Hyperhydricity in Plant Tissue Culture

Light-Emitting Diodes and Liquid System Affect the Caffeoylquinic Acid Derivative and Flavonoid Production and Shoot Growth of Rhaponticum carthamoides (Willd.) Iljin

Plant in vitro cultures can be an effective tool in obtaining desired specialized metabolites. The purpose of this study was to evaluate the effect of light-emitting diodes (LEDs) on phenolic compounds in Rhaponticum carthamoides shoots cultured in vitro. R. carthamoides is an endemic and medicinal plant at risk of extinction due to the massive harvesting of its roots and rhizomes from the natural environment. The shoots were cultured on an agar-solidified and liquid-agitated Murashige and Skoog's medium supplemented with 0.1 mg/L of indole-3-acetic acid (IAA) and 0.5 mg/L of 6-benzyladenine (BA). The effect of the medium and different treatments of LED lights (blue (BL), red (RL), white (WL), and a combination of red and blue (R:BL; 7:3)) on R. carthamoides shoot growth and its biosynthetic potential was observed. Medium type and the duration of LED light exposure did not affect the proliferation rate of shoots, but they altered the shoot morphology and specialized metabolite accumulation. The liquid medium and BL light were the most beneficial for the caffeoylquinic acid derivatives (CQAs) production, shoot growth, and biomass increment. The liquid medium and BL light enhanced the content of the sum of all identified CQAs (6 mg/g DW) about three-fold compared to WL light and control, fluorescent lamps. HPLC-UV analysis confirmed that chlorogenic acid (5-CQA) was the primary compound in shoot extracts regardless of the type of culture and the light conditions (1.19-3.25 mg/g DW), with the highest level under R:BL light. BL and RL lights were equally effective. The abundant component was also 3,5-di-O-caffeoylquinic acid, accompanied by 4,5-di-O-caffeoylquinic acid, a tentatively identified dicaffeoylquinic acid derivative, and a tricaffeoylquinic acid derivative 2, the contents of which depended on the LED light conditions.

Plant Growth Regulation in Cell and Tissue Culture In Vitro

Precise knowledge of all aspects controlling plant tissue culture and in vitro plant regeneration is crucial for plant biotechnologists and their correlated industry, as there is increasing demand for this scientific knowledge, resulting in more productive and resilient plants in the field. However, the development and application of cell and tissue culture techniques are usually based on empirical studies, although some data-driven models are available. Overall, the success of plant tissue culture is dependent on several factors such as available nutrients, endogenous auxin synthesis, organic compounds, and environment conditions. In this review, the most important aspects are described one by one, with some practical recommendations based on basic research in plant physiology and sharing our practical experience from over 20 years of research in this field. The main aim is to help new plant biotechnologists and increase the impact of the plant tissue culture industry worldwide.

Temporary Immersion Systems in Plant Micropropagation

Temporary immersion systems (TIS) are technological tools that support plant micropropagation. Given their high efficiency in the in vitro propagation of shoots, a current goal is to update the protocols addressing micropropagation in semisolid culture systems to protocols involving TIS. To this end, different parameters have been evaluated, including TIS types and designs, immersion times, immersion frequencies, and volume of medium per explant, among other characteristics. This has resulted in the improved production of propagules of plants of economic interest and the production of physiologically upgraded plants with high percent survival during acclimatization. TIS are specialized culture flasks that provide countless advantages during the commercial micropropagation of plants.

