Plant Wonders Are in the Details
When you step on a weed growing out of a crack in the sidewalk, do you have any idea what kind of amazing machinery you stepped on? Maybe a closer look will help.
- Communications and switching systems: When a seed sprouts, it needs to first grow upward in the dark while trying to protect itself. Then when it reaches the air and light, it needs to spread out leaves and collect sunlight. Science Daily talked about work at Carnegie Institute on the chemical signals taking place at these critical junctures, saying that “Many components are involved in this developmental switch….” One of them, a hormone called brassinosteroid, works antagonistically to sunlight in the soil-to-air transition, but only in the presence of another regulator called GATA2. “The Carnegie team’s new research identifies a protein called GATA2 as a missing link in this communications system,” the article said, not using “missing link” in an evolutionary sense, but in a signal-transduction sense. “This protein tells developing seedlings which type of growth to pursue” by switching certain genes on and off. “….It also serves as a communications junction between internal plant systems that are turned on by light and those that are turned on by brassinosteroids.”
- Wallbuilders: Cell walls keep seedlings and large trees standing upright with a molecule called lignin – a complex molecule that requires multiple steps, like a recipe, to make (10/26/2001, 05/30/2008, bullet 2). But lignin cannot be assembled in the kitchen of the cytoplasm. It has to be assembled in the cell wall. That means that the ingredients, called precursors, which are manufactured inside the cell, have to migrate outward through the cell membrane to the construction site. Some of them are temporarily stored in vacuoles (organelles that store substances), requiring additional transport through vacuolar membranes.
It wasn’t clear if the precursors just float to their destinations by diffusion. Scientists at Brookhaven National Labs found out that, instead, energy-driven molecular machines called transporters ferry the precursors to the construction sites. PhysOrg reported on a paper in PNAS1 that described how these transporters actively take the materials where they belong, spending ATP energy like fuel. “The range of assays revealed that pure monolignols move across the cellular membrane while monolignol glucosides move preferentially into vacuoles,” the article said. “But most importantly, very little of either precursor would move across either type of membrane without the addition of ATP, the molecular ‘currency’ for energy in cells.” The paper described how the transporters are very selective in their actions: “In the presence of ATP, the inverted plasma membrane vesicles preferentially take up monolignol aglycones, whereas the vacuolar vesicles are more specific for glucoconjugates, suggesting that the different ATP-binding cassette-like transporters recognize different chemical forms in conveying them to distinct sites….”
- Upward mobility: Did you ever think about what is required to pump sap from the roots to the tops of trees? Scientists at the University of Madrid are some of many who have. Students probably remember the terms xylem and phloem; the former transporting water, the latter, nutrients. Science Daily described “The objective: to discover the keys to the movement of sap in order to apply these advances to new hydraulic systems or to suction pumps.”
“The main conclusion of this study is that the sap in the trunks of trees is in a pressurized situation,” the article said. “It demonstrates, then, that when the pressure is positive in the conduits of the xylem as well as in those of the floem [sic], the model expands in the radial direction. However, when the pressure is negative in the xylem and positive in the floem [sic], which is what is believed to occur during the day, the model contracts in the radial direction.” What can they learn from this information? Better ways to extract water or pump it against gravity, for a couple of things. One of the professors remarked, “Currently – the expert points out – there is no water suction pump capable of raising water more than ten meters at normal atmospheric pressure, but a sequoia tree can raise water to a height of 100 meters, which I think means that anything we can learn from plants is going to be of great interest to people working in this field.”
Scientists at Princeton are also hot on this trail. Publishing in PNAS,2 they first said, “Plant vascular networks are central to botanical form, function, and diversity.” Then they described how transporting material requires tradeoffs between hydraulic safety and efficiency. They developed a model that made “predictions for sap flow, the taper of the radii of xylem conduits from trunk to terminal twig, and how the frequency of xylem conduits varies with conduit radius,” and compared their model with various trees like, oak, maple and pine. Somehow these trees know how to taper the radius of their vessels from bottom to top for maximum efficiency.
