Compositional changes in cell wall polysaccharides from apple fruit callus cultures modulated by different plant growth regulators

Silicon Actuates Poplar Calli Tolerance after Longer Exposure to Antimony

The presence of antimony (Sb) in high concentrations in the environment is recognized as an emerging problem worldwide. The toxicity of Sb in plant tissues is known; however, new methods of plant tolerance improvement must be addressed. Here, poplar callus (Populus alba L. var. pyramidallis) exposed to Sb(III) in 0.2 mM concentration and/or to silicon (Si) in 5 mM concentration was cultivated in vitro to determine the impact of Sb/Si interaction in the tissue. The Sb and Si uptake, growth, the activity of superoxide dismutase (SOD), catalase (CAT), guaiacol-peroxidase (G-POX), nutrient concentrations, and the concentrations of photosynthetic pigments were investigated. To elucidate the action of Si during the Sb-induced stress, the impact of short and long cultivations was determined. Silicon decreased the accumulation of Sb in the calli, regardless of the length of the cultivation (by approx. 34%). Antimony lowered the callus biomass (by approx. 37%) and decreased the concentrations of photosynthetic pigments (up to 78.5%) and nutrients in the tissue (up to 21.7%). Silicon supported the plant tolerance to Sb via the modification of antioxidant enzyme activity, which resulted in higher biomass production (increased by approx. 35%) and a higher uptake of nutrients from the media (increased by approx. 10%). Silicon aided the development of Sb-tolerance over the longer cultivation period. These results are key in understanding the action of Si-developed tolerance against metalloids.

Cell wall polysaccharides from in vitro propagated Cereus hildmannianus K. Schum. plants

Cereus hildmannianus is a cactus exhibiting morphological and physiological adaptation of its cladodes which ensuring growth in climatic and soil conditions unfavourable for many plant species. Currently, limited water resources and increasing demand for renewable energy make cacti a biomass source for the production of biofuels. Somaclones regenerated from callus in vitro can be a source of new raw material in useful plants. The objective of this work was to determine if the regenerated plants showing two different morphologies present polysaccharide composition different from the wild plant. Somaclones aqueous extraction shows the absence of soluble polysaccharides as mucilage. The alkaline extraction of in vivo cultivated plant showed the presence of starch, type I arabinogalactan, and arabinoxylan and the somaclones showed type I arabinogalactan and arabinoxylan in both morphologies. Hemicelluloses found in the somaclones are not different from in vivo cultivated plants, but somaclones not almost biosynthesize mucilage and starch.

Exploring the Use of Fruit Callus Culture as a Model System to Study Color Development and Cell Wall Remodeling during Strawberry Fruit Ripening

Cell cultures derived from strawberry fruit at different developmental stages have been obtained to evaluate their potential use to study different aspects of strawberry ripening. Callus from leaf and cortical tissue of unripe-green, white, and mature-red strawberry fruits were induced in a medium supplemented with 11.3 µM 2,4-dichlorophenoxyacetic acid (2,4-D) under darkness. The transfer of the established callus from darkness to light induced the production of anthocyanin. The replacement of 2,4-D by abscisic acid (ABA) noticeably increased anthocyanin accumulation in green-fruit callus. Cell walls were isolated from the different fruit cell lines and from fruit receptacles at equivalent developmental stages and sequentially fractionated to obtain fractions enriched in soluble pectins, ester bound pectins, xyloglucans (XG), and matrix glycans tightly associated with cellulose microfibrils. These fractions were analyzed by cell wall carbohydrate microarrays. In fruit receptacle samples, pectins were abundant in all fractions, including those enriched in matrix glycans. The amount of pectin increased from green to white stage, and later these carbohydrates were solubilized in red fruit. Apparently, XG content was similar in white and red fruit, but the proportion of galactosylated XG increased in red fruit. Cell wall fractions from callus cultures were enriched in extensin and displayed a minor amount of pectins. Stronger signals of extensin Abs were detected in sodium carbonate fraction, suggesting that these proteins could be linked to pectins. Overall, the results obtained suggest that fruit cell lines could be used to analyze hormonal regulation of color development in strawberry but that the cell wall remodeling process associated with fruit softening might be masked by the high presence of extensin in callus cultures.

In vitro tissue culture of apple and other Malus species: recent advances and applications

Studies on the tissue culture of apple have allowed for molecular, biotechnological and applied breeding research to advance. In the past 8 years, over 100 papers advancing basic biology, genetic transformation and cryobiology have emerged. Apple (Malus × domestica Borkh.; Rosaceae) is an important fruit crop grown mainly in temperate regions of the world. In vitro tissue culture is a biotechnological technique that has been used to genetically improve cultivars (scions) and rootstocks. This updated review presents a synthesis of findings related to the tissue culture of apple and other Malus spp. between 2010 and 2018. Increasingly complex molecular studies that are examining the apple genome, for example, in a bid to identify the cause of epigenetic mutations and the role of transposable elements in this process would benefit from genetically stable source material, which can be produced in vitro. Several notable or curious in vitro culture methods have been reported to improve shoot regeneration and induce the production of tetraploids in apple cultivars and rootstocks. Existing studies have revealed the molecular mechanism underlying the inhibition of adventitious roots by cytokinin. The use of the plant growth correction factor allows hypothetical shoot production from leaf-derived thin cell layers relative to conventional leaf explants to be determined. This updated review will allow novices and established researchers to advance apple and Malus biotechnology and breeding programs.

Genome-wide identification and characterization of WRKY transcriptional factor family in apple and analysis of their responses to waterlogging and drought stress

As one of the largest transcriptional factor families in plants, WRKY genes play significant roles in various biotic and abiotic stress responses. Although the WRKY gene family has been characterized in a few plant species, the details remain largely unknown in the apple (Malus domestica Borkh.). In this study, we identified a total of 127 MdWRKYs from the apple genome, which were divided into four subgroups according to the WRKY domains and zinc finger motif. Most of them were mapped onto the apple's 17 chromosomes and were expressed in more than one tissue, including shoot tips, mature leaves, fruit and apple calli. We then contrasted WRKY expression patterns between calli grown in solid medium (control) and liquid medium (representing waterlogging stress) and found that 34 WRKY genes were differentially expressed between the two growing conditions. Finally, we determined the expression patterns of 10 selected WRKY genes in an apple rootstock, G41, in response to waterlogging and drought stress, which identified candidate genes involved in responses to water stress for functional analysis. Our data provide interesting candidate MdWRKYs for future functional analysis and demonstrate that apple callus is a useful system for characterizing gene expression and function in apple.