Plant tissue integral staining method for ultrathin section
Technical Field
The invention relates to a plant tissue integral staining method for ultrathin sections
Background
Ultrathin sectioning techniques are important methods for studying cellular sub-microstructures. However, in order to obtain a sharp image, the biological sample must be electronically stained. The electronic staining is to bind or adsorb heavy metals in heavy metal salts such as uranium, lead, osmium, and tungsten to some components in the tissue to improve the contrast of the microstructure in the sample. Heavy metal atoms with different numbers are adsorbed on different structural components, areas with more bound heavy metals (namely, areas with compact structure and high atomic number) have strong electron scattering capacity, and are in black with compact electron microscope under the electron microscope, areas with less bound heavy metals are in light black and gray black, and areas without bound heavy metals are in electron transparent areas.
The current common dyeing method is slice dyeing, namely fishing ultrathin slices on a copper net for electronic dyeing. However, sheet dyeing has a number of limitations, such as: in the large-batch net-carrying dyeing process, the net-carrying quantity of each dyeing is limited, and even if the nets are carried in the same batch, the dyeing time is not easy to be uniform; the operation is complicated, the grid is easy to bend and deform, and the focusing effect during the observation of an electron microscope is influenced; due to the fact that liquid is replaced for multiple times, ultrathin slices on the carrying net are prone to damage, and phenomena such as folding and slice dropping occur; in the dyeing process, the lead dye solution is easily combined with carbon dioxide in the air to generate pollution, so that the observation effect is influenced; the method can not carry out large-scale continuous film collection on the specimen, and is an important barrier for realizing three-dimensional reconstruction. Aiming at the phenomenon, an integral dyeing method can be adopted in the preparation process of the electron microscope sample, namely, the electron dyeing is carried out in the sample preparation process, and the secondary dyeing is not needed after the section.
In the past, studies on bulk staining have mostly used animal tissues as materials. However, plant tissues, unlike animal tissues, have cell walls, which is a feature that causes great trouble in the overall staining of plant tissues. Therefore, it is of great significance to study the whole plant tissue staining method for ultrathin sections.
Disclosure of Invention
The invention aims to increase lipid staining through a Thiocarbohydrazide (TCH) bridging agent, and the method does not need staining after slicing, is convenient to operate, and is beneficial to realizing continuous slicing of plant tissues and three-dimensional reconstruction.
The invention provides a plant tissue integral staining method for ultrathin sections. The method uses picea wilsonii pollen as a material. The method specifically comprises the following steps:
(1) fixing the plant material; placing mature picea wilsonii pollen in a fixing solution prepared from glutaraldehyde and paraformaldehyde for pre-fixing, washing with a PBS buffer solution, and then performing post-fixing with 1% osmic acid;
(2) osmium deposition is carried out by TCH; treating with 1% TCH, standing at room temperature for 30min-1h, soaking with 1% osmic acid, and further depositing osmium;
(3) block dyeing: respectively carrying out block dyeing on the plant sample by using 2.5% gadolinium acetate, 2.5% samarium acetate and 2% uranyl acetate, and standing for 8-12 hours at 4 ℃ or standing for 4 hours at normal temperature;
(4) and (3) dehydrating: performing ethanol gradient dehydration on the block-dyed plant sample, and performing gradient dehydration by using 30%, 50%, 60%, 70%, 80%, 90%, 95% and 100% ethanol respectively;
(5) and (3) infiltration: respectively carrying out permeation treatment by using a mixed solution of ethanol and acetone, 100% acetone, a mixed solution of acetone and spurr resin and 100% spurr resin;
(6) embedding and polymerization: adding 100% spurr resin into the embedding plate, putting the plant sample, adjusting the position, and putting the plant sample in an oven for polymerization.
Preferably, in step (1): the concentration of the PBS buffer solution is 0.1M, and the pH value is 7.2; the fixing solution is a mixed solution of 2.4% paraformaldehyde and 2% glutaraldehyde; the PBS buffer solution and the stationary solution are stored in a refrigerator at 4 ℃ and are placed on ice when in use; after the pre-fixation, the plant sample after the pre-fixation is washed for 3 times by PBS buffer solution, each time is 10-15min, and the fixing solution is fully washed away; post-fixation was performed with 1% osmic acid, left at 4 ℃ for 2h, after which it was necessary to wash 3 times with purified water for 10-15min each.
Preferably, in step (2): weighing 0.05g of TCH, dissolving the TCH in 5mL of purified water, wrapping a layer of tinfoil to prevent light, placing the prepared 1% TCH in an oven at 60 ℃ for 1h, shaking once every ten minutes, and finally filtering the TCH by using a filter with the pore diameter of 0.22 mu m for use; adding 300 μ l TCH, standing at room temperature for 30min-1h to avoid TCH precipitation at low temperature, cleaning plant sample treated with TCH with purified water for 3 times, each time for 10-15min, performing osmium deposition with 1% osmate, standing at room temperature for 1h, and cleaning with purified water for 3 times, each time for 10-15 min.
Preferably, in step (3): the block dye of 2.5 percent gadolinium acetate, 2.5 percent samarium acetate and 2 percent uranyl acetate are all prepared by purified water, and the concentration is mass percent.
