Plant Tissue and Cell Wall Staining Methods: Selection of Light Green, Safranin, Fast Green, and Composite Staining Systems
Plant Tissue and Cell Wall Staining Methods: Selection of Light Green, Safranin, Fast Green, and Composite Staining Systems
Composite staining of plant tissues and cell walls is used to distinguish lignified structures, non-lignified parenchyma, vascular bundles, sclerenchyma, cortex, pith, epidermis, and other tissue regions. Light green, safranin, and fast green differ in staining targets, color presentation, differentiation behavior, and suitable sample types. Selection of a composite staining system should focus on tissue-structure interpretation, cell wall differentiation status, and subsequent image analysis requirements.
Keywords: plant tissue staining; cell wall staining; safranin; fast green; light green; composite staining; lignification; vascular bundle
1 Application Logic of Composite Staining for Plant Tissues
1.1 Functional positioning of composite staining
(1) Differentiation of tissue layers
Plant tissues are composed of the epidermis, cortex, endodermis, vascular bundles, pith, mechanical tissues, parenchyma, and other structures. These regions differ in cell wall thickness, degree of lignification, cellular contents, and tissue maturity. Composite staining forms color contrast through red primary staining and green counterstaining, making structures such as xylem, phloem, vessels, fibers, cortex, and pith easier to identify.
(2) Interpretation of cell wall differentiation
Safranin, fast green, and light green are commonly used for morphological analysis of cell wall differentiation. Safranin stains lignified, suberized, and some thick-walled structures strongly. Fast green and light green are mainly used as counterstains for non-lignified tissues, cellulosic cell walls, and cytoplasmic background. Composite staining can reflect differences in tissue structure and cell wall properties, but it is not equivalent to quantitative determination of lignin, cellulose, or pectin.
(3) Microscopic image presentation
Composite staining improves the structural readability of plant sections under bright-field microscopy and is suitable for observing roots, stems, petioles, seeds, ovules, vascular tissues, and lignified tissues. An ideal staining result should show clear red-green boundaries, complete tissue layering, moderate background, and distinguishable cell outlines.
1.2 Principles for selecting staining systems
(1) Selection by research object
When observing vascular bundles, vessels, and xylem, safranin-fast green or safranin-light green counterstaining should be prioritized. For young tissues, parenchyma, or cellular layer analysis, toluidine blue can be included as a structural reference. If the research target involves specific wall components such as lignin, cellulose, pectin, callose, or suberin, further validation with targeted stains or probes is required.
(2) Selection by sample status
In mature stems, roots, and petioles, lignified structures are obvious and safranin counterstaining usually provides good contrast. In young tissues and callus tissues with low lignification, the red signal may be weak, and green counterstaining or structural staining may have greater interpretive value. Leaf samples contain chlorophyll and stronger intrinsic color, so decolorization and background control should be considered before counterstaining.
(3) Selection by result use
For routine morphological observation, the safranin-fast green system is stable and widely used. When a brighter green background is needed, the safranin-light green system can be selected. For structural quantification, section thickness, staining batch, decolorization time, microscope settings, and image thresholds should be fixed to avoid differences in operation affecting result interpretation.
Dye | Main Staining Targets | Typical Color | Role in Composite Staining | Key Control Points |
Safranin O | Lignified cell walls, suberized structures, vessels, fibers, some nuclei | Red to deep red | Highlights xylem, thick-walled tissues, and mature vascular structures | Staining time and differentiation degree |
Fast Green FCF | Non-lignified tissues, parenchyma cells, cellulosic cell walls, cytoplasmic background | Green to blue-green | Forms a classic red-green contrast with safranin | Counterstaining time and ethanol dehydration time |
Light Green SF | Cytoplasm, cellulosic tissues, non-lignified background | Light green to yellow-green | Provides a brighter green background counterstain | Specific dye name and formulation must be confirmed |
Light green-type trade names | Depends on dye type and formulation | Bright green | Should not be assumed to replace plant tissue counterstaining dyes | English name, CAS number, and application must be verified |
Safranin-fast green system | Lignified structures and non-lignified tissues | Red/green contrast | Routine plant paraffin sections and vascular tissue observation | Differentiation and dehydration determine red-green balance |
Safranin-light green system | Lignified structures and bright green background | Red/light green contrast | For samples requiring a bright green counterstained background | Conditions must be re-optimized when replacing fast green |
2 Safranin Staining
2.1 Staining targets
(1) Lignified cell walls
Safranin O can stain lignified structures such as vessels, tracheids, wood fibers, and sclerenchyma cells red to deep red. In transverse sections of roots, stems, and petioles, safranin signals are often used to localize xylem, evaluate vascular bundle maturation, and observe regions with secondary wall thickening.
