Inflictions caused by cold stress can result in disastrous effects on the productivity and survival of plants. Cold stress response in plants requires crosstalk between multiple signaling pathways including cold, heat, and reactive oxygen species (ROS) signaling networks. CBF, MYB, bHLH, and WRKY families are among the TFs that function as key players in the regulation of cold stress response at the molecular level. This review discusses some of the latest understanding on the regulation of expression and the mechanistic actions of plant TFs to address cold stress response. It was shown that the plant response consists of early and late responses as well as memory reprogramming for long-term protection against cold stress. The regulatory network can be differentiated into CBF-dependent and independent pathways involving different sets of TFs. Post-transcriptional regulation by miRNAs, control during ribosomal translation process, and post-translational regulation involving 26S proteosomic degradation are processes that affect the cellular abundance of key regulatory TFs, which is an important aspect of the regulation for cold acclimation. Therefore, fine-tuning of the regulation by TFs for adjusting to the cold stress condition involving the dynamic action of protein kinases, membrane ion channels, adapters, and modifiers is emphasized in this review.

Polyalthia bullata is an endangered medicinal plant species. Hence, establishment of P. bullata callus culture is hoped to assist in mass production of secondary metabolites. Leaf and midrib were explants for callus induction. Both of them were cultured on Murashige and Skoog (MS) and Woody Plant Medium (WPM) containing different types and concentrations of auxins (2,4-dichlorophenoxyacetic acid (2,4-D), α-naphthaleneacetic acid (NAA), picloram, and dicamba). The callus produced was further multiplied on MS and WPM supplemented with different concentrations of 2,4-D, NAA, picloram, dicamba, indole-3-acetic acid (IAA), and indole-3-butyric acid (IBA) media. The quantification of total phenolic content (TPC), total flavonoid content (TFC) and antioxidant capacity was further carried out on P. bullata callus, and the results were subjected to correlation analysis. Among the media, the WPM + 16.56 µM picloram (53.33 ± 22.06%) was the best for callus induction while MS + 30 µM dicamba was the best for callus multiplication. The TPC, TFC, and EC₅₀ of DPPH scavenging activity were determined at 0.657 ± 0.07 mg GAE/g FW, 0.491 ± 0.03 mg QE/g, and 85.59 ± 6.09 µg/mL in P. bullata callus, respectively. The positive correlation between DPPH scavenging activity with TPC was determined at r = 0.869, and that of TFC was at r = 0.904. Hence, the P. bullata callus has an ability to accumulate antioxidants. It therefore can be a medium for secondary metabolites production.

Polyalthia bullata is a woody medicinal plant that contains antioxidant compounds. Finding a suitable solvent is important to obtain a high yield of antioxidants in the phenolic, flavonoid, and terpenoid families. In this study, from different solvent extracts, the leaf methanolic extract exhibited the highest total phenolic content (TPC), total flavonoid content (TFC), total terpenoid content (TTC), and total antioxidant activity. For woody parts of stem and roots, methanol was the best solvent for all phytochemicals except for phenolics, which accumulated in the roots and were extracted more efficiently using ethanol. However, the methanolic extracts from both tissues displayed the best antioxidant capacity. Gas chromatography-mass spectrometry (GC-MS) profiling data showed the presence of antioxidant compounds such as thymol, phytol, and neophytadiene in the leaf; trans-farnesol, n-hexadecanoic acid, and 9-Octadecenamide in the stem; and fatty acid (cis-vaccenic) and its methyl ester (11-Octadecanoic acid, methyl ester and [1,1’-bicyclopropyl]-2-octanoic acid, 2’-hexyl-methyl ester) in the roots. These findings reveal important compounds that are present in different plant parts of P. bullata.