Preferably, in step (4): performing gradient dehydration with 30%, 50%, 60%, 70%, 80%, 90%, 95%, and 100% ethanol respectively, and dehydrating with 100% ethanol for 3 times for 15min to fully dehydrate the sample, wherein the ethanol content is 30%, 50%, 60%, 70%, 80%, 90%, and 95%, and the solvent is purified water.
Preferably, in step (5): respectively treating with solutions of ethanol and acetone at volume ratios of 2:1, 1:1 and 1:2 for 15min, then treating with 100% acetone for 3 times, each time for 15min, respectively treating with solutions of acetone and spurr resin at volume ratios of 2:1, 1:1 and 1:2 for 3h, then treating with 100% spurr resin for at least 3 times, and changing the liquid every 12 h.
Preferably, the recipe of the spurr resin is 26g of NSA hardener (nonylsuccinic anhydride), 10g of ERL4221 resin (vinylcyclohexene dioxide), 6g of DER 736 plasticizer (diethylene glycol) and 0.4g of DMAE catalyst (methylene glycol); in the step (6): the polymerization was carried out for 2h at 40 ℃ and then for 8h at 70 ℃.
The feature of the present invention is the use of TCH as a bridging agent during osmium impregnation, which attaches itself to the osmium already present after initial osmium fixation and acts as a bridge, allowing more osmium to be deposited at the original osmium sites. Therefore osmium-tropic TCH enhances osmium staining of lipid components. And then, a block dyeing agent is used for dyeing, so that the electronic contrast of the internal structure of the cell is effectively enhanced, the problems of lead pollution caused by lead citrate block dyeing and a great deal of inconvenience caused by slice dyeing are solved, and technical support is provided for ultrathin continuous slicing of plant tissues.
Drawings
FIG. 1 is picea wilsonii pollen dyed with 2.5% gadolinium acetate blocks, and FIG. 2 is a partial enlarged view thereof; FIG. 3 is a picea wilsonii pollen stained with 2.5% samarium acetate blocks, and FIG. 4 is a partial enlarged view thereof; fig. 5 is picea wilsonii pollen dyed with 2% uranyl acetate block, and fig. 6 is a partial enlarged view thereof.
Detailed Description
Sample collection
Collecting mature picea wilsonii pollen, and standing at-20 deg.C for use.
Sample preparation
1. Front fixing: and (3) placing the collected mature picea wilsonii pollen in a fixing solution consisting of 2% of glutaraldehyde and 2.4% of paraformaldehyde for fixing, and vacuumizing for 1-2 h. Note that the fixative was stored in a 4 ℃ freezer and placed on ice when used.
2. Rinsing: rinsing the pre-fixed plant sample with 0.1M phosphate buffer solution, and washing for 3 times, each time for 10-15 min; the phosphate buffer was stored in a refrigerator at 4 ℃ and placed on ice when used.
3. Post-fixing: the rinsed plant samples were post-fixed with 1% osmic acid and placed at 4 ℃ for 2 h.
4. Rinsing: washing the fixed plant sample with purified water for 3 times, each for 10-15 min.
5. Preparing 1% TCH: weighing 0.05g TCH, dissolving in 5mL of purified water, wrapping a layer of tinfoil to prevent light, placing the prepared 1% TCH in an oven at 60 ℃ for 1h, shaking once every ten minutes, and finally filtering with a filter with the pore diameter of 0.22 mu m for later use.
6. TCH treatment: and (4) treating the rinsed plant sample by using 1% TCH, and standing for 30min-1h at room temperature.
7. Rinsing: and washing the plant sample treated by TCH with purified water for 3 times, 10-15min each time.
8. Deposition of osmium: the rinsed plant samples were soaked with 1% osmic acid and left at room temperature for 1 h.
9. Rinsing: and (3) washing the plant sample subjected to osmium deposition with purified water for 10-15min each time.
10. Block dyeing: and (3) respectively carrying out block dyeing on the rinsed plant sample by using 2.5% gadolinium acetate, 2.5% samarium acetate and 2% uranyl acetate, and standing at 4 ℃ for 8-12h or at room temperature for 4 h.
11. Rinsing: washing the block-dyed plant sample with purified water for 3 times, each for 10-15 min.
12. And (3) dehydrating: the rinsed plant samples were dehydrated with 30%, 50%, 60%, 70%, 80%, 90%, 95%, 100% ethanol for 15min each time in a gradient manner, and 3 times with 100% ethanol.
13. Ethanol and acetone infiltration: treating with solutions of ethanol and acetone at volume ratio of 2:1, 1:1, and 1:2 for 15min, respectively, and treating with 100% acetone for 15min for 3 times.
14. Acetone penetration with spurr resin: treating with acetone and spurr resin at volume ratio of 2:1, 1:1, and 1:2 for 3 hr, respectively, and treating with 100% spurr resin for at least 3 times, and changing liquid every 12 hr.
15. Embedding and polymerization: firstly, 100% spurr resin is added into an embedding plate, then a plant sample is placed, the position of the plant sample is adjusted, and the plant sample is placed in an oven. Polymerization was first carried out at 40 ℃ for 2h and then at 70 ℃ for 8 h.
And adding a silica gel drying agent into the prepared sample, placing the sample into a sealed bag, and storing the sample at room temperature.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.