(2) Suberized and cutinized structures
Safranin can also strongly stain suberized or partially cutinized structures. Therefore, red staining should not be directly equated with lignin deposition. When red staining appears in root endodermis, exodermis, cork tissue, mature seed coat, or some epidermal barriers, interpretation should combine tissue position and auxiliary staining results.
(3) Nuclei and cellular contents
Under specific staining times, pH values, and differentiation conditions, safranin may also stain nuclei or some cellular contents. If the research focus is cell wall lignification, differentiation should be used to reduce non-target red background while keeping cell wall structures and vascular tissue boundaries clear.
2.2 Control of staining conditions
(1) Staining time
Insufficient safranin staining causes weak xylem and vessel outlines, affecting structural interpretation. Excessive staining makes parenchyma, cytoplasm, or background regions turn red at the same time, weakening the effect of green counterstaining. Paraffin sections, hand sections, and resin sections differ in dye penetration rate, so staining-time windows should be established separately.
(2) Differentiation degree
The differentiation step determines the retention range of the red signal. Insufficient differentiation makes the entire section appear too red and compresses tissue layering. Excessive differentiation weakens red staining in lignified structures and makes vessel and fiber boundaries unclear. In safranin-fast green or safranin-light green counterstaining, differentiation should aim to retain red staining in lignified structures while removing nonspecific background.
(3) Sample maturity
Tissue maturity directly affects the safranin signal. Mature stems, roots with secondary growth, and lignified petioles are usually strongly stained red, whereas young tissues, callus tissues, and insufficiently differentiated tissues show weaker red staining. When comparing treated and control groups, sampling position, developmental stage, and section orientation should be controlled.
2.3 Result interpretation
(1) Red-stained regions
Red-stained regions should be interpreted according to anatomical location. In stem cross sections, red staining of vessels, fibers, and xylem usually indicates lignified structures. Red staining in seed coat, root endodermis, or exodermis may also involve suberization, cutinization, or wall densification.
(2) Color intensity
Safranin color intensity is affected by staining time, differentiation degree, section thickness, and tissue density. For result description, it is more appropriate to use morphological descriptions such as “expanded safranin-positive region,” “increased xylem area,” or “thickened sclerenchyma layer,” rather than directly stating that lignin content is quantitatively increased.
(3) Need for validation
If the research objective involves changes in lignin content or lignin composition, phloroglucinol-HCl staining, Mäule reaction, lignin autofluorescence, acetyl bromide assay, or related gene expression analysis should be added to establish an evidence chain of “tissue localization—component validation—mechanistic interpretation.”
3 Fast Green Staining
3.1 Staining function
(1) Green background counterstaining
Fast Green FCF is a commonly used green counterstain in safranin counterstaining systems. It can stain non-lignified tissues, parenchyma cells, cytoplasmic background, and cellulosic cell walls green to blue-green. Its main role is to provide tissue background for safranin-positive lignified structures.
(2) Display of non-lignified structures
Fast green can display cortex, pith, phloem, mesophyll, and non-lignified cell walls, making tissue layering more complete. Its staining results are suitable for tissue-structure observation but are not cellulose-specific. If cellulose deposition needs to be analyzed, methods such as Calcofluor White, S4B, or Congo Red should be used as supplements.
(3) Establishment of red-green contrast
Fast green and safranin form complementary colors. Safranin highlights vessels, fibers, and thick-walled structures, while fast green supplements the outline of non-lignified tissues. When the balance between the two dyes is poor, the whole section may appear too red, too green, or have blurred structural boundaries. Therefore, fast green counterstaining must be optimized together with safranin differentiation and dehydration steps.
3.2 Counterstaining conditions
(1) Concentration
Low fast green concentration leads to insufficient green background, making parenchyma and phloem layers unclear. Excessive concentration makes the whole section too green and affects the boundary of red structures. In routine counterstaining, fast green is more suitable for short-time treatment at a moderate concentration.
