Anthocyanescence - Used for the development of red pigments as a disease symptom e.g., seen in peach leaf curl which is caused by fungus Taphrina deformans.

Anticodon - A sequence of 3 nucleotides on tRNA which are complementary to a sequence of 3 nucleotides on mRNA (codon). It gets binded to codon on mRN A temporarity during protein synthesis. A tRNAP molecule has specific anticodon which only complexes with one particular amino acid. This absolute correspondence between an amino acid, an anticodon and a codon has been found to determine precise amino acid sequence in a protein.

Antipetalous - Said of the position of stamens which are inserted opposite to petals.

Antipodal Cells - The haploid cells which are usully 3 in number and present in embryo sac at the opposite and of micropyle. They are derived by mitotic division in megaspore and lacking definite cell wall. Their function is not known. At fertilization, they may disintegrate or multiply and enlarge.

Antisepalous - Said of the position of stamens which are inserted opposite to sepals.

Antitranspirant - Any chemical substance which causes reduction in transpiration either by closing sloma or forming a film over the stomata. They also reduce photosynthesis and influence other metabolic activities also.

Aperturate - Said of a pollen grain which is having one or more apertures. If apertures are colpi, pollen is known as colpate and if pores, porate.

Aphid. Used for describing an insect of family Aphidaceae of order Hemiptera. These are small plant bugs living by sucking plant juices. Many are pests themselves where as others become important as vectors of plant viral diseases e.g. CMV.

Apical Cap - Rings on the lateral walls, at the distal ends of the cells in the filament of some of the Oedogoniales.

Apical Cell - (1) The single meristermatic cell which is present at the tips of the branches of the thalius of the more complex Algae.

(2) The meristematic cell present at the tip of a bryophyte thallus. It gives rise to new tissue by division, but may give rise to two apical cell thereby initiating the dichotomy of the thallus.

(3) The single meristematic cell present at the tip of root and shoot branches of the Pteridophyta.

Apical Cell Theory - According to this theory the tissues of higher plants are developed from a single cell. It has been disproved by studying the complex apices of the Gymnosperms.

Apical Dominance - Used for describing inhibitory influence of apical bud on some or all the lateral buds present in a plant shoot. Removal of apical bud releases lateral buds from apical dominance which most probable involves auxins for its effect. It becomes less market when nutrients are in plenty.

Apical Growth - The elongation of a filament of the Thallophyta by involving growth at the apex only.

Apical Meristem - The group of actively dividing cells which are found at, or near the tip of a stem, root or sometimes, a leaf. It originates from a single cell in the Pteridophytes, and form a group of cells in the Spermatophyta. It causes an increase in length by forming the primary plant body.

Apical Placentation - (Pendulous placentation suspended placentation). Used for describing a form of placentation found in ovaries having only one ovule and placenta are developing at the top of the ovary.

Apiculate - Used for describing structure which has a small broad point at the apex.

Aplanetic - Used for describing organisms that lack any motile stage in their life cycle.

Aplanospore - A non-motile spore, having its wall free from the wall' of the cell in which it was formed.

Apocarpous - Used for describing gynoecium in which all carpels of gynoecium are free. Such condition is considered to be primitive than syncarpous condition. Compare syncarpous.

Apoenzyme - The catalytically inactive protein portion of an enzyme which renains after removal of prosthetic group or cofactor. Examples of enzymes requiring both apoezyme and cofactor for catalytic activity are alcohol dehydrogenase requiringZn2+ kinases requiring Mg2+ or Mn2+ and cytochromes requiring Fe2+. See also holoenzyme.

Apogamy - Reproduction without involving the fusion of gametes, and generally without meiosis. The term may include any form of vegatative reproduction.

Apogeny - Sterility.

Apomict - An organism reproducing by apomxis. It may be facultative apomict (e.g. Potentilla) which can reproduce both sexually or apomictically and the incidence of apomixis may be influenced by environmental conditions such as photoperiod. Obligate apomict reproduces only by apomixis and are often triploid or pentaploid and thus fail to form viable pollens.

Apomixis - Used for describing any form of asexual reproduction including vegetative reproduction.

Apomorphy - Used for describing the character state in phylogenetic studies or cladistics which is considered to be derived or advanced. Apomorphies shared by different taxa are known as synapomorphies (Compare auta pomorphy). Only those synapomorphies whose orgin could be traced back to a recent common ancestor find use in constructing phylogenies of cladograms. Analogous synapomorphies which are arising be convergent evolution, if identified are not taken into account. Compare pleisomorphy.

Apopetalous - (i) Having many petals.

(ii) Sometimes employed in exactly the opposite sense, i.e.,having no petals.

Apophysis - (i) The sterile tissue present at the base of a moss capsule.

(ii) The enlargement of the distal end of a pine cone.

(iii) A swelling, or swollen hypha of a fungus.

Apoplasmodial - Of Acrasiales, having non-fusion of the myxamoebae.

Apoplast - The complex made-up of the xylem cell-wall, and the cellulose all and contents of the adjoining cell, through which water, salts etc., have to pass before they reach the other tissues of the plant.

Aporogamy - Used for describing the penetration of the ovule by the pollen-tube, by some other path than the micropyle.

Apospory - The production of a diploid gametophyte from the sporophyte due to the absence of meiosis.

Apothecium - The fructfication of some Ascomycetes which gets flattened or cup-shaped having the asci on the uppersurface in a palisade-like layer, usually mixed with sterile hyphae. It is termed as angiocarpic if it is closed before maturity, and gymnocarpic if open.

Appendage - Any external outgrowth of a plant which is not having apparent essential function.

Appressorium - Used for describing the swelling at the tip of a germ-tube or hypha of some parasitic fungi. It is in close contact with the host, and puts out a fine tube through the host's cell or stoma.

Aquatic - Used for describing the nature of habitat which becomes dominated by excessive water. A pond is example. Plants occurring naturally in aquatic habital are called aquatic plants.

Arabans - The polysachrides which are derived from arabinose. Examples are hemicelluloses, mecilages, gums, pectin. See Pentosans.
Arabinose - A pentose sugar; an aldose.