TGP2 glossary Flashcards
1
Q
acropetal
A
towards the apex
2
Q
adventitious
A
Arising in abnormal position; e.g. roots arising from stem or leaf
cutting, or buds arising from root.
3
Q
aleurone
A
The cell layer which surrounds the embryo and endosperm in cereal grains and which secretes amylase that break down the starch in the endosperm.
4
Q
alpha- (α)
A
Prefix to designate the chirality at carbon atom no 1 of a sugar residue such as glucose (relative to that at its penultimate carbon atom).
5
Q
anamorph
A
asexual form of a fungus
6
Q
androecium
A
collective name for all the stamens of an individual flower
7
Q
angiosperms
A
The seed plants in which the seed is enclosed in a fruit
8
Q
annulus
A
annulus Ring (e.g. of tissue around a mushroom stalk beneath the cap)
8
Q
anther
A
‘Head’ of stamen, in which pollen is formed.
9
Q
antibiotic
A
a substance produced by one living micro-organism which damages or kills another.
10
Q
apex
A
the end of a plant organ furthest from the seed from which that plant grew (adjective: apical); thus, the apex of a shoot is normally the top end, whereas the apex of a downwardly-growing root is the bottom end. In both cases, the apex is the distal end.
11
Q
apoplast
A
the part of the plant external to the plasma membrane i.e. the cell walls, intercellular spaces, and dead cells such as xylem. Essentially the non-living part of the plant body. In a large tree much of the wood of the tree trunk, branches, and roots will be part of the apoplast. (see symplast)
12
Q
appressorium
A
swelling of a germ tube or hypha which usually functions in attachment to a host plant prior to penetration.
13
Q
ascogenous
A
hypha dikaryotic, ascomycete hypha which produces asci.
14
Q
ascoma or ascocarp
A
multi-hyphal, sexual reproductive organ of ascomycetes
which is associated with ascospore production.
15
Q
ascospore
A
sexual spore of ascomycetes which is produced internally within an ascus.
16
Q
ascus
A
cell of ascomycetes within which ascospores are produced immediately following nuclear fusion and meiosis.
17
Q
autotrophic
A
mode of nutrition in which all organic requirements are synthesised from CO2 (compare heterotrophic).
18
Q
avirulence gene
A
of a pathogen encodes a product that is ‘recognised’ by the product of a plant resistance gene.
19
Q
axillary bud
A
A bud situated in the axil of a leaf i.e. in the angle between the upper
side of the leaf and the stem.
20
Q
base
A
the end of a plant organ nearest the seed from which that plant grew (adjective: basal); thus, the base of a shoot is normally the lower end, the base of a root is normally the top. In both cases, the base is the proximal end.
21
Q
basidioma or basidiocarp
A
multi-hyphal, sexual reproductive organ of basidiomycetes which is associated with basidiospore production.
22
Q
basidiospore
A
sexual spore of basidiomycetes which is produced and borne externally on a basidium.
23
Q
basidium
A
cell of basidiomycetes which produces basidiospores externally immediately following nuclear fusion and meiosis.
24
basipetal
Towards the base (see acropetal).
25
beta- (β)
Prefix to designate the chirality at carbon atom no 1 of a sugar residue such as glucose (relative to that at its penultimate carbon atom). Starch is an αglucan; cellulose is a β-glucan.
26
bioassay
A test for a substance based on its ability to induce some response in living cells. A bioassay allows you to detect the substance without knowing anything about its chemistry
27
biotrophy
mode of nutrition in which living host cells are used as a nutrient resource.
28
bract
A leaf-like structure immediately below a flower or inflorescence.
29
calyx
collective name for all the sepals of an individual flower.
30
cambium
A cylinder of meristematic tissue which, by radial growth and anticlinal divisions (parallel to the surface), forms the secondary tissues in woody plants (most of the wood and the inner layers of the bark).