(2) Time
Fast green counterstaining time is usually shorter than safranin staining time. Thin sections, young tissues, and samples with a high proportion of parenchyma should have shorter counterstaining time. Mature tissues and thicker sections may be moderately extended, but excessive green background should be avoided.
(3) Dehydration
Fast green can be further differentiated during ethanol dehydration. Excessive dehydration time weakens the green signal, whereas insufficient dehydration may cause cloudy background or unstable color after mounting. Standardizing ethanol gradients and dwell times is critical for inter-batch consistency.
3.3 Suitable scenarios
(1) Root, stem, and petiole cross sections
Safranin-fast green is suitable for routine histological observation of root, stem, and petiole cross sections. This system clearly displays vascular bundles, xylem, phloem, cortex, pith, and epidermal structures, making it suitable for developmental anatomy, stress-treatment studies, and mutant tissue-phenotype analysis.
(2) Vascular bundle structure comparison
In vascular bundle development studies, fast green provides the background of non-lignified tissues and helps determine xylem area, phloem position, vascular bundle arrangement, and cortex thickness. During quantification, tissue area, vessel number, and cell wall thickness should be combined rather than relying only on color intensity.
(3) Screening for abnormal tissue development
Hormone treatment, salt stress, drought stress, pathogen infection, or genetic mutation may cause cortex collapse, abnormal vascular bundles, changes in xylem proportion, and cell wall thickening. The safranin-fast green system can serve as a histological screening method, providing localization information for subsequent component staining and molecular analysis.
4 Light Green Staining
4.1 Name differentiation
(1) Light Green SF Yellowish
The light green commonly used in plant tissue counterstaining usually refers to Light Green SF Yellowish. It is an acidic green dye that can be used as a counterstain for cytoplasm, cellulosic tissues, and non-lignified background. Its color tends to be light green or yellow-green and can form red/light green contrast with safranin.
(2) Brilliant Green
Brilliant Green may also be translated as light green in Chinese, but its chemical properties and application scenarios differ from those of Light Green SF Yellowish. Brilliant Green is more commonly used in microbiological selective culture or special staining contexts and cannot directly replace Fast Green FCF or Light Green SF Yellowish in plant tissue counterstaining.
4.2 Differences from fast green
(1) Color-tone differences
Fast Green FCF usually appears green to blue-green, whereas Light Green SF Yellowish tends to appear light green or yellow-green. The former is closer to the classic safranin-fast green counterstaining effect in plant tissues, while the latter is suitable for samples requiring a brighter background or softer green contrast.
(2) Tissue retention
Light green and fast green differ in tissue retention strength, sensitivity to ethanol dehydration, and background staining behavior. After replacing the green counterstaining dye, concentration, staining time, and dehydration conditions must be re-optimized. The original fast green protocol should not be directly used for comparison.
(3) Sample compatibility
Light green is suitable for thin sections, samples with light background, or tissues requiring bright green contrast. Fast green is suitable for routine counterstaining of roots, stems, petioles, vascular bundles, and mature lignified tissues. When light green is used for leaves, mature seed coats, or pigment-rich samples, background and color interference should be carefully controlled.
4.3 Safranin-light green system
(1) System features
The safranin-light green system can stain lignified structures red and non-lignified background light green or yellow-green. This system is suitable for displaying tissue layering, especially for plant tissue sections requiring a brighter background.
(2) Counterstaining control
Excessive light green counterstaining strengthens the background and reduces contrast of red structures. Insufficient counterstaining makes parenchyma layers unclear. Staining time should be adjusted according to section thickness, tissue maturity, and pigment content, and the dehydration speed should be fixed to ensure stable green signals.
Table 2 Comparison of Fast Green and Light Green Counterstaining Systems
Comparison Dimension | Fast Green FCF | Light Green SF Yellowish | Experimental Selection Recommendation |
Color tone | Green to blue-green | Light green to yellow-green | Select according to tissue background and imaging contrast |
Common system | Safranin-fast green counterstaining | Safranin-light green counterstaining | Use safranin-fast green first for routine plant anatomy |
Background performance | Stable structural layering, relatively deeper color | Brighter background, softer color tone | Light green is suitable for light-background samples or thin sections |
Contrast with safranin | Classic red-green contrast | Red/light green contrast | Different systems should not be directly compared across batches |
Sensitivity to dehydration | Clearly affected by ethanol dehydration | Varies depending on formulation | Re-optimize dehydration workflow after dye replacement |
Main risks | Insufficient counterstaining or excessive dehydration leads to weak green signal | Confusion of product names or overly bright background | Record English name, CAS number, and staining conditions |
5 Selection of Composite Staining Systems
5.1 Safranin-fast green counterstaining
(1) Scope of application
Safranin-fast green is suitable for routine structural observation of roots, stems, petioles, vascular bundles, seeds, and lignified tissues. This system simultaneously displays red lignified structures and green non-lignified background and is widely used in plant paraffin sections.
