Exogenous Growth Regulators Research Articles

The influence of exogenous growth regulators on the cannabinoid content and the main selection traits of hemp (Cannabis sativa L. ssp. Sativa)

Hemp (Cannabis sativa L.) is a species sensitive to the influence of exogenous growth regulators, both in the treatment of vegetative plant tissues and in vitro culture. 1-naphthylacetic acid, indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, kinetin, 6-benzylaminopurine (BAP), gibberellic acid (GA3), ascorbic acid and nicotinic acid of exogenous origin in the studied concentrations and doses caused a change in the content of cannabinoids in plants of the variety USO 31. Ascorbic acid, auxins and GA3 significantly reduced the content of cannabinoids, whereas nicotinic acid and cytokinins increased it. Under the influence of nicotinic acid and BAP, a higher content of cannabinoid compounds was stably manifested during each of the three years of processing and it is inherited by at least one generation of descendants. An additional method to increase the level of non-psychotropic cannabinoids may be the treatment of vegetative plant tissues with cytokinin BAP (the concentration of 40 mg/l, the consumption rate of 30 ml/m2, the phase of growth and development BBCH 51), which, in contrast to high concentrations of nicotinic acid, significantly increased the content of cannabidiol, and, to a lesser extent, tetrahydrocannabinol. The selection traits of the hemp - stem total length, mass and fiber content, seed productivity and sex determination significantly increased under treatment. A wide range of possibilities for phytohormones of exogenous origin in regulating cannabinoid accumulation, morphogenesis of hemp plants and their productivity was confirmed. Different hemp genotypes may have different responses to plant growth regulators and concentrations, which should be established in each case.

IN VITRO LIQUID CULTURE OF Stevia rebaudiana Bert. FOR MASS PROPAGATION

Stevia leaves are important as a new source of natural sugar substitute which makes it one of the most valuable new crops for Europe. The development of in vitro vegetative propagation strategies, to secure availability of well characterised and healthy clonal accession of plant material capable of providing an economically accepted level of leaf and stevioside harvest, becomes an agricultural priority. Growth and development of new plantles were strongly influenced by the type of in vitro plant support and by the presence of exogenous plant growth regulators added to the medium, the best combination was that of auxin (IBA 0.5 mg/l) and cytokinin (Kin 0.2 mg/l). The sponge-like structure of the fruits of Luffa cylindrica were used as plant support for liquid media. Results confirm that an in vitro multiplication of plant material is a reliable system for mass production of seedling to be cultivated in the field condition. The liquid system allows a superior root system formation. The use of Luffa cylindrica for ex vitro transfer proved to be a technological like approach, the ligno-skeleton cube replacing the usual giffy-pot system.

In vitro propagation and conservation of Leontopodium palibinianum Beauverd (Asteraceae), endemic species of Primorye Territory

The microclonal propagation protocol including initiation, propagation, rootage, and adaptation in the premises of the Botanical Garden-Institute FEB RAS was developed for the first time for a vulnerable endemic species of Primorye Territory Leontopodium palibinianum (Palibin’s edelweiss). It was shown that the medium’s mineral composition as well as changes in the concentration of exogenous growth regulators under the same light and temperature conditions had a substantial impact the processes of growth and morphogenesis of Palibin’s edelweiss. Optimal components of the microclonal propagation medium of the species were full strength Murashige and Skoog medium. Reducing in the salt amount leads to a slowdown and arrest of in vitro culture growth. Adding 2 mg/l of 6-BAP to the full strength MS medium led to mass production of plant material with the propagation factor of 9.8. It should be noted that GK3 has a positive effect on the Palibin’s edelweiss culture development in vitro when used together with low concentrations of 6-BAP. When 2.4-D was used at the concentration of 1 mg/l in the medium, direct organogenesis was observed after 14 days of cultivation and further accompanied by formation of additional plant shoots. Also, addition of 1 mg/l 2iP to the MS medium had the same effect. The growth regulators caused a low propagation factor (2.4), which in turn led to production of 2–3 regenerative plants. The IBA concentration of 2 mg/l stimulated formation of the root system capable of positively withstanding acclimatization under unsterile conditions, but lowering the IBA concentration to 1 mg/L of the medium also contributed to formation of such root system, with a slower pace. During acclimatization to ex vitroconditions plant survival did not depend on the types of mixtures being used. After the acclimatization plants are stretched in height and produced additional shoots on 20–25th day.

