An apicoplast is a reduced nonphotosynthetic plastid in many apicomplexan parasites. Retained biosynthetic outputs can make it essential after photosystems and photosynthetic carbon fixation are lost.

Work hardening is an increase in resistance to further plastic deformation caused by earlier deformation. A useful macroscopic test loads a metal beyond yield, unloads it and reloads in the same direction: further plastic flow then requires a larger stress. In a constitutive equation, this history is represented by evolving internal variables rather than by the current elastic strain alone.^[ref]

In a crystal, multiplication and interaction of dislocations can make later dislocation glide more difficult. Forest hardening and latent hardening describe particular aspects of that obstacle formation. Increased resistance to plastic flow is not the same as a large change in Young's modulus: the elastic unloading slope and the load required to restart permanent deformation measure different properties. Work hardening can delay necking by compensating for the shrinking loaded area.

Cold working is permanent shaping by plastic deformation at a temperature low enough that substantial concurrent recrystallization does not erase the deformed microstructure. The relevant comparison is with the material's thermal response, rather than with a universal room-temperature boundary. Drawing wire and rolling sheet are examples of imposing large controlled shape changes.

In a crystalline metal, cold working changes the dislocation population and can create preferred crystal orientations. Dislocation interactions can increase resistance to further deformation through work hardening, while uneven deformation can leave residual stress. A practical comparison measures the stress-strain curve before and after a fixed amount of shaping, then unloads to identify the permanent strain. Subsequent heating can modify the stored microstructure through recovery or recrystallization, so processing history is part of specifying a specimen rather than a detail recoverable from its chemical composition alone.

Necking is localization of tensile deformation into a narrowing part of a specimen. A thinner cross-section carries greater local stress at the same axial force, encouraging further thinning. Work hardening opposes this feedback by increasing the stress required for additional plastic deformation.

For a uniformly extending specimen whose plastic flow approximately conserves volume, write $A=A_0{e}^{-\epsilon }$ with logarithmic length change $\epsilon =\log (L/L_0)$. Its load is $F=\sigma A$, where $\sigma$ is axial Cauchy stress tensor. ThenThe maximum-load condition is $d\sigma /d\epsilon =\sigma$. This ideal estimate assumes uniform uniaxial deformation up to onset and neglects rate effects and damage. In tensile testing, recording both axial force and local specimen diameter distinguishes the start of localization from the later fracture; the maximum engineering stress need not be the maximum local Cauchy stress tensor.

An expression vector supplies regulatory and maintenance sequences for producing a chosen protein or RNA in a host. The coding insert must have a compatible promoter, initiation signals and reading frame; successful plasmid propagation does not establish successful expression.

A plant hormone involved in water-stress responses, seed dormancy and other processes. In guard cells, ABA-dependent receptor inhibition of phosphatases permits kinase activation and stomatal closure.

A class of growth regulators whose synthesis, directional transport and perception help organize plant growth. A change in auxin abundance and a change in auxin sensitivity are distinct mechanisms.

A class of plant growth regulators. Gibberellin perception can promote degradation of DELLA proteins, releasing constraints on selected growth responses.

A family of growth-regulatory proteins whose degradation is promoted by gibberellin signaling. Direct interactions with phytochrome-interacting factors connect hormone status to light-regulated growth.

A class of plant signals with developmental roles and functions in the rhizosphere, including stimulation of arbuscular mycorrhizal fungal branching.

An alternative regulatory state of a locus associated with an epigenetic difference. Its stability and independence from DNA sequence variation must be tested.

A line from a mapping population segregating experimentally induced epigenetic differences in a comparatively uniform genetic background. New transposon insertions and residual sequence differences still need to be assessed.

An association analysis relating epigenomic measurements to a phenotype. Association alone does not establish causal direction or independence from genetic variation.

Targeted alteration of an epigenetic state, distinguished from cutting or rewriting the target DNA sequence. Persistence after removal of the targeting factor is locus dependent.

RNA-directed DNA methylation, or RdDM, is a plant regulatory pathway in which small RNAs guide methylation of homologous DNA. Canonical components include Pol IV, RDR2, DCL3 and Pol V, connecting production of small RNAs with recognition of target chromatin.

Noncoding transcription can supply scaffold transcripts at the target, rather than serving only to produce a protein. Experiments on specialized polymerases showed how this transcriptional activity participates in silencing adjacent or overlapping regions.^[ref]

Epigenetic silencing of one parental set of ribosomal RNA genes in a hybrid; it is not simply the deletion of those genes.

Vernalization is acquisition of the capacity to flower following prolonged cold. In Arabidopsis thaliana, persistent silencing of the floral repressor FLC helps retain information about winter after temperatures rise.

The memory's lifetime differs from its acquisition. Experiments on resetting between generations show why an individual plant can remember cold while its descendants still need their own cold exposure. Perennial plants can use different seasonal reactivation patterns, as illustrated by PEP1 in Arabis alpina.^[ref][ref]

A prior stimulus changes the response to a subsequent challenge. Persistence may involve metabolites, proteins, regulatory feedback or chromatin; priming alone does not establish epigenetic inheritance.

A tomato vitamin E biosynthetic gene whose expression can be influenced by methylation of a nearby promoter retrotransposon.

An Arabidopsis thaliana gene whose ectopic expression and flowering phenotype can be associated with a stably unmethylated promoter state.