Plant growth hormones: Antagonists cooperate

Jun 24, 2010
This is an pptical cross-section of the growth zone of Arabidopsis. The distribution of an essential regulator is shown in green, the cytokinin and auxin molecule are shown in red and green. Credit: Jan Lohmann

The two most important growth hormones of plants, so far considered antagonists, also work synergistically. The activities of auxin and cytokinin, key molecules for plant growth and the formation of organs, such as leaves and buds, are in fact more closely interwoven than previously assumed.

Scientists from Heidelberg, Tubingen (Germany) and Umea (Sweden) made this surprising discovery in a series of complex experiments using thale cress (), a biological reference organism. The international team of researchers, led by Jan Lohmann, stem cell biologist at Heidelberg University, have now published their results in the scientific journal Nature.

All the above-ground parts of a plant - leaves, buds, stems and seeds - ultimately arise from a small tissue at the shoot tip, which contains totipotent stem cells. Since plant stem cells remain active over the entire life of the organism, plants, unlike animals, are able to grow and develop new organs over many decades. On the periphery of the tip, auxin triggers cells to leave the pool of stem cells, differentiate and form organs like leaves and buds. Cytokinin stimulates stem cells to divide and proliferate; it maintains the number of cells and thus the plant's growth potential.

This shows growth defects after deactivation of the ARR7 and ARR15 genes. Left: control plant. Right: plant after deactivation of the two genes. Lower edge: Growth zones of the corresponding plants viewed under scanning electron microscope. At centre is the stem cell zone, where new buds are being formed on the periphery. Credit: Jan Lohmann

Some of the genetic factors involved in cytokinin's effect on were already known. In the thale cress experiments, which concentrated on the growth zone at the tip of the shoot, Lohmann and his team now studied the role of auxin in the interplay of the two hormones. It turns out that auxin directly interferes with a feedback loop involving two genes activated by cytokinin - ARR7 and ARR15 - which limit the effect of cytokinin. Auxin suppresses these two genes, thereby boosting the effect of cytokinin.

"Auxin acts to support the pool of stem cells", explains Jan Lohmann. "When it triggers cells at the periphery of the growth zone to form organs, it still needs to ensure that enough stem cells are supplied." This keeps the number of from falling below a critical minimum, which is key for plant growth and survival. "We're gradually beginning to understand how hormonal and are interwoven to maintain the activity of the growth zone. We now know that hormones and genes interact in multiple ways, each one affecting the other. There are no solitary factors."

Explore further: Micro fingers for arranging single cells

More information: Z. Zhao, S.U. Andersen, K. Ljung, K. Dolezal, A. Miotk, S.J. Schultheiss, J.U. Lohmann: Hormonal control of the shoot stem-cell niche, Nature (24 June 2010), doi: 10.1038/nature09126

Related Stories

Circadian clock controls plant growth hormone

Aug 13, 2007

The plant growth hormone auxin is controlled by circadian rhythms within the plant, UC Davis researchers have found. The discovery explains how plants can time their growth to take advantage of resources such ...

How Your Garden Grows

May 25, 2005

Stumped scientists figure out plant growth mechanism Just how does your garden grow? Plant scientists have long pondered the same question. For decades, the plant science community has known that auxins--a ...

Recommended for you

Micro fingers for arranging single cells

Apr 24, 2015

Functional analysis of a cell, which is the fundamental unit of life, is important for gaining new insights into medical and pharmaceutical fields. For efficiently studying cell functions, it is essential ...

Detailed structure of human ribosome revealed

Apr 24, 2015

A team at the Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC - CNRS/Université de Strasbourg/Inserm) has evidenced, at the atomic scale, the three-dimensional structure of the complete ...

How to kill a protein

Apr 24, 2015

For decades scientists have been looking closely at how our cells make proteins. But the inverse is equally important: how cells kill them.

How RNA machinery navigates our genomic obstacle course

Apr 24, 2015

Once upon a time, scientists thought RNA polymerase—the molecule that kicks off protein synthesis by transcribing DNA into RNA—worked like a wind-up toy: Set it down at a start site in our DNA and it ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.