Plant Diversity and the Evolution of Land Plants

1. Plant Diversity Fossilized plant spores place plants on land over 500 mybp. Sporopollenin in cell wall is the most durable organic material known C&R distinguish Green Algae from Plants by adaptations to terrestrial living

2. Plants and nearest relative green algae use chlorophyll a as photosynthetic pigment & chlorophyll b as an accessory (catch photons at other colors - see ch 10) Photosynthesis uses light energy to split H2O, release O2, make ATP &NADPH, and put the ‘hydrate’ in carbohydrate. 12H2O 6CO2 Fig 10.4 Fig 10.13 6O2 6H2O 1C6H12O6 Fig 10.8 Plants w/ chlorophyll look green because chlorophylldoes NOT absorbgreen - it absorbs red and violet.

3. Note reduced ratio of red/(far-red) in shade: Because chlorophyll selectively absorbsred wavelengths, the ratioof red (R) tofar-red (FR) wavelengths isan accurate signal {to phytochrome, Fig 39.20} ofvegetation shade and neighbor proximity. Manyplants respond to lowR : FR with a suite of photomorphogenic changes suchas stem elongation, suppressionof branching, altered biomassallocation, and accelerated flowering,commonly referred to as the "shade avoidance syndrome". Such responsesare often elicited byFR reflected from neighboringplants before canopy closure, indicating that plants candetect and respond to potential future competitors … {bolt - race up high to compete for scarce light vs branch – spread out low to collect abundant light} • Manipulative approaches to testing adaptive plasticity: Phytochrome-mediated shade-avoidance responses • in plants. {see C&R ch 39}Schmitt et al. 1999. AM NAT 154:S43-S54.

4. C&R Fig 29.2: Several lines of evidence suggest that modern Chara (common pond algae) is in sister group to modern plants. {It is not the ancestor, any more than chimps are ancestors to humans} The cellulose-manufacturing rosettes found only in the plasma membranes of charophyceans and land plants are evidence of cell wall homology. Charophyceans are the only algae with their anti-photorespiration enzymes packaged in peroxisomes, as they are in plants. Phragmoplasts occur during cell division only in plants and charophyceans Many plants have flagellated sperm, which match charophycean sperm closely in ultrastructure. Comparisons of chloroplast DNA place the charophyceans as the green algae most closely related to land plants. Molecular systematics of key nuclear genes for cytoskeletal proteins support all the other evidence connecting charophyceans and plants to a common ancestor.

5. 1. apical meristems In terrestrial habitats, the resources that a photosynthetic organism needs are found in two very different places. Light and carbon dioxide are mainly available aboveground; water and mineral nutrients are found mainly in the soil. Thus, the complex bodies of plants show varying degrees of structural specialization for subterranean and aerial organs - roots and leaf-bearing shoots … Though plants cannot move from place to place, the elongation and branching of their shoots and roots maximize their exposure to environmental resources. This growth in length is sustained by the activity of apical meristems localized regions of cell division at the tips of shoots and roots Fig 35-12. Apical meristems near the tips of roots and shoots are responsible for primary growth in length. Woody plants also have lateral meristems that function in secondary growth. Five derived characters unique to land plants.

6. 2. “the embryophyte condition” Multicellular plant embryos develop from zygotes that are retained within tissues of the female parent. The parental tissues provide the developing embryo with nutrients, such as sugars and amino acids. The embryo has specialized placental transfer cells … This interface is analogous to the nutrient-transferring embryo-mother interface of eutherian (placental) mammals. Land plants are also known as embryophytes, a distinction that recognizes multicellular, dependent embryos as a derived characteristic common to the land plants. {note: only seed plants package these embryos into a seed} embryophytes Five derived characters unique to land plants.