31
carpel
One of the individual floral organs of the fourth (most distal) floral whorl. Collectively make up the ovary (gynoecium). They produce the female gametes.
32
caryopsis
simple one-seeded fruit with pericarp firmly united all around the seed coat (e.g. a cereal grain)
33
cellulose
a highly insoluble, crystalline polysaccharide [β-(1→4)-D-glucan] of the plant cell wall. Occurs in the form of microfibrils.
34
chitin
a highly insoluble, structural polysaccharide [a β-(1→4)-linked polymer of N- acetyl-D-glucosamine] of many fungal cell walls.
35
clamp connection
hyphal outgrowth of basidiomycetes associated with dikaryon formation which, during hyphal septation, makes a connection between the resulting two hyphal compartments.
36
coleoptile
A sheath enclosing the embryonic leaves in grass and cereal seedlings. Its growth is limited to several centimetres. The young leaves then break through its tip as they grow on. The coleoptile is a classical object for the study of the effects of auxin on cell elongation.
37
collenchyma
A type of cell found in the outer cortex in which the cell walls are unevenly thickened and the intercellular spaces are often absent.
38
colony
(in mycology) a mycelium, frequently with reproductive structures (filamentous fungi); a group of cells of the same species living together (yeasts).
39
commensalism
intimate association between two organisms where one partner benefits without affecting the other.
40
companion cells
Phloem cells which are nucleated and densely protoplasmic, being ‘companions’ to the sieve tubes.
41
compatible reaction
(in plant pathology) : reaction between a susceptible host and a virulent pathogen.
42
conidiogenous cell
directly produces conidia.
43
conidioma
multi-hyphal, asexual reproductive organ which is associated with
conidium production.
44
conidiophore
hypha which bears conidiogenous cells.
45
conidium
type of non-motile, asexual spore produced from a conidiogenous cell.
46
cork
A tissue formed on the outside of woody stems and roots by a special meristem, the cork cambium. Cork cells soon die, but before they do the walls are impregnated with a secretion, suberin, which makes them impermeable to water and gases.
47
corolla
collective name for all the petals of an individual flower.
48
cortex
The tissue system between the epidermis and the stele, often mainly of parenchyma but often also containing sclerenchyma. The innermost layer of the cortex is the endodermis, which surrounds the stele.
49
cotyledon
A seed leaf, specialised for storage of food material and formed in the embryo before the shoot apex is formed. Sometimes the cotyledons become transformed into the first leaves (e.g. tomato). In other plants they emerge from the soil but soon wither (e.g. runner beans); in others they remain below the soil (e.g. peas).
50
cuticle
A hydrophobic secretion on the outside of the cell wall, especially on the outer (epidermal) surfaces of plants exposed to the air. It is often coated by wax and is relatively impermeable to water and gases.
51
D-
Prefix to designate the chirality at the penultimate carbon atom of a sugar
residue. Opposite is L-.
52
determinate
describing growth that stops at a genetically pre-determined size.
Typical of leaves and flowers but not roots.
53
dicot
dicots) One of the two groups into which the angiosperms are divided and consisting of plants that have two cotyledons in the embryo. Dicotyledons characteristically have broad, net-veined leaves, are often woody, and have floral parts typically in fours or fives. (see also monocotyledons)
54
dikaryon
cell containing two, usually genetically distinct, haploid nuclei
55
dimorphic
a fungus able to grow in either a yeast or mycelial form.
56
distal
Nearer the tip.
57
elicitor
The term ‘elicitor’ was originally used to refer to molecules and other stimuli that induce phytoalexin synthesis in plant cells, but the term is now used to describe molecules that elicit any of the observed plant defence responses.
58
endodermis
The innermost layer of the cortex which surrounds the stele and which can act as a barrier to radial movement of solutes. The endodermis of the root has bands of suberin (the Casparian strip) on the radial cell walls.
59
endoglycanase
Enzyme that can split a polysaccharide molecule by hydrolysing a glycosidic bond in mid-chain.