(2) Workflow control
A typical workflow includes dewaxing, rehydration, safranin staining, differentiation, fast green counterstaining, rapid dehydration, clearing, and mounting. Safranin staining determines the intensity of lignified structures, differentiation controls the red background, fast green counterstaining displays parenchyma, and the dehydration process affects green retention.
(3) Result features
An ideal safranin-fast green result should show clear red staining of vessels, fibers, and xylem, moderate green staining of cortex, pith, phloem, and parenchyma, and clear overall structural boundaries. If the whole section is too red, insufficient safranin differentiation is often involved. If the section is too green, excessive safranin differentiation or overly strong fast green counterstaining may be involved.
5.2 Safranin-light green counterstaining
(1) Scope of application
Safranin-light green is suitable for root, stem, petiole, and some seed tissue sections requiring a brighter green background. This system can be used for routine structural observation and can also serve as an alternative to the safranin-fast green system for preliminary experimental comparison.
(2) Formulation requirements
The safranin-light green system should clearly specify that the light green is Light Green SF Yellowish and should define staining-solution concentration, solvent composition, counterstaining time, and dehydration steps. If the experiment only records “light green,” reproducibility and result traceability will be poor.
(3) Comparison principles
Results from safranin-light green and safranin-fast green systems should not be mixed in the same dataset. If treatment effects are being studied, all samples should use the same staining system, the same batch of staining solution, and the same dehydration conditions to reduce methodological variation.
5.3 Selection of single staining and counterstaining
(1) Safranin single staining
Safranin single staining is suitable for rapid localization of lignified structures such as vessels, tracheids, fibers, and sclerenchyma cells. This method is simple, but non-lignified tissue layering is insufficient, so it is not suitable for complete tissue-structure presentation.
(2) Green counterstain alone
When fast green or light green is used alone, it can display non-lignified background and cytoplasmic structures, but it is insufficient for highlighting lignified tissues. Green staining alone is more suitable as a special background counterstain or preliminary method test, and it is not preferred for interpretation of vascular tissue structures.
(3) Combination with specific staining
When composite staining suggests cell wall changes, supplementary methods should be selected according to the target component. Lignin changes can be examined with phloroglucinol-HCl or Mäule reaction. Cellulose changes can be analyzed with Calcofluor White, S4B, or Congo Red. Callose can be stained with aniline blue. Pectin can be analyzed with ruthenium red, alcian blue, or pectin antibody labeling.
Table 3 Selection of Composite Staining Systems for Plant Tissues
Research Purpose | Recommended System | Main Advantages | Limitations | Result Description Focus |
Routine structural observation of roots, stems, and petioles | Safranin-fast green | Classic red-green contrast and stable tissue layering | Sensitive to differentiation and dehydration time | Distribution of lignified structures and non-lignified tissues |
Localization of vascular bundles and xylem | Safranin single staining or safranin-fast green | Clear display of xylem, vessels, and fibers | Single staining has insufficient background layering | Xylem area, vessel number, fiber-layer thickness |
Display with bright green background | Safranin-light green | Brighter green background and clear structure display | Dye name must be strictly confirmed | Contrast between red lignified structures and light green background |
Observation of young tissue structures | Toluidine blue or light safranin-fast green | Clearer cell layering and wall structures | Safranin signal may be limited when lignification is weak | Meristem, parenchyma cells, and developmental layers |
Validation of lignin changes | Safranin-fast green + phloroglucinol-HCl | Combines structural background and lignin localization | Chemical quantification is still required | Lignified regions, lignin-related color reaction, and tissue structure |
Observation of cellulose wall outlines | Calcofluor White or S4B | Clear cell wall outlines | Different logic from safranin counterstaining | Cell wall continuity and cellulose-related signals |
Analysis of pectin or callose | Ruthenium red, alcian blue, aniline blue | More component-directed | Not suitable for replacing whole-tissue counterstaining | Deposition sites of pectin or callose |
6 Experimental Workflow and Quality Control
6.1 Paraffin section counterstaining workflow
(1) Dewaxing and rehydration
Paraffin sections should be fully dewaxed and rehydrated through graded ethanol before counterstaining. Insufficient dewaxing leads to uneven dye entry, showing mottled staining, locally pale regions, or abnormal edges. Insufficient rehydration affects the binding of water-soluble dyes and makes red-green staining unstable.
