br Results and discussion br
Results and discussion
Conclusion In normal and curd coconuts, full-length cDNA and parental genomic DNA sequences encoding endosperm specific AGal were sequenced and characterized. At least, three mutation nucleoside analogs were identified in CnAGal gene. In vitro expression in K. phaffii showed all recombinant mutant protein containing no AGal activity. Loss of AGal activity in curd coconut causes no hydrolysis and accumulation of oligogalactomannan in endosperm, leading to curd coconut phenotype. Curd coconut phenotype is obvious in the late stage of coconut endosperm development that corresponds to degradation of galactomannan during germination stage of embryo in normal coconut endosperm.
Acknowledgements This work was financially supported by the ASEAN UNINET On-Place Thailand Scholarship Program, the Thailand Research Fund-Commission of Higher Education-Mahidol University MRG5380133, and the New Researcher Supporting Fund, Faculty of Science, Mahidol University, Thailand, . D.A. received the Dean's fund 2011 from the Faculty of Tropical Medicine, Mahidol University, Thailand. We also cordially thank Mr. Somchai Wattanayothin, the former head of coconut breeding program, Department of Agriculture, Ministry of Agriculture and Cooperative, Thailand for normal coconut samples, Dr. Utai Charanasri, the owner of the curd coconut island for curd coconut samples.
Introduction Somatic cells irreversibly arrest at a stage of replicative senescence after a limited number of doublings in culture. In this state, they are characterized by flat cell morphology, increased cytoplasmic and nuclear volume, lack of DNA synthesis, and resistance to apoptosis. The senescent cells do not respond to mitogens and display altered patterns of gene expression, high levels of ROS and oxidative DNA damage, and high activity of β-galactosidase activity detectable at pH 6.0, defined as senescence-associated β-galactosidase (SA-β-gal) (Wang and Dreesen, 2018). It was found that the senescent phenotype can also be induced by a variety of stress factors (stress-induced senescence) or by the expression of activated oncogenes (oncogene-induced senescence) (Campisi and d'Adda di Fagagna, 2007; Collado et al., 2007). Cellular senescence is viewed as a model for cellular and organismal aging. Several studies demonstrated that cellular senescence also occurs in vivo. The existence of senescent cells was observed in several mouse models (Braig et al., 2005; Chen et al., 2005; Collado et al., 2005). Evidence has been presented that senescent cells accumulate with age in renewable tissues at the sites of age-related pathologies (Campisi, 2005; Erusalimsky and Kurz, 2005; Matthews et al., 2006; Price et al., 2002). It was found that somatic senescent cells secrete many kinds of factors that can promote aging and exert a detrimental effect (Campisi, 2011). In contrast to somatic cells, gamete cells do not undergo mitotic divisions, thus they cannot run into the stage of replicative senescence. However, gamete cells do age and they can experience various damaging stresses, leading to the loss of their quality and accelerated degradation. In fact, progressive age-dependent worsening of oocyte quality is thought to represent one of the major causes of infertility and abnormal embryo development in different organisms, including mammals. Aging of fully-grown immature oocytes arrested at the diplotene stage of the first meiotic division occurs in the ovaries, as they pass through their reproductive age, in the physiological process called “ovary aging” (Tatone et al., 2008). On the other hand, mature oocytes age outside of the ovaries. Hormonal stimuli induce oocyte ovulation and meiotic maturation, leading to the release of fertilization-competent MII-arrested oocytes from the ovaries. Normally, in most mammalian species, these oocytes are fertilized within several hours after oviposition. If fertilization does not occur within the optimal time span, the unfertilized oocytes undergo a time-dependent deterioration of quality in the process of postovulatory oocyte aging.