60
endosperm
The tissue formed in the developing seed by divisions of the nucleus, in the embryo sac, that results from fusion of one or more embryo sac nuclei with the haploid vegetative nucleus from the pollen tube. The resulting cells, usually triploid, form a nutritive tissue which in cereal grains is the main source of starch for the brewing industry. In many seeds (non- endospermous) the endosperm is digested and the products absorbed by the cotyledons which then become the main food store for the developing seedling (e.g. as in peas).
61
epidermis
(plural: epidermises) The outermost tissue of the plant, usually consisting of a single layer of cells (although sometimes it proliferates to give several layers) and, in stems and leaves, covered by the cuticle except where there are stomatal apertures.
62
epigeal
Type of germination in which the cotyledons emerge above the soil and may simply serve as food stores and then wither (e.g. runner bean) or may also become the first photosynthetic organs (e.g. mustard, tomato). (see hypogeal)
etiolation the characteristics of a plant grown in the dark, typically an elongated stem and unexpanded leaves that are yellow or white instead of green.
63
exoglycanase
Enzyme that can release sugars from a polysaccharide by hydrolysing glycosidic bonds at or near a non-reducing terminus.
64
fibres
Elongated cells, typically pointed at both ends, with thick, lignified walls and having no protoplast when mature. Sclerenchyma is a tissue composed solely of fibres.
65
filament
stalk’ of stamen.
66
flowering
In many plants flowering is promoted by environmental signals. Promotion of flowering by photoperiod (or, strictly, night-length) occurs in three major steps: induction of the leaves by the light stimulus to produce a signal;
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evocation (the action of this signal at the shoot apex to commit it to flowering; and realisation (the actual formation of the flowers).
67
fruit
The tissues which enclose and support the ovules and, later, the seeds. Usually the result of post-fertilisation development of the gynoecium (ovary wall).
68
galacturonan
Any polysaccharide with a backbone composed mainly of galacturonic acid residues.
69
gametangium
single-celled sex organ; or cell that contains gametes.
70
gametophyte
The gamete-producing (haploid or n) generation in plants (which in angiosperms is very much reduced but which is the main part of the plant in mosses).
71
gel-permeation chromatography
(gel filtration, size exclusion chromatography) Method for fractionating substances on the basis of their Mr values. The largest molecules elute from the column first.
72
germ tube
hypha which emerged from a germinated spore.
73
glucan
Any polysaccharide with a backbone composed mainly of glucose
residues.
74
glucuronoarabinoxylan
A xylan with side-chains containing glucuronate and arabinose residues. [Further polysaccharide names can be constructed on a similar basis.]
75
glycoprotein
A protein with mono-, oligo- or polysaccharides glycosidically linked to it.
76
glycosidic bond
Covalent linkage formed between a sugar (usually at carbon atom No. 1) and some other molecule (which may be a sugar), with the loss of 1 molecule of H2O.
77
guard cell
One of the pair of cells which enclose the pore (aperture) of a stoma and which control the size of the stomatal aperture by their degree of turgidity.
78
gymnosperms
(Conifers and their relatives) Seed plants in which the seeds are borne naked on scales, in cones, and not enclosed in a fruit. (see Angiosperms)
79
gynoecium
(gynaeceum) collective name for all the carpels of an individual flower (synonymous with ovary).
80
haustorium
specialised hyphal branch produced within a host cell and which functions in nutrient absorption.
81
hemicellulose
one of a group of non-pectic polysaccharides that can be extracted from the plant cell wall with cold concentrated alkali. In vivo, they hydrogen-bond to the cellulosic microfibrils. Examples of hemicelluloses are xyloglucans, xylans, mannans and (only in grasses and cereals) mixed linkage β-(1→3),(1→4)-glucans.
82
heterokaryon
cell containing two or more genetically distinct nuclei.
83
heterothallic
condition in which sexual reproduction requires the interaction of two
different individuals of the same species (self-sterile).
