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Somatic embryogenesis (SE) is a mode of stimulated plant cell totipotency wherein embryos form without fertilization either through somatic or vegetative origins. SE has two main phases: induction and a developmental phase. The induction phase comprises cell proliferation and dedifferentiation, whereas the developmental phase involves the differentiation of somatic embryos under appropriate stimuli. As such, SE is categorized into two main types: direct (without an intervening callus) and indirect (includes a callus phase). This review presents the influence of various major factors such as explants, abiotic stresses, and the concentrations and variations of plant growth regulators on SE. In addition, genetic components such as miRNA, transcription factors, and epigenetic events (DNA methylation and chromatin remodeling) that are potentially implicated in SE are described briefly. Furthermore, SE applications and SE-related abnormalities are also discussed in detail.

The influence of putrescine (Put), spermidine (Spd), and spermine (Spm) on somatic embryogenesis (SE) and plant regeneration of three indica rice cultivars (ASD16, IR64, and ADT43) were evaluated since polyamines (PAs) are reported to play vital roles in SE and plant regeneration. Significant increases in the regeneration potential of the rice cultivars upon polyamine treatments were observed. Put (1.0 mM) induced the highest regeneration frequencies, somatic embryos, and shoot numbers. PAs influenced the fresh weights of the suspension cultures. Spd was found to be detrimental to cultivar ADT43 towards embryogeneicity, regeneration, and somatic embryo induction. Among the cultivars, ASD16 was found to respond superiorly to the polyamine treatment. Experiments with long-term cultures of the rice revealed that Put and Spm enhanced the regeneration potential, and the highest frequencies were recorded for ASD16 and IR64. Results indicate that PAs can be effectively used as growth modulators to achieve success in in vitro tissue and genetic manipulation studies with elite recalcitrant indica rice cultivars.

Ever since the flavonoids and other antioxidants in rice were demonstrated with immense health benefits, much interest has been diverted to study the native indigenous rice landraces. In the present investigation, three pigmented rare Indian rice landraces and two non-pigmented rice varieties were analyzed for their phytoconstituents like total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content and antioxidant potential using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. The phytochemical profile was compared between seed, seedling, stem, leaf and root tissues of the different varieties. Pigmented rice cultivars demonstrated higher levels of bioactive compounds as compared to the non-pigmented cultivars exhibiting a strong correlation between the antioxidant activity of the grain and their phenolic and flavonoid content. Among the five different rice studied, black navara was found to be superior in terms of its phytochemical composition. Further, the expression levels of flavonoid genes among pigmented and non-pigmented rice was studied. Higher gene expression profiles were observed in the 8 flavonoid genes studied in pigmented rice varieties as compared to non-pigmented varieties. The colorlessness of non-pigmented rice and its lower levels of phytoconstituents correlated with the low transcript levels of flavonoid genes recorded in them. This study provides a basis for understanding the health-promoting properties of pigmented rice over non-pigmented rice at the biochemical and molecular levels.

Ever since a positive correlation between rice consumption and reduced risk of developing chronic diseases was recognized, numerous researches on native indigenous rice landraces have been carried out. In the present investigation, ten pigmented and non-pigmented rare Indian rice landraces were analyzed for their total phenolic content (TPC), total flavonoid content (TFC), total protein, total anthocyanin, and antioxidant potential. Three different parameters in raw, cooked, strained cooking water were taken into consideration and phytochemical analysis revealed that pigmented rice varieties displayed higher levels of bioactive compounds as compared to the non-pigmented cultivars. Higher TPC (398 ± 0.23 mg GAE/100 g), TFC (1308 ± 0.04 mg QE/100 g), total anthocyanin (13.36 ± 0.00 mg/100 g), total protein (2590 ± 0.03 mg/100 g), total antioxidant activity (316 ± 0.03 mg AAE/100 g) was recorded with the pigmented varieties. A strong correlation was found between the antioxidant activity and the phenolic, flavonoid content in pigmented rice cultivars. Further, the phytochemical composition and antioxidant activities in cooked rice and strained cooking water were lower as compared to raw. Among the tested landraces, navara was found to be superior in terms of higher phytochemical contents and antioxidant activity. Our study revealed the various health-promoting properties of pigmented rice over non-pigmented rice. It was also found that pressure cooking without straining away the water would be ideal to retain the nutrients and pigmented rice can alleviate numerous health disorders upon regular consumption.

A comprehensive study of various components of rice tissue culture media and physical parameters was carried out to characterize the factors affecting in vitro plantlet regeneration and subsequent transformation from two recalcitrant indica rice cultivars, ASD16 and IR64. The choice and concentrations of carbon sources, light/dark incubation, gelling agents, amino acid supplementation and hormone combinations in the regeneration medium greatly influenced the regeneration potential. Among four different carbon sources tested maltose (3%) was identified as the best for callus and shoot induction. Among different formulations of hormones tested, both cultivars recorded the highest regeneration frequencies when the medium was supplemented with 3.0 mg/L BAP+1.0 mg/L NAA. Partially desiccating the calli for 48 h resulted in a higher frequency of regeneration and among different gelling agents, gelrite induced maximum callus induction while agarose was found to be a better choice in regeneration. Callus induction and embryogenic calli initiation were higher when the calli were incubated in the dark, whereas high shoot numbers and regeneration efficiency in both cultivars were enhanced when incubated in the light. The optimized conditions yielded higher regeneration frequencies during transformation experiments and the transformants were analyzed by PCR, Southern blotting and GUS histochemical staining for asserting successful transformation. The results indicated that manipulation of media supplements and partial desiccation reported here used either individually or in combination can greatly enhance plantlet regeneration which is essential for an efficient genetic transformation system in recalcitrant indica rice cultivars.

Nanoparticles (NPs) are widely used in various domestic products and their usage is constantly increasing which in turn can raise several environmental health issues. Like other abiotic stresses, nanomaterials also affect the growth of crop plants. Solanum melongena is a common vegetable crop grown in the tropics and subtropics regions with medicinal properties. In this study, S. melongena was analyzed for its response to three commercially important metallic nanoparticles, namely NiO, CuO, and ZnO, at four different concentrations (100, 250, 500 and 1000 mg/L). The growth of the eggplant seedlings was suppressed by all the NPs in a concentration-dependent manner and among them, NiO was shown to be more toxic as it suppressed the root and shoot growth effectively. Total chlorophyll contents were decreased in the NP-treated plants compared to control plants. Significant changes were found in the secondary metabolites such as anthocyanins, total phenolic and total flavonoid contents in the NP-treated plants. A dose-dependent increase in the reactive oxygen species (ROS) generation was noticed in the NP-treated plants which are evidenced by the 4-nitro blue tetrazolium chloride (NBT) and 3,3′-diamiobenzidine (DAB) histochemical staining. The DNA damage imposed by the NP in the seedlings of eggplants may be due to the elevated ROS and MDA (malondialdehyde) production. NiO NP was found to be more toxic comparable to CuO and ZnO NPs in the present study. Apart from the toxic effects, nanoparticles also showed profound effects on the production of important secondary metabolites such as phenolics and flavonoid compounds. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13205-018-1386-9) contains supplementary material, which is available to authorized users.