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Plants and the Environment > lecture 7 Control of plant development > Flashcards

lecture 7 Control of plant development Flashcards

1
Q

What is the role of a plant growth regulator?

A

PGRs play an important role. The idea that their individual roles can be defined by the nature of the response to each of them (auxins -> cell expansion, cytokinin -> celldivision) doesn’t fit the facts and must be discarded. At different times they can function in either of 2 rather different types of interaction:

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2
Q

How are plant growth regulators developed?

A

PGRs may be generated by development in one part of theplant (xylem differentiation in lfs -> auxin, senescence orripening -> ethylene, plastid differentiation -> gibberellins,ripening fruit tissue ->abscisic acid, cell division in root tips ->cytokinin).

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3
Q

Phase 1 of leaf morphogenesis determines:

a) leaf position
b) leaf length
c) leaf width
d) leaf thickness

A

a) leaf position

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4
Q

A permanent change in position of a plant part in response to external stimuli is called ____.

a) a circadian movement
b) a tropism
c) a sleep movement
d) a turgor movement
e) solar tracking

A

b) a tropism

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5
Q

Gibbelins:

a) cause cells to divide
b) stimulate flowering
c) inhibit cell elongation
d) cause buds and seeds to go dormant
e) none of the above

A

a)cause cells to divide

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6
Q

thylene:

a) is a gas
b) interacts with auxin in leaf abscission
c) promotes seed germination
d) all of the above
e) b, c and d

A

d) all of the above

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7
Q

The leaf abscission zone is:

at the base of the petiole
at the base of the leaf blade
at the apical meristem
above the axillary bud
none of the above
A

a) at the base of the petiole

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8
Q

A number of angiosperm species grow in locations where they are periodically submerged in seawater, these plants

a) Mesophytes
b) Xerophytes
c) Halophytes
d) Calcicoles
e) none of the above

A

c)Halophytes

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9
Q

Plants adapted to grow on acidic soils are termed:

a) Calcifuges
b) Calcicoles
c) Gymnosperms
d) Angiosperms
e) Mesophytes

A

a)Calcifuges

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10
Q

Which of the following genera of angiosperms DOES NOT contain insectivorous species:

a) Nepenthes
b) Sarracenia
c) Drosera
d) Pinguicula
e) Limonium

A

e)Limonium

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11
Q

In relation to PGR other parts of the same plant may be programmed to produce an?

A

appropriate developmental response, WHATEVER IS APPROPRIATE FOR THAT TISSUE OF THATSPECIES AT THAT DEVELOPMENTAL STAGE. The constant feature is the link between the particular PGR and the particularDevt which produced it.

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12
Q

The same PGR is produced in response to?

A

certain stimulus. But, the plant response to the PGR is species, tissue and time specific!

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13
Q

How are PGRs synthesized in response to an environmental signal?

A

(drought -> abscisic acid, light -> gibberelins, mineral nutrients -> cytokinins, physical stress -> ethylene).

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14
Q

The most important co-ordinating influence on primaryvegetative growth, and differentiation, shoot branching and cambial activity is?

A

auxin synthesized in developing leaves.

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15
Q

This auxin is swept root tip wards by a process termed?

A

polar transport (at 1cm per hr) as the xylem differentiates and the contents of vessels lyse through the living parenchymacells of the stele.

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16
Q

Cell expansion determining internode length is auxin-dependent, so the?

A

developing leaf influences the size of internodes below it that will support and supply it.

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17
Q

Tropic curvature enables?

A

the expanding internodes to respond to light and gravity, but the mechanism remains obscure.

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18
Q

The environmental signals are picked up by ?

A

specialized plastids (chloroplasts, chromoplasts, amyloplasts & aleoplasts’).

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19
Q

Statoliths are large?

A

amyloplasts which do not disappearwhen the plant is starved and, unlike other starch grains, are ‘loose’ inside the cell, rolling down to the lowest point when the plant is tilted.

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20
Q

Phototropism, growth in response to?

A

the direction of light is mediated by a yellow flavoprotein photoreceptor maximally sensitive to blue light.

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21
Q

Sensitivity to phototropic stimuli in coleoptiles correlates with special bright yellow plastids unique to cells of the?

