‘Water balloons’ uncovered

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‘Water balloons’ uncovered

The leaves of quinoa and ice plants are covered with fine hairs. Long was believed that these hairs help plants coping during water shortage and salt stress. But now Danish researchers show in Current Biology that this is not true: they protect against herbivory insects.

Quinoa and ice plants are salt tolerant and can cope well with water shortages. For a long time it was assumed that the hairs that are covering these plants, are of the same type as the hairs that protect plants of another family against water and salt stress. At the same time more and more indications suggest that these hairs have a different function in quinoa and ice plants. The Danish researchers decided to investigate.

The first thing they did was comparing quinoa plants with and without hairs. They noticed that quinoa plants without hairs survived a period without water better than plants with hairs. The hairs actually made the quinoa plants less able to cope with water stress. This it turned out was also the case for ice plants. Moreover, in case of salt stress the hairless plants were no worse off than the hairy plants.

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They do have a protecting function

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The question remained, what is the reason for these hairs? The researchers received a hint during a trips infestation. They observed that the hairless plants survived less well than the hairy plants. During a closer analysis, they observed that the hairs prevent trips feeding from young leaves. In absence of hairs, the trips drained the leaves before they even had a chance to fully unfold. The hairs of the hairy plants appeared to be spaced so closely together that the sucking mouth of the trips could not reach the surface of the leaf.

Subsequently the researchers studied if the hairs in addition to a physical barrier also created a chemical barrier. For this the researchers analysed the presence of toxic compounds in the hairs. One of them, oxalic acid, appeared to be present in high amounts. High enough, it turned out to kill spider mites. Moreover it also had a negative influence on the growth of bigger herbivory insects.

The hairs of quinoa and ice plants do have a protecting function. Only not the one we thought it to be. They protect against herbivory insects, and not salt or water stress. The study also shows once again that assumptions need to be taken with a grain of salt till proven.

Literature

Max W. Moog, Xiuyan Yang, Amalie K. Bendtsen, Lin Dong, Christoph Crocoll, Tomohiro Imamura, Masashi Mori, John C. Cushman, Merijn R. Kant, Michael Palmgren. Epidermal bladder cells as a herbivore defense mechanism. Current Biology, 2023; 33 (21): 4662 DOI: 10.1016/j.cub.2023.09.063

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