Impact of Exogenous Plant Growth Regulators on Physiological Traits, Tendril and Flowering in Horsegram (Macrotyloma uniflorum Lam) under Kharif Season

Background: Horsegram is an important pulse crop grown as Rabi crop in Tamil Nadu. Kharif sown crop could not flowers may be because of more number of tendrils produced as compare to Rabi sown crop. Hence, an attempt was made to reduce the number of tendrils and induce flowering in horsegram during Kharif season by plant growth regulators. Methods: A field experiment was conducted to study the impact of plant growth regulators viz., salicylic acid (100 ppm), chlormequat chloride (CCC - 250 ppm), mepiquat chloride (250 ppm), tri iodo benzoic acid (TIBA - 200 ppm) and nitrobenzene (0.2%) on physiological traits and tendril growth associated with flowering in horsegram during Kharif. Different treatments were applied through foliar application at 25 Days after sowing. Result: Among the PGRs, foliar application of TIBA registered the lowest number of tendrils (2.3) followed by CCC (3.0) compared to other treatments. Higher root length of 16.8 cm and RWC of 82.3% was found in CCC treatment. CCC also registered the highest photosynthetic rate (27.15 µmol m-2 s-1), transpiration rate (18.06 mmol m-2 s-1) and lowest leaf temperature (26°C) compared to other treatments. The highest soluble protein content of 13.1 mg g-1 was also estimated in CCC treatment followed by mepiquat chloride (12.51 mg g-1). Sucrose phosphate synthase (SPS) activity did not show any significant difference between the treatments. Number of flowers buds formed per plant was zero and hence the flowering did not take place in any treatments. Among the plant growth regulators used, TIBA and CCC registered its positive action on reduced the number of tendrils and leaf temperature, but not enough to induce flowering under Kharif season.

Quantitative and qualitative study of endogenous and exogenous growth regulators in eggplant (Solanum melongena) microspore cultures

In eggplant microspore embryogenesis, embryos are produced and then transformed into undifferentiated calli, instead of developing as true embryos. This is the main current bottleneck that precludes this process from being efficient. In this work we aimed to shed light on the factors involved in the successful in vitro development of eggplant haploid embryos by evaluating the role of growth regulators (GRs) in this process. We analyzed the endogenous levels of different GRs, including auxins, cytokinins and gibberelins, as well as salicylic, jasmonic and abscisic acid, in microspores and microspore-derived embryos at different culture stages. We also analyzed the same GR profiles in leaf and anther wall tissues of different eggplant backgrounds. Finally, we assessed the application of different GR combinations to the culture medium. Our results showed that in eggplant there are no genotype-specific endogenous GR profiles that can be associated to a high embryogenic response. Instead, the embryogenic response seems related to different GR accumulation patterns during in vitro culture. The changes observed in the endogenous levels of salicylic and abscisic acid were not related to the embryo transition. There were, however, changes in the levels of indole acetic acid and dihydrozeatin. The best GR combination to promote callus production was 0.5 mg/L 1-naphthaleneacetic acid (NAA) and 0.5 mg/L 6-benzylaminopurine (BAP). A 20% reduction of NAA and BAP reduced embryo production but produced structures more anatomically similar to embryos. These results shed light on the role of GRs during the development of microspore-derived embryos in eggplant microspore cultures.

