Glossary of Crop Science Terms - Browse
maillard browning reaction See browning.
maintenance respiration See respiration.
male-sterile plant A plant that produces no functional pollen or is devoid of staminate flowers. See also maintainer line; restorer line.
marker A gene for which the function or specific trait has been identified that facilitates the study or detection of that gene in a cell or organism.
mass-flow flux The movement of solutes along with the flow of solvent. The amount moved is the product of solute concentration and the volume of solvent moved.
mat Thatch, intermixed with soil, that develops between the zone of green vegetation and the original soil surface.
mature fibers In cotton: fibers that, when treated with a sodium hydroxide (NaOH) solution, swell into a nonconvoluted and almost rodlike shape, have a total wall width equal to or greater than the lumen width.
maturity index Any mechanical, physiological, chemical, visual or other method used to determine the time of maturity for a plant species.
mean length, array In cotton: the average length of all the fibers in the test specimen based on weight-length data.
medium See culture medium.
melting temperature (Tm) The midpoint temperature of the temperature range across which a double-stranded DNA or RNA molecule denatures into separate single strands. The melting temperature is characteristic of each DNA sequence and gives an indication of its base composition. The three hydrogen bonds between G-C pairs require more thermal energy to denature than the two hydrogen bonds between A-T pairs; thus G-C-rich sequences denature at a higher temperature than A-T-rich sequences.
meristem A localized group of actively dividing cells, from which permanent tissue systems (root, shoot, leaf, flower) are derived. The main categories of meristems are (i) apical meristems, in root and shoot tips; (ii) lateral meristems (vascular and cork cambiums); and (iii) intercalary meristems, in the nodal region and at the base of certain leaves. adj. meristematic.
meristemming See mericloning.
mesophyll The leaf cells that contain chloroplasts and that are located between the upper and lower epidermis.
messenger RNA See mRNA.
metabolic pool See reserves.
metered-release fertilizer See slow-release fertilizer.
microfiber-mediated DNA transfer A method for introducing DNA into plant cells in which the cells, DNA, and silicon carbide microfibers ~0.6 µm in diameter are vortexed briefly in a culture medium. Penetration of the cell wall by the microfibers facilitates passage of DNA into the cell.
micrometer A unit of length (equal to 10-6 m) that is often used to describe DNA molecules. 1 µm of DNA duplex is ~2 x 106 daltons, or ~3 kb. Symbol: µm. Usage: Avoid the short form micron (symbol: µ), since in the SI system (µ is a prefix rather than a standalone form.
micropropagation Synonymous with in vitro propagation, especially in reference to enhanced axillary branching or adventitious plantlet regeneration.
middlings A by-product of flour milling that contains varying proportions of endosperm, bran, and germ.
milling, dry Processes in which grains and other commodities are subjected to grinding followed by sifting, sizing, or other separation techniques to produce more refined products for human use or in animal feeds. The process usually involves only a small amount of water to temper the grain prior to the milling operation. For example, in the milling of wheat, the grain is tempered to approximately 15 to 17% moisture, which facilitates the separation of the endosperm, the pericarp, and germ. Another example is in corn dry milling, where the grain is tempered to 20% or slightly higher moisture levels to ensure the separation of the germ from the endosperm.
minimum tillage (1) Minimal soil manipulation in combination with chemicals for adequate seedbed preparation and vegetation control. (2) Minimal soil manipulation in combination with chemicals and residue incorporation for minimum moisture loss, reducing energy input and labor requirement. Synonym: conservation tillage. See also no-till; till-plant.
miniprep A small-scale preparation of plasmid or phage DNA commonly used after cloning to analyze the DNA sequence inserted into a cloning vector. Usage: Shortened (and preferred) form of minipreparation.
mitosis Process of cell reproduction whereby the daughter cells are identical in chromosome number to the parent cells. Compare meiosis.
mixture, seed (1) Seed of more than one kind or cultivar, each present as >5% by weight of the whole. (2) A combination of seed of two or more species.
mobilization Chemical change of stored materials (see reserves) that enables translocation of the compounds or their use for synthesis or energy. Usage: The term remobilization is sometimes used to denote mobilization of structural materials (e.g., proteins during senescence).
modulus The ratio of change in stress to change in strain in the initial straight-line portion of a stress-strain curve following the removal of any crimp.
modulus, secant The ratio of change in stress to change in strain between two points on a stress-strain diagram, particularly the points of zero stress and breaking stress.
moisture equilibrium (1) In seed: equilibrium of the moisture content of the seed and the relative humidity of the surrounding air. (2) More generally, the condition reached by a sample when it no longer takes up moisture from, or gives up moisture to, the surrounding atmosphere. Synonym: hygroscopic equilibrium.
molecular genetics The study of how genes function to control cellular activities and how they are physically organized within the genome.
monoculture The use of one crop or family of crops either continuously, year after year, or alternated with fallow.
monostand A turfgrass community composed of only one cultivar.
morphogenesis (1) The process of development of form (i.e., differentiated structures). Usage: Morphogenesis combines growth and differentiation and is often used in a limited sense to define specific morphogenetic events, such as lateral root or leaf initiation and development. (2) The evolution of a structure from an unorganized to a differentiated and organized state.
motes Small black specks seen in cotton yarn or cloth.
mowing frequency (1) The number of mowings per unit of time (usually, per week). (2) The interval in days between one mowing and the next.
mowing pattern The orientations of travel while mowing turf. Patterns may regularly be changed to distribute wear and compaction, to aid in grain control, and to create visually aesthetic striping effects.
multicopy (1) Characterizing plasmids that replicate to produce many plasmid molecules per host genome; for example, there are usually 50 pBR322 molecules per Escherichia coli genome. (2) Characterizing a gene or DNA sequence that occurs many times per haploid genome. See also copy number. See also single-copy; low-copy.
multigenic Part II.
multispecies grazing Usage: Not an acceptable term: 'multi' refers to 'many', while this grazing method most often employs only two animal species. See mixed grazing.
mutagen A substance that induces mutations.
mutant Part II.
mutation A heritable change in the genetic material of a cell. See also suppressor mutation.
mycotoxin A toxin or toxic substance produced by a fungus.