ABSTRACT
High-pressure freezing/freeze substitution has been used to preserve biological samples for ultrastructure study instead of chemical fixation. For most plant samples, the water content is too high and cannot be properly preserved during cryofixation. Additionally, the cell wall is a barrier that prevents the substitution of water with the resin. In this chapter, we will discuss modified high-pressure freezing and subsequent processing protocols based on our routinely used methodology for examining Arabidopsis seeds in transmission electron microscopy and electron tomography.
Subject(s)
Arabidopsis , Electron Microscope Tomography , Seeds , Seeds/ultrastructure , Electron Microscope Tomography/methods , Arabidopsis/ultrastructure , Freezing , Cold Temperature , Pressure , Microscopy, Electron, Transmission/methods , Cryopreservation/methods , Freeze Substitution/methodsABSTRACT
Basic helix-loop-helix proteins (bHLHs) comprise one of the largest families of transcription factors in plants. They have been shown to be involved in responses to various abiotic stresses, such as drought, salinity, chilling, heavy metal toxicity, iron deficiency, and osmotic damages. By specifically binding to cis-elements in the promoter region of stress related genes, bHLHs can regulate their transcriptional expression, thereby regulating the plant's adaptive responses. This review focuses on the structural characteristics of bHLHs, the regulatory mechanism of how bHLHs are involved transcriptional activation, and the mechanism of how bHLHs regulate the transcription of target genes under various stresses. Finally, as increasing research demonstrates that flavonoids are usually induced under fluctuating environments, the latest research progress and future research prospects are described on the mechanisms of how flavonoid biosynthesis is regulated by bHLHs in the regulation of the plant's responses to abiotic stresses.