Of all the flowering plants in existence, 1% of the plants are more special, they do not rely on photosynthesis to synthesize organic matter, and there is no need to dig the roots deep into the soil to absorb nutrients, so how do they live for a plant?
As we all know, since we don't produce, we can only get it from other people, just like if you can't cook, you can choose to order takeout, but unlike these plants, we need to pay an equal amount of value of resources to obtain, and they are simply "taking", simply "white prostitution". Biologically, this behavior is called "parasitism", and plants that live from it are called "parasitic plants".
Sylvestris, a common parasitic plant
Their most common form of parasitism is through an invasive organ called a "sucker." This organ forms after detecting the suction inducible factor from the host plant, and then gradually penetrates into the stem or root of the host and connects with its vascular system. Through the pipette, parasitic plants can extract various substances from the host, such as water, proteins, nucleotides and even retrotranspositors, and sometimes the pathogens infected by the host will also be transmitted to the parasitic plants.
Cross-sectional optical microscopy photographs of the seeds and their host stems can be seen piercing into the host stem through a pipette. Penetrates the host tissue, the image source wellcome image
However, the unique unity characteristics of this parasitic plant are not homologous structures. Over the centuries, the sucker has evolved independently in flowering plants about 12 to 13 times, which is a typical case of "convergent evolution", meaning that different angiosperms have evolved similar characteristics at different times, and also explains why parasitic plants are now distributed in different plant families.
Although everyone is doing "parasitic" work, but from the life cycle, parasitic location and the amount of nutrients obtained from the host, parasitic plants also have different classifications, for example, can complete the life cycle independently of the host as facultative parasitism, can not be independent of the host to complete the life cycle is obligatory parasitism; attached to the host stem is called stem parasitism, attached to the root of the host is root parasitism; only from the host to obtain part of the nutrients is called semi-parasitism, and from the host to obtain all nutrients is total parasitism.
Shepara, an obligate stem semi-parasitic plant
Usually, parasitic plants will hit multiple characteristics, such as the well-known silkworm is an all-parasitic plant with an obligate stem, which will use a sucker to enter the host's stem to absorb nutrients, and at the same time cannot survive without the host. In all parasitic plants, there is a more extreme type of existence - endophytic plants, their entire life cycle is carried out in the tissues of the host plant, and most of their lives can be regarded as a root hyphae in the host body, until the time of flowering and seeding will not show their original appearance.
The world's largest flower is an endophytic plant
In vivo parasites are not unfamiliar to scientists, and even most people know about them, such as roundworms common in our bodies, but the "roundworms" in plants are unprecedented. Of the 4750 parasitic plants found so far, only more than 80 are endophytic plants, which are derived from the Pear family, Cytophoridae, Asteraceae and Raffles family (Macrophyllaceae), whose hosts, although different, all have a characteristic - they belong to wood parasitism and have a fixed parasitic range, especially the great king flower, which basically only stares at several species of the grape family Tetrastigma .10.
Four representatives of the inner parasitic plants: Great King Grass (left), Capsicum (middle), Tufted Grass (right), Bean Flower (Top)
What's even more amazing is that with the in-depth study of endophytic plants by scientists since the 21st century, it has been surprising to find that their life history has a large degree of similarity with some fungi. For example, after invading the host, the endophytic plant will camouflage from the molecular level, so as to maintain stealth growth without being perceived by the host, and at the same time show the characteristics of intermittent growth, which is very similar to the invasion method of some fungi.
On the other hand, both endophytic plants and fungi will show filamentous growth in the host tissue, with slight differences in that endophytic plants choose to grow in cell crevices, while endophytic fungi invade the interior of the host cell, that is, intracellular growth. But for host plants, they are like two hidden and ancient parallel world lines, both eating away at its vitality step by step.
Life cycle comparison of macrophylla plants with living vegetative fungi
Of course, this encroachment also comes at a cost, and in the transition to this extreme and "faceless" mode of life, they also lose some of their genes, for example, endophytic plants lose their photosynthesis genes, and the genes used to encode certain enzymes in fungi gradually disappear.
In addition to gene loss, the close connection between endophytic plants and fungi and their hosts has led to the accumulation of new genes, known as horizontal gene transfer (HGT) — a rare exchange of genetic material between non-mating organisms that was once common in fungi and bacteria and has now been shown to be particularly rampant in endophytic plants. For example, genes from cucumber and carrot relatives have appeared in plants of the family Macrophyllaceae, revealing the historical parasitism of species other than the Family Vividae.
As a result, HGTs are also considered "DNA fossils," and scientists may be able to use these clues to unravel extinction links between plants. Through them, the mystery of the evolution of the plant kingdom across infinite time, there are sure to be further amazing discoveries waiting!
Main reference sources:
https://pubmed.ncbi.nlm.nih.gov/33403666/
https://doi.org/10.1111/nph.17556
Wikipedia——Parasitic plant
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