ABAXIAL The side of a lateral organ that initiates away from (ab, away from) the meristem.
ADAXIAL The side of a lateral organ that initiates next to (ad, close to) the meristem.
AUXINS A class of plant hormones, typified by indole-3-acetic acid, that is required for many aspects of plant development and for plant cell growth in culture. The term auxin is derived from the Greek afksano, meaning 'to increase'.
AWN A slender bristle-like structure found on the spikelets (structure that contains the flowers) of many grasses.
BIPINNATE A dissected leaf that has two orders of leaflets (or pinnae) so the first-order leaflets are themselves dissected into a second order of leaflets.
CAMV 35S PROMOTER 35S RNA promoter from cauliflower mosaic virus that is commonly used to drive constitutive gene expression in plants.
CARPEL The female reproductive organ of a flower that encloses the ovules.
CLASS I KNOX GENES Knotted1-like homeobox (KNOX) genes in all plants can be divided into two classes based on sequence similarity and expression pattern. The sequenced genome of Arabidopsis contains four class I KNOX genes (STM, KNAT1 (KN1-like in Arabidopsis thaliana 1), KNAT2 and KNAT6).
CYCADS (Phylum Cycadophyta). One of four divisions of gymnosperms. They resemble palms but have naked seeds on the scales of cones.
DICOT (Eudicotyledonous plants). The largest group of angiosperms, characterized by two cotyledons (seed leaves) and three symmetrically placed pollen apertures.
GARP DOMAIN A conserved DNA-binding domain that is distantly related to the MYB DNA-binding domain. It is defined by the acronym of the founding members of the GARP family: maize Golden 2, ARR (Arabidopsis response regulators) and Psr1 (phosphorus stress response1 from Chlamydomonas).
HETEROCHRONIC REGULATORY MUTATIONS Mutations that alter the relative timing of developmental events as an organism grows (from the Greek heteros, meaning 'other' or 'different', and chronos, meaning 'time').
HIGH MOBILITY GROUP (HMG) DOMAIN A conserved domain that is present in HMG proteins, which are non-histone proteins involved in chromatin structure and gene regulation.
HIGHER PLANTS Seed plants, including gymnosperms (in which the seed is 'naked') and angiosperms, or flowering plants (in which the seed is contained in an ovary).
HOMEOBOX A 180-base-pair sequence that encodes a DNA-binding helix–turn–helix motif termed a homeodomain.
HOMEODOMAIN A highly conserved sequence motif. It comprises 60 amino acids and contains a DNA-binding helix–turn–helix motif, indicating that homeodomain-containing proteins function as transcription factors.
INDETERMINATE Refers to a pattern of growth and development that is open-ended. In meristems, this is associated with the continuous ability to produce determinate lateral organs (such as leaves). By contrast, determinate refers to growth and development that is restricted in time or space.
INTERCALARY LEAFLETS Leaflets that develop between the primary leaflets of a dissected leaf. They are usually smaller than primary leaflets.
LAMINA The (usually flattened) parts of a leaf on either side of the midvein.
LATERAL ORGAN Organs that are produced from the shoot apical meristem such as leaves and putatively homologous organs such as cotyledons (embryonic leaves), bracts (modified leaves that subtend reproductive structures) and floral organs.
LEAF FOUNDER CELLS A group of cells that encompasses several layers of the shoot apical meristem and from which a leaf primordium is derived. Founder cells do not function as stem cells but rather have a determinate fate and can be defined by histological, clonal and molecular criteria.
MEGAPHYLLOUS LEAVES The basic leaf type in ferns and seed plants. They are typically large, with a distinct adaxial and abaxial plane and have a complex branched vascular structure.
MERISTEM A structure that is found at the growing tip of the roots or shoots of a plant and in which stem cells (undifferentiated cells that can undergo unlimited division) are maintained and organogenesis occurs.
MONOCOT (Monocotyledonous plants). Angiosperms with one cotyledon (seed leaf).
MYB TRANSCRIPTION FACTOR A family of transcription factors defined by the presence of a structurally conserved DNA binding domain first identified in a viral oncogene. The Arabidopsis genome contains over one hundred MYB-like genes that function in diverse regulatory systems, including secondary metabolism, cell morphogenesis, the cell cycle and circadian rhythms.
NON-AUTONOMOUS Function of a gene product that is not restricted to the cell in which it is expressed.
PALMATE A dissected leaf with leaflets arising from a central point at the end of the leaf stem
PETAL SPUR An outgrowth of a petal in which nectar can collect.
PHENOCOPY A mimic of another phenotype.
PINNATE A dissected leaf with a central axis and a single order of leaflets (or pinnae) on either side of it.
PLASMODESMATA Cell-wall channels that allow symplastic connections between plant cells.
PLASTOCHRON The time interval between successive primordia.
QA REPRESSION DOMAIN A repressive domain that is conserved in insect Ultrabithorax proteins. It contains a Gln-Ala-Gln-Ala-Lys motif and a stretch of Ala residues.