Review: Regulation of Phytohormones and Environmental Stresses to Increase the Production of Plant Secondary Metabolites

Secondary metabolites are synthesized by plants when subjected to abiotic and biotic stresses as a defense mechanism and play an ecologically vital role both as pollination attractants and as repellents. These compounds are not essential for the process of growth and development but provide a significant impact on human welfare in various aspects as pharmaceuticals and therapeutics, aroma and taste, biopesticides, and agrochemicals. This natural product has high economic and commercial value, so it is important to explore it along with the increasing needs of consumers and industry at a large scale. Various extensive studies were carried out to improve and increase the production and accumulation of secondary metabolites. One of the strategies adopted in this review is the role of exogenous phytohormones in triggering the production of important secondary metabolites based on their classification, namely terpenoids, phenols, and flavonoids, as well as alkaloids and nitrogen-containing compounds. Bioregulators work as elicitors to induce the production of secondary metabolites through up-regulation of specific gene expression. In some cases, the application of phytohormones combined with exposure to extreme abiotic stresses showed overexpression of secondary metabolite synthesis compared to treatment with only those subjected to phytohormone. The abiotic stress of irradiation, UV-B, temperature, drought, ultrasonic, salinity, and metal stress was discussed in this study. Oxidative conditions under environmental changes trigger the plant to produce reactive oxygen species (ROS), which induce various secondary metabolites as part of the regulation of antioxidant systems. Micropropagation of medicinal plants by the addition of exogenous growth regulators could enhance the production and accumulation of important secondary metabolites.

Roles of exogenous plant growth regulators on phytoextraction of Cd/Pb/Zn by Sedum alfredii Hance in contaminated soils

Plant growth regulators (PGRs) assisted phytoextraction was investigated as a viable phytoremediation technology to increase the phytoextraction efficiency in contaminated soils. This study aimed to evaluate the cadimum (Cd)/lead (Pb)/zinc (Zn) phytoextraction efficiency by a hyperaccumulator Sedum alfredii Hance (S. alfredii) treated with 9 PGRs, including indole-3-acetic acid (IAA), gibberellin (GA3), cytokinin (CKs), abscisic acid (ABA), ethylene (ETH), brassinosteroid (BR), salicylic acid (SA), strigolactones (SL) and jasmonic acid (JA), in slightly or heavily contaminated (SC and HC, respectively) soil. Results demonstrated that PGRs were able to improve S. alfredii biomass, the most significant increases were observed in GA3 and SL for HC soil, while for SC soil, IAA and BR exhibited positive effects. The levels of Cd, Pb and Zn in the shoots of S. alfredii treated with ABA and SL were noticeably greater than in the CK treatment in HC soil, while the uptake of metals were increased by IAA and CKs in SC soil. Combined with the results of biomass and metal contents in shoots, we found that ABA showed the highest Cd removal efficiency and the maximum Pb and Zn removal efficiency was observed with GA3, which was 62.99%, 269.23%, and 41.18%, respectively higher than the control in HC soil. Meanwhile, compared to control, the maximum removal efficiency of Cd by IAA treatment (52.80%), Pb by JA treatment (165.1%), and Zn by BR treatment (44.97%) in the SC soil. Overall, our results suggested that these PGRs, especially, ABA, SL, IAA, BR and GA3 had great potential in improving phytoremediation efficiency of S. alfredii grown in contaminated soils.

Transcriptomics of tapping and healing process in frankincense tree during resin production

Frankincense tree (Boswellia sacra Fluek) has been poorly known on how it responds to tapping and wound-recovery process at molecular levels. Here, we used RNA-sequencing analysis to profile transcriptome of B. sacra after 30 min, 3 h and 6 h of post-tapping. Results showed 5525 differentially expressed genes (DEGs) that were related to terpenoid biosynthesis, phytohormonal regulation, cellular transport, and cell-wall synthesis. Plant-growth-regulators were applied exogenously which showed regulation of endogenous jasmonates and resulted in rapid recovery of cell-wall integrity by significantly up-regulated gene expression of terpenoid biosynthesis (germacrene-D synthase, B-amyrin synthase, and squalene epioxidase-1) and cell-wall synthesis (xyloglucan endotransglucosylase, cellulose synthase-A, and cell-wall hydrolase) compared to control. These findings suggest that tapping immediately activated several cell-developmental and regeneration processes, alongwith defense-induced terpenoid metabolism, to improve the healing process in epidermis. Exogenous growth regulators, especially jasmonic acid, can drastically help tree recovery from tissue degeneration and might help in tree conservation purposes.