A

bundle-sheath.

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22
Q

Leaves have statoliths in the?

A

bundle sheaths

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23
Q

Only stems have the bundle sheaths in the?

A

endodermis

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24
Q

In roots the bundle sheaths are in the?

A

Root cap

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25
Q

The most likely explanation behind the sensitivity is?

A

that the specialised plastids influence the transport of auxin fromthe polar transport stream in the stele tothe expanding tissues of thecortex, blocking the radial outwards movement of auxin on the illuminated or upper side.

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26
Q

Differentiating leaves export gibberellins which promotes?

A

cell expansion (& directly regulate the activity of the subapicalmeristem, promoting cell divisions that increase internode length).

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27
Q

Growing root tips export cytokinins, which promote?

A

ell expansion in leaves, but not in stems.

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28
Q

When more mineral nutrients are available in the soil more?

A

cytokinin is exported from roots, and leaves are larger in response.

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29
Q

Cell expansion is also sensitive to?

A

ethylene, part of a response to physical stress.

30
Q

The production of ethylene by plant tissues increases when you?

A

bend, shake or stress them.

31
Q

Elevated ethylene alters the orientation of?

A

cortical utubules in expanding cells, which alters the orientation of cellulose micro-fibrils synthesized.

32
Q

Subsequentely, so as to increase radial cell expansion at the expense of?

A

longitudinal expansion -> STOUTER AXIS,able to push up paving stones!

33
Q

Vascular tissue: Primary xylem requires auxin from developing lvs in order to?

A

differentiate.

34
Q

Vascular tissue: Primary phloem requires?

A

cytokin in from growing roots.

35
Q

Vascular tissue: cells in the appropriate position do not differentiate into?

A

fibres unless supplied with both auxin and gibberellin.

36
Q

Vascular tissue: These PGRs influence the program of

A

differentiation.

37
Q

Vascular tissue: Increased [GA] -> larger fibres increased [IAA] -> …….

A

Thicker walls

38
Q

Meristemoids: .The way plants generate the little, tiny organs which have only a few cells, in what appears to be a?

A

homogenous array of identical cells, divide assymmetrically.

39
Q

Formation of meristemoid: What happens after the nucleus moves to one end of the cell?

A

which may show a ‘gradient’ of organelles across it, oriented to some outside influence

40
Q

Formation of meristemoid: The small cell usually re-commences cell division &,acting as tiny meristem (‘meristemoid’) goes on to generate?

A

one of the various types of glands, hairs& other little structures wh are dotted throughout & especially over the surface of plants.

41
Q

Formation of meristemoid: The stomata arise from meristemoids in the?

A

epidermis

42
Q

Control: The purpose of meristemoids seems to be to allow?

A

independent control of the development of these ‘tiny’ organs , e.g. the timing of maturation and the spacing of the guard cells is obviously important for the leaf.

43
Q

Branching: Lateral roots arise deep inside the?

A

Root

44
Q

Branching: From a single layer - the PERICYCLE - just inside the?

A

endodermis so that the integrity of the stele isn’t breached.

45
Q

Branching: Shoot branches arise from ?

A

Similarly arrested cells , but in pockets on the outside surface of the axis where they monitor light.

46
Q

branching: The mechanisms of control of shoot branching vary from?

A

Plant to plant

47
Q

Collective developmental transitions: Plant organs and especially meristems, sometimesundergo a major shift in?

A

biochemistry and/or pattern of growth

48
Q

Collective developmental transitions: Rather like differentiation for a single cell but this time for a whole group of cells there is a coordinated, synchronous change from the expression of?

A

one set of genes to the expression of a new set. Such changes we refer to as ‘transformations’.

49
Q

Collective developmental transition: Transformations are large scale qualitative transitions which form:

A

the life cycle of organs and individuals.

50
Q

What is senscene?

A

This is terminal transformation for any tissue/individual, involving the breakdown of cell structures & macromolecules - but note that the initiation of this phase is by gene de-repression +synthesis of a range of hydrolytic enzymes = energy-consuming,so waterlogged, dried or poisoned lvs STAY GREEN!

51
Q

The onset of tissue senescenceis controlled by?

