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The use of light and electron microscopy in the study of experimentally altered spores and pollen grains
Author(s) -
Sengupta S.,
Muir M. D.
Publication year - 1977
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1977.tb01124.x
Subject(s) - sporopollenin , spore , atmospheric pressure , materials science , pollen , botany , analytical chemistry (journal) , chemistry , biology , chromatography , oceanography , geology
SUMMARY Plant spores and pollen grains were heated to different temperatures, from room temperature to 350°C at atmospheric pressure, in a nichrome‐wire resistance furnace, and to different temperatures from 100 to 500°C at 1 kb pressure in a modified apparatus normally used for triaxial rock‐deformation studies. In the temperature and pressure experiments, the grains were mixed with silica sand and sea water in the proportions of 1:4:5. For optical microscopy, the pollen grains were mounted in glycerine jelly: for SEM, they were mounted on aluminium stubs rinsed with water and sputter‐coated with gold. STEM and HVEM were used on thick sections of spores of Lycopodium clavatum embedded in Epon‐Araldite. The different layers of the spore or pollen‐grain (i.e. exine+intine) degrade differently. The ornamented part of the exine (the sexine−mainly composed of sporopollenin, lipids and polysaccharides) begins to degrade at approximately 300–350°C and 1 kb pressure, exposing the non‐ornamented nexine layer. The nexine seems able to withstand high temperatures and pressures. Between 300 and 500°C with 1 kb pressure, the grains begin to form an amorphous mass. Compared with other work in which the outer exine layer of L. clavatum was removed by oxidation with ozone, here the same layer was gradually removed by pressure and temperature effects. The smell of phenolic compounds is very prominent at higher temperatures (400°C with 1 kb pressure and upwards) and production of other gas, unidentified so far, is evident from about 300°C and 1 kb pressure. The degraded exposed nexine layer at 500°C resembles thin plates in the SEM. A similar structure was also found in L. clavatum heated at 300°C and 1 kb pressure. The exposed nexine of L. clavatum was sectioned and examined in the TEM, which showed the trilamellar units, of which the main bulk of the nexine is composed, to be very resistant to high temperatures and pressures. STEM and HVEM have been used to study globular structures observed in the L. clavatum spore cavity.