The Quiet Branches

The history of science is vast. And even though the term science is recent in human history, humans have always been tinkerers and explorers. The history of plant science is no less interesting or complex. It is obviously is bigger than a single blog post. So here, I’ll give a highlight reel and get into some of the stories that are less-well known. Plant science is an area of science often not noticed, underfunded. But is just as curiosity driven, important, and fascinating as the sciences that do make headlines.

The Twitter version of plant science history might say agriculture invented, Mendel experimented with pea plants, and GMOs get planted. These are the biggest moments most people learn about at some point. As with a lot of history in life science history, the story starts with observations of the natural world. Observations lead to experiments that uncover mechanisms life uses to, well, live. The closer to modern day you get, scientists uncover finer and finer details of how life works. For example, cells, the base unit of life. And the DNA encoded genes in those cells. Genes are the sequences of DNA that store information to build an organism arranged in groups called chromosomes with thousands of genes. Humans have 46 total chromosomes, half from Mom and half from Dad.

The beginnings of agriculture is a huge story. It “officially” started in the fertile crescent in the modern day Middle East, but people domesticated plants in cultures the world over. Grain species like wheat and rice as well as fruits & vegetables became farmed and selectively bred. As globalization proceeds, we seem to be eating fewer and fewer different plants in our diets. Many plants can get transformed and processed into many different kinds of food. I’ll cover more specifics in the history of agriculture in the future. It is an important and ongoing story in the history of plant biology. The future of agriculture matters too, as humans will have to produce more food on less land than we do now to feed the projected 9 billion people by 2050.

In the mid 1600s, early in the days of the scientific revolution that was set off by Copernicus, Galileo, Kepler, and others was furthered by the ability to look more closely at the living world. The exploration of the solar system with the telescope expanded the universe. But another curious and inventive person, Antonie van Leeuwenhoek, figured out how to augment human vision the other way to look at every day things up close. He looked at drops of pond water, discovering “animalcules”, or what we would call microbes. A contemporary, Robert Hooke, using a Antonie van Leeuwenhoek microscope looked at cork (yes, the same plant that seals bottles of wine). Up close, it looked to Hooke like little rooms. He was in fact seeing the cell walls of the dead cork cells…and he called them cells, after the rooms in monasteries where monks resided. In the early 1800s, Schleiden and Schwann, the former a plant scientist, proposed the idea that all life is cellular— plants, animals, and microbes.

Part of the colonial era was the founding of botanical gardens like Kew in London, England. Through Kew’s operations, plants from around the world were cultivated in England. Plants were also shifted to new places around the world as well. Generally, a lot more learning about previously unknown plants took place and enriched economies. Though a success, it is certainly a mixed legacy for it was the plundering of nature and distrupting cultures around the world. The story of the beginnings of Kew and it’s first director, Joseph Banks, is told by Kathy Willis in the fantastic BBC series ‘From Roots to Riches’ (Available as a podcast). The whole series is a great telling of the history of much of plant biology (note, this is a limited series so listen to it while it’s up).

Charles Darwin was also a plant biologist. As much attention as his finches get, plants were a key in developing natural selection. Darwin also did some experiments with canary grass. He showed that some “factor” produced in the apex of the shoot could induce bending in the seedling stem (technical term: coleoptile). Decades later, that factor was identified as the plant growth regulator auxin.

The Russian plant biologist Nikolai Vavilov researched “centers of origin” of various plants. He mapped where trait diversity of specific plants was greatest. He reasoned that centers of plant origin would have the most diversity where the plants had existed the longest in nature. During plant domestication, humans only took a small subset of plants with limited, but still useful, genetic variation. Vavilov was the father of seed banking too. A practice of collecting seeds of wild as well as commercial plants to keep genetic diversity in storage for the future. A common example of a trait to look at wild varieties for is disease resistance. The potato blight that struck Ireland was caused by a phytopthora fungus. If a seed bank had existed with a diverse panel of wild potatoes can be tested for resistance to that pathogen. If found, a wild resistant variety carying that genetic trait can bred into the commercial variety and distributed.