Використання домішок для підвищення врожайності насіння харчового призначення

The growth-stimulating activity of the drug "Humir", created on the basis of humates, polyethylene oxides, wastes of yeast production, hydrated fullerenes and other BAS is investigated. The introduction of these components in the technology of crop production requires careful study of the properties of drugs based on them in specific soil and climatic conditions of different zones and on different types of seeds. The use of growth regulators is one of the main elements of modern technology. Changing the hormonal status of plants under the influence of exogenous growth regulators increases the activity of metabolic processes in the plant, resistance to biotic and abiotic stresses, increases yields and product quality. Growth regulators are very effective not only for field crops but also for other crops. The use of growth regulators is determined by the stage of ontogenesis, environmental conditions and tasks that are solved by phytoregulators (root formation, removal of seeds from dormancy, regulation of vegetative generative organs, regulation of fruit formation and maturation, regulation of plant stability, product quality, etc.). A number of regulators have a complex effect on the plant, stimulating seed germination, disease resistance, increasing yields and quality. The regulatory effect on the plant organism is closely related to the trophic factor (mineral and carbon nutrition), water regime, metabolism of phenolic compounds, natural conditions. It is possible to regulate the transition of a plant or organ to a state of rest, which is important before laying the fruit and seeds for storage. This served as the basis for our research to create a complex drug with growth-promoting effect. The object of research was selected mustard seeds "Talisman".

Plant Regeneration via Somatic Embryogenesis in Larix principis-rupprechtii Mayr

Prince Rupprecht’s larch (Larix principis-rupprechtii Mayr) is a native conifer in North China with great economic and ecological values. Somatic embryogenesis (SE) is a powerful tool for the mass clonal propagation in plants. In this study, we described a high-efficiency SE system via indirect pathways and investigated the effect of genotype, culture conditions and phytohormones on SE. Immature zygotic embryos (IZEs) of L. principis-rupprechtii Mayr were used as explant materials. In the induction stage, embryogenic tissues (ETs) were induced on mLV medium supplemented with 2.0 mg L−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.0 mg L−1 6-benzylaminopurine (6-BA). The initiation frequencies showed significant differences (p < 0.05) among 20 genotypes of open-pollinated mother trees with the highest induction frequency reaching 30%. For tissue proliferation, proliferation in liquid medium was more efficient compared with proliferation in semi-solid medium, providing a multiplication rate of 3.12 in an 8-day subculture period. As a necessary exogenous plant growth regulator (PGR) for somatic embryo maturation in conifers, abscisic acid (ABA) was optimized at 16 mg L−1 in this system. Next, an orthogonal test on osmotic pressure factors showed 50 g L−1 sucrose, 7 g L−1 phytagel and 75 g L−1 polyethylene glycol (PEG) was the optimal combination for somatic embryo maturation in L. principis-rupprechtii Mayr. Moreover, the dispersion culture method provided a more efficient somatic embryo maturation, up to 545 per gram of fresh weight (FW). Finally, 2 g L−1 of active charcoal (AC) was found to increase the somatic embryo germination rate to 63.46%. The improved protocol of SE will serve as a foundation for establishing mass propagation and genetic transformation of L. principis-rupprechtii Mayr.

