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 angiospe ...

s that do not survive drying and freezing during

ex-situ conservation Svalbard GLOBAL SEED BANK, an ''ex situ'' conservation. ''Ex situ'' conservation literally means, "off-site conservation". It is the process of protecting an endangered species, variety or breed, of plant or animal outside its natural habitat; ...

. 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 Orthodox seeds are seeds which will survive drying and/or freezing during ex-situ conservation, as opposed to recalcitrant seeds, which will not. According to information from the U.S. Department of Agriculture, there is variation in the ability o ...

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 the Americas and was first domesticated by Mesoamerican tribes more than 5,000 years ago. Then as now it was prized for ...

, mango, mangosteen,

lychee Lychee (US: ; UK: ; ''Litchi chinensis''; ) is a monotypic taxon and the sole member in the genus ''Litchi'' in the soapberry family, ''Sapindaceae''. It is a tropical tree native to Southeast and Southwest China (the Guangdong, Fujian, Yun ...

, cocoa,

rubber tree ''Hevea brasiliensis'', the Pará rubber tree, ''sharinga'' tree, seringueira, or most commonly, rubber tree or rubber plant, is a flowering plant belonging to the spurge family Euphorbiaceae originally native to the Amazon basin, but is now ...

, some horticultural trees, aquatic plants such as ''

Nymphaea caerulea ''Nymphaea nouchali'' var. ''caerulea'', is a water lily in the genus ''Nymphaea'', a botanical variety of ''Nymphaea nouchali''. It is an aquatic plant of freshwater lakes, pools and rivers, naturally found throughout most of the eastern half ...

'''','' and several plants used in traditional medicine, such as species of ''

Virola ''Virola'' is a genus of medium-sized trees native to the South American rainforest and closely related to other Myristicaceae, such as nutmeg. Species are known commonly as ''epená'', ''patricá'', or ''cumala''. They have glossy, dark green le ...

'' and ''

Pentaclethra ''Pentaclethra'' is a small genus of trees from the tropics. They are flowering plants in the family Fabaceae. They belong to the mimosoid clade of the subfamily Caesalpinioideae. The name ''Pentaclethra'' is derived from Ancient Greek, ''penta ...

''. Generally speaking, most tropical

pioneer species Pioneer species are hardy species that are the first to colonize barren environments or previously biodiverse steady-state ecosystems that have been disrupted, such as by wildfire. Pioneer flora Some lichens grow on rocks without soil, so ...

have orthodox seeds but many

climax species Climax species, also called late seral, late-successional, K-selected or equilibrium species, are plant species that can germinate and grow with limited resources; e.g., they need heat exposure or low water availability. They are the species wi ...

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 acorns 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 ''Castanea sativa'', the sweet chestnut, Spanish chestnut or just chestnut, is a species of tree in the family Fagaceae, native to Southern Europe and Asia Minor, and widely cultivated throughout the Temperate climate, temperate world. A substa ...

''), 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 Cryo-preservation or cryo-conservation is a process where organisms, organelles, cells, tissues, extracellular matrix, organs, or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by co ...

(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.

References

{{reflist, 25em Plant reproduction Seeds

Mechanisms of damage

Storage

See also

References