Ever looked carefully at the leaves on a plant and noticed their various sizes and shapes? Why are they different? What controls the size and shape of each individual leaf? Very little is known about the developmental control of leaf size and shape, and understanding the mechanisms behind this is a major issue in plant biology.
A leaf's size is determined by a combination of cell number, cell size, and intercellular space. Michael Marcotrigiano from Smith College, Massachusetts, wanted to find out what role cell layers played in regulating leaf size and shape. He utilized a powerful tool—the synthesis of graft chimeras—that has allowed him to carefully analyze the developmental regulation of leaf size and shape in Nicotiana and has published his findings in the February issue of the American Journal of Botany (http://www.amjbot.org/cgi/content/full/97/2/224).
By grafting plants of different Nicotiana genotypes Marcotrigiano was able to recover shoots from the graft union that were chimeras. These shoots were composed of both genotypes. Eventually he recovered leaves with two genetically distinct cell layers. He grafted N. tabacum, a large-leaf genotype, and N. glaucum, a small-leaf genotype, to produce leaves where the resulting epidermal cell layer was a different genotype than the mesophyll cell layer—but on only one side of the leaf, allowing for direct comparison of the growth of the leaf from one side to the other. Thus, one side of the leaf could act as a "control" for the other side of the leaf. This enabled him to set up some nicely designed comparisons where on one side of the leaf the outer cell layer (the epidermis) differed in genotype from the rest of the leaf.
"Since leaves generally vary in size along the length of the stem and leaf size is strongly influenced by environmental factors, my method allowed me to compare one side of a leaf to the other, negating the complications that arise when comparing different leaves on a single plant or leaves on different plants," Marcotrigiano said.
Creating these graft chimeras was time-consuming and involved an element of chance; often the growing tip of the chimeral shoots reverted back to a non-chimeral shoot rendering the leaves generated from that point on useless for analysis. However, over the past decade enough leaves were recovered that were perfectly bisected, homogeneous on one side of the midvein and with a unique epidermis on the other. This allowed Marcotrigiano to use them to examine how leaf cell layer affects leaf size and shape.
Marcotrigiano's most striking finding was the important role that the epidermal cells played in determining leaf size. He found that leaves grew asymmetrically when one side of the midvein contained identical cell layer arrangements and the other side contained epidermal cells that differed genetically from the mesophyll cells. When big-leaf epidermal cells surrounded small-leaf mesophyll cells in an otherwise all small-genotype leaf, the big-leaf epidermal cells caused that side of the leaf to be bigger than the other side. In contrast, when small-leaf epidermal cells surrounded big-leaf mesophyll cells in an otherwise all big-genotype leaf, the small-leaf epidermal cells caused that side to be smaller than the other side.
Epidermal cells not only controlled overall leaf size, but also influenced the number of cells produced in the mesophyll layer. For example, small-leaf epidermal cells surrounding big-leaf mesophyll cells caused the mesophyll cells to have many fewer cell divisions than when they were surrounded by big-leaf epidermal cells. Interestingly, the epidermal cells did not influence, or change, the size of the mesophyll cells.
Marcotrigiano concludes that while regulation of leaf size is complex and influenced by many factors and many genes, his findings show that communication between adjacent cell layers plays an important role in determining leaf size. Cells in one tissue layer can control the rate of division of cells in another tissue layer, which in turn influences overall leaf size.
The full article in the link mentioned is available for no charge for 30 days following the date of this summary at http://www.amjbot.org/cgi/content/full/97/2/224. After this date, reporters may contact Richard Hund at email@example.com for a copy of the article.
The Botanical Society of America (www.botany.org) is a non-profit membership society with a mission to promote botany, the field of basic science dealing with the study and inquiry into the form, function, development, diversity, reproduction, evolution, and uses of plants and their interactions within the biosphere. It has published the American Journal of Botany (www.amjbot.org) for nearly 100 years. In 2009, the Special Libraries Association named the American Journal of Botany one of the Top 10 Most Influential Journals of the Century in the field of Biology and Medicine.
For further information, please contact the AJB staff at firstname.lastname@example.org.
Richard Hund | EurekAlert!
How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH
A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology