A less penetrable skin
Sap-sucking insects like white flies and aphids are a disaster for plants. With their needle-like mouth do these insects look for the perfect place on the leaf to suck dry. The problem is not so much that these bugs are consuming a little plant sap and nutrients, but more what they give in return. Sap-sucking insects often give the plant viruses or bacteria. Not really the gift plants hope for.
It is therefore not surprising that the plant does everything to make those sap-sucking insects so difficult as possible. They cover their leaves in a minefield. They make sure their leaves taste bad. And they add some toxic compounds, just for good measure. But maybe the easiest and effective way is to make it difficult for the insects to pierce the leaves.
Insects have more trouble to find a good piercing location when plants have a sturdier wax layer on their leaves. That was exactly what a new study of Chinese researchers showed in the paper: “A GDSL lipase confers resistance to piercing-sucking insects in tobacco by strengthening leaf cuticle”.
In this study the researchers analyse hoe the gene CRF increases insect resistance. They zoom on to CRF as this gene is activated in tobacco plants in response to a white fly infestation. The first thing that the researchers did was analysing the effects of the absence of this gene. It appears that white flies on those plants are quicker finding a good spot to pierce the leaf. But that was not the only effect. The insects also lay more eggs on those CRF missing plants. In contrast, insects on plants that made more CRF had more difficulty with finding a good spot to pierce the leaf.
Sturdier wax layer
In first instance the researchers thought that this maybe had something to do with the defence response of the plant. But it turned out that the defence response was just as active in CRF missing plants than in control plants.
The next step of the researchers was to study the wax layer on the leaves. In control plants this layer was nicely equally smooth. But in CRF missing plants the wax layer was more uneven and less smooth. The researchers also treated the plant with toluidine blue, a dye that is taken up by the cells. But only when the dye can reach the cell membrane. In control plants this hardly was the case. But in plants without CRF toluidine blue penetrated the cell. CRF turned out to influence the penetrability of the wax layer.
The last thing the researchers did was to analyse the composition of the wax layer. Thereby it turned out that plants that produce more CRF proteins, have more dioic acid in their wax layer. It appears that the amount of dioic acid is a measure for how easy the insects find a good place to pierce the leaf. But for how exactly CRF is influencing the production of dioic acid, for that more research is needed.
Literature
Chen, N., Xiong, Y.-D., Zou, C., Zhong, Y.-W., Du, H., Chi, Y.-J., Zhao, C., Liu, S.-S. and Wang, X.-W. (2025), A GDSL lipase confers resistance to piercing-sucking insects in tobacco by strengthening leaf cuticle. Plant J, 123: e70440. https://doi.org/10.1111/tpj.70440
Plant en Zo 