7. 3. Alternation of generations two multicellular body forms alternate, diploid sporophytes & haploid gametophytes, each form producing the other. Alternation of generations is a special type of haploid - diploid sexual cycle w/ both stages represented by multicellular bodies. C&R Fig 30.1 In bryophytes, the gametophyte is larger and more conspicuous. In pteridophytes, gymnosperms, and angiosperms the sporophyte form is the dominant. The fern plant most of us are familiar with is the diploid sporophyte. The gametophyte is a tiny plant. In gymnosperms & angiosperms the gametophyte is retained within the sporophyte. Five derived characters unique to land plants.

8. 4. Walled spores{in flowering plants - pollen} Plant spores are haploid reproductive cells, produced by the diploid sporophyte sporangia, that grow into multicellular, haploid gametophytes by mitosis. This chemical adaptation makes it possible for wind-carried spores {pollen} to disperse through dry air without harm. All four major plant groups produce spores. Fossilized plant spores place plants on land over 500 mybp. Sporopollenin in cell wall is the most durable organic material known 5. Multicellular gametangia … Five derived characters unique to land plants.

9. note sperm need water film to swim to egg C&R Fig 30.1 C&R Fig 29.16 sporophyte (2n) sphagnum - future peat moss liverwort Gametophyte (n) dominates hornwort Life cycle w/ alt of gen in Bryophytes

10. Pteridophytes:Seedless Vascular Plants Life cycle w/ alt of gen in Ferns C&R Fig 29.23 C&R Fig 30.1 division Pterophyta - ferns ground pines or club mosses whisk ferns ferns horsetails w/ a little independent gametophyte ‘homosporous condition’ - note sperm need water film to swim to egg

11. C&R Fig 30.1 Seed plants are vascular plants that produce seeds.   The two clades of seed plants are gymnosperms and angiosperms Three important reproductive adaptations: reduction of the gametophyte, the advent of the seed, and the evolution of pollen.

12. Vascular Seed Plants - Gymnosperms Life cycle w/ alt of gen in Pine C&R Fig 30.9 wind-blown pollen wind-blown pollen - works in dry air - no swimming sperm Sporophyte dominates seed > year after pollination

13. http://taggart.glg.msu.edu/bot335/cycads.htm Although significant elements of Mesozoic vegetation, cycads today are represented by only 10 genera, confined to the semi-arid tropics and subtropics. Mexico has the highest diversity of living cycads. http://daphne.palomar.edu/wayne/plapr96.htm#ginkleaf The unique, fan-shaped leaves and naked seeds of living Ginkgo biloba trees have changed very little in more than 200 million years. Although the naked, stalked seed resembles a cherry, IT IS NOT A FRUIT! The perfectly preserved cell structure of 15 million-year-old Ginkgo beckii wood http://www.botany.utoronto.ca/courses/BOT307/D_Families gnetophytes - WelwitschiaHook. f., monotypic genus of the deserts of Namibia and southern Angola. Gymnosperms: Conifers +

14. Plants are adapted to terrestrial/air env: separation of light (and CO2) from soil nutrients & water - distribution problems: Fig 36.1,11; lignin, vascular system etc {wood is former plumbing}

15. Vascular Flowering Seed Plants - Angiosperms Life cycle w/ alt of gen in ‘a flower’ C&R Fig 30.17 seed self incompataiblity C&R Fig 38.7 http://hortwww-2.ag.ohio-state.edu/hcs/TMI/hcs200/seed.html … tomatoes, as well as squash, strawberries, water melons, peanuts and wheat are all fruits, according to the definition of a fruit as a mature ovary {all angiosperms produce their seeds inside a ‘fruit’} often carried by an animal Double fertilization: 1. of 1n egg: diploid 2n zygote 2. of 2x1n double haploid cell: triploid 3n endosperm (food) also in gnetophytes

