328 lecture notes - 8 July 98

PLANTS AND PEOPLE - Botany 328 - LECTURE NOTES - Summer 1998 Hugh D. Wilson - rm. 306, Butler Hall 8 July 98

REVIEW: PHOTOSYNTHESIS = LIGHT + H20 + CHLOROPLAST = O2 +H+ AND ENERGY (ATP), THEN: ENERGY IS USED TO 'FIX' CARBON [CO2] INTO HYDROCARBONS, MOSTLY POLYSACCHARIDES STARCH AND CELLULOSE. (WHAT DO THESE TWO HAVE IN COMMON? [GLUCOSE] - AND HOW DO THAT DIFFER? (LINEAR VS. LINKED - BONDING - SEE FIG. 11-11, P. 362]. Also, (added 10 Sep 97) with regard to the question on Cellulose digestion in humans, it appears that we lack the required enzymes (cellulases). These are only produced by 'hardcore' decomposing elements of the biosphere (fungi, bacteria, etc.) and mammals must evolve 'cooperative' systems (ruminants) to deal with cellulose digestion. Rabbits have a large, pouch-like structure (cecum) that carries cellulase-producing bacteria and our G.I. tracts have a reduced cecum (with vermiform appendix), suggesting a similar set up in our phylogenetic past (vestigial), BUT herbivorious primates (Gorilla) are also (like Homo) not equipped to digest cellulose. Since cellulose digestion is an active topic from an environmental point of view (re-cycling), there is a lot of info on this topic available on the web. Use a web search engine, like Alta-Vista, to explore by inserting a series of words in the query box, in this case "cellulose digestion animal" will produce 49, 460 references with those most relevant to the 'set' of terms on the 1st page. CAUTION: web-based info comes in varying qualities - consider the source.

LAST TIME, TALKED ABOUT SHUNT OF 'PHOTOSYNTHATE' INTO VEGETATIVE PARTS OF THE PLANT [SHOOT, LEAVES AND ROOT]. MAN INTERVENES TO HARVEST BULBS, TAP/TUBEROUS ROOTS, TUBERS BEFORE THEY CAN BE USED BY THE PLANT.

NOW TIME TO LOOK AT THE DIRECT SHUNTING OF PHOTOSYNTHATE TO THE NEXT GENERATION TO FORM THE ANGIOSPERM EMBRYO AND ITS NUTRIENT SUPPLY - THE ENDOSPERM. UNIQUE TO FLOWERING PLANTS.

What is endosperm? (triploid nutritive tissue)

Where is endosperm found? (seed)

Where are seeds found? (fruit)

Where are fruits found? (flower)

What is a flower?

WHAT IS A FLOWER? - MODIFIED SHOOT. THUS, FLORAL PARTS ARE MODIFIED LEAVES.

FLOWER AS A MODIFED SHOOT - 4 FLORAL WHORLES - PHYLETIC ORIGIN OF THE STAMEN AND PISTIL (BASIC 201 APPROACH-FOCUS ON GYNOECIUM)

Lowermost two whorles are asexual:

1. CALYX - BRIEF

2. COROLLA - POLYPETALOUS/SYMPETALOUS, REGULAR/IRREGULAR (FLOWERING PLANT TRENDS). DO WE EAT PETALS? (CUCURBITA)

DIVERT=====to explanation:

Next two whorles are sexual - too understand these, must look at angiosperm evolution:

ALTERNATION OF GENERATIONS - MOSSES VS. ANGIOSPERMS - REDUCTION OF THE GAMETOPHYTE

START OF ANGIOSPERM SEX:

SPOROPHYTE (DIPLOID - MEIOSIS - MICROSPORES/MEGASPORES - MICROSPORANGIA/MEGASPORANGIA)

GAMETOPHYTE (MICRO AND MEGA)

ENDOSPORIC GAMETOPHYTE DEVELOPMENT (within spore wall)

DOUBLE FERTILIZATION/ENDOSPERM

BACK TO STRUCTURE: Fertile fern frond - sporangia producing identical spores which germinate to produce identical, photosynthetic bisexual gametophytes (homosporus) - for angiosperm, imagine:

simple leaf with all sporangia combined (synangium

reduction of the photosynthetic tissue

all spores (produced from microspore mother cell [2n] with sporangium) will produce only a sperm-producing gametophyte reduced to 3 nuclei (1 'generative' and two sperm) and this develops within the spore wall (= pollen grain)

for the other, egg-producing sporangium, imagine:

each megasporangium is enclosed within two thin layers of tissue (=integuments - at maturity = seed coat or testa) which is known as the 'ovule' or - at maturity - the seed.

