Yelda Özden Çiftçi

Excess boron responsive regulations of antioxidative mechanism at physio-biochemical and molecular levels in Arabidopsis thaliana

This work was aimed to evaluate the effect of boron (B) toxicity on oxidative damage level, non-enzymatic antioxidant accumulation such as anthocyanin, flavonoid and proline and expression levels of antioxidant enzymes including superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) and their respective activities as well as expression levels of miR398 and miR408 in Arabidopsis thaliana. Plants were germinated and grown on MS medium containing 1 mM B (1B) and 3 mM B (3B) for 14 d. Toxic B led to a decrease of photosynthetic pigments and an increase in accumulation of total soluble and insoluble sugars in accordance with phenotypically viewed chlorosis of seedlings through increasing level of B concentration. Along with these inhibitions, a corresponding increase in contents of flavonoid, anthocyanin and proline occurred that provoked oxidative stress tolerance. 3B caused a remarkable increase in total SOD activity whereas the activities of APX, GR and CAT remained unchanged as verified by expected increase in H2O2 content. In contrast to GR, the coincidence was found between the expressions of SOD and APX genes and their respective activities. 1B induced mir398 expression, whereas 3B did not cause any significant change in expression of mir408 and mir398. Expression levels of GR genes were coordinately regulated with DHAR2 expression. Moreover, the changes in expression level of MDAR2 was in accordance with changes in APX6 expression and total APX activity, indicating fine-tuned regulation of ascorbate-glutathione cycle which might trigger antioxidative responses against B toxicity in Arabidopsis thaliana.

Novel Methods in Micropropagation of Pistachio

The focus of this paper is to describe the novel methods developed for the different stages of micropropagation: installation of mature apical shoot tips and elimination of browning exudates; forcing hardwood shoots from the lignified stem sections; forcing axenic leaves; initiation of embryogenic masses (EMS); encapsulation of somatic embryos and cryopreservation of axillary buds for storage, and the facilitation of rooting. These developed methods are not being used by commercial micropropagation laboratories yet. Exudation of phenolics is inhibited when the disinfested and rinsed explants are cut at the base of the shoot tips and washed twice for 1 h by shaking them in sterile distilled water on a shaker at 100 rpm. For shoot initiation, 15–20 cm long terminal stem sections are cut into 3–4 cm sections and placed in pots filled with peat, perlite and soil. Two or three weeks later, the developed softwood shoots are excised; or freshly harvested three to nine apical tips of 1–2 cm are disinfested and used as explants. Leaves excised from axenic shoot cultures were also used to induce organogenesis on a Murashige and Skoog (MS) medium with Gamborg vitamins supplemented with combinations of different concentrations of 6-benzylaminopurine (BA) and indole-3-asetic acid (IAA). Calcium alginate gel was used to encapsulate somatic embryos to produce synthetic seeds. The encapsulated somatic embryos can be stored under refrigerated conditions for short-term conservation. For long-term conservation, some axillary buds can also be stored by using vitrification and one-step freezing technique; however, other cryogenic techniques should also be tested. With these improved stages, application of Pistachio vera L. micropropagation in commercial clonal orchards will be feasible as an alternative to traditional propagation in the near future.

Cryopreservation of Somatic Embryos of Ornamental Plants

Ornamental plants play a social and economic role in human society since antic ages, and its production consists about 78 % of total production. Thus, in situ and ex situ germplasm conservation techniques must be applied to preserve elite varieties. Since in situ strategies are more prone to environmental factors (e.g., biotic and abiotic stress) and ex situ approaches are open to cross-pollination or homologous recombination during gamete formation, currently in vitro strategies are the good complementary mechanism to avoid these problems. Among in vitro conservation techniques, cryopreservation seems to be the best candidate as it enables to preserve selected germplasm theoretically unlimited period of time with maintaining genetic stability, which is very important in ornamental plant cultivation. Besides, embryogenic cultures are used for in vitro propagation; the tissues are also utilized as target materials for gene transfer studies. These cultures have the potential to produce cisgenic or intragenic plants and cryogenic technology offers opportunities to conserve germplasm to introduce genes from crossable ornamental plants especially for cisgenesis. Thus cryopreservation also plays an important role in maintaining transgenic, cisgenic, or intergenic somatic embryos of ornamentals in a stable way. In this chapter, efficient cryopreservation technique including one-step and two-step freezing methods together with vitrification- and dehydration-based techniques for conservation of somatic embryos and related tissues of ornamentals is discussed.