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From teosinte to maize in five steps
research news research is needed to develop a sound basis for a Level II approach.
literature
focus
Future impact One example of the problems that high tropospheric ozone levels might pose concerns the intention to use cloned trees for forest plantations. According to a recent investigation 4, 25% of silver birch (Betula pendula Roth) clones that were selected for micropropagation (due to their fast growth) showed high ozone sensitivity, and only 35% were ozone tolerant when exposed to ozone concentrations that were 60-70% higher than ambient levels. It may be that ozone tolerance should be incorporated into the selection criteria for tree breeding. The ecological significance of a rapid increase in tropospheric ozone on a global scale remajn.q unclear. For example, almost nothing is known of the effects of ozone on sedges and mosses 5 in peatland ecosystems. There is an urgent need to extend the present study to arctic and boreal forests and peatlands, where net primary productivity often exceeds heterotrophic respiration because of cold, wet soils, which limit decomposition. Productivity within these ecosystems is expected to increase as a result of high-latitude warming and elevated CO2 concentrations. However, the current annual rate of increase in CO~ concentration is only 0.5%, while the concentration of ozone increases by 0.5-2.0% annually 2. If increasing ozone concentration reduces primary productivity in arctic and boreal ecosystems, then these areas might not become the important net sinks of CO2 that have been predicted. The working group reports and a sumrnal'y of the workshop are available on the World Wide Web (http://www.uku.fi/departments/ ecolenvsci/workshop.html).
Jarmo K. Holopainen Dept of Ecology and Environmental Science, University of Kuopio, POB 1627, FIN-70211 Kuopio, Finland ([email protected])
References 1 Lefohn,A.S. (1992)Surface Level Ozone Exposures and their Effects on Vegetation, Lewis Publishers 2 Runeckles, V.C. and Krupa, S.V. (1994)The impact ofUV-bradiation and ozoneon terrestrial vegetation, Environ. Pollut. 83, 191-213 3 Karenlampi, L. and Sk~by, L., eds (1996) Critical Levels for Ozone in Europe: Testing and Finalizing the Concepts (UN-ECE Workshop Report), University of Kuopio 4 P~iakk6nen,E., Holopainen,T. and I~renlampi, L. Variation in ozone sensitivity of Betula pendula and Betula pubescens clones from southern and central Finland, Environ. Pollut. (in press) 5 Gagnon, Z.E. and Karnosky, D.F. (1992) Physiologicalresponse of three species of Sphagnum to ozoneexposure,J. Bryd. 17, 81-91 6 Oechl, W.C. and Vourlitis, G.L. (1994) The effects of climate change on land-atmosphere feedbacks in arctic tundra regions, Trends Ecol. Evol. 9, 324-329 Copyright © 1996 Elsevier Science Ltd. All rights reserved. 1360 - 1385/96/$15.00
AUX1 •a n a u x i n transporter? Bennett, M.J., Marchant, A., Green, H.G., May, S.T., Ward, S.P., Millner, P.A., Walker, A.R., Schulz, B. and Feldmann, K.A. (1996) Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism, Science 273, 948-950 Although auxin is an important regulator of many developmental processes (e.g. apical dominance, phototropism and gravitropism), the mechanisms underlying its action are still not fully understood. Gravity is thought to promote root curvature by creating an asymmetric distribution of auxin that leads to an inhibition of cell elongation. The paper by Bennett et al. throws light on this process by describing the Arabidopsis agravitropic mutant auxl-lO0, which was obtained by a T-DNA tagging procedure. The phenotypic characteristics of the mutant include a reduced sensitivity to the synthetic auxin 2,4-D and an abnormal thigmotropic response. Using the T-DNA as a marker for the AUX1 locus, a genomic DNA fragment was isolated and a homologous cosmid clone identified. This in turn was used to probe a cDNA library - a transcript of approximately 2 kb was isolated, encoding a putative polypeptide of 54.1 kDa. Four of the auxl alleles were found to contain nucleotide sequence changes consistent with a lesion in this gene. The AUX1 gene was also used to transform auxl-7 plants, where it was shown to complement auxin-resistant root growth and the agravitropic and athigmotropic phenotypes. The predicted amino acid sequence of AUX1 was found to be similar to the sequences of amino acid transport proteins from plants, fungi and Caenorhabditis elegans, suggesting that AUX1 plays a similar role. Since the naturally occurring auxin, IAA, is structurally similar to tryptophan, the authors suggest that IAA might itself be transported by AUXl. Also, in situ hybridizations revealed that AUX1 was expressed in the root apex, and the authors indicate that this occurs mainly in the epidermal cells where basipetal transport occurs. It therefore appears that AUX1 is a key component of the auxin transport pathway. The next step is to determine how gravity might regulate this process. November1996,Vol. 1, No. 11
36g
literature
focus
Future impact One example of the problems that high tropospheric ozone levels might pose concerns the intention to use cloned trees for forest plantations. According to a recent investigation 4, 25% of silver birch (Betula pendula Roth) clones that were selected for micropropagation (due to their fast growth) showed high ozone sensitivity, and only 35% were ozone tolerant when exposed to ozone concentrations that were 60-70% higher than ambient levels. It may be that ozone tolerance should be incorporated into the selection criteria for tree breeding. The ecological significance of a rapid increase in tropospheric ozone on a global scale remajn.q unclear. For example, almost nothing is known of the effects of ozone on sedges and mosses 5 in peatland ecosystems. There is an urgent need to extend the present study to arctic and boreal forests and peatlands, where net primary productivity often exceeds heterotrophic respiration because of cold, wet soils, which limit decomposition. Productivity within these ecosystems is expected to increase as a result of high-latitude warming and elevated CO2 concentrations. However, the current annual rate of increase in CO~ concentration is only 0.5%, while the concentration of ozone increases by 0.5-2.0% annually 2. If increasing ozone concentration reduces primary productivity in arctic and boreal ecosystems, then these areas might not become the important net sinks of CO2 that have been predicted. The working group reports and a sumrnal'y of the workshop are available on the World Wide Web (http://www.uku.fi/departments/ ecolenvsci/workshop.html).