Dynamics of growth parameters of Gentiana lutea L. in vitro plants under different lighting conditions

Aim. Study of the dynamics Gentiana lutea L. plant growth processes in vitro depending on the light regime changes of their cultivation in order to develop a scheme to increase their adaptive potential. Methods. Methods of plant cultivation in vitro, biometric method, as well as ANOVA variance analysis and middle group analysis in pairs using the Tukey test (Tukey test) were used. Results. It is shown that the cultivation of G. lutea plants in vitro using 25 W/m2 light flux intensity in the region of photosynthetically active radiation and the ratio of blue (Eb): green (Eg): red (Er) ranges = 41.8%: 42.7 %: 15.5% triggers non-specific photomorphogenesis reactions for intact plants, which lead to poor root system development, stem elongation, formation of small leaves with a thin leaf blade, overall low productivity and low adaptation potential of G. lutea plants to ex vitro and in situ conditions. Increasing the light flux intensity to 44 W/m2 and increasing the red wave proportion up to 20.3% allows not only to improve the bioproductivity of G. lutea plants which are cultivated in vitro, but also to increase the coefficient of microclonal reproduction without the additional use of exogenous growth regulators. The greatest growth of the aboveground and underground parts, increase in effective leaf surface are observed in vitro plants during cultivation at 135 W/m2 light flux intensity and spectral composition Eb: Eg: Er = 29.5%: 32.5%: 38.0%. Conclusions. It is possible to improve plant bioproductivity by changing the light conditions of plant cultivation in vitro, and, accordingly, to increase the adaptive potential to ex vitro and in situ conditions.
 Keywords: Gentiana lutea L., in vitro plants, light flux intensity, spectral composition, growth parameters.

Genome-wide identification, gene cloning, subcellular location and expression analysis of SPL gene family in P. granatum L

BackgroundsPomegranate is an excellent tree species with nutritional, medicinal, ornamental and ecological values. Studies have confirmed that SPL factors play an important role in floral transition and flower development.ResultsUsed bioinformatics methods, 15 SPL (SQUAMOSA promoter-binding protein-like) genes were identified and analyzed from the ‘Taishanhong’ pomegranate (P. granatum L.) genome. Phylogenetic analysis showed that PgSPLs were divided into six subfamilies (G1 ~ G6). PgSPL promoter sequences contained multiple cis-acting elements associated with abiotic stress or hormonal response. Based on the transcriptome data, expression profiles of different tissues and different developmental stages showed that PgSPL genes had distinct temporal and spatial expression characteristics. The expression analysis of miR156 in small RNA sequencing results showed that miR156 negatively regulated the expression of target genes. qRT-PCR analysis showed that the expression levels of PgSPL2, PgSPL3, PgSPL6, PgSPL11 and PgSPL14 in leaves were significantly higher than those in buds and stems (p < 0.05). The expression levels of PgSPL5, PgSPL12 and PgSPL13 in flower buds were significantly higher than that in leaves and stems (p < 0.05). The full-length of coding sequence of PgSPL5 and PgSPL13 were obtained by homologous cloning technology. The full length of PgSPL5 is 1020 bp, and PgSPL13 is 489 bp, which encodes 339 and 162 amino acids, respectively. Further investigation revealed that PgSPL5 and PgSPL13 proteins were located in the nucleus. Exogenous plant growth regulator induction experiments showed that PgSPL5 was up-regulated in leaves and stems. PgSPL13 was up-regulated in leaves and down-regulated in stems. When sprayed with 6-BA, IBA and PP333 respectively, PgSPL5 and PgSPL13 were up-regulated most significantly at P2 (bud vertical diameter was 5.1 ~ 12.0 mm) stage of bisexual and functional male flowers.ConclusionsOur findings suggested that PgSPL2, PgSPL3, PgSPL6, PgSPL11 and PgSPL14 played roles in leaves development of pomegranate. PgSPL5, PgSPL12 and PgSPL13 played roles in pomegranate flower development. PgSPL5 and PgSPL13 were involved in the response process of different plant hormone signal transduction in pomegranate development. This study provided a robust basis for further functional analyses of SPL genes in pomegranate.

Effect of different concentrations of IAA, GA3 and chitosan nano-fiber on physio-morphological characteristics and metabolite contents in roselle (Hibiscus sabdariffa L.)

