Kenan Turgut

Apomictic development in Arabis gunnisoniana

Apomixis in model systems has been of growing interest for many scientists around the world. A limited number of species belonging to Brassicaceae has been described as apomictic and considered as a model system to study molecular biology of apomixis. In this study, we report the use of an ovule-clearing technique to characterize embryo sac development in Arabis gunnisoniana. The embryo sac development was detected by Taraxacum-type diplosporous dyad formation. Hence, the reproductive pathways in Arabis gunnisoniana were revealed by using flow cytometric seed screen (FCSS) analysis. Arabis gunnisoniana appears to display pseudogamous apomixis.

Agrobacterium-mediated transformation of Arabis gunnisoniana

An efficient method for adventitious shoot regeneration for Arabis drummondii and a transformation protocol for A. gunnisoniana from hypocotyl explants are described. Hypocotyl explants from 7-day-old aseptically grown seedlings were cultured on MS medium containing plant growth regulators (6-benzylaminopurine, 1-phelyl-3- (1,2,3-thiadiazol-5-yl) urea, α-naphthaleneacetic acid and 2,4-dichlorophenoxy-acetic acid). After 4 weeks in culture, high frequency of adventitious shoot regeneration was observed. Regenerated shoots were rooted on half-strength MS basal medium supplemented 1% (w/v) sucrose, with or without NAA. This protocol was then used to produce transformed Arabis gunnisoniana plants. A. gunnisoniana hypocotyl explants were co-cultivated with Agrobacterium tumefaciens strain GV3101 harbouring pBJ40. Transgenic shoots were selected on MS 21 medium supplemented with 50 mg l kanamycin. PCR analysis verified the presence of the nptII gene in the plant DNA isolated from kanamycin resistant shoots.

Apomeiotic pollen mother cell development in the apomictic Boechera species

Pollen mother cell (PMC) development in the apomictic Boechera species B. holboellii, B. gunnisoniana and B. divaricarpa were investigated by various cytological methods. In prophase I, in triploid species B. holboellii and B. gunnisoniana the individual chromosomes condensed into long strands within the nucleus. Then, in metaphase I, each PMC formed a restitutional nucleus thereby bypassing the rest of the first meiotic division. This is interpreted as representing apomeiosis. Subsequently, the restitution nuclei underwent a single cytokinesis as evidenced by the production of dyads. The cells within each dyad were separated by a callose wall. Most of the PMC in B. holboellii and B. gunnisoniana produced dyads, but a small proportion generated conspicuous tetrads. In contrast, diploid apomict B. divaricarpa produced only tetrads by simultaneous cytokinesis.

The effect of different nitrogen levels on yield and quality of stevia (Stevia rebaudiana bert.)

ABSTRACT In the present work, the efficiency of different nitrogen doses (0, 50, 100, 150, and 200 kg ha−1) on growth, yield, and quality of stevia (Stevia rebaudiana Bert.) was investigated in 2011–2013. The study was conducted in Antalya located in the Mediterranean Region of Turkey. Terra rossa type soil (LVx, FAO) characteristics of the experimental field were clay loam, with high amounts of lime (33,9%) and slightly alkaline (pH 7.7). The experiment was carried out in randomized block design with four replications. All the results were summarized as mean of three years. The highest fresh and dry biomass yields (26.75 t ha−1 and 7.5 ha−1, respectively) were obtained from 150 kg ha−1 N dose and followed by 100 kg ha−1 N dose (26.29 t ha−1 and 7.24 ha−1, respectively). Whereas the highest fresh and dry leaf yields (13.27 t ha−1 and 3.82 t ha−1, respectively) were realized in 100 kg ha−1 N dose. Actually, all nitrogen doses gave higher biomass and leaf yields compared to the control. On the hand, major steviol glycosides (stevioside and rebaudioside A) in the leaf were not influenced by nitrogen levels. In conclusion, 100 kg ha−1 N dose was found to be suitable for cultivation of stevia under field conditions.