© Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE
December 7, 2000
CHRISTOPHER SURRIDGE

Pore-like ‘stomata’ are the main way plants exchange gas with their surroundings. But a plant’s need to take up CO2 as a raw material for photosynthesis is balanced against its need to prevent water loss through transpiration. When CO2 is plentiful, most plants try to conserve water by reducing the number of stomata in their leaves.

Now it has emerged that the small plant Arabidopsis thaliana has a gene, ‘HIGH CARBON DIOXIDE’ (HIC), whose loss results in an increase rather than a decrease in stomatal numbers in response to raised atmospheric CO2. This finding, reported in Nature by Alistair Hetherington and colleagues from Lancaster University, UK, is the first step on the road to understanding how plants will cope with human-induced CO2 increases.

Hetherington’s group found that HIC is only expressed in cells that encircle or ‘guard’ stomata. Although mutations in HIC produced leaves with inappropriately high numbers of stomata in response to elevated CO2, these abundant stomata functioned completely normally.

Sequencing the HIC gene showed it to be similar to another gene, KCS1. KCS1 encodes an enzyme involved in synthesizing the specialized waxes found between the plant’s cells. With hindsight, Hetherington found that other mutations in genes involved in wax production, both in Arabidopsis and Barley, also alter the density of stomata.

Some think that the regular spacing of stomata across the leaf surface arises because stomata inhibit the production of other stomata in their immediate neighbourhood, perhaps by producing something that suppresses stomatal development. HIC may make the extracellular matrix more permeable, enlarging a suppressor’s area of influence.

This inverse correlation has existed for over 400 million years, so counting fossil plant stomata can also be used to infer ambient conditions and provide clues to the causes of global extinctions, while museum specimens provide a silent witness to the steady rise in our production of CO2 since the industrial revolution.

As Laura Serna and Carmen Fenoll of the Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Toledo, Spain, say, "The main message of this work is that plants are well armed to face atmospheric CO2 enrichment".

Christopher Surridge is a Senior Biological Sciences Editor at Nature

Gray, J. E. et al. The HIC signalling pathway links CO2 perception to stomatal development. Nature 408, 713-716 (2000). Error: Unable to read footer file.