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Evaluation of the stress-inducible production of proline in transgenic sugarcane (Saccharum spp.): osmotic adjustment, chlorophyll fluorescence and oxidative stress

Authors

  • Hugo Bruno Correa Molinari,

    1. Plant Biotechnology Laboratory, Agricultural Research Institute of Parana (IAPAR), CP 481, CEP 86001-970 Londrina PR, Brazil
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  • Celso Jamil Marur,

    1. Plant Biotechnology Laboratory, Agricultural Research Institute of Parana (IAPAR), CP 481, CEP 86001-970 Londrina PR, Brazil
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  • Edelclaiton Daros,

    1. Department of Agronomy and Plant Protection, Federal University of Parana (UFPR), CEP 80035-050 Curitiba PR, Brazil
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  • Marília Kaphan Freitas De Campos,

    1. Plant Biotechnology Laboratory, Agricultural Research Institute of Parana (IAPAR), CP 481, CEP 86001-970 Londrina PR, Brazil
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  • Jane Fiuza Rodrigues Portela De Carvalho,

    1. Plant Biotechnology Laboratory, Agricultural Research Institute of Parana (IAPAR), CP 481, CEP 86001-970 Londrina PR, Brazil
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  • João Carlos Bespalhok Filho,

    1. Department of Agronomy and Plant Protection, Federal University of Parana (UFPR), CEP 80035-050 Curitiba PR, Brazil
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  • Luiz Filipe Protasio Pereira,

    1. Plant Biotechnology Laboratory (IAPAR), Embrapa Café, CP 481, CEP 86001-970 Londrina PR, Brazil
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  • Luiz Gonzaga Esteves Vieira

    Corresponding author
    1. Plant Biotechnology Laboratory, Agricultural Research Institute of Parana (IAPAR), CP 481, CEP 86001-970 Londrina PR, Brazil
      *e-mail: lvieira@iapar.br
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*e-mail: lvieira@iapar.br

Abstract

Proline accumulates in a variety of plant species in response to stresses such as drought, salinity and extreme temperatures. Although its role in plant osmotolerance remains controversial, proline is thought to contribute to osmotic adjustment, detoxification of reactive oxygen species and protection of membrane integrity. In the present study, we evaluated the effects of stress-inducible proline production on osmotic adjustment, chlorophyll fluorescence and oxidative stress protection in transgenic sugarcane transformed with a heterologous P5CS gene. In well-watered conditions, free proline, malondialdehyde (MDA) levels, Fv/Fm ratios and chlorophyll contents (Chls) in transgenic sugarcane were not statistically different from non-transformed control plants. After 9 days without irrigation, proline content in transgenic events was on the average 2.5-fold higher than in controls. However, no osmotic adjustment was observed in plants overproducing proline during the water-deficit period. The photochemical efficiency of PSII observed was higher (65%) in the transgenic events at the end of the water-deficit experiment. The effects of proline on lipid peroxidation as MDA levels and on the decline of Chl in paraquat-treated leaf discs along the drought period suggest that proline protected the plants against the oxidative stress caused by the water deficit. The overall capacity of transgenic plants to tolerate water-deficit stress could be assessed by the significantly higher biomass yields 12 days after withholding water. These results suggest that stress-inducible proline accumulation in transgenic sugarcane plants under water-deficit stress acts as a component of antioxidative defense system rather than as an osmotic adjustment mediator.

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