84
heterotrophic
mode of nutrition in which all organic requirements are synthesised
from pre-formed organic compounds (compare autotrophic).
84
holomorph
fungus in all its forms (i.e. anamorph + teleomorph).
85
homeotic mutant
in which organs are replaced by other organs not normally
occurring in that position.
86
homothallic
condition in which sexual reproduction can occur without the interaction of two different individuals of the same species (self-fertile).
87
hymenium
spore-bearing layer of ascomata or basidiomata.
88
hypersensitivity
recognition phenomenon involving an increased sensitivity of a
host plant to a pathogen and resulting in rapid host cell death.
89
hypha
cellular filament of a fungus.
90
hypocotyl
The main axis of the plant below the cotyledons but above the root. Most obvious in seedlings in which the cotyledons emerge above the soil. The hypocotyl is where the transition region between stem and root structure is found.
91
hypogeal
Type of germination in which the cotyledons remain below the ground and shrivel up as they serve as a food reserve for the growing seedling (e.g. peas, broad beans). (see epigeal)
92
incompatible reaction
(in plant pathology) : reaction between a resistant host and an avirulent pathogen.
93
indeterminate
describing growth not limited by the plant’s genetically determined programme of development; e.g. growth of the stems of most trees.
94
inflorescence
That part of the plant consisting of the flowers and the immediate branches or structures which bear them.
95
intercellular space
Air space between cells in a tissue.
96
internode
The stem between successive nodes. The internode is derived from the same modular unit of growth as the leaf above it, not the leaf below it as morphologists sometimes used to assume.
97
ion-exchange chromatography
Method for fractionating substances on the basis of their charge. Negatively charged substances (acids) will temporarily bind to a chromatography column that carries fixed positive charges.
98
L-
Prefix to designate the chirality at the penultimate carbon atom of a sugar. Opposite is D-.
99
lamina
leaf blade.
100
lateral root
initiated in the pericycle behind the main root tip, usually responding to gravity by growing horizontally. Sometimes called secondary roots. Lateral roots themselves may bear further laterals and so on. Some grass plants have been estimated to have several kilometres of root.
101
leaf
An organ of limited growth, borne on the stem and having a bud in its axil (see axillary bud). A leaf is usually flattened dorso-ventrally into a blade (lamina) which is the main site of photosynthesis. The leaf stalk is the petiole and the blade may be subdivided into leaflets (leaflets do not have axillary buds). In grasses the leaves are not stalked but the leaf sheath clasps the stem or the inner leaves which may be rolled up inside it. Leaves originate as leaf primordia on the flanks of the shoot apex. (see also primordium)
102
lignin
A complex phenolic polymer found in certain primary and secondary cell walls, especially those of fibres and xylem elements. Lignin makes the cell wall rigid, inextensible, waterproof and indigestible.
103
ligule
A small scale-like structure at the junction of the leaf sheath and lamina in
grasses.
104
local acquired resistance
induced on a single leaf following challenge of that leaf with an avirulent pathogen.
105
meristem
An organised tissue of apparently undifferentiated dividing cells, found at the apices of shoots and roots, in growing leaves and (as cambium) in stems and roots undergoing secondary thickening. Meristems may also be formed in callus and at the surface of wounds. Meristems are the source of new cells in the growing plant.
106
mesophyll Parenchymatous
chloroplastcontaining cells making up the middle layer of the leaf and being the main site of photosynthesis. Often differentiated into palisade cells and the more loosely packed spongy mesophyll.
microfibril a ‘bundle’ of cellulose molecules. Microfibrils form the rigid scaffolding of the plant cell wall.
107
palisade
cells and the more loosely packed spongy mesophyll.
108
microfibril
a ‘bundle’ of cellulose molecules. Microfibrils form the rigid scaffolding of the plant cell wall.
109
micropyle
The aperture left by the incomplete meeting of the integuments, the outermost layers of the ovule, and so the port of entry of the pollen tube as it grows into the ovule and gains access to the egg for fertilisation.
