Plant size morphs dramatically as scientists tinker with outer layer

Mar 07, 2007

Jack's magical beans may have produced beanstalks that grew and grew into the sky, but something about normal, run-of-the-mill plants limits their reach upward. For more than a century, scientists have tried to find out which part of the plant both drives and curbs growth: is it a shoot's outer waxy layer? Its inner layer studded with chloroplasts? Or the vascular system that moves nutrients and water? The answer could have great implications for modern agriculture, which desires a modern magical bean or two.

Now, in the March 8 issue of the journal Nature, researchers in the Plant Biology Laboratory at the Salk Institute for Biological Studies provide the answer. They succeeded in making tiny plants big and big plants tiny by controlling growth signals emanating from the plant's outer layer, its epidermis.

These findings could eventually be used by agronomists to manipulate plant growth pathways to maximize crop yield, or even reduce leaf size or leaf angle in plants that need to be spaced closely together, says the study's lead author, Joanne Chory, Ph.D., professor and director of the Plant Biology Laboratory and investigator with the Howard Hughes Medical Institute.

Chory and her laboratory team have spent years helping to define how a plant "knows" when to grow and when to stop – which is a "big question in developmental biology," she says. For their experiments, they rely on the model system Arabidopsis thaliana, a small plant related to cabbage and mustard whose genome has been decoded. Over the years, the researchers have built up a whole tool kit, learning how to add and subtract genes in order to determine form and function. Among their discoveries is a class of dwarf plants whose size is about one-tenth the size of a single leaf of the full-sized plant.

Over the past decade, Chory's laboratory and others have shown that these dwarf plants are defective in making or responding to a steroid hormone called brassinolide. Among the genes identified was the plant steroid receptor, BRI1 ("bry-one") that is activated by the steroid. The dwarfed Arabidopsis doesn't express BRI1 at all, unlike normal Arabidopsis, which expresses BRI1 on both the outer waxy, protective epidermis (covering the whole leaf and shoot), and the inner sub-epidermal layer, which contains the chloroplasts that conduct photosynthesis.

In the current study, first author Sigal Savaldi-Goldstein, Ph.D., a postdoctoral researcher in the Plant Biology Laboratory, and Charles Peto, an electron microscopy specialist in the Laboratory of Neuronal Structure and Function, conducted a series of experiments that addressed an old debated question: what tissues of the leaf drive or restrict growth? The answer was simple: the epidermis is in control.

They found that when they drive the expression of the BRI1 receptor in the epidermis of a dwarf Arabidopsis, while leaving the sub-epidermal layer as it was (without BRI1 receptors), the tiny plant morphed into a full-sized plant. In the second set of experiments, they used an enzyme to break down the steroid hormones in the epidermis, and found that a normal sized plant shrunk into a dwarf. "These are simple experiments, but it took 10 years of work in order for us to be able to ask this question," Chory says.

"A second remarkable finding from the study is that "cells in the outer layer talk to the cells in the inner layers, telling them when to grow or to stop growing. This communication is very important to the life of a plant, which can't move and so must have a coordinated system to respond to a changing environment," explains Savaldi-Goldstein.

Source: Salk Institute

Explore further: Honey bees sting Texas man about 1,000 times

add to favorites email to friend print save as pdf

Related Stories

A global view of oceanic phytoplankton

Jul 18, 2014

University of Maine oceanographer Ivona Cetinic is participating in a NASA project to advance space-based capabilities for monitoring microscopic plants that form the base of the marine food chain.

NASA's ten-year-old Aura satellite tracks pollutants

Jul 17, 2014

(Phys.org) —NASA's Aura satellite, celebrating its 10th anniversary on July 15, has provided vital data about the cause, concentrations and impact of major air pollutants. With instruments providing key ...

Tracking the breakup of Arctic summer sea ice

Jul 16, 2014

As sea ice begins to melt back toward its late September minimum, it is being watched as never before. Scientists have put sensors on and under ice in the Beaufort Sea for an unprecedented campaign to monitor ...

Recommended for you

Study indicates large raptors in Africa used for bushmeat

10 hours ago

Bushmeat, the use of native animal species for food or commercial food sale, has been heavily documented to be a significant factor in the decline of many species of primates and other mammals. However, a new study indicates ...

The microbes make the sake brewery

11 hours ago

A sake brewery has its own microbial terroir, meaning the microbial populations found on surfaces in the facility resemble those found in the product, creating the final flavor according to research published ahead of print ...

Fighting bacteria—with viruses

12 hours ago

Research published today in PLOS Pathogens reveals how viruses called bacteriophages destroy the bacterium Clostridium difficile (C. diff), which is becoming a serious problem in hospitals and healthcare institutes, due to its re ...

User comments : 0