Recalcitrant seeds are
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
s that do not survive drying and freezing during
ex-situ conservation. By and large, these seeds cannot resist the effects of drying or temperatures less than 10 °C (50 °F); thus, they cannot be stored for long periods like
orthodox seeds because they can lose their viability. Plants that produce recalcitrant seeds include
avocado
The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated by Mesoamerica, Mesoamerican tribes more than 5,000 years ago. Pre-Columb ...
,
mango,
mangosteen,
lychee,
cocoa
Cocoa may refer to:
Chocolate
* Chocolate
* ''Theobroma cacao'', the cocoa tree
* Cocoa bean, seed of ''Theobroma cacao''
* Chocolate liquor, or cocoa liquor, pure, liquid chocolate extracted from the cocoa bean, including both cocoa butter and ...
,
rubber tree, some horticultural trees,
aquatic plants such as ''
Nymphaea caerulea''
'','' and several plants used in traditional medicine, such as species of ''
Virola'' and ''
Pentaclethra''. Generally speaking, most tropical
pioneer species have orthodox seeds but many
climax species have recalcitrant or intermediate seeds.
Mechanisms of damage
The two main mechanisms causing damage to recalcitrant seeds are
desiccation effects on the
intracellular structures and metabolic damage from the formation of toxic chemicals such as
free radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
s. An example of the first type of damage would be found in some recalcitrant nontropical
hardwood seeds, specifically the
acorn
The acorn, or oaknut, is the nut of the oaks and their close relatives (genera '' Quercus'' and ''Lithocarpus'', in the family Fagaceae). It usually contains one seed (occasionally
two seeds), enclosed in a tough, leathery shell, and bo ...
s of recalcitrant
oaks, which can be stored in a non-frozen state for up to two years provided that precautions are taken against drying. These seeds show deterioration of cell membrane lipids and proteins after as few as 3–4 days of drying. Other recalcitrant seeds, such as those of the sweet chestnut (''
Castanea sativa''), show oxidative damage resulting from uncontrolled metabolism occurring during the drying process.
Storage
Preservation of recalcitrant seeds remains experimental. Some approaches include:
* Removal of the embryo inside for
cryopreservation (liquid nitrogen).
* Cryopreservation of the whole seed in an anti-freezing solution.
Intermediate seeds are between orthodox and recalcitrant seeds in their survivablity. They are initially identified by their inability to survive conventional dry-freezing storage while being able to survive cryopreservation as a whole. The storage guideline is to put them in refrigeration at 45–65% RH, for a maximum of five years.
See also
*
Micropropagation
*
Orthodox seed
*
Plant propagation
*
Seedbank
References
{{reflist, 25em
Plant reproduction
Seeds