(2) Safranin staining and differentiation
After safranin staining, nonspecific background should be removed using ethanol or the differentiation step specified in the formulation. Differentiation should retain clear red staining in lignified structures while reducing red staining of parenchyma. Because different tissues vary in lignification degree, differentiation time should be determined through preliminary experiments.
(3) Green counterstaining and dehydration
After fast green or light green counterstaining, rapid and standardized dehydration is required. Excessive ethanol dwell time weakens the green signal, while insufficient dwell time may affect clearing and mounting. Counterstaining and dehydration steps should be consistent within the same batch.
6.2 Counterstaining of hand sections
(1) Section thickness
Hand sections are suitable for rapid observation of root, stem, and petiole structures, but variation in thickness significantly affects color intensity. For result presentation, sections with uniform thickness, complete structures, and no obvious compression deformation should be selected.
(2) Rapid counterstaining
Hand sections can be stained briefly with safranin-fast green or safranin-light green for preliminary screening of vascular bundles and cell wall thickening regions. Because they are not embedded and thinly sectioned, their results are more suitable for qualitative observation and should not be used as strict quantitative evidence.
(3) Mounting method
Aqueous mounting can be used for short-term observation, while resin mounting after dehydration and clearing can be used for long-term preservation. If the green counterstain fades obviously in organic solvents, the mounting method should be adjusted according to the staining system, and imaging should be completed promptly.
6.3 Quality control of counterstaining
(1) Sampling consistency
Plant tissue staining results are strongly affected by developmental stage and anatomical position. When comparing treatment and control groups, sampling site, node position, root segment, leaf position, and tissue maturity should be unified to avoid misinterpreting developmental differences as staining differences.
(2) Section consistency
Section thickness affects color intensity, cell wall boundaries, and image quantification. Paraffin sections should maintain a uniform thickness, and hand sections should be screened. Sections with uneven thickness are not suitable for positive-area or color-intensity comparison.
(3) Consistency of microscopy parameters
Bright-field imaging should use consistent light intensity, white balance, exposure time, and magnification. Image post-processing should avoid altering color relationships between groups. Quantitative analysis should use unified thresholds, ROIs, and background-subtraction methods.
Table 4 Abnormal Counterstaining Results and Optimization Directions
Abnormal Result | Common Causes | Priority Checks | Optimization Direction |
Entire section appears too red | Safranin staining too strong or insufficient differentiation | Safranin time, differentiation solution, differentiation time | Shorten safranin staining or extend differentiation |
Xylem red staining is too weak | Insufficient safranin staining or excessive differentiation | Safranin concentration, staining time, differentiation degree | Increase safranin time or reduce differentiation intensity |
Green background is too strong | Excessive fast green/light green counterstaining | Green dye concentration and counterstaining time | Reduce concentration or shorten counterstaining time |
Green background is too weak | Excessive dehydration or insufficient counterstaining | Ethanol dehydration steps, counterstaining time | Shorten dehydration dwell time and extend counterstaining |
Red-green boundary is unclear | Section too thick, insufficient differentiation, or overly strong green counterstaining | Section thickness, safranin differentiation, counterstaining conditions | Select thin sections and optimize red-green balance |
Tissue structure appears gray | Aged staining solution, insufficient dewaxing, or incomplete clearing | Staining solution status, dewaxing, and clearing steps | Replace staining solution and standardize dewaxing and clearing |
Obvious inter-batch variation | Inconsistent staining batches, dehydration times, or sampling stages | Staining batch, sampling standard, microscopy parameters | Process samples in the same batch and increase biological replicates |
Results become unstable after replacing with light green | Dye type inconsistent or formulation mismatched | English name, CAS number, concentration, and solvent | Re-establish light green system conditions |
7 Image Interpretation and Quantitative Analysis
7.1 Color interpretation
(1) Interpretation by structural localization
Composite staining images should first be interpreted based on tissue structure. Red staining in xylem, vessels, fibers, and sclerenchyma cells has strong structural significance. Green counterstaining in cortex, pith, phloem, and parenchyma provides tissue background and cellular layering.
