Table 1. Content of 5hmC in (A) genomic DNA and (B) RNA in different tissues of various plants using several methods.

Sample	5-hmC as % of total cytosine	Method	Comment	Reference
(A)
Leaves, flowers of A. thaliana	0.055	Fluorescent antibody	Suggested further studies with advanced techniques	[89]
Leaves, flowers of A. thaliana	0.068–0.075	Antibody-based dot-blot	Suggested passive DNA demethylation	[86]
Protoplasts of Cucumis sativus, Brassica oleracea	0.2–0.3	Fluorescent antibody	Removal of DNA methylation may result from biological activity rather than oxidative DNA damage	[87]
Leaves of A. thaliana	0.033	Liquid chromatography-multi-stage mass spectrometry (LC-MS/MS/MS)	Observed passive DNA demethylation as a result of oxidative DNA damage, and suggested further studies to detect other oxidative compounds, foC and caC	[88]
Leaves, floral buds of A. thaliana	Undetectable in comparison with 0.2% synthetic DNA with 5hmC	Thin layer chromatography (TLC)	No 5hmC present as an intermediate of DNA demethylation	[69]
Leaves, panicles of Oryza sativa L. ssp. indica	1.39 and 2.17/106	LC-MS/MS/MS	Detected higher levels of 5hmC in heterochromatin regions, particularly in transposable elements (TE)-related genes. Suggest significant association between chromatin structure and levels of 5hmC.	[90]
Shoots of A. thaliana; Flower bud of A. thaliana; Seedling, shoot, root, leaves of A. thaliana and Z. mays; Seeds, pollen of A. thaliana	Range from 0.07–0.17. Higher level in seedling of both species.	TLC; Antibody; Enzyme-linked immunosorbent assay (ELISA); β-glucosyltransferase radiolabeling MS	Not detectable, 5hmC less than control of 0.5%; Detectable but less than control; Quantity not biologically significant; Not detectable	[91]
Leaves of heat-stressed Brassica napus	0.324	Methyl flash hydroxylated DNA quantification (colormetric)	Slight increase in level of 5hmC in line with increase of 5mC in response to heat stress	[92]
Leaves of a range of O. sativa cultivars	1.32/106 to 1.98/106	Chromatography-tandem mass spectrometry with isotope dilution	Levels of 5hmC lower than in animals	[93]
(B)
A.thaliana	0.00485	LC-MS/MS	First report of 5hmC in plant RNA	[94]