Woad (Isatis tinctoria L.) is a member of the Brassicaceae family and was used in Neolithic times as a source of blue dye, used by warriors to paint their faces and scare their enemies. The plant, which is no longer commonly cultivated in Europe, is also a rich source of indole glucosinates, including glucobrassicon (GBS).
Researchers from the University of Bologna in Italy, led by Stefania Galletti, were aware of the body of research linking GBS and some of its by-products to anti-tumoural activity, particularly in breast cancer. However the lack of a sufficiently rich vegetable source has meant that to date it has not been possible to study the metabolic pathway of GBS in vivo, they said.
Galletti and team therefore set out to assess whether the GBS in woad leaves could be stimulated to such as level as to enable purification of the compound.
Their first experiments took place in a greenhouse. From one month after seeds of the Casolavalsenio variety were sewn, the researchers wounded the leaves using carborundum powder to cause abrasions or puncturing using a brass brush. Some evidence suggests that leaf injury, whether caused by insects, fungal infection or artificial puncturing, can affect the GBS level.
Another group of plants was spray with a solution of jasmonic acid (JA). All interventions were carried out both on plants fertilised with nitrogen and sulphur and unfertilised plants, and applications were repeated at two-day intervals.
Compared to the control, the group that received the JA showed a seven-fold increase in glucobrassicin compared to the untreated, unfertilised control and 2.5-fold increase compared to the fertilised control.
However, due to cost reasons, JA is not considered an appropriate method as it would be too uneconomical on a large scale. It was included in the design just to give a comparable framework for cheaper methods.
The mean GBS level of 29.5 micro-mol per gram -1, caused by a combination of fertiliser and physical treatments, was judged sufficient for purification.
In the field experiments, leaf puncturing was used instead of JA treatment and abrasions. Interestingly in this instance fertilisation with nitrogen and sulphur was not seen to have an impact on GBS levels.
But the punctured leaves reached a GBS level almost on a par with the fertilised control leaves in the greenhouse - 28.2 micro-mol per gram -1.
This led the researchers to conclude that "an enriched source of GBS is easily obtainable in the open field".