So, well, we might start series as well, because we’re back to anti-sunlight adaptations.
Plants can’t move, or when they do, it’s still still-nature like more than those fasty animal races. Basic fact, but cruel reality.
We’d therefore expect them to have evolved various ways to get protected against sunburns, and here we go. There are plenty of reasons light is not as good as might be, and excess of photons is not trivially harmless (e.g. photoinhibition), but let’s speak about things not too biochemical in details today…
The target of interest is a rather common plant in temperate areas, therefore its nick Common Ivy (Hedera helix).
And here’s the thingie for today: this time, hypothesized light protection is not specialisation of pigments in the epiderm layer, but rather protection exsudates from the flower itself: nectar . As you might guess from a look at the above picture, nectar production in this species is not confined within special organs or structure but is directly going out of the plant at the very base of the flower. Secretion secrecy. Technically, the nectaries are located just above the ovary, which is thus said ‘inferior’ (well, more because it is below all the other reproductive organs), and are fairly simple: they consist in stomata surrounded by masses of conducting tissues (nectaries are sometimes made up this easy way anyway, even if this is clearly not their primary evolutionary function).
This species is litterally dropping nectar aside, and that’s why it’s so gross. Leaves are often icky sticky around the inflo down to the ground. But then, there’s the surprising bit about it: nectar composition changes along flowering season. Okay, nectaries themselves change and turn from greenish to unpalatable browny due to accumulation from accumulation of anthocyanins in subepidermal layers of their parenchyma. Very probably sunburn protection just like Ophrys did. But then, the content of nectar itself show an increase in light protective components such as β‐carotene. This study hypothesize a protective role of nectar against sun light for the ovary. Indeed, this is typically a place you’d like to protect against hazards, since that’s the place you put your offspring in.
But then, an increase in photosynthetic pigments was found in leaves at the end of flowering season, just along with the increase of β‐carotene in the nectar. I would bet that the other way such a nectar is benefiting the plant, since it drops onto the leaves, is also to protect these from rising sun exposition (Common Ivy is flowering in fall, when other plant species just lose their leaves or their lives). This would be especially true if they have greater photosynthetic activity (a consequence of increased access to light). Note that these two components of protection are not necessarily contradictory: a more efficient protection to both ovaries and leaves against harmful light would be two more reasons to be selected for…
Finally, evolution is definitely immoral. It teaches us that being gross can be good… :-)
- Maurizio Vezza et coll., “Ivy (Hedera helix L.) Flower Nectar and Nectary Ecophysiology,” International Journal of Plant Sciences 167, no. 3 (Mai 1, 2006): 519-527, doi:10.1086/501140.