Abstract
BackgroundLaser microdissection (LMD) has been established for isolation of individual tissue types from herbaceous plants. However, there are few reports of cell- and tissue-specific analysis in woody perennials. While microdissected tissues are commonly analyzed for gene expression, reports of protein, enzyme activity and metabolite analysis are limited due in part to an inability to amplify these molecules. Conifer stem tissues are organized in regular patterns with xylem, phloem and cortex development controlled by the activity of the cambial zone (CZ). Defense responses of conifer stems against insects and pathogens involve increased accumulation of terpenoids in cortical resin ducts (CRDs) and de novo formation of traumatic resin ducts from CZ initials. These tissues are difficult to isolate for tissue-specific molecular and biochemical characterization and are thus good targets for application of LMD.ResultsWe describe robust methods for isolation of individual tissue-types from white spruce (Picea glauca) stems for analysis of RNA, enzyme activity and metabolites. A tangential cryosectioning approach was important for obtaining large quantities of CRD and CZ tissues using LMD. We report differential expression of genes involved in terpenoid metabolism between CRD and CZ tissues and in response to methyl jasmonate (MeJA). Transcript levels of β-pinene synthase and levopimaradiene/abietadiene synthase were constitutively higher in CRDs, but induction was stronger in CZ in response to MeJA. 3-Carene synthase was more strongly induced in CRDs compared to CZ. A differential induction pattern was observed for 1-deoxyxyulose-5-phosphate synthase, which was up-regulated in CRDs and down-regulated in CZ. We identified terpene synthase enzyme activity in CZ protein extracts and terpenoid metabolites in both CRD and CZ tissues.ConclusionsMethods are described that allow for analysis of RNA, enzyme activity and terpenoid metabolites in individual tissues isolated by LMD from woody conifer stems. Patterns of gene expression are demonstrated in specific tissues that may be masked in analysis of heterogenous samples. Combined analysis of transcripts, proteins and metabolites of individual tissues will facilitate future characterization of complex processes of woody plant development, including periodic stem growth and dormancy, cell specialization, and defense and may be applied widely to other plant species.
Highlights
Laser microdissection (LMD) has been established for isolation of individual tissue types from herbaceous plants
LMD was not effective in cutting spruce stem tissue mounted on glass slides because the laser power required was sufficient to etch the surface of a glass polyethylene naphthalate (PEN)-membrane slide resulting in diffusion of the beam and decreased laser cutting efficacy
The gravity assisted collection method of LMD permits the use of glass-free, steel frame polyethylene terephthalate (PET)-membrane slides that eliminates the need for glass support, facilitates the use of increased laser power and allows collection of microdissected tissues in an empty PCR tube cap, which is required for metabolite extractions
Summary
Laser microdissection (LMD) has been established for isolation of individual tissue types from herbaceous plants. Conifer stem tissues are organized in regular patterns with xylem, phloem and cortex development controlled by the activity of the cambial zone (CZ). Defense responses of conifer stems against insects and pathogens involve increased accumulation of terpenoids in cortical resin ducts (CRDs) and de novo formation of traumatic resin ducts from CZ initials. These tissues are difficult to isolate for tissue-specific molecular and biochemical characterization and are good targets for application of LMD. In spruce species (Picea spp.), large cortical resin ducts (CRDs) in the bark carry terpene-rich oleoresin that plays a role in defense against biotic stress such as insect feeding, egg deposition, or pathogen inoculation [2,3]. Treatment of spruce stems with methyl jasmonate (MeJA) has been shown to elicit a response that mimics the response to biotic stress [6,7]
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