Populus nigra l. klonlarında soğuğa dirençli genlerin farklı ifadeleri.

Poplar has been adopted as a model perennial woody species for forest tree genetics to understand molecular processes of growth, development and responses to environmental stresses. In this study, seasonal changes in antioxidant enzymes activities including glutathione reductase (GR), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and catalase (CAT) were examined in black poplar (Populus nigra L.) clones. It was found that GR, APX and DHAR activities increased with low air temperatures in winter, whereas they decreased under high temperatures. CAT activity indicated exactly the opposite seasonal variations. The identification and characterization of differentially expressed genes responsive to low temperatures were also carried out by using microarray techniques. Although 4421 genes differentially expressed in cold resistant genotype, 4187 genes were significantly expressed in cold sensitive genotype (fold change ≥ 5, p value ≤ 0.05). It was observed that especially the genes related with carbohydrate metabolic processes and sugar transport activities, i.e., beta-galactosidase, beta-1,3-glucanases and monosaccharide transporters were significantly up-regulated in cold resistant genotype. Glutathione peroxidases and gibberellin 20-oxidase were also over-expressed as defense related genes. In cold sensitive genotype, especially transcription factors including AP2 domain containing protein, WRKY-type DNA binding protein and myb-like protein were significantly up-regulated. Genes involved in scavenging of reactive oxygen species, i.e., cytochrome P450, 5-oxoprolinase-like protein and metallothioneins were also highly expressed. These genes identified by comparative transcriptome analyses may play key roles in protecting black poplars against low temperature stress. Informations generated from this study can be used for further understanding of the molecular mechanisms of cold tolerance in black poplars. Low temperature related antioxidant enzyme activities and gene expression data could be effectively used in breeding programmes for the purpose of high productivity in low temperature areas.Ph.D. - Doctoral Progra

Improved in vitro micropropagation method with adventitious corms and roots for endangered saffron

The objective of this study was to investigate development of an efficient in vitro tissue culture system for saffron (Crocus sativus L.) complete with roots and corms. In indirect organogenesis, Murashige and Skoog (MS) media with 3% (w/v) sucrose, 100 mg L(-1) ascorbic acid, and the combination of 0.25 mg L(-1) 2,4-dichlorophenoxyacetic acid (2,4-D) and 1 mg L(-1) 6-benzylaminopurine (BAP) were best for callus initiation and growth while 1.5 mg L(-1) BAP was excellent for high rate of adventitious shoot formation. 1 mg L(-1) indole-3-butyric acid (IBA) was more preferable for adventitious corm and root initiation as well as growth. Overall, 64% rooting and 33% corm production rates were achieved in indirect organogenesis. In direct organogenesis, MS medium supplemented with 3 % sucrose, 100 mg L(-1) ascorbic acid and 1 mg L(-1) BAP was optimum for shoot growth. While 1 mg L(-1) IBA was best for adventitious corm formation, 2 mg L(-1) IBA promoted adventitious root initiation and growth. Overall, 36% and 57% of explants had corm and contractile root, respectively. The high rates suggest that efficient tissue culture system could be achieved for mass propagation and ex situ conservation of threatened saffron genetic resources