Agriculture Reference
In-Depth Information
tetrazolium. Although pH of the TZ solution is not critical, 6.5-7.5 pH is optimum. TZ solutions should be
kept away from direct sunlight and in dark-colored containers.
Standardization of the TZ test can be affected by the kind of TZ salt used (e.g., chloride or bromide),
concentration of solutions, staining period, and subjectivity of interpreting the staining patterns.
PrEPArATIon for EVALuATIon
In the preparation for interpretation of staining patterns, the embryos must be exposed to full view. The
amount of preparation needed to do this depends on the techniques applied prior to staining. Seeds with
bisected embryos may be examined directly. Other seeds will require some additional manipulation;
for example, the embryo may be removed from the surrounding seed tissues, opaque seed coats may be
removed, or the outer coverings of grasses may be treated with lactic acid for easier visibility of the embryo
and a more precise evaluation. Lactophenol solution was used for that purpose, but the use of lactic acid has
become more common due to the need for safety precautions when using lactophenol solution.
The following preparation techniques are recommended for precise evaluation of groups of seeds
depending on their internal anatomy:
1. Spread apart or tear away the semi-transparent seed coat to expose the embryo [
Arrhenatherum,
Poa, Phleum
and
Dactylis
(Poaceae);
Freesia
(Iridiaceae);
Trifolium
(Fabaceae);
Ailanthus
(Sima-
roubaceae)].
2. Expose the embryo by removing seed coat and residual nutritive tissue [
Kochia
(Chenopodia-
ceae);
Carthamus
and
Carlina
(Asteraceae);
Cornus
(Cornaceae);
Citrullus, Cucumis
and
Cucur-
bita
(Cucurbitaceae);
Cupressus
and
Libocedrus
(Cupressaceae);
Lathyrus
(Fabaceae);
Elaeagnus
(Elaeagnaceae);
Geranium
(Geraniaceae);
Castanea
(Fagaceae);
Acer
(Aceraceae);
Crambe,
Camelina, Lepidium, Raphanus, Rorippa
and
Sinapis
(Brassicaceae);
Cuscuta
and
Convolvulus
(Convolvulaceae);
Alnus
and
Betula
(Corylaceae); most Liliaceae, Fabaceae, Lamiaceae, Malva-
ceae, Rosaceae, and Asteraceae].
3. Expose the embryo and adjoining nutritive tissue by tearing into the nutritive tissue or by spreading
the cut surfaces suficiently to develop the desired tear [
Beta
(most Chenopodiaceae);
Magnolia
(Magnoliaceae);
Fagopyrum, Rheum
and
Rumex
(Polygonaceae);
Coffea
and
Nertera
(Rubia-
ceae); most Poaceae, Saxifragaceae, Apiaceae and Liliaceae].
4. Expose the embryo and nutritive tissue by removal of slices of the nutritive tissue [
Asparagus
(Liliaceae);
Howea
(Palmaceae);
Gladiolus
(Iridaceae)].
5. Expose the interior tissues of the embryonic axis by cutting through the midsection of the axis, then
separate the seed halves [
Arachis, Glycine, Lupinus, Phaseolus, Pisum
and
Vicia
(most Fabaceae);
Prunus
(Rosaceae);
Citrus
and
Poncirus
(Rutaceae);
Fagus, Quercus
and
Nothofagus
(Fagaceae);
most Brassicaceae].
6. Expose the embryo and the nutritive tissue (if present) by cutting longitudinally almost through
the midsection of the seed or by cutting through one-half or more of the circumference of the seed
coat(s) [
Amaranthus
(Amaranthaceae);
Carya
and
Juglans
(Juglandaceae);
Araucaria
(Araucaria-
ceae);
Apios
(Fabaceae);
Strelitzia
(Musaceae)
Cephalanthus
and
Crusea
(Rubiaceae);
Amaran-
thus
(Amaranthaceae); most Rosaceae and Malvaceae].
7. Use a clearing solution to remove pigmentation of the seed coat, then observe the embryo through
the resulting semi-transparent seed coat [
Zoysia, Panicum, Eragrostis
and
Setaria
(Poaceae)].
8. If numerous fractures are encountered within the embryonic axis, expose the intact embryo for
detection of existing fractures by removal of thin slices of the cotyledonary tissues near the basal
end. The cotyledons can then be separated for additional observation [
Spartium
spp.,
Ulex euro-
paes
(Fabaceae)].
9. Observe the major embryo structures [
Carya, Juglans
and
Pterocarya
(Juglandaceae)].
