Mi Kwon

2,4-dichlorophenoxyacetic acid-induced leaf senescence in mung bean (Vigna radiata L. Wilczek) and senescence inhibition by co-treatment with silver nanoparticles

Leaf senescence induced by 2,4-dichlorophenoxyacetic acid (2,4-D) and senescence inhibition caused by supplementation with silver (Ag(+)) ions in the form of silver nitrate (AgNO(3)) or silver nanoparticles (AgNPs) were investigated in 8-day-old mung bean (Vigna radiata L. Wilczek) seedlings. Inhibition of root and shoot elongation were observed in mung bean seedlings treated with 500μM 2,4-D. Concomitantly, the activity of 1-aminocyclopropane-1-carboxylic acid synthase was significantly induced in leaf tissue. Leaf senescence induced by 2,4-D was closely associated with lipid peroxidation as well as increased levels of cytotoxic hydrogen peroxide (H(2)O(2)) and superoxide radicals (O(2)(·-)). Despite decreased catalase activity, the activities of peroxidase, superoxide dismutase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase were increased during 2,4-D-induced leaf senescence. Further, the levels of reduced ascorbate, oxidized ascorbate, and reduced glutathione were markedly decreased, whereas the level of oxidized glutathione increased. 2,4-D-induced leaf senescence in mung bean was accompanied by an increase in positive terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, nuclear DNA fragmentation, and the activity of a 15-kDa Ca(2+)-dependent DNase. Supplementation with 100μM AgNO(3) or AgNPs inhibited 2,4-D-induced leaf senescence. The present results suggest that increased oxidative stress (O(2)(·-) and H(2)O(2)) led to senescence in mung bean leaves. Furthermore, significantly induced antioxidative enzymes are not sufficient to protect mung bean cells from 2,4-D-induced harmful ROS.

Overexpression of constitutively active Arabidopsis RabG3b promotes xylem development in transgenic poplars

An Arabidopsis small GTPase, RabG3b, was previously characterized as a component of autophagy and as a positive regulator for xylem development in Arabidopsis. In this work, we assessed whether RabG3b modulates xylem-associated traits in poplar in a similar way as in Arabidopsis. We generated transgenic poplars (Populus alba × Populus tremula var. glandulosa) overexpressing a constitutively active form of RabG3b (RabG3bCA) and performed a range of morphological, histochemical and molecular analyses to examine xylogenesis. RabG3bCA transgenic poplars showed increased stem growth due to enhanced xylem development. Autophagic structures were observed in differentiating xyelm cells undergoing programmed cell death (PCD) in wild-type poplar, and were more abundant in RabG3bCA transgenic poplar plants and cultured cells. Xylogenic activation was also accompanied by the expression of secondary wall-, PCD- and autophagy-related genes. Collectively, our results suggest that Arabidopsis RabG3b functions to regulate xylem growth through the activation of autophagy during wood formation in Populus, as does the same in Arabidopsis.

Exogenously applied 24-epi brassinolide reduces lignification and alters cell wall carbohydrate biosynthesis in the secondary xylem of Liriodendron tulipifera.

The roles of brassinosteroids (BRs) in vasculature development have been implicated based on an analysis of Arabidopsis BR mutants and suspension cells of Zinnia elegans. However, the effects of BRs in vascular development of a woody species have not been demonstrated. In this study, 24-epi brassinolide (BL) was applied to the vascular cambium of a vertical stem of a 2-year-old Liriodendron, and the resulting chemical and anatomical phenotypes were characterized to uncover the roles of BRs in secondary xylem formation of a woody species. The growth in xylary cells was clearly promoted when treated with BL. Statistical analysis indicated that the length of both types of xylary cells (fiber and vessel elements) increased significantly after BL application. Histochemical analysis demonstrated that BL-induced growth promotion involved the acceleration of cell division and cell elongation. Histochemical and expression analysis of several lignin biosynthetic genes indicated that most genes in the phenylpropanoid pathway were significantly down-regulated in BL-treated stems compared to that in control stems. Chemical analysis of secondary xylem demonstrated that BL treatment induced significant modification in the cell wall carbohydrates, including biosynthesis of hemicellulose and cellulose. Lignocellulose crystallinity decreased significantly, and the hemicellulose composition changed with significant increases in galactan and arabinan. Thus, BL has regulatory roles in the biosynthesis and modification of secondary cell wall components and cell wall assembly during secondary xylem development in woody plants.

In vitro analysis of the monolignol coupling mechanism using dehydrogenative polymerization in the presence of peroxidases and controlled feeding ratios of coniferyl and sinapyl alcohol

In this study, dehydrogenative polymers (DHP) were synthesized in vitro through dehydrogenative polymerization using different ratios of coniferyl alcohol (CA) and sinapyl alcohol (SA) (10:0, 8:2, 6:4, 2:8, 0:10), in order to investigate the monolignol coupling mechanism in the presence of horseradish peroxidase (HRP), Coprinus cinereus peroxidase (CiP) or soybean peroxidase (SBP) with H(2)O(2), respectively. The turnover capacities of HRP, CiP and SBP were also measured for coniferyl alcohol (CA) and sinapyl alcohol (SA), and CiP and SBP were found to have the highest turnover capacity for CA and SA, respectively. The yields of HRP-catalyzed DHP (DHP-H) and CiP-catalyzed DHP (DHP-C) were estimated between ca. 7% and 72% based on the original weights of CA/SA in these synthetic conditions. However, a much lower yield of SBP-catalyzed DHP (DHP-S) was produced compared to that of DHP-H and DHP-C. In general, the DHP yields gradually increased as the ratio of CA/SA increased. The average molecular weight of DHP-H also increased with increasing CA/SA ratios, while those of DHP-C and DHP-S were not influenced by the ratios of monolignols. The frequency of β-O-4 linkages in the DHPs decreased with increasing CA/SA ratios, indicating that the formation of β-O-4 linkages during DHP synthesis was influenced by peroxidase type.

