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Physiology - Plant Development

	What kinds of plant exhibit secondary growth - in terms of classification and growth cycle?
	dicot and gymnosperm trees and shrubs long-lived plants which often have capacity to survive in dormant state through winter or other harsh conditions

	Why is this impossible for monocots?
	The vascular bundles are "closed" after differentiation of primary xylem and phloem Because bundles are scattered in the stem, it would be impossible to have organized secondary growth.

	Where do the meristems involved in secondary growth arise?
	from cambium in primary vascular bundles and interfascicular cambium; cork cambium arise from parenchyma cells in the cortex

	What kinds of cells are present in the vascular cambium and to what do they give rise?
	fusiform initials divide to form tracheids, vessel elements, sieve elements and fibers ray initials produce ray parenchyma (in xylem and phloem)

	What tissues and cell types are present in "bark"?
	suberized parencyma (cork), cork cambium, phelloderm (parencyma), sieve elements, companion cells, ray parenchyma and usually fibers

	How do the outer tissues adjust to the growth of the xylem?
	pholem ray parenchyma divides radially to provide extra circumference, cork and cork cambium may split or peel

	How do scaly and papery barks arise?
	new cork cambia arise beneath the old (which then split or peel)

	What are two important anatomical differences between so-called hard and soft woods?
	Hard woods (dicots) have vessel elements and tracheids and conspicuous rays. Soft woods (gymnosperms) have only tracheids and small rays.

	How does the early season wood differ from late wood in some dicots?
	Large vessels formed in spring lead to ring porous (as opposed to difuse porous) structure.

	How do stems of conifers and dicot trees thicken in response to stress?
	Horizontal branches will often form reaction wood on the lower side in gymnosperms (compression wood) and on the top in dicots (tension wood).

	What is the difference between roots and shoots in terms of the beginning of secondary thickening?
	In roots parenchyma cells in pericycle join with cambium remaining rom primary growth to form vascular cambium. Cork cambium also forms in pericycle (as opposed to cortex in stems).

	What are the 5 groups of plant hormones?
	auxins cytokinins ethylene abscisic acid gibberellins

	What kinds of chemicals make up plant hormones?
	auxins - IAA derived from amino acid cytokinins - zeatin, nucleotide derivatives ethylene - hydrocarbon dervied from amino acid, methionine via ACC abscisic acid - ABA, terpenoid derived from carotene gibberellins - (the largest group of plant hormones) terpenoids related to sterols

	What is one function of each group of plant hormones in the life of the plant?
	auxin - stem elongation, root initiation, apical dominance cytokinins - cell division, shoot initiation, delay senescence ethylene - fruit ripening, leaf and flower senescence and abscission abscisic acid - water stress, seed and bud dormancy gibberellins - food mobilization (especially in germination), stem elongation

	Which hormones have practical uses?
	ethylene fruit ripening flowering breaking dormancy auxin analogs herbicides rooting cuttings gibberellic acid antagonists compact plants

	What do hormones do at the cellular level?
	Induce new gene activity: transcription of messenger RNA from DNA translation into proteins which are usually enzymes that causes changes we see; e.g. GA, amylase, starch hydrolysis in seed germination

	What do we mean by "totipotency", what kinds of manipulation can we do with plant cells (which we cannot with animals)?
	the ability of somatic cells to divide and develop into any kind of cell in the plant so that we can grow a new plant from a single cell from a leaf, root or whatever

	How can we put foreign genes into plant cells?
	The crown gall bacterium, Agrobacterium tumefaciens can be a gene vector and is probably the commonest method at least for dicots; also particle bombardment, micro-injection.

	What plant is being used in experiments on the control of plant development?
	thale cress (Arabidopsis thaliana) main vehicle for plant genome project

	What kinds of genes might we want to put into plants?
	resistance to: disease pest stress herbicides controlling plant development: starch accumulation flowering lower color dwarfing

	What are the problems and the promises of chemical and genetic manipulation of plant growth?
	total control of the make-up of the genome (i.e. designer plants) don't know which genes control many of the things we want to alter escape of foreign genes to weeds Who owns the genes?

	What kinds of plant structure become dormant?
	meristematic regions in apex (buds and seeds) cambium in woody plants

	What is dormancy's survival value for the plant?
	They can live through the tough times, particularly winter.

	Can seeds survive indefinitely in the dormant state?
	No, they still respire and gradually lose viability.

	Why is dormancy of horticultural importance?
	survival of plants through winter control of flowering in Easter lilies.

	What can we do to influence dormancy?
	cold treatments to promote dormancy and hardening (acclimation) in fall period of cold required to escape from dormancy (stratification of seeds) may also promote flowering in herbaceous or woody perennials (vernalization).

	What are three examples of plant movement?
	nyctinastic - "night closure", up and down movement of plant parts in response to day and night heliotropism - solar tracking thigmotropism - touch sensitive (Mimosa and insectivorous plants)

Plant hormones: are produced in one place and act in another are used in metabolism coordinate internal processes and external events

This would be true for animal hormones but plant hormones are often produced in the structure or tissue in which they act.   Hormones are present in minute amounts and they act on specific protein receptors without getting used up or altered. Thus they are unlike compounds like sugars or amino acids that are used in normal metabolism.   Plant hormones seem to coordinate growth and development in different parts of the plant, and help the plant respond to environmental signals.