16. Seed dispersal – Directed deterrence by capsaicin in chillies.Tewksbury JJ, Nabhan GPNATURE 412 (6845): 403-404 JUL 26 2001 Plant ManipulationMany plants have ripe, fleshy, coloured fruit in order to attract animals that will eat them and then disperse their seeds in droppings. However, the chilli plant has developed another way of ensuring its seeds are spread far and wide.What raises the roof of your mouth when you eat a chilli is a substance called capsaicin. This stimulates the areas of the skin and tongue that normally sense intense heat and pain, falsely telling the brain that the area affected is burning. New research carried out by scientists in Arizona, has discovered that this characteristic peppery taste repels certain animals {mammals} – which are no good at dispersing the seeds. Digestion And Dispersal… scientists observed … animals living around a group of wild-growing chillies in Arizona. … desert mice and rats avoided spicy chillies, but birds fed almost exclusively on the plants.{the vanilloid receptor subtype 1 (VR1) in birds does NOT react w/ capsaicin} … when birds ate the chillies, many seeds germinated, but there was no germination after mice had eaten the chilli seeds. … seeds pass through a birds’ digestive systems very quickly and come out unharmed, whereas in mice, rats and other mammals, the seeds don’t make it out in one piece … The researchers suggest that chilli plants have evolved to produce capsaicin as a repellent for animals {mammals} … whilst still allowing birds to eat their seeds.

17. Molecular basis for species-specific sensitivity to "hot" chili peppers.Jordt SE, Julius D . CELL 108 (3): 421-430 FEB 8 2002Abstract:Chili peppers produce the pungent vanilloid compound capsaicin, which offers protection from predatory mammals. Birds are indifferent to the pain-producing effects of capsaicin and therefore serve as vectors for seed dispersal. Here, we determine the molecular basis for this species-specific behavioral response by identifying a domain of the rat vanilloid receptor that confers sensitivity to capsaicin to the normally insensitive chicken ortholog. Our findings provide a molecular basis for the ecological phenomenon of directed deterrence and suggest that the capacity to detect capsaicin-like inflammatory substances is a recent acquisition of mammalian vanilloid receptors. {then exploited by chilli peppers}

18. http://farrer.csu.edu.au/ASGAP/APOL15/sep99-1.html Some relationships between flower shape, pollination vector and flower colour http://bio.fsu.edu/~winn/3402L/WinnCH4.html Bee eyes have trichromatic vision … sensitive to green, blue, or ultraviolet. Bees are blind to red. Typical bee flowers are open in the daytime, have a minty fragrance, and offer their visitors nectar, pollen, or both. … are brightly colored (often yellow or blue) … but are not red. Butterflies are sun lovers that like to perch while feeding. They have long and slender probosces, can perceive a wide spectrum of colors, and have an excellent sense of smell. With few exceptions, they are nectar feeders. … typical butterfly-pollinated flowers are open in the daytime, possess a long, thin corolla tube … and are generally vividly colored (often red), although sometimes white. They also provide their butterfly visitors with a platform to land and walk on. Coevolution w/ pollinators: Pollination Syndromes C,R&M Fig 30.9

19. Birds have excellent color vision and appear to favor red. … their sense of smell is very poor. Bird-pollinated flowers have no odor. The amount of nectar produced can be quite large, up to a cupful a day The colors … vary enormously. Many are red, but others are yellow or blue or almost any other color. … bird pollinated flowers are generally open all day. … corollas are often tubular (and are larger in diameter than butterfly flowers) Moths: Hawkmoths, also known as sphinx moths are the nocturnal counterparts of hummingbirds. … normally feed on the wing, … quite large, fly at high speeds … like warm blooded animals, having higher energy requirements … can consume a good teaspoon of nectar at a single sitting. … equipped with a long, thin, and very flexible proboscis … flowers that cater to hawkmoths open in the evening and are extremely fragrant. They are snow-white or light-colored, offer no landing platform … Many have both visual and olfactory nectar guides. The corolla tube is long and narrow, a feature that discriminates short-tongued visitors, and nectar is abundant. http://daphne.palomar.edu/wayne/manduca2.htm#manduca2.gif