The roselle (Hibiscus sabdariffa L., Malvaceae) is one of the most widely used medicinal plants due to its economic importance and high bioactive compounds. In the present study, the effects of two exogenous plant growth regulators (PGRs), [gibberellic acid (GA3) and Indole-3-scetic acid (IAA) at 400, 800 and 1200 mg L−1], along with chitosan-based nanofiber (CNF, at 50, 100 and 200 mg L−1) were investigated, individually and in combination, on plant height, calyx fresh and dry weights, number of flowers, total chlorophyll and ß-carotene, soluble sugar, anthocyanin, vitamin C, total polyphenols and flavonoids as well as antioxidant capacity in roselle plants. According to the results, a synergistic effect was observed between employed PGRs. Of interest, CNF was observed inside the calyxes using scanning electron microscopy (SEM) technique. Because of its unique physio-chemical properties, CNF further influenced the PGRs function on most of the traits evaluated. It was found that the combined use of IAA and GA3 could improve plant height, number of calyxes per plant, total chlorophyll, β-carotene, flavonoids and antioxidant activity in roselle. Furthermore, the results clearly demonstrated that PGRs in combination with CNF have a significant impact on various growth parameters in roselle plant. The present results suggest that the use of combined IAA+GA3+CNF (at 800 + 800 + 100 mg L−1) stimulate both growth parameters and health-promoting phytochemicals content in roselle plants.

Effect of different treatments and light quality on Ulmus pumila L. germination and seedling growth

Ulmus pumila L. has potential benefits for erosion control, landscape ornamentals, and the bark contains substances that may have therapeutic value. To determine optimal growth conditions, we investigated the effect of water, sucrose, and exogenous plant growth regulator (6 benzylaminopurine: BA, indolebutyric acid: IBA and gibberellic acid: GA3) treatments as well as light quality (dark, fluorescence, and 2:1 or 4:1 Red:Blue (R:B) LED) on U. pumila seed germination and seedling growth. Seeds soaked in a 3% sucrose solution had the highest germination rate and germination energy in addition to the shortest germination time compared to seeds treated with water or PGRs, except the control. Light quality only affected germination energy, with seeds exposed to 2:1 R:B LED light having the highest germination energy and those exposed to fluorescent light having the lowest. Following transfer to a greenhouse with exposure to natural sunlight, the performance of seedlings varied depending on the light conditions under which they were germinated. In contrast, treatments during the germination stage such as incubation with PGRs had no effect on seedling growth in the greenhouse. Seedlings that germinated under 2:1 or 4:1 R:B LED lights grew taller and had thicker root collars compared to those grown in the dark or under fluorescent lights. The influence of light conditions persisted for at least seven months after the germination, even though the chlorophyll content was similar among seedlings exposed to different growth conditions. Taken together, these results show that light quality in particular during the germination stage can positively affect the growth of the U. pumila seedlings.

Збереження представників роду Drosera L. з використанням біотехнологічних методів

The peculiarities of obtaining planting material of rare representatives Drosera spatulate L. and Drosera aliciae L. using microclonal propagation in order to preserve and cultivate them in ex vitro conditions were studied. The method of sterilization of D. spatulate and D. aliciae explants with 80-90% obtaining aseptic material has been developed. The influence of different sterilization options on the development of microshoots has been studied. The best mode of sterilization is 0,1% solution of AgNO3 and 12.5% solution of H2O2. The features of organogenesis and regeneration of the whole organism from cultivated tissues and organs of Drosera L. was investigated. The effect of exogenous growth regulators at different stages of plant morphogenesis in vitro is shown. Improved conditions of rhizogenesis in vitro. It was found experimentally that MS nutrient media with the addition of 2 g∙l-1 PVP is optimal at the stage of introduction into culture in vitro D. spatulate and D. aliciae. The regeneration of microshoots of D. spatulate and D. aliciae depending on the type of explant and the composition of nutrient media was studied. Morphogenesis was most effective on nutrient media with the addition of 0.25 mg∙l-1 kinetin and on the hormone free MS media. Such cultivation conditions provided 100% regeneration of plants with a reproduction rate of 1:8. Studying the effect of cytokinins on the microclonal reproduction of D. spatulate and D. aliciae, it was found that the development and induction of multiple shoot formation in vitro is best performed on hormone free MS media. To induce the formation of the root system, it is necessary to add into MS nutrient media 0.5 mg∙l-1 IBA. According to the results of the research, a method of microclonal propagation was developed by cutting stem culture, which made it possible to obtain genetically stable, disease-free regenerating plants of D. spatulate and D. aliciae with an optimally formed root system and vegetative mass. The obtained homogeneous planting material can be used in floriculture, creation of terrariums, for pharmacological purposes and for the purpose of introduction. Keywords: Drosera L., microclonal reproduction, morphogenes.