	The only naturally occurring auxin, indole-3-acetic acid (IAA) is chemically related to: nucleotides an amino acid terpenoids
	No that would be true for another group, the cytokinins.   IAA has the indole ring structure of the amino acid, tryptophane, although its side chain is different .   No that would be true for two other groups, ABA and gibberellins.

	Synthetic auxins are mainly used for: fruit ripening rooting compounds weed killers
	Ethylene is used for fruit ripening   Auxins do promote root initiation and synthetic compounds such as indole butyric acid (IBA) are used in "rooting powders" but this has to be counted a minor use.   Far and away the major use of auxin-like compounds is as herbicides, particularly for broad-leaved weeds. Examples are 2,4-D and MCPA.

	Cytokinins are related to or derived from: nucleotides amino acids terpenoids
	All naturally occurring cytokinins are derived from the nucleotide base, adenine (which is also part of the structure of DNA, RNA, NAD and ATP).   This would be true for auxins and ethylene but not cytokinins.   The side chains of some cytokinins (such as isopentenyladenine) are derived from the terpene pathway, but not the bulk of the molecule.

	Ethylene is related to or derived from: nucleotides amino acids terpenoids
	This is true for cytokinins but not ethylene.   Ethylene is derived from the cyclic amino acid, ACC which is itself a derivative of the more common amino acid methionine.   This is true for ABA and gibberellins but not ethylene.

Ethylene can be used: in enclosed rooms and outdoors for a variety of purposes only in an enclosed room to ripen fruit to promote flower development in many kinds of plants

Ethylene gas is used in ripening rooms and also in the field as the ethylene releasing compound, ethrel to control growth and promote leaf and fruit abscission.   This is the major use of the gas but it can also be used in the form of ethrel, an ethylene generating liquid sprayed on plants.   In general ethylene damages or causes abscission of flowers and flower buds. Its use to promote flowering in pineapple is exceptional.

	The abscisic acid molecule contains: 13 carbon atoms 15 carbon atoms 17 carbon atoms
	ABA is an is a terpenoid and contains three isoprene units.   ABA is a terpenoid consisting of three isoprene units (each with 5 carbons) so it is a 15 carbon compound.   ABA is an is a terpenoid and contains three isoprene units.

	Gibberellins are chemically related to: amino acids nucleotides terpenoids
	This is true for IAA and ethylene but not gibberellins.   This is true for cytokinins but not gibberellins.   Like abscisic acid, gibberellins are derived from the terpenoid biosynthetic pathway.

Gibberellins help in germination of some seeds by: breaking down starch encouraging water uptake causing amylase to be produced

Hormones do not get directly involved in this kind of process.   Seeds take up or "imbibe" water of their own accord and this may or may not lead to germination. GA is involved in germination itself.   As often happens with hormones, GA stimulates gene activity so that mRNA is transcribed and an enzyme (amylase in this case) is produced. It is the enzyme that produces the phenotypic change - amylase breaks down starch (in the endosperm or cotyledons) to sugars and the embryo uses the sugars for growth.

Amyloplasts are involved in response of plants to: gravity light touch and wind

Amyloplasts (also called "statoliths" in this context) are heavy because they contain starch so they tend to settle to the bottom of the cell; somehow this stimulates the growth response towards gravity (roots) or away from it (shoots) or for that matter at right angles to it.   Amyloplasts are colorless and light perception would have to involve a pigment. We don't exactly know how plants sense that they have been touched but amyloplasts do not appear to be part of the picture.

Cholodny and Went developed a hypothesis about plant growth involving: lateral redistribution of auxin photoperiodic effects thigmotropism

Cholodny and Went hypothesized that growth in response to light and gravity involved movement of auxin to one side of the root or shoot: opposite the direction of the stimulus for light and adjacent to the stimulus for gravity.   Their hypothesis has something to say about phototropic effects, but not photoperiodism.   Their hypothesis could conceivably apply to thigmotropic growth but they were mainly thinking about light and gravity effects.

	Circadian rhythms of plant growth, movement and metabolism are: not affected by red light entrained by light and dark not affected by darkness
	Phytochrome does seem to be involved in setting the clock, so red light has a role.   Alternation of light and dark over a 24 hour period is necessary to set and maintain the rhythms.   Clock effects die away in continuous darkness, or continuous light for that matter.

	Auxin moving down from the shoot tip seems to promote: stem elongation and bud break lateral root initiation and elongation stem elongation and lateral root initiation
	Auxin promotes stem elongation but inhibits bud break (apical dominance effect)   Auxin promotes lateral root initiation but inhibits root elongation.   Paradoxically, auxin promotes stem elongation and lateral root initiation, but inhibits bud break and root elongation

	Ethylene stimulates abscission by increasing the activity of: amylase rubisco pectinase
	Amylase breaks down starch, how would this cause abscission?   Ethylene stimulates leaf senescence and this involves breakdown of rubisco (which has nothing to do with abscission)   Since abscission involves separation of cells prior to shedding of plant parts it is natural that a pectinase should be produced to break down the pectin in the middle lamella.

Perennial herbaceous and woody plants that have become dormant in the winter will emerge from this state once: they are warmed up a period of cold has elapsed days get longer

When plants are truly dormant they will not grow, even if provided with optimum conditions of light, temperature and water supply.   Dormant plants (and some seeds) need to "see" a period of cold before they are prepared to grow (of course they need the right conditions for growth to actually occur)   Long days may have some influence on breaking dormancy, but are not usually sufficient in themselves.

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