(2) Comparison within the same batch
Counterstaining colors should not be directly compared across batches. Treatment and control groups should use the same fixation, sectioning, staining, dehydration, and imaging conditions. If cross-batch analysis is unavoidable, internal controls or standardized image acquisition parameters should be used.
(3) Supplementation with morphological parameters
Color intensity should be combined with morphological parameters. Vascular bundle area, xylem area, vessel diameter, vessel number, cell wall thickness, number of sclerenchyma layers, and cortex thickness are usually more suitable for statistical analysis than color intensity alone.
7.2 Quantitative indicators
(1) Area indicators
Xylem area, safranin-positive area, vascular bundle area, cortex area, and pith area can be used to compare tissue development and cell wall thickening. ROI range and threshold rules should be unified during analysis.
(2) Structural indicators
Vessel number, vessel diameter, cell wall thickness, fiber-layer thickness, and number of cell layers can be used to describe vascular tissue maturation and structural changes. These indicators are less dependent on staining intensity and are suitable for group comparisons.
(3) Quality indicators
Red-green contrast, background intensity, boundary clarity, and staining uniformity can be used as method-optimization indicators, but they should not be treated as biological conclusion indicators. Formal sample statistics should be performed after the method is optimized.
Table 5 Common Analytical Indicators for Composite Staining Images
Analysis Object | Recommended Indicators | Suitable System | Interpretation Focus |
Xylem development | Xylem area, vessel number, vessel diameter | Safranin-fast green, safranin-light green | Interpret maturity status together with tissue position |
Thick-walled tissue | Number of sclerenchyma layers, wall thickness, safranin-positive area | Safranin single staining or counterstaining | Consider section thickness and differentiation effects |
Vascular bundle structure | Vascular bundle number, area, arrangement | Safranin-fast green | Suitable for mutant, stress, and developmental comparisons |
Cortex and pith | Cell layer number, cell area, green-region range | Fast green or light green counterstaining | Green signal does not represent cellulose quantification |
Tissue integrity | Cell collapse ratio, cavity area, tissue boundary | Safranin-fast green, toluidine blue | Suitable for analysis of treatment injury and developmental abnormalities |
Method quality | Red-green contrast, background intensity, staining uniformity | All counterstaining systems | Used for workflow optimization and batch quality control |
8 Reagent and Material Selection for Plant Tissue Composite Staining
Table 6 Primary Stains, Counterstains, and Cell Wall-Related Chromogenic Reagents
Product Type | Representative Product | CAS No. | Application Positioning | Selection Points |
Red primary stain | Safranin O | Staining of lignified and suberized structures and some nuclei | Core primary stain in safranin-fast green and safranin-light green systems | |
Green counterstain | Fast Green FCF | Counterstaining of non-lignified tissues and cytoplasmic background | Commonly used in classic red-green counterstaining of plant tissues | |
Green counterstain | Light Green SF Yellowish | Light green background counterstaining | Must be distinguished from Brilliant Green | |
Green dye | Brilliant Green | Special staining or microbiology-related use | Should not be assumed to replace fast green or Light Green SF | |
Rapid tissue dye | Toluidine Blue O | Semi-thin sections and rapid tissue-structure observation | Can serve as a structural reference before optimizing counterstaining systems | |
Pectin dye | Ruthenium Red | Staining of acidic pectin and middle lamella | Used for preliminary screening of pectin distribution | |
Acidic polysaccharide dye | Alcian Blue 8GX | Acidic polysaccharides, mucilage, and pectin-related structures | Staining targets are affected by pH conditions | |
Cellulose-related dye | Congo Red | Cellulose and β-glucan staining | Specificity is limited; background controls are required | |
Callose dye | Aniline Blue | Fluorescent staining of callose | Suitable for pollen tubes, sieve plates, and infection-site analysis | |
Lipid dye | Sudan III | Staining of cutin, suberin, and lipid deposition | More suitable for fresh or frozen samples | |
Lipid dye | Sudan IV | Staining of lipid barrier structures | Avoid lipid loss caused by routine dehydration and clearing | |
Lipid dye | Oil Red O | Staining of neutral lipids and some lipid structures | Used for observation of cutin, suberin, or lipid droplets |