The leaf that carries these 'packages' (ovules) FOLDS to join at the margins (conduplicate carpel theory) and thereby enclose the ovules (not so enclosed in the other seed-plant lineage - gymnosperms) in a 'vessel' (angiosperm = 'vessel seed', gymnosperm = 'naked seed'). This folded megasporophyll known as a carpel which matures to form an ovary (when mature = fruit). It is unique to flowering plants and the most important natural produce for our species. Angiosperm evolution has proceeded in such a way that fruits are often composed of more than one carpel fused together.

3. ANDROECIUM - [STAMENS] DO WE EAT STAMENS? NO - MICROSPOROPHYLL TO STAMEN

4. GYNOECIUM - WE EAT GYNOECIA - MEGASPOROPHYLL [GYMNOSPERM VS. ANGIOSPERM] TO CARPEL - SPECIALIZATION OF THE CARPEL [STIGMA (SAFFRON), STYLE, OVARY], SYNCARPY, SIMPLE PISTIL VS. COMPOUND

Variation and Classification

REVIEW ANGIOSPERM SEXUAL CYCLE:

SPOROPHYTE (THE 'PLANT'' OAK TREE OR GARDEN SQUASH) PRODUCES - MEGA- (OVULE) AND MICROSPORANGIA (ANTHER)

ALL SPOROPHTIC TISSUE IS DIPLOID AS ARE MEGA- AND MICROSPORE 'MOTHER' CELLS WHICH DIFFERENTIATE WITHIN THE SPORANGIA - THESE UNDERGO MEIOSIS TO PRODUCE HAPLOID MEGA- AND MICROSPORES WHICH UNDERGO NUCLEAR DIVISIONS TO PRODUCE (WITHIN THE SPORE WALL - ENDOSPORIC) MEGA- AND MICRO GAMETOPHYTES THAT REMAIN IN THE SPORANGIA (8-NUCLEATE MEGAGAMETOPHYTE IN THE OVULE AND 3-NUCLEATE [2 SPERM, 1 GENERATIVE] IN THE POLLEN GRAINS OF THE ANTHER).

POLLEN GRAINS (MICROSPORE WITH MICROGAMETOPHYTE INSIDE) ARE MOVED (VECTORS) TO AN APPROPRIATE (SAME SPECIES) GYNOECIUM, GAMETOPHYTES EMERGE THROUGH (USUALLY PORES) THE MICROSPORE WALL AND GROW THROUGH THE STYLE TO THE OVULE 'POINT OF ENTRY' (MICROPYLE) WHERE THE TWO SPERM (DOUBLE FERTILIZATION) FUSE WITH THE MEGAGAMETOPHYTE EGG NUCLEUS (SYNGAMY) TO PRODUCE A ZYGOTE (RETURN TO DIPLOIDY - EMBRYO)- AND EMBRYO AND ENDOSPERM

This is a biological process comparable to photosysthesis with regard to survival of the animal (human) element of the biosphere. Why? 1) subsistance over the short term (fruit/seed production), and 2) Darwinian development/maintenance of ethnofloristic biodiveristy.

VARIATION:

TERMS: GENOME = [HAPLOID SET OF CHROMOSOMES] - OURS (H. sapiens) IS COMPOSED OF HOW MANY CHROMOSOMES? - 23

EACH CHROMOSOME CARRIES CODED INFORMATION [GENES] THAT CAN OCCUR IN DIFFERENT FORMS [ALLELES]. IF THE SAME ALLELE IS PRESENT IN BOTH GENOMES WHEN COMBINED [SPOROPHYTE] THE GENE IS HOMOZYGOUS [TRUE BREEDING], IF DIFFERENT ALLELES = HETEROZYGOUS

EXAMPLE: FLOWER COLOR - WHITExWHITE=WHITE, REDxRED=RED, REDxWHITE=PINK[F₁], PINKxPINK=RATIO OF PROGENY[F₂] 1WHITE,1RED,2PINK

PUNNET SQUARE FOR F₁ (Aa x Aa) CROSS if 'a' allele is not fully recessive (maybe partially inhibits pigment production):

	A	a
A	AA	Aa
a	Aa	aa

IF THE RED ALLELE ('A') IS DOMINANT, (maybe allele 'a' blocks pigment production but only if homozygous) THEN 3RED:1WHITE

