Victoria cruziana blooms at night. On the first night, these flowers are typically white, while on the following night they are slightly pink. We would like to explain what causes this color change. Initial results and a description of the genome sequence of Victoria cruziana are already described in a manuscript on bioRxiv (Nowak, Harder, Meckoni et al., 2024).
For various plant species, it has already been observed that flower color changes after pollination by insects. It is therefore conceivable that this is also the case with Victoria. To investigate this, we shield some flowers from insects before they open. If these flowers later bloom exclusively white, it would be an indication of the importance of insects for the color change. If, on the other hand, the color of the flowers changes to pink, insects are apparently not crucial for the color change.
Additionally, we are investigating which insects are present near the flowers. These observations are then compared with other parts of the greenhouse. This allows us to determine whether insects preferentially visit the flowers. This could indicate a targeted attraction of the insects.
Red plant pigments, the anthocyanins, are often produced in response to light exposure. A good example is apple varieties, whose apples are particularly strongly colored on the sun-exposed side. It is therefore also possible that Victoria reacts to light exposure and that the flowers gradually change color due to the accumulation of red pigments when exposed to sunlight at the water's surface. To investigate this, we protect young flowers with opaque material before they reach the water's surface. If light is responsible for the color change, these flowers should not change color but remain white.
In addition to the intensity of sunlight, the length of the day might also play a role. To check this effect, we observe the color changes of Victoria flowers throughout the year. If long days are necessary for the color change, the flowers should show a weaker coloration during the summer as the days get shorter and the nights get longer.
It is known that red anthocyanins can be produced by plants in response to temperature changes. This usually occurs with a significant reduction in temperature when the plant is under cold stress. Since the water temperature is kept constant and the temperature in the Victoria greenhouse also hardly changes, we currently do not assume that temperature has an influence.
Anthocyanins are often formed in old leaves, which explains the red coloration of leaves in some plant species in autumn. It is assumed that anthocyanins prolong the lifespan of the leaves, allowing more important nutrients to be transferred from the leaves to other parts of the plant before the leaf falls off. Anthocyanins thus serve a function in reducing stress effects. Therefore, it is possible that the formation of anthocyanins in the flower reduces stress at a molecular level and thereby prolongs the lifespan of the flowers. If this is the cause of anthocyanin formation, the process would be determined by flower development. In this case, external factors should not have a significant impact on the coloration of the flower.
Through sequencing, we have already decoded the genome of Victoria cruziana. Therefore, we know nearly all the genes present in this plant. We have also compared the activity of genes between white and pink-colored flowers. Now, we are investigating the cause of differences in the activity of certain genes between the white and pink-colored flowers. The possible causes described above do not exclude each other. It is entirely plausible that various factors of varying significance may influence the intensity of the color change from white to pink.
We look forward to being contacted via email and are happy to answer further questions or discuss creative explanations for the color change of the Victoria flowers: Boas Pucker.