Recalcitrant

Recalcitrant
adj./ n.
[ɹɪ.ˈkæl.sɪ.tɹənt]
Definition: a distinguished ability to resist change in some property

Table of Contents

Several words of the English language find wide usage in subjects as diverse as literature, science, social science, environmental science, and soil science to humanity. Let’s focus on one such word — “recalcitrant”. Since we mainly deal with recalcitrant meaning in biology, we’ll provide only a brief description of the term in a general sense.

Recalcitrant Definition

What does recalcitrant mean in biology? The word recalcitrant finds vivid and wide usage in different fields of biology. When asked to define recalcitrant, one can define it as a distinguished ability to resist change in some property.

It is used in plant seed biology for describing certain types of seeds. It is used in plant tissue cultures to define the nature of some plant cells or tissues to be unresponsive to tissue culture procedures. It is used in soil science and biogeochemistry to describe the material property of organic matter to resist decomposition. It is used in biotechnological biofuel production to describe the resistance of biomass towards enzymatic hydrolysis.

Let’s learn more about each of them in this piece.

Recalcitrant General Meaning

Recalcitrant is a word generally used to define a state of stubborn resistance or non-governance under a defined set of rules. It is typically used to define a person who is uncooperative, non-compliant, and has a habit of obstinately and boldly resisting authority. A recalcitrant child, recalcitrant members of a family, recalcitrant health care system, recalcitrant demonstrators, or a recalcitrant person is an adamant one who doesn’t obey authority. Some of the recalcitrant synonyms are uncooperative, rebellious, intractable, etc.

Recalcitrant Etymology

Recalcitrant (adjective) is an English word with its root in French and Latin language. It has been derived from the French word “recalcitrant”, which has been derived from two Latin words “recalcitrans” and “recalcitrantis”. These two words have their root further in older Latin verbs (present participle form) “recalcitro” and “recalcitrare”, which means ‘to kick with the heels’.

Watch this vid about the term “recalcitrant”:

Biology definition:
Being recalcitrant is defined as a distinguished ability to resist change in some property. The term is used to describe the inability of a seed to germinate in plant seed biology or the inability of a plant cell or tissue to respond to tissue culture manipulation in plant tissue cultures. It is also used to determine the material property of organic matter to resist decomposition in soil science and biogeochemistry and the resistance property of biomass towards enzymatic hydrolysis in biotechnological biofuel production.

FAQ

Let’s look at the commonly associated terminologies to recalcitrant terms.

What is a recalcitrant example?

There are several fields of Biology in which terminologies like recalcitrant or recalcitrance are used. Let’s discuss them here.

- Recalcitrant Seed

There are 2 types of seeds on the basis of the ability to retain viability and survivability post-desiccation:

(1) Recalcitrant seeds

(2) Orthodox seeds

Recalcitrant seeds are unable to thrive in a frozen or desiccated state for longer durations. This nature of recalcitrance makes their ex-situ conservation relatively very difficult to orthodox seeds.

recalcitrant seeds charts — Figure 1: Recalcitrant seeds will be broadly placed in the 2A category here. They rapidly germinate after shedding. They usually don’t enter into a quiescent phase. They prefer to quickly germinate as their viability is short-lived and post-shedding drying severely limits the germination potential. Image Credit: Berjak, P., Farrant, J.M., Pammenter, N.W. (1989).

There are different stages of seed maturation. The last phase of seed maturation is “maturation drying”. This is a normal step in the case of orthodox seeds but not in recalcitrant seeds. Both of these terms were coined by Roberts in 1973. There is no clear-cut boundary that defines seed as recalcitrant or not.

According to a long-term study by Farrant, Pammenter, and Berjak, there is a continuum of the types of recalcitrant seeds. They proposed three categories to objectively look at this phenomenon.

Category I (FAIRLY LESS RECALCITRANT): Tolerance for a fair amount of desiccation and freezing conditions. These plant species are found in temperate to subtropical regions.
Category II (MODERATELY RECALCITRANT): Tolerance for an intermediate degree of desiccation and mid-range temperature conditions. These plant species are found in tropical regions.
Category III (HIGHLY RECALCITRANT): Tolerance for only minimal amount of desiccation and highly temperature-sensitive. These plant species are found in tropical to wetland regions.

orthodox and recalcitrant seeds comic — Figure 2: A cartoon strip showing the difference between the orthodox and recalcitrant seeds. Image Credit: Pat Bradley of EcoMythsAlliance.org.

Look at the table below to note the differences between orthodox and recalcitrant types of seeds.