The authors spoke of “evolutionary drivers” in their paper, but really were talking about design requirements – i.e., “(i) space-filling geometries to maximize carbon uptake by leaves and sap flow through conduits; (ii) increasing hydraulic conductance and resource supply to leaves; (iii) protection against embolism and associated decreases in vascular conductance; (iv) enforcement of biomechanical constraints uniformly across a plant; and (v) independence of terminal twig size, flow rate, and internal architecture with plant size.” Nowhere did they describe a plausible sequence of mutations that might produce the necessary structures; they merely assumed that “selection” would somehow fulfill the requirements.
Speaking of plant evolution, another article on PhysOrg summarized another paper in PNAS3 that tried to trace flowering plants to a common ancestor that had cones. That paper opened with, “The origin and rapid diversification of the angiosperms (Darwin’s ‘Abominable Mystery’) has engaged generations of researchers,” adding in the Introduction, “The evolutionary origin of flowering plants, or angiosperms, remains one of the greatest unsolved biological mysteries.”
So did they solve the mystery? If the summary on PhysOrg is any indication, they only assumed evolution by couching it in terms of emergence: “New research published this week in the Proceedings of the National Academy of Sciences provides new insights into their genetic origin, an evolutionary innovation that quickly gave rise to many diverse flowering plants more than 130 million years ago.” The co-leader of the team used similar circumlocutions: “Water lilies and avocado flowers are essentially ‘genetic fossils’ still carrying genetic instructions that would have allowed the transformation of gymnosperm cones into flowers,” said Doug Soltis. “We show how the first flowering plants evolved from pre-existing genetic programs found in gymnosperm cones and then developed into the diversity of flowering plants we see today,” Soltis continued, hiding the actual evolutionary process in passive voice verbs. “A genetic program in the gymnosperm cone was modified to make the first flower.”
His explanation also begs the question of how the cone-bearing plant produced the genetic program for flowers in the first place – and why it was not used for that purpose during the prior millions of years in the evolutionary timeline. In the end, the article filed the answer away in the Stuff Happens folder: “Somehow a genetic change took place allowing a male cone to produce female organs as well—and, perhaps more importantly, allowed it to produce showy petal-like organs that enticed new interactions with pollination agents such as bees.” But does “allowing” something provide necessary and sufficient conditions for its accomplishment? If that were true, building permits would by themselves build buildings.
1. Miao and Liu, “ATP-binding cassette-like transporters are involved in the transport of lignin precursors across plasma and vacuolar membranes,” Proceedings of the National Academy of Sciences, published online before print December 13, 2010, doi: 10.1073/pnas.1007747108 PNAS December 13, 2010.
2. Savage et al, “Hydraulic trade-offs and space filling enable better predictions of vascular structure and function in plants,” Proceedings of the National Academy of Sciences, published online before print December 13, 2010, doi: 10.1073/pnas.1012194108.
3. Chanderbali et al, “Conservation and canalization of gene expression during angiosperm diversification accompany the origin and evolution of the flower,” Proceedings of the National Academy of Sciences, published online before print December 13, 2010, doi: 10.1073/pnas.1013395108.
A new law of nature, the DAM law, is hereby described. Any article or paper on the evolution of flowering plants will be accompanied by the phrase, “Darwin’s Abominable Mystery” (DAM). This is a time-invariant law describing the predicament of not only Darwin, but his disciples down to the present. For evidence, see entries over the last decade like 11/08/2000, 04/03/2001, 01/30/2002, 05/03/2002, 06/07/2002, 01/17/2003, 03/15/2007, 12/21/2007, 04/28/2008, 09/15/2009, 12/04/2009 bullet 4, and 09/22/2010.
Darwinists are MAD about the DAM law, too; showing the law is commutative: the Mystery’s Abominable Darwin. Notice that the DAM Law does not assert that the plants themselves are abominable. No; they are wonderful. They are incredibly well designed. The mystery of their origins is only abominable when the premise, Darwinism, is the seed plot of abomination, watered by the toxic rhetoric of things “arising” and “developing” apart from design. In such explanatory gardens, nothing grows – no mystery there.