Drought-induced changes in antioxidant system and osmolyte content of poplar cuttings

Poplars are widely utilized in the intensive and biomass production, as well as in breeding and environment protection programs. This experiment was performed to investigate the effect of drought stress on poplar clones (M-1, PE19/66 and B-229). Poplar clones were grown hydroponically under controlled conditions and exposed to drought stress by applying polyethylene glycol (PEG) 6000. The plant samples were collected and separated into roots and leaves. For estimation of antioxidant status, activities of different antioxidant enzymes were determined (superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), glutathione peroxidase (GPX), glutathione reductase (GR) and ascorbate peroxidase (APX)), as well as antiradical power (ARP) against hydroxyl (˙OH) radical using ESR spin-trapping. The water stress parameters proline (PRO) content, activity of proline dehydrogenase (PDH) and glycine betaine (GB) content were determined. Drought stress had significant effects on PRO and GB contents, SOD, APX and CAT activities when compared to control. All investigated extracts were determined as good inhibitors for ˙OH radical reduction, especially clone M-1where there was an increase of ARP against ˙OH radical in drought condition what could help to prevent or meliorate oxidative damage. Results indicated that the M-1 clone had a greater accumulation of substances for osmotic adjustment and a more efficient enzymatic detoxification cycle for eliminating the negative effects caused by ROS under drought stress than clones B-229 and PE19/66. This study provides valuable information for understanding drought - responsive mechanisms in leaves and roots of poplar clones M-1, B-229 and PE19/66. Key words: antioxidant enzymes, climate change, drought, glycine betaine, proline.

Coexpression analysis of a large-scale transcriptome identified a calmodulin-like protein regulating the development of adventitious roots in poplar

Poplars are important woody plants, and the ability to form adventitious roots (ARs) is the key factor for their cultivation because most poplars are propagated by cloning. In previous studies, Ca2+ was confirmed to regulate AR formation in poplar. In this study, wild-type poplar cuttings grown in 1.0 mM Ca2+ solution showed the best visible performance of AR development. Coexpression analysis of a large-scale RNA-Seq transcriptome was conducted to identify Ca2+-related genes that regulate AR development in poplar. A total of 15 coexpression modules (CMs) were identified, and two CMs showed high association with AR development. Functional analysis identified a number of biological pathways, including ‘oxidation-reduction process’, ‘response to biotic stimulus’ and ‘metabolic process’, in tissues of AR development. The Ca2+-related pathway was specifically selected, and its regulation in poplar AR development was predicted. A Ca2+ sensor, PdeCML23-1, which is a member of the calmodulin-like protein (CML) family, was found to promote AR development by phenotypic assay of overexpressed PdeCML23-1 transgenic lines at various growing conditions. By measuring cytosolic Ca2+ in AR tips, PdeCML23-1 seemed to play a role in decreasing cytosolic Ca2+ concentration. Additionally, the expression profiles of some genes and phytohormone indole acetic acid (IAA) were also changed in the overexpressed PdeCML23-1 transgenic lines. According to this study, we were able to provide a global view of gene regulation for poplar AR development. Moreover, we also observed the regulation of cytosolic Ca2+ concentration by PdeCML23-1, and this regulation was involved in AR development in poplar. We also predicted that PdeCML23-1 possibly regulates AR development by modulating IAA content in poplar.

Investigation of rooting and growth characteristics of poplar clones in hydroponic and soil cultures

In this study, rooting and growth characteristics of different poplar clones from six species including Populus deltoides Bartram ex Marshall clone Lux, Populus nigra subsp. betulifolia (Pursh) W. Wettstein clone 17/13, Populus euramericana (Dode) Guinier clone 561/41, P. deltoides clone Samsun, Populus alba Linnaeus clone 49/9, Populus caspica (Bornmüller) Bornmüller, and Populus euphratica Olivier in hydroponic and soil cultures have been evaluated. In hydroponic culture, poplar cuttings were grown in plastic tanks and in soil culture, poplar cuttings were planted into plastic pots with 12 replications for each clone. The pot experiment was a Complete Randomized Design. Root length, stem diameter, stem height, and root and shoot dry matter of poplar plants were studied in hydroponic culture after 84 days and in soil culture three times at 6, 12, 18 weeks in 2017. In hydroponic culture, the cuttings of P. deltoides Lux and P. nigra betulifolia 17/13, and of P. deltoides Samsun and P. euphratica were among the first and last clones that rooted, respectively. Also, the lowest rate of rooting was observed in P. deltoides Samsun and P. euphratica clones. The highest values of all parameters except root length were obtained in P. euphratica. The highest root length and stem diameter were observed in clones of P. deltoides Lux, P. nigra betulifolia 17/13, P. euramericana 561/41, and P. deltoides Samsun. In soil culture, P. deltoides Lux, P. nigra betulifolia 17/13, and P. alba 49/9 showed the highest percentage of rooting compared to the other clones at the first measurement. All the clones except the clone of P. euphratica reached above 40 cm root length in each of the three measurement periods. The highest stem diameter, stem height, and shoot dry matter were obtained in clone of P. deltoides Lux and root dry matter in clone of P. alba 49/9.

An attempt to determine the resistance of poplars to infection by Chondroplea populea (Sacc. Kłęb.) = Dothichiza populea Sacc. et Briard) on the basis of the composition of epiphytic bacterial microflora

Epiphytic bacteria isolated from the bark of shoot nodes of two year poplar cuttings hydrolyse chitin whereas those isolated from the internodes do not show this property. The epiphytic microflora of the sensitive variety P. 'Robusta' embraces coryneform bacteria and <i>Pseudomonas</i> which can as a carbon source utilize o-OH benzoic acid, gentisic acid or trans-cinnamic acid in 10^-2M concentration. The resistant variety P. 'NE-42' is featured by Pseudomonas capable of catabolizing only genetisic acid in 10^-2M con-centration. The ability of the bacteria to grow media containing either water extracts from the bark or phenolic acids (lignin model precursors) is correlated which the aromatic compound composition of the bark and resistance to infection by fungi.