PHOTOSYNTHETIC PARAMETERS AS PHYSIOLOGICAL INDICATORS OF TOLERANCE TO CADMIUM STRESS IN SUNFLOWER GENOTYPES

Bárbara Lima Do Sacramento,Andréia Teixeira Alves,Silvany Cardim Moura,André Dias De Azevedo Neto,Rogério Ferreira Ribas

doi:10.1590/1983-21252018v31n413rc

Bárbara Lima Do Sacramento, Andréia Teixeira Alves + Show 3 more

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https://doi.org/10.1590/1983-21252018v31n413rc

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Abstract

ABSTRACT The objective of the present study was to evaluate the tolerance to cadmium (Cd) of sunflower genotypes grown in greenhouse conditions, and the effectiveness of using photosynthetic parameters as physiological indicators of this tolerance. Seeds of two sunflower genotypes previously identified as tolerant (H358) and Cd-sensitive (AG960) to Cd were used. The seeds were germinated in plastic cups containing plant substrate; after 9 days, the seedlings were transplanted to plastic basins containing a nutrient solution with 0 or 10 µM of Cd, where they remained for 16 days. Samples of the plants were harvested every 5 days. The experiment was carried out in a randomized complete design, using a 4×2×2 factorial arrangement (4 days of grown in a nutrient solution with Cd, 2 sunflower genotypes, and 2 Cd levels) with four replications. Cd stress decreased CO2 net assimilation, stomatal conductance, carboxylation efficiency, photosynthetic pigment contents, potential quantum yield (Fv/Fm), and effective quantum yield of plants of the two evaluated genotypes. The decrease in photosynthetic rates of these plants was caused by both stomatal and non-stomatal limitations. Plants of the AG960 genotype showed more pronounced deleterious effects due to Cd stress than those of the H358 genotype. Thus, CO2 net assimilation rate, stomatal conductance, and chloroplast pigment content are good physiological indicators of sunflower tolerance to Cd and can at least in part, explain the greater tolerance of the H358 genotype to Cd stress when compared to the AG960 genotype.

Highlights

Sunflower (Helianthus annuus) is an oleaginous plant of the Asteraceae family that is native to North America
Several studies have shown the capacity of sunflower crops to retain several heavy metals (CHAVES; ESTRELA; SOUZA, 2011; GAJDOS et al, 2012; NASCIMENTO et al, 2014), such as cadmium (Cd), whose presence in soils has receiving considerable attention due to its increasing rates in the soil and impacts on human health throughout the food chain
The objective of the present study was to evaluate the tolerance to cadmium (Cd) of sunflower genotypes grown in greenhouse conditions, and the effectiveness of using photosynthetic parameters as physiological indicators of this tolerance by analyzing the gas exchanges, chlorophyll-a fluorescence, and pigment content of leaves of these plants

Summary

Introduction

Sunflower (Helianthus annuus) is an oleaginous plant of the Asteraceae family that is native to North America It produces an oil of excellent nutritional quality and has great capacity of adaptation, with good responses to several environmental conditions due to its diversity of genotypes (CAPONE et al, 2012). Cd causes inactivation and denaturation of enzymes, blocking of metabolically important functional groups, translocation or substitution of essential metal ions of biomolecules and functional cell units, changes in protein conformation, and membrane integrity disorders (HOSEINI; ZARGARI, 2013). This toxicity is due to the affinity of Cd to sulfhydryl groups in proteins, which inhibits their activity or ruptures their structures. These effects alter cellular metabolism, affecting essential processes, such as respiration and photosynthesis of plants grown in environments with this metal (BENAVIDES; GALLEGO; TOMARO, 2005)

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