Jargon busters

Demystifying plant science jargon

Jargon is a useful shortcut for experts, but it leaves novices and outsiders in the dark. To do something about it I explain in the weekly Plant & Zo roundup one plant science jargon at a time. Here they are all collected and ordered alphabetically. If you miss what you are looking for drop a comment and I will explain it in one of the upcoming weekly roundups

Abaxial/Adaxial: These related terms can cause some confusion, even for the more experience plant scientist. It probably has to do with the almost identical terms. But to refresh your memory. With abaxial plants scientists mean the surface of an organ facing away from the organ’s axis, in general this is the lower surface (or bottom side) of a lateral organ such as a leaf. With adaxial plant scientist mean the surface of an organ facing toward the organ’s axis, in general this is the upper surface (or top) of a lateral organ such as a leaf. As a memory aid both abaxial and bottom have a b in it.

Apomixis: When botanist or plant scientists are talking about apomixis they mean the asexual development of an embryo or seed without fertilisation. As such, as no fertilisation has taken place, apomictically produced offspring are genetically identical to their parent. Moreover the seeds produced in this manner germinate. As such apomixis is seen as the holy grail in crop breeding as it would breeders allow to keep the traits of F1 crossings, which are often better performing that the subsequent generations.

Autotrophs: Autotrophs are organisms that produce their own food. Plants use sunlight, water, carbon dioxide to produce food via photosynthesis. Because plants use sunlight they are photoautotrophs. This to distinguish them from chemoautotrophs who don’t use sunlight but get their energy from inorganic chemical reactions. Because of their ability to produce their own food, autotrophs are standing at the base of the food chain, supporting all the organisms that eat other organisms (also called heterotrophs).

Chimera: In general, a chimera is an organism whose body is composed of cells that are genetically distinct. As such it can look like they are two different individuals. This week’s paper highlight shows an unusual example of chimeras, seedlings that inherited their mitochondria from both their parents. These seedlings have cells with distinct mitochondria genomes, some strictly with a maternal origin, other strictly paternal origin, but also with a mix.

In science the term chimera can also be used for proteins that are modified to contain parts of two different proteins. Researchers create these chimera proteins to find out the function of the different parts of the protein.

Cotyledon: Cotyledons are the leaf-like structures a seedling emerges with. Seedlings have often one or two cotyledons. Botanists use this as one of the traits by which to classify flowering plants. Although, plants most often appear with one (the monocots) or two (the dicots) cotyledons, there are also plants, like many orchids, that have none, whereas others like Psittacanthus schiedeanus a kind of mistletoe, that have more than two, in the case of Psittacanthus schiedeanus there are twelve.

Epiphyte: An epiphyte is a plant or plant-like organism that grows on a plant or plant-like organism. Although, they use another plant as a structural support to grow on, epiphytes are no parasites as they don’t siphon of nutrients form the plant they grow on. Many mosses, lichens, ferns and orchids are epiphytes. They obtain their moisture and nutrients from the air, rain and debris accumulating around them.

Guard cells: When botanists and plant scientists are talking about guard cells, they mean the two kidney shaped cells that encircle the stomata, or pores. These two cells are in essence the gate keepers of the pore. They close the pore – by swelling – in unfavourable conditions, like when it is hot and dry, and open the pore – by shrinking – in favourable conditions like when the sun shines and enough water.

Haustorium: the haustorium is a rootlike structure from parasitic plants that grows into or around another structure, like its hosts xylem and or phloem, so that it can absorb water and/or nutrients.

Maybe confusingly, in plants haustorium also refers to the tissue of the developing embryo that transfer nutrients for the seed’s endosperm to the embryo. So context is important.

Meristem: Meristems are the growth centres of the plant. The cells in this region divide slowly, and with each round of division, one of the daughter cells is pushed outside the slow dividing group of cells. Cells in the first layer outside the meristem divide a few more times before they mature. Scientists recognise three types of meristems, those at the root tips, those at the shoot tips and those from which flowers develop. Each type of meristem is regulated by its own set of regulatory genes. And while most root meristems can keep dividing endlessly, those of the shoot can get told that they are redirected into inflorescence meristems, whose time is limited.