Growth, photosynthetic function, and stomatal characteristics of Persian walnut explants in vitro under different light spectra

Light plays a crucial role in photosynthesis, which is an essential process for plantlets produced during in vitro tissue culture practices and ex vitro acclimatization. LED lights are an appropriate technology for in vitro lighting but their effect on propagation and photosynthesis under in vitro condition is not well understood. This study aimed to investigate the impact of different light spectra on growth, photosynthetic functionality, and stomatal characteristics of micropropagated shoots of Persian walnut (cv. Chandler). Tissue-cultured walnut nodal shoots were grown under different light qualities including white, blue, red, far-red, green, combination of red and blue (70:30), combination of red and far-red (70:30), and fluorescent light as the control. Results showed that the best growth and vegetative characteristics of in vitro explants of Persian walnut were achieved under combination of red and blue light. The biggest size of stomata was detected under white and blue lights. Red light stimulated stomatal closure, while stomatal opening was induced under blue and white lights. Although the red and far-red light spectra resulted in the formation of elongated explants with more lateral shoots and anthocyanin content, they significantly reduced the photosynthetic functionality. Highest soluble carbohydrate content and maximum quantum yield of photosystem II were detected in explants grown under blue and white light spectra. In conclusion, growing walnut explants under combination of red and blue lights leads to better growth, photosynthesis functionality, and the emergence of functional stomata in in vitro explants of Persian walnuts.

Plant Regeneration via Organogenesis in Jerusalem Artichokes and Comparative Analysis of Endogenous Hormones and Antioxidant Enzymes in Typical and Atypical Shoots

The Jerusalem artichoke (Helianthus tuberosus) is a tuberous plant with considerable nutrient and bioactive compounds. The optimization of the in vitro clonal propagation protocol is critical for large-scale reproduction and biotechnological applications of Jerusalem artichoke production. In this work, in vitro plant regeneration from the stem nodes of the Jerusalem artichoke via direct organogenesis is presented. In the shoot induction stage, the stem segments produced more shoots with vigorous growth on MS medium containing 0.5 mg/L 6-benzylaminopurine (6-BA). The concentrations of 6-BA and gibberellic acid (GA3) were both optimized at 0.5 mg/L for shoot multiplication, and the combination of 0.05 mg/L indole-3-butyric acid (IBA) and 0.05 mg/L 1-naphthylacetic acid (NAA) was the most responsive for root induction, yielding the largest number of roots. The regenerated plantlets were successfully hardened at a 96% survival rate and vigorously grew in the field. The genetic stability of the regenerated plants was confirmed by flow cytometry and simple sequence repeat (SSR) analysis. However, 17.3% of shoots on the optimum shoot induction medium had withered leaves and excessive callus (atypical shoots), which greatly reduced the induction efficiency. Enzyme activity in the typical and atypical shoots was compared. The atypical shoots had significantly higher levels of endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA), as well as increased activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), whereas the content of 6-BA, zeatin (ZT), and GA3 was significantly reduced. The activity of the three enzymes was positively correlated with the content of IAA and ABA, while being negatively correlated with that of 6-BA, ZT, and GA3. The results suggest that the poor growth of the atypical shoots might be closely related to the significant accumulation of endogenous IAA and ABA, thus significantly increasing antioxidant enzyme activity.

Effects of Monochromatic Light on Growth and Quality of Pistacia vera L

Light-emitting diodes (LEDs) are popular as a light source for in vitro plants because they save energy and allow the morphology of the plant to be altered. The purpose of this study was to show that switching from classical fluorescent light (FL) to LED light can have both beneficial and adverse effects. Pistacia vera plantlets were exposed to FL, monochromatic Blue LED light (B), monochromatic Red LED light (R), and a 1:1 mixture of both B and R (BR). R increased the total weight, shoot length, number of shoots ≥ 1 cm, and proliferation. It also reduced hyperhydricity (HH), but also dramatically increased shoot tip necrosis (STN) and leaf necrosis (LN). B cured plants of HH and STN, but hardly enabled proliferation. It did not solve the problem of LN, but the plants were high in total chlorophyll and carotenoids. BR reduced HH but enabled limited proliferation, high STN, and LN. All three LED treatments reduced HH compared to FL. B induced both high total phenolic and flavonoid content and high DPPH-scavenging activity. These results show that switching from FL to LED can have a significant positive or negative effect on proliferation and quality. This suggests that finding an optimal lighting regimen will take a lot of trial and error.

Water Content of Plant Tissues: So Simple That Almost Forgotten?