110
middle lamella
That part of the cell wall which glues together the faces of walls of adjoining cells. It is rich in pectins.
111
mitosis
The process of nuclear division which results in daughter nuclei with identical genetic constitutions and the same number of chromosomes as the parent nucleus.
112
Mr
Relative molecular mass (‘gram formula mass’; ‘molecular weight’)
112
monocotyledons
(monocots) One of the two groups into which the angiosperms are divided, and consisting of plants that have only one cotyledon in the embryo. Monocotyledons characteristically have parallel-veined leaves, which are often grass-like, and floral parts typically in threes or sixes. Monocotyledons include grasses, cereals, onions, bananas and palms. (see also dicotyledons)
113
mutualism
intimate association between organisms in which all partners benefit.
114
mycelial cord (or mycelial strand)
relatively undifferentiated, parallel aggregation of hyphae.
115
mycelium
mass of hyphae
116
mycorrhiza
fungus–root association.
117
mycotoxin
toxin produced by a fungus.
118
necrotrophy
mode of nutrition in which living tissues of an organism are first killed by the fungus and then used as a nutrient resource.
119
node
The point on a stem at which a leaf (or pair or whorl of leaves) is attached (see also internode).
120
non-reducing terminus
A sugar residue that is glycosidically linked within a polysaccharide but has no other sugar residue glycosidically linked to it; a polysaccharide may have many nonreducing termini.
121
oligosaccharide
As polysaccharide but with fewer sugar residues.
122
oligosaccharin
An oligosaccharide (derived by partial breakdown of a plant or fungal cell wall), which if applied (in low concentrations) to a plant evokes a biological response.
123
oogonium
female gametangium of oomycetes.
124
oospore
non-motile spore produced by oomycetes within an oogonium immediately after the fusion of antheridial and oogenial nuclei.
125
organ
a part of the body of a multi-cellular organism that forms a structural and functional unit and is composed of more than one tissue. E.g. a leaf, a stamen or a root.
126
ovary, ovule
The ovary is the female reproductive organ in the flower and consists of one or more carpels (free or fused together) each of which contains one or more ovules, each ovule containing an embryo sac within which is an egg cell. See gynoecium.
127
paraphysis
sterile hypha within a hymenium.
128
parasitism
intimate association between two organisms in which one partner harms
the other.
129
parenchyma
A type of cell that is unspecialised, often isodiametric, sometimes elongated, and constituting most of the cortex and pith.
130
partial veil
a layer of tissue which joins the stalk to the cap of a mushroom or toadstool.
131
pathogen
a parasite able to cause disease.
132
pectin (pectic polysaccharide)
one of a group of plant polysaccharides, found in primary walls and the middle lamella, rich in -(14)-linked galacturonic acid residues. Can often be extracted from the wall with chelating agents e.g. EDTA.
133
pericycle
The outermost cell layer of the stele (immediately internal to the endodermis) which gives rise to lateral roots.
134
periphysis
hypha which lines the neck of a flask-shaped fruitbody (e.g. a perithecium).
135
perithecium
flask-shaped ascoma produced by pyrenomycetes.
136
petal
One of the individual floral organs of the second floral whorl, usually brightly
coloured. Collectively make up the corolla.
137
petiole
leaf stalk
138
phagocytosis
process in which particles are taken into cells.
139
phloem
A tissue of the vascular system consisting (in angiosperms) of sieve tubes, companion cells, and usually parenchyma and fibres as well. Its main function is the transport of metabolites from sources to sinks.
140
phytoalexin
A natural ‘antibiotic’: a low Mr compound made by a plant in response to infection. Suppresses the growth of fungi.
141
pileus
mushroom or toadstool cap.
142
pith
The central parenchymatous tissue of the stele, and characteristic of the
stem of dicotyledons.
