leaf surface. She also explored the distribution of fibre (muka) in the leaves of different varieties.
Point of interest: The fibre that Bronwyn describes is used by Māori weavers to make clothing, mats and other items. Traditionally, weavers strip the fibre from the harakeke leaf using a shell.
DR BRONWYN LOWE
The great thing about the SEM is that you see things in three dimensions, and you can see three-dimensional shapes on the surface of whatever you’re looking at, or if you have been able to prepare a cross-section, you can see the structure inside the sample as well. So with the harakeke, the things we were looking for there was mostly to do with the leaf surfaces and the kind of waxes that grow on the surface of a leaf.
If you look at a harakeke bush, you can see there’s often a white bloom on the surface of the leaf, and that bloom is actually a wax, and the gorgeous thing about the wax is that it actually grows in all kinds of beautiful crystals, and those different shapes are distinctive to different varieties of harakeke, so not only to different species of plant but also within one species, different plants grow different shaped waxes on the surface of their leaf.
So some of the varieties we’re looking at had little blocky sort of shapes, and others had shapes that looked like gorgeous little leaves on the surface. Also we used the SEM to look at cross-sections so we can see how the fibre is distributed in the harakeke leaf. And if you look at a harakeke leaf, you can see it on the surface as little ridges, so those little ridges are where the veins are running along the leaf, and those veins are protected by these little fibre bundles, and that’s the fibre that the weavers are extracting from the leaf.
Now if you’ve got a harakeke variety that you can extract good fibre from, what you’ll find is there’ll be quite a large bundle of fibre around each vein, whereas a plant that doesn't have as much fibre or the fibre is weaker, those fibre bundles are smaller or more spread apart. So what we were looking for was those kind of subtle differences between the leaves from different varieties in the sizes and shapes and distribution of the fibre, and so when we did the cross-sections through the leaves, we could see that.