For the reason above and more, genetic diversity is an important resource. Seed banks now are becoming networked. The seed bank in Svalbard, Norway (high about the arctic circle) is designed to be a backup seed bank to store the genetic legacy of the world’s plants in case of crisis. Seed banks are also important for storing genes themselves. Thanks to technological advances, we are not limited to within-species genetic diversity. Modern recombinant DNA techniques, we can take genes from one species and place them into another. It is human assisted horizontal gene transfer (horizontal gene transfer is a genetically encoded trait moved between species). The combination of seed banks and recombinant DNA technology is one more tool to ensure our survival and thriving.

One story from that comes from World War II and the siege of Leningrad is that one of Vavilov’s seed banks there. Housing valuable samples of plant diversity. Plants’ economic value was well established by the example of other botanical gardens. Like museum art pieces, they’re a heritage of a place, a culture, and of the nature in a specific place. Several staffers of the seed bank guarded it. Nine of them starved to death, refusing to eat the banked grains that could have fed them during the 28-month siege. I cannot here speak to why they were willing to starve to protect the seed bank. But part of it surely was dedication to the long term preservation of genetic diversity. It is a powerful thing to feel that the future is in your hands. And that is what banked seeds are. A resource for the future, for all time. Plants provide a sense of renewal that is possible in the natural world. They say that new growth is possible, even out of dire straights or disaster.

Plants are different from many multi-cellular animals because they are regenerable from a single living cell. Many seeds are also designed for long periods of dormancy. For instance, a 32,000 year old plant was grown again through cell culture methods of Siberian Silene plant preserved in an ancient squirrel den¹. As scientific manuscripts go it’s one of the most accessible articles to any non-plant scientist.

In further contributions to basic biology, Barbara McClintock, studied maize chromosomes. Her work provided insight into the mechanisms of trait inheritance between generations. In other words, answering just how the DNA that makes up chromosomes relate to the physical plant we see. She also determined some of the dynamic processes chromosomes undergo. She was further exploring what Mendel had uncovered with his pea plants with better technology. McClintock showed direct evidence for a hypothesis of ‘crossing over’. Crossing over is the exchange of genetic material (DNA) between two parents’ gametes (sex cells) that occurs between similar chromosomes. This phenomenon is why some patterns of inheritance are observed². More famously, McClintock also discovered so called ‘jumping genes’, or transposons³. Transposons are genetic elements that jump around the genome causing direct affects on gene function and physical traits. Transposons do not just exist in plants. They are ubiquitous in the cellular world. Once confirmed, McClintock did end up winning the 1983 Nobel Prize in Physiology or Medicine.

This is just a primer on the vast and important history of plant science and some of the scientists that study it. The American Society of Plant Biologists created a timeline of milestones in plant science from 1920–present.

I hope to tell some of these stories in greater detail in the future. For now, I hope I’ve left you with a sense that plant science is a vast world with a huge number of stories to tell. And that plant science often informs and intersects with other scientific fields. A point I made in my last post was that plants are everywhere. Even if we are several steps removed from them in the form of plant-derived products, they are a part of us. And we them.

References:

1. Svetlana Yashina, Stanislav Gubin, Stanislav Maksimovich, Alexandra Yashina, Edith Gakhova, and David Gilichinsky, 2012. Regeneration of whole fertile plants from 30,000-y-old fruit tissue buried in Siberian permafrost. PNAS 109(10): p4008–4013.

2. Harriet B. Creighton and Barbara McClintock. 1931. A Correlation of Cytological and Genetical Crossing-Over in Zea Mays. PNAS 17(8): p492–497.

3. Barbara McClintock. Induction of Instability at Selected Loci in Maize. 1953. Genetics 38(6): p579–599.