Table: Differences between orthodox and recalcitrant seeds.
Feature	Orthodox Seeds	Recalcitrant Seeds
Tolerate post-shedding desiccation	Yes	No (only maximally up to 3-4 days)
Undergo the last phase of seed maturation i.e., “maturation drying”	Yes	No
Chill-sensitive	Yes	No (most often)
Oxidative damage upon desiccation	No	Yes
Deterioration of cell constituents upon desiccation	No	Yes
Ease for ex-situ conservation	Easy	Difficult
Lifespan	Longer than recalcitrant seeds	Shorter than orthodox seeds
Size	Relatively smaller in size	Relatively larger in size
Common occurrence	In pioneer plant’s species of tropical areas	In climax plant’s species of tropical areas
Examples	Cereal seeds (wheat, barley, rice), pulses seeds (gram, beans, pigeon pea), guava, dates, capsicum	Usually the larger seeds like mango seeds, lychee seeds, jackfruit seeds

Data Source: Akanksha Saxena of Biology Online.

3 vitrification-plasticization curve for the different types of seeds — Figure 3: The illustration shows the vitrification-plasticization curve for the different types of seeds. When the different types of seeds are desiccated and frozen to different water content levels, an important point surfaces. The orthodox seeds end up in a ‘glass state’ at merely –20°C (conventional freezing temperature) while intermediate and recalcitrant seeds need to be cooled to extremely low temperatures (equivalent to liquid nitrogen temperatures) in order to make them reach the ‘glass state’ and avoid ‘ice state’. Ice formation can severely harm the cell organelles and cause injury. This is the reason cryopreservation has proven better than conventional freezing for recalcitrant seed conservation efforts. Image Credit: Center for Plant Censervation.

Lychee seed — Figure 4: The lychee seed is an example of a recalcitrant seed. Image Credit: Growables.

Figure 5: Jackfruit seeds are another example of recalcitrant seeds. Image Credit: In the Kitchen with Matt.

- Recalcitrant Plant Tissue Cultures

Recalcitrant plant tissue in ‘in vitro cultures’ is the inability of certain plant cells, tissues, or organs to elicit any response to the applied tissue culture manipulations. It restricts and limits the biotechnological exploitation as the plant tissue fails to respond in terms of growth, regeneration, etc. Three main factors are being studied to develop a clear understanding of the plausible causes of this recalcitrance. They are as follows:

Plant’s physiology (explant choice/selection, plant health, environment, life cycle)
In vitro manipulations (techniques applied, media selection, entails culture environment too)
Stress physiology post-culture (embodies both positive and negative effects)

Recalcitrant Plant Tissue Cultures — Figure 6: A shows the normal elongated plant while B shows the rosette formation (recalcitrant to treatment). This problem is often encountered by researchers working with plant tissue cultures where the tissue under the lens remained recalcitrant even after protocol manipulations. Image Credit: Neama Abdalla.

- Recalcitrant Soil Organic Matter

The term recalcitrant is also used in soil science and biogeochemistry to describe the organic matter of soil that’s intrinsically resistant to the microbial decomposition process. Recalcitrant organic matter is also sometimes called molecular recalcitrance or intrinsic chemical recalcitrance or refractory organic matter.

Recalcitrant Soil Organic Matter — Figure 7: A cartoon depiction of the geographic recalcitrance concept in soil science or biogeochemistry. Image Credit: Omar R. Harvey.

- Recalcitrant Biomass in Biofuel Production

This term is also used in biotechnological biofuel production to describe the resistance of biomass towards enzymatic hydrolysis. This property is endowed upon by the ‘lignocellulosic content’ as it’s highly resistant to enzymatic degradation. This is because of the rigid, compact structure of the plant cell wall. The chemical composition is majorly lignin and hemicellulose.

The structure and the spatial network of the biomass further determine the extent of recalcitrance (cellulose crystallinity plus the degree of polymerization).

There are several factors that affect the reachability and accessibility of biomass lignin and cellulose to be degraded. Some of them are:

1. 1. Direct factors (accessible surface area)
  2. Indirect factors (biomass structure, pore size, particle size, specific surface area)

Recalcitrant Biomass in Biofuel Production — Figure 8: There are several factors that collectively account for biomass recalcitrance. Image Credit: Dr. Xianzhi Meng.

- Recalcitrant Compounds

Fungi are well-known to grow luxuriantly in the presence of recalcitrant media and compounds. This ability of fungi is exploited for their usage in bioremediation processes. Both saprophytic and symbiotic fungal species possess this distinguished ability to feed on and degrade N-containing recalcitrant compounds present in wastewater. The release of extracellular enzymes by these ligninolytic fungi mediates the process of recalcitrant compound breakdown.

