Chloroplast thylakoid ascorbate peroxidase PtotAPX plays a key role in chloroplast development by decreasing hydrogen peroxide in Populus tomentosa.

Chloroplast development is a complex process that is critical to the growth and development of plants. However, the detailed mechanism of chloroplast development in woody plants remains unclear. In this study, we showed that chloroplasts with elaborate thylakoids could develop from proplastids in the cells of calli derived from leaf tissues of Populus tomentosa upon exposure to light. Chloroplast development was confirmed at the molecular and cellular levels. Transcriptome analysis revealed that genes related to photoreceptors and photosynthesis were significantly up-regulated during chloroplast development in a time-dependent manner. In light-induced chloroplast development, a key process was the removal of hydrogen peroxide, in which thylakoid-localized PtotAPX played a major role; light-induced chloroplast development was enhanced in PtotAPX-overexpressing transgenic P. tomentosa callus with lower levels of hydrogen peroxide, but was suppressed in PtotAPX antisense transgenic callus with higher levels of hydrogen peroxide. Moreover, the suppression of light-induced chloroplast development in PtotAPX antisense transgenic callus was relieved by the exogenous reactive oxygen species scavenging agent N,N'-dimethylthiourea (DMTU). Based on these results, we propose that PtotAPX-mediated removal of reactive oxygen species plays a key role in chloroplast development from proplastids upon exposure to light in P. tomentosa.

Profiling the onset of somatic embryogenesis in Arabidopsis.

BACKGROUND: Totipotency is the ability of a cell to regenerate a whole organism. Plant somatic embryogenesis (SE) is a remarkable example of totipotency because somatic cells reverse differentiation, respond to an appropriate stimulus and initiate embryo development. Although SE is an ideal system to investigate de-differentiation and differentiation, we still lack a deep molecular understanding of the phenomenon due to experimental restraints. RESULTS: We applied the INTACT method to specifically isolate the nuclei of those cells undergoing SE among the majority of non-embryogenic cells that make up a callus. We compared the transcriptome of embryogenic cells to the one of proliferating callus cells. Our analyses revealed that embryogenic cells are transcriptionally rather than metabolically active. Embryogenic cells shut off biochemical pathways involved in carbohydrate and lipid metabolism and activate the transcriptional machinery. Furthermore, we show how early in SE, ground tissue and leaf primordia specification are switched on before the specification of a shoot apical meristem. CONCLUSIONS: This is the first attempt to specifically profile embryogenic cells among the different cell types that constitute plant in vitro tissue cultures. Our comparative analyses provide insights in the gene networks regulating SE and open new research avenues in the field of plant regeneration.

Influence of Plant Growth Regulators and Artificial Light on the Growth and Accumulation of Inulin of Dedifferentiated Chicory (Cichorium intybus L.) Callus Cells.

Chicory (Chicorium intybus L.) is a perennial herb of the family Asteraceae, widely distributed in Asia and Europe, commonly used industrially as a raw material for extracting inulin because of a high content of inulin and biologically active compounds. Light conditions and plant growth regulators (PGRs) are two of many factors that affect the growth and inulin content of chicory callus. The aim of this work is to study the effect of PGRs and light conditions on proliferation and accumulation of inulin of chicory callus in vitro. In this study, we used semi-solid MS medium supplemented with different auxins (including Indole-3-acetic acid (IAA), naphthylacetic acid (NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D)) at a concentration of 5.5−9.5 mg/L in combination with 2.0 mg/L 6 benzylaminopurine (BA) to determine induction and proliferation of callus. The increasing value of callus fresh weight was used to assess the growth of the callus in treatments. The results showed that a steady increase in callus fresh weight and inulin content in callus cells was obtained when they were cultured on MS medium supplemented with a combination of 2.0 mg/L BA with 7.5 mg/L IAA in lighting conditions with radiation equalized by the flux density of photosynthetic photons and ratios of radiation levels in the region of FR­far red > R­red. Increasing demand for organic inulin sources in production practice can be met by our finding.

The modulation of ion homeostasis by silicon in cadmium treated poplar callus cells.

One of the major reasons why cadmium is toxic in plants is because it disturbs their nutrient balance. The aim of this work is to investigate the effects of cadmium (Cd) and/or silicon (Si) on the nutrient status of poplar callus cells after 3 and after 9 weeks of Cd exposure and to study its possible relationship with the changes in the fresh and dry mass, the plasma membrane integrity, and cadmium tolerance patterns. A principal component analysis (PCA) was performed to reveal the associations among the elements, and the variability between both treatments, and between the 3- and 9-week stages. Cadmium reduced the fresh and dry mass, the plasma membrane integrity, and the concentration of all nutrients except for P. After 9 weeks of exposure, the Cd concentration in callus cells had almost doubled, in spite of an improvement in all studied parameters. These changes may be due to the callus acclimatizing to the Cd stress. In the Cd + Si treatment, the fresh and dry mass, the plasma membrane integrity, and the concentration of nutrients, as well as the growth tolerance index, increased in comparison with the Cd treatment. We assumed that the enhancement in the plasma membrane integrity mediated by Si under Cd stress had caused the improvement in the uptake of nutrients and, consequently, the fresh and dry mass of callus cells had increased. The reduction in Cd concentration due to the Si impact also contributed to the increase in fresh and dry mass.

Cadmium impact, accumulation and detection in poplar callus cells.

Effect of cadmium cations and their interaction with silicon cations was determined in poplar calli and expressed as changes in callus growth, cell viability and cadmium cation accumulation. Cell viability throughout culture versus cadmium cation accumulation in cells is discussed. At the same time, the study sought appropriate methods for cadmium cation detection in callus cells and also in experiments with low plant material (e.g. protoplasts). Cadmium cations were determined by atomic absorption spectroscopy and using fluorescence microscopy with a specific cadmium cation fluorescent dye. The detection of cadmium cations in callus cells by the latter method appears suitable because the callus cells are surrounded by primary cell walls without auto-fluorescence and these values fit well with atomic absorption spectroscopy quantification. However, the visualisation method has some limits discussed below.