143
plasma membrane or plasmalemma
The boundary membrane of the cell which regulates the passage of molecules between the protoplast and its surroundings. Unlike the cell wall, the plasma membrane is composed of phospholipids and proteins. The cell wall is outside the plasma membrane.
144
plasmodesma
One of the narrow cytoplasmic strands of complex structure through the cell wall which connect the cytoplasms of adjacent cells, so providing the
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continuity of cytoplasms which constitutes the symplast. Plasmodesmata do not
normally seem to allow the passage of molecules with Mr over ~800
145
plasmodium
wall-less, motile, multinucleate mass of protoplasm which is characteristic of myxomycetes.
146
plasmolysis
The withdrawal of the protoplast away from the cell wall owing to loss of water from the vacuole. This results when the cell’s water potential is reduced below the point at which any turgor can be maintained.
147
plumule
The embryonic shoot.
148
polysaccharide
Polymer composed of many sugar residues, linked to each other.
Examples are starch, cellulose, hemicelluloses, pectins and chitin.
149
primary wall
a layer of the plant cell wall whose cellulosic microfibrils were laid down while the cell was still expanding. The secondary wall (if any) is deposited internal to the primary wall.
150
primordium
The early stage in the development of a root, shoot, or organ when it is just a small protuberance. (Plural: primordia)
151
procambium
A tissue which differentiates in the apical and leaf meristems and which itself differentiates into the xylem, cambium, and phloem of the vascular system.
152
protoplast
The ‘living’ part of the cell, bounded by the plasma membrane, i.e. excluding the cell wall. An isolated protoplast is one that has been released from the tissue e.g. by enzymic digestion of the cell wall.
153
proximal
Nearer the base.
154
radicle
The embryonic root.
155
reducing terminus
The single sugar (at one end of a polysaccharide molecule) which is not glycosidically linked to another sugar (and will therefore reduce Fehling’s solution).
156
resistance gene
of a plant encodes a plant protein that ‘recognises’ the product of
a pathogen’s avirulence gene.
157
resistant/susceptible
(in plant pathology) terms applying to a host which indicate whether the development of pathogen can be restricted or not.
158
rhizoid
(in mycology) short, tapering and often branched, root-like structure of a chytrid which functions in nutrient absorption.
159
rhizomorph
(in mycology) relatively differentiated, parallel aggregation of hyphae which possesses an organised apical growing point.
160
rhizosphere
a plant’s roots plus their living and non-living surroundings.
161
saprotrophy
mode of nutrition in which non-living organic material is used as a
nutrient resource.
162
scale leaf
Modified leaf, usually rather dry, protective in function, and enclosing buds.
163
sclerotium
a firm, frequently rounded, multi-hyphal, vegetative organ which is
resistant to unfavourable conditions.
164
secondary thickening
The radial growth as a result of cambial activity which gives the growth in girth of woody plants (see cambium)
165
secondary wall
a layer of the plant cell wall whose cellulosic microfibrils were laid
down (internal to the primary wall) after the cell had stopped expanding.
166
seed
A structure, containing an embryo, formed by the maturation of the ovule following fertilisation.
167
sepal
One of the individual floral organs of the first (most basal) floral whorl, usually green. Collectively make up the calyx.
168
septum
cross wall.
169
sessile
immobile
170
shoot
The aerial part of the plant consisting of the stem and its appendages.
171
sporangiophore (a) hypha
(a) hypha which bears one or more sporangia.
172
sporangiophore (b) asexual
(b) asexual, non-motile spore produced within a sporangium.
173
sporangium
asexual reproductive cell within which sporangiospores are produced by cytoplasmic cleavage.
174
stamen
One of the individual floral organs of the third floral whorl. Collectively make up the androecium. They bear the anthers, which produce the male gametes.
175
starch
A mixture of two polysaccharides (amylose and amylopectin), composed of α-D-glucose residues linked by (1→4) bonds (amylose) or by (1→4)- and (1→6)-
bonds (amylopectin). A major food reserve in seeds, tubers etc.
