Flooding and anoxia tolerance in higher plants
2. The Role Of Peroxidase Isoenzymes
In Wood Lignin Biosynthesis:Localisation And Function In Soft- And Hardwood
Kurt V. Fagerstedt, senior
1.Flooding and anoxia intolerance of agricultural crops has been studied for a number of years, however, the causes for the remarkable tolerance of our native wetland plant species is still largely unknown. We are concentrating our research activity on this gap in our knowledge. During flooding oxygen depletion in the tissues is one of the major harmful factors for the tissues. Under oxygen deprivation the death of tissues is due to a number of events but lactic acid fermentation and cytoplasmic acidosis are the two most important immediate reasons. Anoxia affect mitochondria, which most probably take part in signalling the lack of oaxygen to the cell nucleus. Native wetland species have in most cases developed aerenchyma to overcome the problem of oxygen deprivation, but there is also metabolic tolerance of low oxygen levels in the plant kingdom. In our studies Iris pseudacorus rhizomes can tolerate up to a month of anoxia at +20 C without apparent damage to the tissues, while the dryland species Iris germanica dies within a week under total oxygen deficiency. To find out the mechanisms behind this tolerance are the main aims in our research. We have a very broad approach to the problem: We study the consumption of carbohydrate reserves under experimental anoxic conditions and in natural conditions in the field throughout the year, the production of ethanol and the amount of ATP, ADP and AMP under experimental anoxic conditions, the changes in cytoplasmic and vacuolar pH (by NMR) during anoxia in the two Iris species and in barley (Hordeum vulgare) seedlings, lipid peroxidation during and after the anoxic period, and antioxidant protection of the tissues (ascorbic acid, -tocopherol, phenolic compounds and superoxide dismutase levels) in order to explain the differences in anoxia (and flooding) tolerance of these species and to improve the flooding tolerance of our agricultural crops species. One of the most interesting experiments we are conducting at the moment is the effect of anoxia on the mitochondrial permeability transition pore, which may be regulated by anoxia.
2.The aim of the study is to find out the exact role of wood peroxidase isoenzymes in lignin formation in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karsten) and Silver birch (Betula pendula Roth). Peroxidases are a large group of enzyme proteins using hydrogen peroxide as an oxidant and either organic or inorganic compounds as reductants. Even though peroxidases seem to play an important role in the final biosynthesis of plant cell wall lignin from coumaryl, coniferyl and sinapyl alcohol precursors, it is still difficult to unambiguously prove the necessity in lignification for a specific peroxidase. The physiologically and genetically most studied plant secretory peroxidases are alkaline and acidic horse radish peroxidase isoenzymes. It has been proposed recently that in softwood (spruce), soluble alkaline peroxidases are associated with lignin formation, whereas soluble acidic peroxidases have been regarded as unrelated to the developmental regulation of lignification. Accurate localisation and activity of wood peroxidase isoenzymes is essential prior to genetic manipulation of the amount or composition of lignin in wood tissues. The latter is generally considered as a reasonable biotechnical remedy for more environmentally friendly utilisation of wood by pulp and paper industry. By generating more easily extractable lignin or less lignin containing wood raw material, the less harsh cooking and bleaching processes are required in the future. Wood peroxidase isoenzyme analysis, enzyme activity assays, and histochemical and immunogold localisation and 'peroxidase gene hunt' methods are applied in this study.
This study is a part of a
larger consortium on lignin biosynthesis funded by the WOOD WISDOM' programme
of the Academy of Finland. This consortium investigates lignin biosynthesis
from molecular genetics to lignin formation and structure both in vitro
and in situ.
Olga Blokhina, M.Sc, Kaisa Haakana, M.Sc., Anne Hanhijärvi,
M.Sc., Eija Kukkola, Ph.D., Eija Virolainen, M.Sc.
Hanhijärvi, A. M. & Fagerstedt, K. V. Comparison of the effect of natural and experimental anoxia on carbohydrate and energy metabolism in Iris pseudacorus rhizomes. Physiol. Plant. 90:437-444, 1994.
Hanhijärvi, A. M. & Fagerstedt, K. V. Comparison of carbohydrate utilization and energy charge in the yellow flag iris (Iris pseudacorus) and garden iris (Iris germanica) under anoxia. Physiol. Plant. 93:493-497, 1995.
Vartapetian, B.B., Pulli, S. & Fagerstedt, K.V. Plant response and adaptation to anaerobiosis. Ann. Bot. 79(suppl. A): R 1.1996
Fagerstedt, K.V., Saranpää, P. and Piispanen, R. 1998: Peroxidase activity, isoenzymes and histological localisation in sapwood and heartwood of Scots pine (Pinus sylvestris L.). J. Forestry Res. 3: 43-47.
Pretorius, J.C., Small, J.G.C. and Fagerstedt, K.V. 1998: The effect of soaking injury in seeds of Phaseolus vulgaris L. on germination, respiration and adenylate energy charge. - Seed Science Research 8: 17-28.
Blokhina, O.B., Fagerstedt, K.V. & Chirkova, T.V. 1999: Relationships between lipid peroxidation and anoxia tolerance in a range of species during post-anoxic reaeration. – Physiologia Plantarum 105: 625-632.
Seppänen, M. M. & Fagerstedt, K. 2000: The role of superoxide dismutase activity in response to cold acclimation in potato. – Physiologia Plantarum 108: 279-285.
Blokhina, O. B., Virolainen,
E., Fagerstedt, K.V., Hoikkala, A., Wähälä, K. & Chirkova,
T. 2000: Antioxidant status of anoxia-tolerant and –intolerant plants species
under anoxia and reaeration. – Physiologia Plantarum 109: 396-403.
Academy of Finland, Finnish Cultural Foundation, the Ehrnrooth Foundation, The Centre for International Mobility (CIMO).
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