Optimization of Different Factors for Initiation of Somatic Embryogenesis in Suspension Cultures in Sandalwood (Santalum album L.)

Santalum album (L.) is a prized tropical tree species of high therapeutic and industrial importance. The wood of these naturally grown plants is extensively harvested to acquire therapeutically important metabolite santalol and be used for additional functions such as in wood statuette industries. Due to high demand, it is crucial to maintain a sufficient plant population. An easy protocol for establishing cell suspension culture initiated from the loose embryogenic callus mass of sandalwood was realized by shifting 6–8-week-old morphogenic calli acquired from the mature embryonic axis and cotyledon explant cultures in fluid media. The asynchronous embryogenic cultures were sloughed with clumps of flourishing cell clumps and embryos of various progressive phases along with diffident non-embryogenic tissues. The frequency of embryo proliferation was evidenced to determinethe expansion pace of embryogenic masses under diverse conditions. The intonation of initiation and creation of cell suspension was under the directive of the influence of exogenous plant growth regulators amended in the nutrient medium at different concentrations and combinations. Maximum relative growth rate (386%) and clumps/embryoids in elevated integers (321.44) were accomplished on MS nutrient medium fortified with 2.0 mg L−1 2,4-D in association with 0.5 mg L−1 BA and 30.0 g L−1 sucrose raised from mature embryonic axis-derived calli. Plantlet regeneration in higher frequency (84.43%) was evidenced on MS medium amended with 1.0 mg L−1 each of TDZ and GA3 in conjunction with 0.5 mg L−1 NAA and 20.0 g L−1 sucrose. Mature embryonic axis-derived calli were found to be constantly better than mature cotyledon-derived calli for raising profitable and reproducible cell suspension cultures. Regenerants displayed normal growth and morphology and were founded successfully in the external environment after hardening.

Exogenous salicylic acid ameliorates waterlogging stress damages and improves photosynthetic efficiency and antioxidative defense system in waxy corn

Salicylic acid (SA) is an endogenous growth regulator. It is vital for the growth and development, photosynthesis, disease resistance, and abiotic stress tolerance of plants. This study aimed to investigate the effects of exogenous SA on photosynthetic characteristics and antioxidant system in the four-leaf-stage waxy corn inbred seedlings SY-MY13 (waterlogging-resistant) and SY-XT1 (waterlogging-sensitive) under waterlogging stress. Waterlogging stress negatively influenced the morphology, plant height, biomass, photosynthetic characteristics, and chlorophyll content of waxy corn seedlings, obstructing their growth and development. SY-MY13 exhibited better growth and photosynthesis than SY-XT1 under waterlogging, this was due to SY-MY13 possessed excellent scavenging ability to reactive oxygen species (ROS). However, the application of exogenous SA could not only reduce the accumulation of ROS and regulate the activities of antioxidant enzymes but also improve photosynthesis in leaves and promote the growth of seedlings. Hence, the results revealed that the potential of SA as a promising exogenous growth regulator mediated physiological and photosynthetic adaptation of waxy corn seedlings under waterlogging stress, which might prove helpful for other plants suffering from waterlogging stress.

Exogenous DA-6 Improves the Low Night Temperature Tolerance of Tomato Through Regulating Cytokinin.

