Lower oxidative damage and cell wall loosening, mediated or not by auxin, as part of the tolerance mechanism of Paubrasilia echinata morphotypes in the shade and full sun

Vinícius Novo Gama,Leonardo Valandro Zanetti,Geraldo Rogério Faustini Cuzzuol,Bernardo Pretti Becacici Macieira

doi:10.1590/0102-33062020abb0504

Vinícius Novo Gama, Leonardo Valandro Zanetti + Show 2 more

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https://doi.org/10.1590/0102-33062020abb0504

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Abstract

Paubrasilia echinata presents three morphotypes that differ from each other in leaf morphology (small morphotype-SM, medium morphotype-MM, and large morphotype-LM) with indications of divergence between them regarding irradiance tolerance. The present study aimed to identify possible physiological and growth patterns in P. echinata morphotypes under contrasting irradiance. The growth and photosynthesis of SM were inhibited in the full sun, and those of MM and LM, in the shade. The auxin contents of the three morphotypes increased in the full sun. However, in MM and LM, this increase was 5 times greater. The oxidative damage (hydrogen peroxide-H2O2 and lipid peroxidation-MDA content) of SM were higher in the full sun and of MM and LM in the shade. The stem hemicelluloses and CO2 assimilation decreased in shade for SM, and sun for MM and LM. The shade tolerance of SM and the full sun tolerance of MM and LM were associated with lower oxidative damage and cell wall loosening (lower hemicelluloses content) in the photo-promoted treatments. The integration of the lower oxidative damage with cell wall loosening seems to represent an essential part of the tolerance mechanism of P. echinata morphotypes in the shade and full sun.

Highlights

Tropical pioneer species are characterized by a level of photosynthesis higher than the non-pioneer species (Whitmore 1991; Huc et al 1994; Nogueira et al 2004; Portes et al 2010), this variable did not present a well-defined pattern of responses in some tropical shadetolerant and sun-tolerant tree species under contrasting solar irradiance
The highest values of growth and net carbon assimilation rates (A) of the SM were found in the shaded condition, and of the MM were observed in the full sun, confirming the shade-tolerant habit of the former morphotype (Mengarda et al 2009) and the sun-tolerant habit of the latter (Gama et al 2019)
The higher adjustment capacity of growth and A of the sun-tolerant morphotypes compared to the shade-tolerant one reinforces the tendency of the pioneers to exhibit a higher adjustment capacity compared to non-pioneer tropical species (Portes et al 2010; Souza & Válio 2003; Valladares et al 2000)

Summary

Introduction

The few studies about the physiology of sun-tolerant (pioneer) and shade-tolerant (non-pioneer) tropical forest tree species under contrasting solar irradiances (shade and full sun) in the early growth phase have presented unclear responses regarding growth (Souza & Válio 2003), photosynthesis (Ribeiro et al 2005), and oxidant metabolism (Contin et al 2014) between these two functional classes This makes it difficult to understand the ecophysiology of sun-tolerant and shade-tolerant tree species of tropical forests under shade and full sun conditions. Lower oxidative damage and cell wall loosening, mediated or not by auxin, as part of the tolerance mechanism of Paubrasilia echinata morphotypes in the shade and full sun shade and full sun conditions (Souza & Válio 2003) For these authors, inter-specific differences in growth parameters such as root:shoot ratio and leaf mass area did not show differentiated responses between sun-tolerant and shadetolerant species under shade and full sun. Some sun-tolerant and shadetolerant tropical trees presented higher photosynthesis in full sun conditions, showing that this variable did not show a clear difference between these two successional groups under contrasting intensity irradiance (Kitajima 1994; Ribeiro et al 2005)

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