Selenium and spermine alleviate cadmium induced toxicity in the red seaweed Gracilaria dura by regulating antioxidants and DNA methylation

The protective role of exogenously supplied selenium (Se) and polyamines (PAs) such as putrescine (Put) and spermine (Spm) in detoxifying the cadmium (Cd) induced toxicity was studied in the marine red alga Gracilaria dura in laboratory conditions. The Cd exposure (0.4 mM) impede the growth of alga while triggering the reactive oxygen species (ROS viz. O 2•- and H 2O 2) generation, inhibition of antioxidant system, and enhancing the lipoxygenase (LOX) activity, malondialdehyde (MDA) level and demethylation of DNA. Additions of Se (50 μM) and/or Spm (1 mM) to the culture medium in contrast to Put, efficiently ameliorated the Cd toxicity by decreasing the accumulation of ROS and MDA contents, while restoring or enhancing the level of enzymatic and nonenzymatic antioxidants and their redox ratio, phycobiliproteins and phytochelatins, over the controls. The isoforms of antioxidant enzymes namely superoxide dismutase (Mn-SOD, ∼ 150 kDa; Fe-SOD ∼120 kDa), glutathione peroxidase (GSH-Px, ∼120 and 140 kDa), glutathione reductase (GR, ∼110 kDa) regulated differentially to Se and/or Spm supplementation. Furthermore, it has also resulted in enhanced levels of endogenous PAs (specially free and bound insoluble Put and Spm) and n-6 PUFAs (C20-3, n-6 and C20-4, n-6). This is for the first time wherein Se and Spm were found to regulate the stabilization of DNA methylation by reducing the events of cytosine demethylation in a mechanism to alleviate the Cd stress in marine alga. The present findings reveal that both Se and Spm play a crucial role in controlling the Cd induced oxidative stress in G. dura. © 2011 Elsevier Masson SAS

Growth and agarose characteristics of isomorphic gametophyte (male and female) and sporophyte of Gracilaria dura and their marker assisted selection

The characteristics of agarose and growth for three isomorphic life phases of G. dura with their bio-molecular marker assisted selection have been described in this study. The tetrasporophyte showed superior quality of agarose over gametophytes and recorded growth rate was highest for females. The genetic relatedness studied with ISSR markers showed quadratic line of correlation between these phases (R2=1). Their genetic diversity determinants as percentage of polymorphic loci (PPL), average heterozygosity (He) and Shannon's Weaver index (I) were 55.55%, 0.5±0.07 and 0.33 respectively. The cytological analysis for chromosome count revealed 8 chromosomes in haploid gametophytic thallus (N) and 16 for diploid tetrasporophyte (2N) together with genetic structure analysis confirmed to their sexual mating behaviour. Their marker assisted selection based on ISSR generated characteristic band of 430bp specific to male, 860bp for female and two bands of 800 and 1600bp for tetrasporophytic thallus from primer 'A'. Similarly ISSR primer 'E' also generated bands specific to male, female and tetrasporophytes while others gave bands specific to either of life phase. Interestingly, endogenic ABA content was significantly higher for haploid gametophytes (female more than male) than diploid tetrasporophyte while no significant difference was observed in IBA content. Thus the study described not only the features of three life phases of G. dura but also reliable biomarkers for differentiating such isomorphic life phases which could be beneficial for the selection of cultivar and in breeding programmes. © 2011 Elsevier B.V