Recalcitrant Compounds — Figure 9: Recalcitrant orange fungus (*Laetiporus sulphureus*) has the ability to eat cellulose out of wood. Image Credit: Bio.brandeis.edu.

Preserving Recalcitrant Seeds by the “Cryopreservation Method”

Bio-conservation efforts have ramped up since the severe detrimental effects of global warming and human invasion into preserved ecosystems started showing up in the past 20-30 years. One of the many types of floral conservation efforts is seed banking.

This is an ex-situ effort in which seeds of threatened and critically threatened plant species are conserved outside their natural habitats. As we now know that seeds are of two types — orthodox and recalcitrant, not both types survive the desiccation process. Recalcitrant seeds of threatened and critically threatened (IUCN Red-listed or CITES-listed) plant species don’t thrive in the drying phase.

According to a study report by scientists from the Royal Botanic Gardens in Kew in 2018, seed banking is a futile effort toward the conservation of threatened species with recalcitrant seeds (Wyse et al., 2018).

Emphasis was laid to maximize the search for better conservation methods for such seed types. Research underpinning exploration and optimization of the ‘cryopreservation technique’ for such seed types could be an answer to this problem.

Cryopreservation is a method of preserving seeds, embryos, and other plant tissues in liquid nitrogen rather than directly freezing them. It has been tried and proved successful for orthodox seed types with shorter storage durations. Cryopreservation increased the viability durations in those cases.

Post-2020, the Global Strategy for Plant Conservation (GSPC) instructs to put in concerted efforts at exploring this technique intensively for recalcitrant seeds. They see immense potential in this technique to conserve genetic diversity, threatened and critically threatened plant species of tropical moist forests, and mangroves of wetlands that are typically recalcitrant in nature!

Cryopreservation chart — A Global Strategy for Plant Conservation (GSPC) was started in the year 2002 to put a halt to the continuing plant diversity loss at a global scale. This graph represents the likely proportions of how the different seed types behave in long-term storage conditions. The different types of plant seeds included here are the IUCN red-listed (LC-least concern, NT-near threatened, VU-vulnerable, EN-endangered, CR-critically endangered), global trees (trees in the GlobalTreeSearch database for all the known tree species of the world), medicinal plants and crop wild relatives (CWR). The orange part of the bar represents the recalcitrant seeds proportion while the blue part of the bar represents the orthodox seed proportion. ‘Targets’ of this initiative as a percentage of preservation are marked by the dotted line. Image Credit: Sarah V. Wyse, John B. Dickie, Katherine J. Willis, 2018 (Link)

Cryopreservation process — Cryopreservation is the direct plunging of recalcitrant seeds into liquid nitrogen to store them for longer durations of time. Image Credit: Saikat Gantait.

Answer the quiz below to check what you have learned so far about the term “recalcitrant”.

References

Berjak, P., Farrant, J.M., Pammenter, N.W. (1989). The Basis of Recalcitrant Seed Behaviour. In: Taylorson, R.B. (eds) Recent Advances in the Development and Germination of Seeds. NATO ASI Series, vol 187. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-0617-7_8
Berjak, P., & Pammenter, N. W. (2008). From Avicennia to Zizania: seed recalcitrance in perspective. Annals of Botany, 101(2), 213–228. https://doi.org/10.1093/aob/mcm168
Benson, E. E. (2000). In vitro Plant Recalcitrance: An Introduction. In Vitro Cellular & Developmental Biology. Plant, 36(3), 141–148. http://www.jstor.org/stable/4293329
Sarah V. Wyse, John B. Dickie, Katherine J. Willis. Seed banking not an option for many threatened plants. Nature Plants, 2018; 4 (11): 848 DOI: 10.1038/s41477-018-0298-3
Farrant, J.M., Pammenter, N.W. and Berjak, P. (1988a), Recalcitrance – a current assessment, Seed Sci. & Technol., 16:155.
Farrant, J.M., Pammenter, N.W. and Berjak, P. (1988b), Development of the recalcitrant seeds of Avicennia marina, Proc. Electron Microsc. Soc. South. Afr., 18:109.
Benson, E.E. Sepecial symposium: In vitro plant recalcitrance in vitro plant recalcitrance: An introduction. In Vitro Cell.Dev.Biol.-Plant 36, 141–148 (2000). https://doi.org/10.1007/s11627-000-0029-z
Kleber M. (2010). What is recalcitrant soil organic matter? Environ. Chem. 2010, 7, 320–332. doi:10.1071/EN10006
Zoghlami, A., & Paës, G. (2019). Lignocellulosic Biomass: Understanding Recalcitrance and Predicting Hydrolysis. Frontiers in chemistry, 7, 874. https://doi.org/10.3389/fchem.2019.00874