Chemical modification of secondary xylem under tensile stress in the stem of Liriodendron tulipifera

Tension wood is a specialized tissue that develops in the upper side of leaning stem and branches in angiosperm. In yellow poplar, tension wood does not form a G-layer, which is one of the most characteristic features of typical tension wood. In order to determine whether the chemical modification associated with tension wood formation in yellow poplar is consistent with those of G-layer-forming angiosperm species, tension wood was induced via mechanical bending treatment for 7 and 14 days in the stem of 2-year-old yellow poplars, and its major cell wall components were analyzed. Whereas the cellulose contents of the tension wood were higher than those in opposite wood, its lignin contents were lower; the result is consistent with that seen in other angiosperm tension wood. Interestingly, the lignin contents differed between tension wood and opposite wood sides at 7 days in the bent sample, but became similar levels to each other at later stages of tension wood formation. The S/G ratio of tension wood was also higher than that of opposite wood. Additionally, the composition of hemicelluloses (glucomannan and xylan) was altered significantly under tensile stress conditions in the yellow poplar stem. Therefore, the majority of the cell wall polymers were altered significantly in the tension wood relative to those in opposite wood, and these changes appear to be developmentally regulated, regardless of the existence of the G-layer in the fiber.

Identification of salt and drought inducible glutathione S-transferase genes of hybrid poplar

Recent genome annotation revealed that Populus trichocarpa contains 81 glutathione S-transferase (GST) genes. GST genes play important and varying roles in plants, including conferring tolerance to various abiotic stresses. Little information is available on the relationship . if any . between drought/salt stresses and GSTs in woody plants. In this study, we screened the PatgGST genes in hybrid poplar (Populus alba × Populus tremula var. glandulosa) that were predicted to confer drought tolerance based on our expression analysis of all members of the poplar GST superfamily following exposure to salt (NaCl) and drought (PEG) stresses, respectively. Exposure to the salt stress resulted in the induction of eight PatgGST genes and down-regulation of one PatgGST gene, and the level of induction/repression was different in leaf and stem tissues. In contrast, 16 PatgGST genes were induced following exposure to the drought (PEG) stress, and two were down-regulated. Taken together, we identified seven PatgGSTs (PatgGSTU15, PatgGSTU18, PatgGSTU22, PatgGSTU27, PatgGSTU46, PatgGSTU51 and PatgGSTU52) as putative drought tolerance genes based on their induction by both salt and drought stresses.

Water stress effects on growth of dipterocarpus turbinatus seedlings

Selecting the right species for the right location is a challenge for the forestry industry in Bangladesh, given the increasing risk of extreme weather and geophysical events posed by climate change. The occurrence of prolonged drought in northern Bangladesh has highlighted the need for drought‐resistant plant varieties in this region. The present study reports growth and yield performance of Dipterocarpus turbinatus (Garjan) seedlings grown under two different soil water supply regimes: watered control (WC) and unwatered (UW) for over a period of 40 days. Seedlings were grown following assignment to WC or UW groups by a completely randomized block design. Growth was in black polythene tubes containing a 3:1 compost mixture of nursery soil and cow dung. The experiment was conducted in the nursery of Institute of Forestry and Environmental Sciences, University of Chittagong. Growth and yield of D. turbinatus declined in the water‐limited condition along with the reduction of shoot water content. A strong relationship between soil moisture content and shoot water content was evident. Total plant mass production also declined in the absence of water due to the significant reduction in stem elongation and leaf expansion, which eventually influenced root, stem and leaf mass production. UW seedlings displayed marked recovery in stem elongation and leaf expansion with simultaneous influence in total mass and root mass, within a few days of re‐watering. The results indicate the potential of D. turbinatus as a drought‐resistant tree species.

Efficiency of RAPD and ISSR markers in assessing genetic diversity and relationships in black gram (Vigna mungo L. Hepper) varieties

The DNA fingerprinting methodologies, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR), were used to estimate genetic diversity and relationships among 20 black gram (Vigna mungo L. Hepper) varieties. Thirty selected RAPD primers amplified 255 bands, 168 of which were polymorphic (66.5%). On average, these primers produced 8.5 bands, 5.6 of which were polymorphic. Polymorphic band number varied from 2 (A-05) to 10 (OPA-02), with sizes ranging from 100 to 2550 bp. Twenty-four selected ISSR primers produced 238 amplified products, 184 of which were polymorphic (77.8%). On average, these primers generated 9.8 bands, with 7.7 polymorphic bands ranging in number from 4 (ISSR-13) to 11 (ISSR-03), and size from 100-2650 bp. Genetic relationships were estimated using similarity coefficient (Jaccard’s) values between different accession pairs; these varied from 30.7 to 85.0 for RAPD, and from 37.2 to 88.4 with ISSR. UPGMA analysis indicated that the varieties ranged in similarity fro...