Low night temperature (LNT) causes environmental stress and has a severe and negative impact on plant growth and productivity. Synthetic elicitors can regulate plant growth and induce defense mechanisms from this type of stress. Here, we evaluated the effect of the exogenous growth regulator diethyl aminoethyl hexanoate (DA-6) in tomato leaf response to LNT stress. Our results showed that exogenous DA-6 activates the expression of chlorophyll synthesis and photosystem-related genes, and results in higher photosynthetic activity and chlorophyll production. Furthermore, DA-6 can regulate the synthesis of endogenous cytokinin (CTK) and the expression of decomposition genes to stabilize chloroplast structure, reduce oxidative damage, and maintain the photochemical activity of tomato leaves under LNT stress. DA-6 maintains a high level of ABA content and induces the expression of CBF genes, indicating that DA-6 may participate in the cold response signaling pathway and induce the expression of downstream low temperature response genes and accumulation of compatible osmolytes. This study unravels a mode of action by which plant growth regulators can improve low temperature tolerance and provides important considerations for their application to alleviate the harmful effects of cold stress.

In vitro and ex vivo vegetative propagation and cytokinin profiles of Sceletium tortuosum (L.) N. E. Br.: a South African medicinal plant

Sceletium tortuosum is a South African protected species with tremendous value in traditional and modern medicine. The plants’ mesembrine-type alkaloids are potential therapeutics for a plethora of psychological, neurological and inflammatory disorders. In our in vitro and ex vivo studies, vegetative propagation and growth of this species were investigated. Cytokinin (CK) profiles were also explored. Shoot multiplication was induced on Murashige and Skoog (MS) medium supplemented with 2.5 µM indole-3-butyric acid (IBA). In vitro-generated shoots were inoculated on MS medium supplemented with 0, 2.5, 5.0 and 10.0 µM IBA or indole-3-acetic acid (IAA). Optimal rooting (55%), mean number of roots (3.80 ± 0.83) and new leaf pairs (4.65 ± 0.67) were achieved by 10.0 µM IBA. After greenhouse acclimatization, 45–90% of plantlets survived. All ex vivo shoot cuttings rooted well (90–100%). The highest mean number of roots (11.20 ± 1.37) and root length (57.18 ± 3.85 mm) were obtained by 5.0 µM IBA. Although spontaneous rooting was observed in both experiments, auxins enhanced multiple growth parameters. Cytokinin analyses of tissue-cultured (auxin-treated) and greenhouse (untreated) plants revealed higher cytokinin levels in vitro. These investigations provide rapid and efficient propagation techniques for Sceletium tortuosum which will be valuable to conservationists and pharmaceutical companies. Plant tissue culture and cuttings enabled rapid propagation of Sceletium tortuosum. Exogenous plant growth regulators were not essential for shoot multiplication, flowering and rooting. Auxins effectively improved growth parameters.

Impact of exogenous growth regulators on growth and photosynthetic activity in dwarf mandarin plants (Citrus unshiu Marc.)

The impact of synthetic regulators on the growth and development of mandarin plants was investigated. It was shown that the exposure of plants to growth regulators had no effect on leaf chlorophyll content. Non-root application of nanoelicitor and siliplant synthetic regulators elevated the carotenoid content to 2.69-3.11 mg/g (control, water: 2.57 mg/g) and stimulated protective response. The total chlorophyll- carotenoid ratio in plants treated with nanoelicitor (4.29 mg/g) and siliplant (4.12 mg/g) was less than in the control, reflecting the degree of plant adaptation to adverse conditions in the growing season. Exposure to growth regulators improved photosynthetic activity and overall functionality. Chlorophyll fluorescence assays were used to evaluate photosynthetic activity coefficient as falling within a range of 0.54-0.57, which exceeded the control by 1.2-fold. Nanoelicitor was shown to induce active shooting and reduce fruit shedding. Compared to the control, growth regulators increased the retained fruit value by 1.5-1.9-fold and improved plantation productivity. Phytoregulators have shown promise in both improving the functional condition and reducing preharvest shedding in dwarf mandarin plants.