Plant Physiology: Stomata on guard

Early vascular land plants were either leafless or had short cylindrical leaves or tiny microphylls. By the end of the Devonian about 345 million years ago, following a botanical equivalent of the 'Cambrian Explosion', many of the major plant lineages had developed, together with the stem/leaf/root form of the modern plants. But for 70 years, botanists have sought to explain the time-lag of 40 million years between the appearance of the first land plants and the emergence of the more energy efficient, flat-leafed 'modern' plants. An analysis of fossil leaves and their presumed biophysical properties now provides a quantitative explanation. The key seems to be a 90% fall in atmospheric CO₂ during the late Palaeozoic. While the CO₂ level was high, early plants needed relatively few stomata on their cylindrical leaves to absorb enough CO₂ for photosynthesis. A flat leaf with similarly few stomata would have overheated owing to insufficient evaporation and cooling of the leaf. As the CO₂ declined, plants responded by developing more stomata, which allowed the flat-leaf form to develop whilst staying cool.

The function of the guard cells around stomata is critical to plant growth and interaction with the environment. Schroeder et al. review recent advances that open the possibility of engineering drought hardiness into plants by manipulating stomatal responses of plants to control CO₂ intake and plant water loss.

Evolution of leaf-form in land plants linked to atmospheric CO₂ decline in the Late Palaeozoic era
D. J. BEERLING, C. P. OSBORNE, W. G. CHALONER
Nature 410, 352-354 (15 March 2001)
| First Paragraph | Full Text | PDF |

Guard cell abscisic acid signalling and engineering drought hardiness in plants
JULIAN I. SCHROEDER, JUNE M. KWAK, GETHYN J. ALLEN
Nature 410, 327-330 (15 March 2001)
| Summary | Full Text | PDF|

Palaeontology: Turning over a new leaf
PAUL KENRICK
A model based on biophysical principles of plant physiology, and drawing on fossil and environmental data, indicates that the origin of leaves was triggered by falling levels of atmospheric CO₂.
Nature 410, 309-310 (15 March 2001)
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15 March 2001 table of contents