Pangenome: Pangenomes are a collection of genomes of many individuals or varieties of a species. Pangenomes combine conserved core genes that are shared by all varieties with genes that only occur in some of the varieties. As such pangenomes are comprehensive reference genomes that bypass the potential bias by focussing on only the genome of a single variety of a species. Because they capture the genetic diversity of s species, pangenomes are used to find traits for crop improvement.

Petiole: When botanists or plant scientists are talking about the petiole, they mean the leaf stem or leaf stalk via which the leaf is attached to the twigs, branches or stems of a plant. The petiole allows leaves to twist towards the light. Petioles vary in size. And in some plants, like in grasses, they might be completely absent. To distinguish between species that have and haven’t a petiole botanists use respectively the terms petiolate and apetiolate.

Phyllotaxis: The arrangement of leaves on a plant stem. Plants tend to arrange their leaves according to one of two major patterns. Opposite, whereby leaves are placed on the same level at an angle of 180 degrees. Alternated, whereby leaves are placed on different levels in an angle of approximately 137 degrees, which results in a spiral pattern.

Stolons and rhizomes: Stolen and rhizomes are elongated horizontal stems, respectively above and below ground, from which daughter plants grow. They are ways for plants to vegetatively propagate themselves. Plants that produce stolons or rhizomes can be found in a wide range of environments.

Stomata: Stomata are the pores on stems and the underside of the leaves through which the plant exchange gases, like CO₂ and water vapour. These pores are made up from two kidney shaped cells. And the plant controls both the number as well as the opening and closing of these pores. For example, a plant closes its stomata when it perceives a water shortage.

Transcription: Making an RNA copy of a gene is called transcription. When plant scientist (and other scientists who study living organisms) talk about transcription they like to know how often a cell is making an RNA copy of its genes. Or in other words how active the genes are. This gene activity is also called gene expression.

Transposons: Transposons, also nicknamed jumping genes, are a bit of DNA that can change its position within a genome. Transposons have a specific DNA sequence at each end. This sequence is recognised by transposase an enzyme that cuts the transposon free from its chromosome, after which the transposon integrates itself into another place of the genome. While transposons don’t jump that often, when they do, they can create havoc. Such as changing the colour of maize kernels. It was this observation that led to the discovery of transposons by Barbara McClintock and a Noble prize. Subsequently transposons were also discovered in other organisms than plants.

Turgor: When plant scientists talk about turgor, or turgor pressure, they talk about a force within the cell that presses the cell membrane against the cell wall. In general, this pressure, or lack there off, is caused by the osmotic flow of water. In hypertonic environments when the ion concentration outside the cell is higher than inside the cell pumps out its water, then the turgor pressure inside cells gets low, and the cell membrane loses most connection with the cell wall, the cell becomes plasmolysed. In an isotonic environment the osmotic water flow is in balance and so is the cell, this turgor pressure is called flaccid. On the other end, in hypotonic environments, when the ion concentration inside the cell is higher than outside the cell, the cell takes up more water than it is comfortable with, the cell membrane is pressing extra hard against the cell wall, the cell has become turgid. All with all keeping the perfect turgor pressure is a balancing act.

Volatile Organic Compounds (VOCs) / Plant Volatiles: This are basically scent molecules, although we might not all smell them. Plants produce volatile molecules like methyl salicylate to communicate with the world around them. Most people are familiar with the volatiles produced by flowers to attract pollinators. But plants also sent out volatiles to attract natural enemies of herbivores that attack a plant. They also release volatile molecules when damaged. And while there is some debate if plant deliberately or accidently release volatile molecules that other plants pick up, plants do use those signals from other plants to inform their action and if needed prepare to defend themselves.

This is all so far.

- Femke de jong

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