	A	a
A	AA	Aa
a	Aa	aa

EVOLUTION - CHANGE THROUGH TIME - BASE MECHANISM = NATURAL SELECTION - 1859 - DARWIN - BASIC NOTIONS:

1. THERE IS VARIATION IN EVERY GENE POOL
[GENE POOL] = POPULATIONS CAPABLE OF HYBRIDIZATION

2. MOST OF THIS VARIATION IS GENETICALLY BASED [PASSED ON FROM ONE GENERATION TO THE NEXT] PHENOTYPIC PLASTICITY - ENVIRONMENTAL [NOT GENETIC] VARIATION

3. ALL PROGENY OF A GENE POOL DO NOT SURVIVE TO PRODUCE PROGENY

4. INDIVIDUALS CARRYING ADAPTIVE GENES ARE MORE LIKELY TO SURVIVE TO PRODUCE PROGENY THAN OTHERS IN THE POPULATION
- USE UNUSUAL - CULTURAL - EXAMPLES: ANTIBIOTIC RESISTANCE [PENICILLEN, PESTICIDES, HERBICIDES]

5. THUS, ALLELIC [DEFINE] FREQUENCIES AT MANY GENES [DEFINE] WILL CHANGE THROUGH TIME - EVOLUTION

USE BELL CURVE TO DEFINE - STABLIZING/DIRECTIONAL VS. DISRUPTIVE SELECTION

ARTIFICIAL VS. NATURAL SELECTION: MAN CONTROLS THE FATE OF PROGENY - CULTURALLY DIRECTED - RECENT - MAJOR MORPHOLOGICAL CHANGES

AGAIN - BELL CURVE - NOTE DEBATE ON DIRECTIONAL [PHYLETIC] VS. DISRUPTIVE [BI-DIRECTIONAL] PHYLOGENETIC RESULTS OF ARTIFICIAL SELECTION

SUCCESS IN EVOLUTION - INCREASE NUMBERS OF INDIVIDUALS/POPULATIONS AND INCREASE GEOGRAPHIC RANGE - I.E., INCREASE THE AMOUNT, DIVERSITY, DISTRIBUTION OF 'HOME' DNA

VARIATION - MUTATION [MINOR, LONG-TERM] - MAJOR INPUT IS FROM GENETIC RECOMBINATION - THE MORE ALLELES PER GENE THE BETTER - CAN ONLY HAVE 2 ALLELES PER GENE PER INDIVIDUAL. THUS, POPULATIONS WITH VARIABLE INDIVIDUALS ARE PREFERRED

TRADITIONAL AGRICULTURE [EXP. NATIVE AMERICAN] - FIELDS WITH MANY CULTIVARS MUCH GENETIC VARIATION

WESTERN AGRICULTURE - IN THE PAST - HAS PLACED UNIFORMITY AS A HIGH PRIORITY [ASTHETICS, MECHANICAL PROCESSING] - NOW AN INCREASED INTEREST IN 'BIODIVERSITY' - STABILITY - [F₁ MAIZE - LEAF WILT DISEASE OF THE 70s]

Domestication - An evolutionary process that involves changes in gene frequencies through time. The process produces domesticated SPECIES. Non domesticated plant species can be cultivated and domesticated species can grow wild.

Summary from: Charles Darwin (Origin of Species, Chapter 1 Variation Under Domestication: (see whole chapter 1 and index for full document)

"To sum up on the origin of our Domestic Races of animals and plants. I believe that the conditions of life, from their action on the reproductive system, are so far of the highest importance as causing variability. I do not believe that variability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought. The effects of variability are modified by various degrees of inheritance and of reversion. Variability is governed by many unknown laws, more especially by that of correlation of growth. Something may be attributed to the direct action of the conditions of life. Something must be attributed to use and disuse. The final result is thus rendered infinitely complex. In some cases, I do not doubt that the intercrossing of species, aboriginally distinct, has played an important part in the origin of our domestic productions. When in any country several domestic breeds have once been established, their occasional intercrossing, with the aid of selection, has, no doubt, largely aided in the formation of new sub-breeds; but the importance of the crossing of varieties has, I believe, been greatly exaggerated, both in regard to animals and to those plants which are propagated by seed. In plants which are temporarily propagated by cuttings, buds, &c., the importance of the crossing both of distinct species and of varieties is immense; for the cultivator here quite disregards the extreme variability both of hybrids and mongrels, and the frequent sterility of hybrids; but the cases of plants not propagated by seed are of little importance to us, for their endurance is only temporary. Over all these causes of Change I am convinced that the accumulative action of Selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more efficiently, is by far the predominant power."

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