Jarmo K. Holopainen Dept of Ecology and Environmental Science, University of Kuopio, POB 1627, FIN-70211 Kuopio, Finland ([email protected])
References 1 Lefohn,A.S. (1992)Surface Level Ozone Exposures and their Effects on Vegetation, Lewis Publishers 2 Runeckles, V.C. and Krupa, S.V. (1994)The impact ofUV-bradiation and ozoneon terrestrial vegetation, Environ. Pollut. 83, 191-213 3 Karenlampi, L. and Sk~by, L., eds (1996) Critical Levels for Ozone in Europe: Testing and Finalizing the Concepts (UN-ECE Workshop Report), University of Kuopio 4 P~iakk6nen,E., Holopainen,T. and I~renlampi, L. Variation in ozone sensitivity of Betula pendula and Betula pubescens clones from southern and central Finland, Environ. Pollut. (in press) 5 Gagnon, Z.E. and Karnosky, D.F. (1992) Physiologicalresponse of three species of Sphagnum to ozoneexposure,J. Bryd. 17, 81-91 6 Oechl, W.C. and Vourlitis, G.L. (1994) The effects of climate change on land-atmosphere feedbacks in arctic tundra regions, Trends Ecol. Evol. 9, 324-329 Copyright © 1996 Elsevier Science Ltd. All rights reserved. 1360 - 1385/96/$15.00
AUX1 •a n a u x i n transporter? Bennett, M.J., Marchant, A., Green, H.G., May, S.T., Ward, S.P., Millner, P.A., Walker, A.R., Schulz, B. and Feldmann, K.A. (1996) Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism, Science 273, 948-950 Although auxin is an important regulator of many developmental processes (e.g. apical dominance, phototropism and gravitropism), the mechanisms underlying its action are still not fully understood. Gravity is thought to promote root curvature by creating an asymmetric distribution of auxin that leads to an inhibition of cell elongation. The paper by Bennett et al. throws light on this process by describing the Arabidopsis agravitropic mutant auxl-lO0, which was obtained by a T-DNA tagging procedure. The phenotypic characteristics of the mutant include a reduced sensitivity to the synthetic auxin 2,4-D and an abnormal thigmotropic response. Using the T-DNA as a marker for the AUX1 locus, a genomic DNA fragment was isolated and a homologous cosmid clone identified. This in turn was used to probe a cDNA library - a transcript of approximately 2 kb was isolated, encoding a putative polypeptide of 54.1 kDa. Four of the auxl alleles were found to contain nucleotide sequence changes consistent with a lesion in this gene. The AUX1 gene was also used to transform auxl-7 plants, where it was shown to complement auxin-resistant root growth and the agravitropic and athigmotropic phenotypes. The predicted amino acid sequence of AUX1 was found to be similar to the sequences of amino acid transport proteins from plants, fungi and Caenorhabditis elegans, suggesting that AUX1 plays a similar role. Since the naturally occurring auxin, IAA, is structurally similar to tryptophan, the authors suggest that IAA might itself be transported by AUXl. Also, in situ hybridizations revealed that AUX1 was expressed in the root apex, and the authors indicate that this occurs mainly in the epidermal cells where basipetal transport occurs. It therefore appears that AUX1 is a key component of the auxin transport pathway. The next step is to determine how gravity might regulate this process. November1996,Vol. 1, No. 11
36g