THE MORE I STUDY plant cells and their operation, the more I start to examine our own world and indeed our universe in terms of cellular makeup and function. When you think about it, the world could be just one big cell. All the functions I studied can be analogized to something, just as microtubules are like railroads. Our world could be just an organelle in one cell in the universe. It is truly a mind-boggling comparison, kind of like the worlds in Dr. Seuss’s Horton Hears a Who.
Think about it. Everything in our world can be likened to something in a cell. Membranes? We have them: border crossing guards that regulate traffic between countries. Tubules and microfibrils? We have them. They are the tracks and the roads along which we travel. Those complicated route maps at the back of airline magazines look like some of the diagrams I have seen that show how proteins move through a cell. Enzymes? Hormones? Metabolites? Our world has analogous entities, along with garbage collections sites, power-generating factories, and package assembly and delivery systems that are exactly like those in a tiny plant cell. We have signaling systems, water transportation systems, and the list goes on.
By the time I finished the research for this book, I had developed my own cell theory of life: we are all part of a cell, which is part of a larger universe of cells. I will forever look at a power generator and think of mitochondria. I will travel along roads, bike paths, railroads, and air routes around the country and think of tubules and microfibrils. I might even start to think of myself as a cell-made enzyme, strung together in a ribosome to become an agent dedicated to speeding up the return to organics and the soil food web by gardeners and farmers. I will see ribosome factories, endoplasmic reticulum manufacturing centers, and Golgi body packaging, assembly, and delivery sites.
Could it be that we and all the other organisms on Earth are all parts of one big cell? Part of a system as bacteria are inside humans, carrying out functions so the larger organism will thrive? Is our cell and the universe it’s in small enough so that we could be part of a plant and not have any idea?
It is so easy to find analogies to cells, cell parts, and even the chemical reactions that occur in cells. Everything we do affects that system. How we use water and nutrients is similar, right on down to how we are recycled in the end. Or is that the beginning? Maybe our whole universe is just one cell, connected to another universe by some plasmodesmata in a sea of similar cells. It is amazing to contemplate.
At the same time, I cannot stop thinking about how all of the cellular activity that is life started. It’s not just the 15 trillion cells in the tree outside your window, but all the cells of plants everywhere. They operate the same way. How did they come to be?
I can imagine a bunch of membranes forming, like plastic shopping bags, floating around and occasionally entrapping some flotsam or jetsam in the primordial soup. Things would eventually accumulate inside them to the point that chemical reactions start to occur. Maybe some waste vacuole had the right mix of ingredients to do something with less energy, thus becoming a better vacuole. A protozoan swam into the new vacuole and found it could live there if it just provided some energy to its host. The protozoan divides and thrives, and when the vacuole divides, each part gets protozoa.
Just thinking about the process that duplicates DNA and RNA leaves my head spinning. And the little machines, the spindles that lay down the cellulose in every plant cell wall like spinning cotton candy. Whew. Duplication of cells and cell parts, an enzyme for every one of the mind-boggling number of reactions, a transport protein for each nutrient to move across membranes, and membranes whose molecules line up like Alaskan yaks to keep young ones in and evil ones out. Amazing, simply amazing—and something we gardeners give very little thought to. As little thought as we do to the wonder that a plant can take seventeen nutrients, grow, and recreate itself.
Plant cells are distinct from animal cells in having an additional external envelope, the cell wall, outside the plasma membrane. In this micrograph, the cell wall, made of proteins and polysaccharides, appears as the thin layer between the cells. The wall defines the shape of the cell and expands as it grows.
Nutrients can travel through and along cell walls in the apoplastic pathway. Eventually they must either exit via the same path or enter the cell by traveling through the plasmalemma, the thin, double-layered phospholipid membrane that is adjacent to the cell wall. Once inside the cell, nutrients mix with the cytoplasm and are converted to whatever building blocks the cell needs by the myriad enzymes floating in it. These new compounds are then assimilated or transported to other cells.
The prominent round organelle in the cell is the nucleus, which contains a smaller nucleolus (red). The double-layered membrane around the nucleus is extremely important for controlling what gets in and out of the nuclear envelope. It is here that the DNA is stored. Some nutrients are stored in vacuoles, seen as the yellow areas in the cytoplasm. These nutrients are available for transport to where they are needed.
Despite knowing what goes on in a plant cell, one can’t help but see a similarity between a cell and the universe: millions of tiny parts, each affecting the others, floating in a cytoplasmic soup. Is our universe nothing more than just one cell, part of larger collection of cells? Yes, it helps to know what goes on in a cell. However, we should appreciate the mystery, too.
This false-color transmission electron micrograph shows a cell in the root tip of a maize plant.
I am learning to look at a picture of a cell and see myself reduced down to the size of a cell-traveling nutrient. When I work in the gardens these days, I think about how my plants are eating, synthesizing the essential elements into everything they need, and, come to think of it, I need as well. But I also now look at a picture of a cell and see a whole universe. When I’m working with my plants, I see myself as just a mere enzyme performing my assigned cellular functions. What goes on in a plant cell is all too amazing to be ignored.