Table 7 Reagents Related to Fixation, Dehydration, Clearing, and Mounting
Product Type | Representative Product | CAS No. | Application Positioning | Selection Points |
Fixative | Paraformaldehyde | Tissue fixation and morphology preservation | Suitable for some downstream fluorescence or immunoanalysis | |
Fixative | Formaldehyde solution | FAA or routine tissue fixation | Control fixation time to avoid excessive tissue hardening | |
Fixative component | Glacial acetic acid | FAA fixative component, differentiation, or pH adjustment | Helps preserve tissue structure and nuclear structure | |
Buffer component | Sodium dihydrogen phosphate | Fixative or washing buffer system | Used to maintain buffer pH | |
Buffer component | Disodium hydrogen phosphate | Fixative or washing buffer system | Used with sodium dihydrogen phosphate to prepare phosphate buffer | |
Clearing reagent | Xylene | Clearing of paraffin sections | Suitable for clearing before resin mounting | |
Clearing substitute | Limonene | Xylene substitute clearing agent | Lower odor; compatibility with mounting medium should be verified | |
Embedding material | Paraffin | Paraffin embedding and serial sectioning | Suitable for routine safranin-fast green/light green counterstaining | |
Mounting material | Neutral balsam | Long-term mounting of bright-field sections | Suitable for counterstained sections after dehydration and clearing | |
Aqueous mounting material | Glycerol | Temporary mounting or aqueous mounting system | Suitable for short-term observation of some water-soluble staining results |
9 Common Questions
9.1 Can light green and fast green be regarded as the same dye?
No. Fast green usually refers to Fast Green FCF. In plant tissue counterstaining, light green often refers to Light Green SF Yellowish. Brilliant Green may also be translated as light green in Chinese, but its use and staining properties are different. The English name and CAS number should be confirmed when establishing the method.
9.2 Can safranin-fast green and safranin-light green be directly interchanged?
They should not be directly interchanged. Both systems can form red-green contrast, but their green tone, tissue retention, dehydration sensitivity, and background intensity differ. After replacing the dye, concentration, counterstaining time, and dehydration conditions should be re-optimized.
9.3 Does a safranin-positive region equal lignin deposition?
Safranin-positive regions often indicate lignified or thick-walled structures, but they may also include suberized, cutinized, or other wall-modified structures. To prove lignin changes, phloroglucinol-HCl staining, Mäule reaction, lignin autofluorescence, or chemical quantification should be combined.
9.4 What are the main causes of weak fast green counterstaining?
Common causes include low fast green concentration, insufficient counterstaining time, excessive ethanol dehydration time, or aged staining solution. Optimization should first standardize dehydration time, then adjust counterstaining time and concentration.
9.5 How should an overall reddish section be optimized?
An overall reddish section is often related to excessive safranin staining or insufficient differentiation. Safranin staining time can be shortened, the differentiation step can be moderately extended, and green counterstaining intensity can be controlled so that lignified structures retain red color while non-lignified background is not excessively red-stained.
9.6 What causes unclear red-green boundaries?
Common causes include sections that are too thick, insufficient safranin differentiation, overly strong green counterstaining, unstable dehydration time, or inconsistent microscopy parameters. Uniform thin sections should be selected first, followed by optimization of differentiation and counterstaining steps.
9.7 Are leaf samples suitable for safranin-fast green or safranin-light green counterstaining?
Leaf samples can be stained with safranin-fast green or safranin-light green, but chlorophyll, intrinsic color, and tissue thickness may affect the green background. The research focus should usually be placed on veins, vascular bundles, epidermis, and mesophyll structure rather than simply comparing green intensity.
Composite staining of plant tissues should focus on tissue-structure interpretation and analysis of cell wall differentiation.
Safranin highlights lignified and thick-walled structures. Fast green is used as a classic background counterstain for non-lignified tissues. Light green can be used as a specific green counterstaining option, but the dye type must be strictly confirmed. The reliability of counterstaining results depends on sampling consistency, section thickness, differentiation control, dehydration conditions, and image quantification rules.