The aim of the present review was to reconsider basic information about various functional aspects related to plant water content and provide evidence that the usefulness of measuring absolute water content in plant sciences is undervalued. First, general questions about water status in plants as well as methods for determining water content and their associated problems were discussed. After a brief overview of the structural organization of water in plant tissues, attention was paid to the water content of different parts of plants. Looking at the influence of environmental factors on plant water status, the differences caused by air humidity, mineral supply, biotic effects, salinity, and specific life forms (clonal and succulent plants) were analyzed. Finally, it was concluded that the expression of absolute water content on a dry biomass basis makes easily noticeable functional sense, but the physiological meaning and ecological significance of the drastic differences in plant water content need to be further elucidated.

Prunus Knotted-like Genes: Genome-Wide Analysis, Transcriptional Response to Cytokinin in Micropropagation, and Rootstock Transformation

Knotted1-like homeobox (KNOX) transcription factors are involved in plant development, playing complex roles in aerial organs. As Prunus species include important fruit tree crops of Italy, an exhaustive investigation of KNOX genes was performed using genomic and RNA-seq meta-analyses. Micropropagation is an essential technology for rootstock multiplication; hence, we investigated KNOX transcriptional behavior upon increasing 6-benzylaminopurine (BA) doses and the effects on GF677 propagules. Moreover, gene function in Prunus spp. was assessed by Gisela 6 rootstock transformation using fluorescence and peach KNOX transgenes. Based on ten Prunus spp., KNOX proteins fit into I-II-M classes named after Arabidopsis. Gene number, class member distribution, and chromosome positions were maintained, and exceptions supported the diversification of Prunus from Cerasus subgenera, and that of Armeniaca from the other sections within Prunus. Cytokinin (CK) cis-elements occurred in peach and almond KNOX promoters, suggesting a BA regulatory role in GF677 shoot multiplication as confirmed by KNOX expression variation dependent on dose, time, and interaction. The tripled BA concentration exacerbated stress, altered CK perception genes, and modified KNOX transcriptions, which are proposed to concur in in vitro anomalies. Finally, Gisela 6 transformation efficiency varied (2.6-0.6%) with the genetic construct, with 35S:GFP being more stable than 35S:KNOPE1 lines, which showed leaf modification typical of KNOX overexpression.

Optimizing Medium Composition and Environmental Culture Condition Enhances Antioxidant Enzymes, Recovers Gypsophila paniculata L. Hyperhydric Shoots and Improves Rooting In Vitro

Gypsophila paniculata L. is one of the most important commercial cut flowers worldwide. The plant is sterile and propagated mainly by in vitro culture techniques. However, hyperhydricity hinders its micropropagation and increases mortality during ex vitro acclimatization. Hyperhydric shoots of G. paniculata were proliferated from nodal explants on MS medium without growth regulators that contained 30 g L^-1 sucrose, and gelled with 6.0 g L^-1 agar. Medium components and environmental culture conditions were optimized to revert hyperhydricity in G. paniculata microshoots and develop an efficient micropropagation protocol for commercial production. Multiple shoots with high quality were successfully regenerated on MS medium fortified with potassium and ammonium nitrate at full concentration, 2.0 mg L^-1 paclobutrazol, solidified with 9.0 g L^-1agar in Magenta boxes of 62.87 gas exchange/day and incubated under light density of 60 µmol m^-2s^-1. We recorded 4.33 shoots, 40.00 leaves, 6.33 cm, 2.50 g and 95.00% for number of shoots/explant, number of leaves/shoot, shoot length, shoot fresh weight and normal shoots percentage, respectively. Well-rooted plantlets of G. paniculata were developed from the reverted microshoots, with the rooting percentage (95.00%) on MS medium augmented with 1.0 mg L^-1 IBA in Magenta boxes of 62.87 gas exchange/day and 60 µmol m^-2s^-1 light density. In vitro-rooted plantlets exhibited reduced electrolyte leakage, and enhanced antioxidant enzymes activity of peroxidase, catalase, and polyphenol oxidase due to good ventilation at the highest gas exchange rate of the culture vessels.