A

by auxin levels in the tissue wh, post dffn, slowly declines until eventually at v. low [auxin], tissues begin to respond to the tiny amounts of ethylene they produce all the time by producing excess ethylene wh activates the senescence process.

52
Q

The onset of tissue senescence is adaptively entrained to:

A

nutrient stress via CKs, water stress via ABA, & day length via GA, the effective levels of wh. Increase with day length.

53
Q

Senscence: The [ethylene] also activates abscission, the final stage of?

A

tissue senescence.

54
Q

Semscence: Scattered through the plant are groups of cells which?

A

do not -> cell expansion response to auxin.

55
Q

In some spp, the entire plant may be ‘switched over’into senescence which includes?

A

monocarpic species (die at end of fruiting season e.g. banana plant).

56
Q

In soybean (Glycine max)it is the maturing seeds which?

A

induce the onset of whole plant senescence which in spp where it occurs, usually follows flowering& seed formation.

57
Q

Tachigalia versicolor in Panama, a large (40m) dicot tree,produces?

A

70,000 winged seeds & promptly dies. Also, bamboos& Agave - the Century tree.

58
Q

Induction of flowering: Explain developmental control

A

For many plants the switch is part of the internal development of the individual (therefore we cannot control it). Sometimes we observe that the transition is related to the accumulation of a fixed number of leaves (8 lvs in Datura ‘thorn apple’ 30 to40 years growth in beech).

59
Q

induction of flowering: Explain Environmental control

A

(therefore we can control it and do expts!) For plants which grow in regions away from the equator, the sh m’stems -> producing flws is adaptively entrained to day length to make the plant flowers at a precise time of the year.

60
Q

Photoperiodism: For other plants, especially biennials, the entrainment is to a?

A

prolonged period of chilling (equiv temperate winter) :vernalisation.

61
Q

For photoperiodism, the ‘detector’ system is?

A

phytochrome as primary light sensor, linked to the endogenous circadian rhythm, which connects phytochrome -> apex at a fixed time after sunset every night.

62
Q

In both cases (photoperiodism & vernalisation) the ‘detector’ system is in the?

A

developing leaves

63
Q

These dvlp lvs produce the bulk of the?

A

GA & auxin & as they mature produce the bulk of the ABA& relay all the CK, which arrives from the root, on to the shoot apical meristem.

64
Q

The ‘detector’ system triggers an altered pattern of GR production/relay by the lf which the shoot’ meristem are adapted to interpret by?

A

transforming into floral m’stems

65
Q

Detector system: Sometimes the connection is simple,e.g. effective [GA] rises in long days, &in some plants which flower in long days exogenous GA will induce flowering, but mostly the interactions are?

A

complex & prolonged, because the transition to flowering is critical for survival & is therefore subject to careful, multiplecross-checking,

66
Q

Detector system: As well as complex it also includes?

A

species-specific, because the transition to floweringforms part of the machinery for adaptation to the environmentby individual spp in a very wide range of environments.

67
Q

Germination: Explain different methods of germination in plants?

A

Many seeds will germinate as soon as the chemical inhibitors of the fruit sap have been washed off & conditions are favourable: water & warmth. Other types stubbornly refuse - they have an innate dormancy. There are 3 basic types, characterised by the treatment required to break dormancy.

68
Q

Explain After ripening in the 3 basic types characterised by the treatment required to break dormancy.

A

no germ’n unless dry at room temp for several wks, e.g. grasses & cereals, clover & the evening primrose (Oenothera).

69
Q

Explain Chilling req’t in the 3 basic types characterised by the treatment required to break dormancy.

A

Seed needs to have imbibed before it responds & several wks at 0 to 5o C are required = stratification. Same ‘dectector’ system as vernalisation.

70
Q

Explain Light req’t in the 3 basic types characterised by the treatment required to break dormancy.

A

Mediated by phytochrome : Pfr = primary sensor (Pr inhibits).

71
Q

Chilling and light trigger increases in?

A

GA, or CK, or both

72
Q

The PGR’s initiate the?

A

mobilisation of reserves in the seed, ending metabolic dormancy. The dormant state, then, is stable until these growth substances trigger the transformation to active growth.

Plants and the Environment (12 decks)

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