176
stele
The innermost tissue system of the plant, surrounded by the cortex and epidermis. The outermost layer of the stele is the pericycle (from which lateral roots originate), which surrounds the vascular tissues, which in turn surround the central pith.
177
stem
The usually aerial (above-ground) axis of the plant, of potentially unlimited growth. Bears the leaves. An axillary bud arises close to each stem/leaf junction.
178
sterigma
basidiospore-bearing projection of a basidium.
179
stipe
fruitbody stalk.
180
stipule
Scale-like or leaf-like appendage at the base of some leaves.
181
stoma
A pore in the epidermis, bounded by a pair of guard cells. Regulates gas exchange between the plant and the atmosphere.
182
suberin
A complex of polyphenolic and polyester compounds impregnating walls of cork cells and the Casparian strip, making them impermeable to water.
183
sugar residue
A sugar molecule that is linked to some other molecule via a glycosidic bond.
184
symbiosis
an intimate association between organisms (can include parasitism,
mutualism and commensalism).
185
symplast
The continuum of protoplasts in adjacent cells, the cytoplasms of which are linked by plasmodesmata and bounded by a common plasma membrane. Essentially the ‘living’ part of the plant
186
systemic acquired resistance
resistance induced throughout all the leaves of an individual plant.
187
teleomorph
sexual form of a fungus.
188
tendril
A modified leaf or leaflet, having no lamina, and specialised for twining.
Function: support.
189
testa
The seed coat
190
tiller
An axillary bud of a grass or cereal plant which grows out and may eventually resemble and rival the main stem.
191
tissue
A collection of one or several cell types that are usually found together and are specialised for a particular function e.g. xylem and phloem.
192
totipotency
The capacity of individual cells, immature or mature, to grow and divide to produce a new, whole organism.
193
transporting cell
A sieve element, joined to its neighbours to form longitudinal sieve tube by the sieve plates between the cells. Sieve plates are perforated by sieve pores.
194
urediospore
(uredospore, urediniospore) a type of asexual spore produced by rusts.
195
uredium
(uredinium) multi-hyphal asexual reproductive organ of rusts associated with urediospores production.
196
vascular tissue
A collection of tissues (xylem and phloem, often with cambium and sclerenchyma) specialised for transport, usually occurring as distinct vascular strands or vascular bundles, which are usually arranged longitudinally in the plant and connect the roots, stems, leaves and other organs.
197
vegetative
not associated with sexual reproduction (e.g. referring to growth).
198
vessel, xylem
Tube formed in the xylem and made of many short vessel elements fused end to end with the end walls dissolved away. When mature they have lost all cytoplasmic contents and are nonliving, and so xylem sap is part of the apoplast. Mainly responsible for the upward movement of water and solutes from the root to the shoot.
199
virulent/avirulent
terms applying to a pathogen: a virulent pathogen will penetrate and have a severe effect on the host; an avirulent pathogen will penetrate but have little effect on the host.
200
water potential
The chemical potential of the water of the cells, measured in units of pressure, megapascals (MPa). A cell in equilibrium with water will be turgid and have a water potential of zero, which by definition is the water potential of pure water. When the cell becomes less turgid its water potential will become increasingly negative. Water movement in the plant is always down gradients of water potential.
201
xylan
Any polysaccharide with a backbone composed mainly of xylose residues.
202
xylem
Wood: a tissue of the vascular system and consisting of vessels, tracheids, fibres, and parenchyma. The vessels, tracheids and fibres, when mature, lack protoplasts and consist only of cell walls, which are usually lignified.
203
xyloglucan
A glucan with side-chains containing xylose residues.
204
zoospore
asexual, motile, flagellate spore.
205
zygospore
sexual spore of zygomycetes which results from gametangial fusion.
206
zygote
The first diploid cell of a new individual formed by the fusion of two gametes.
207
What does SAR stand for
Systemic Acquired Resistance