20. http://bio.fsu.edu/~winn/3402L/WinnCH4.html … a number of flies and beetles are not really adapted to flowers at all (although the flowers are adapted to them!). These are the carrion, dung, and mushroom flies and beetles that are {tricked} trapped by various flowers or inflorescences. Species in this group are primarily attracted by smell. Some are looking for food, others are looking for egg-laying sites. In either case, they are tricked by the flower odor into thinking that they have found their normal prey. They … figure out that they have been fooled, then move on. Common traits of the flowers that use such pollinators include dull colors, often large, open flowers, (although some species instead have enclosures, which trap the pollinator for a time), and distinct odors, which are sometimes quite unpleasant to humans. Symplocarpus foetidus(skunk cabbage)

21. http://web.ngdc.noaa.gov/paleo/image/gsafinal.gif Pollen profile Shelton Mastodon Site (Oakland County, Michigan) http://www.calvin.edu/academic/geology/mastodon/shel2.htm Carbon date:  9.6kybp  11 kybp Global warming? Ranges of white pine hickory from pollen record Most pollen misses its target. If it falls into anaerobic, acidic bogs, it fossilizes. Core & construct pollen profiles: shows the surrounding plant community. Date the strata with carbon-14 dating.

22. Another economically significant use of grasses islawns… grasses are well adapted for use in lawns, because their basal meristems (growing points) are not lost with mowing. {or grazing, or burning - used in prairie restoration} http://www.colostate.edu/Depts/CoopExt/PUBS/NATRES/06108.html Grass plants and grazing mammals appeared in the fossil record at the same time in the lower Miocene Epoch about 20 million years ago. {recent!} Grass plants, grazing mammals, and grassland plant communities have evolved together. Prairie Meadows Burning by George Catlin Grasses are flowering plants http://fwkc.com/encyclopedia/low/articles/g/g010000624f.html Most grasses are pollinated by wind, so that their flowers are highly reduced … All the world's cereal crops are grasses. The world's 5 top crops produce more tonnage than the next 25 combined, and 4 of the top 5 are the cereals rice, wheat, corn, and barley. Human well-being depends on these few grasses, Grasses are the primary source of food for domestic and wild grazing animals … The total land area devoted to these kinds of croplands is greater than the land area for all other kinds of croplands combined.

23. Plants are sensitive! Fig 39-26. Altering gene expression by touch in Arabidopsis . The shorter plant on the left was touched twice a day. {hiding from grazers?} The unmolested plant (right) grew much taller. Calmodulin as a versatile calcium signal transducer in plants.Snedden WA, Fromm H. 2001. NEW PHYTOLOGIST 151: 35-66.… This review summarizes current knowledge of the Ca2+-calmodulin messenger system in plants and presents suggestions for future areas of research.

24. http://entomology.wisc.edu/~raffa/rafres.html (a) Chemical change in pines during induced defensive response. (b) Bark beetle killed by induced defensive response Sometimes they call for help! Induced defenses: Plants facultatively allocate more to defense after attack. … and warn their neighbors! (“Talking Trees”) see: http://dogbert.gi.alaska.edu/ScienceForum/ASF7/762.html

25. Abstract:Field experiments with manually defoliated black alders (Alnus glutinosa) showed that defoliation affected herbivory by the major alder antagonist, the leaf beetle Agelastica alni. Herbivore damage increased with increasing distance to the defoliated tree, suggesting induced resistance not only on the damaged tree, but also on the neighbouring trees. The beetles also avoided leaves from the nearest neighbours for both feeding and oviposition in a laboratory assay, so the alders showed interplant resistance transfer. Natural enemies did not appear to shape this pattern, … Fig. 1. Number of individuals of phytophagous arthropods on the defoliated trees, their nearest neighbours and their farthest neighbours (0, 1.3 and 10.6 m distance to the manually defoliated tree), 81 days after defoliation … (b) phytophagous specialists: F=6.43, n=30, p<0.005. Herbivory, induced resistance, and interplant signal transfer in Alnus glutinosa.Tscharntke et al. 2001. Biochemical Systematics and Ecology 29:1025-1047.

26. Mechanisms causing this pattern, found in the field, were studied in more detail using biochemical analyses and further bioassays. Responses of alder leaves to herbivory of A. alni were shown to include ethylene emission and the release of a blend of volatiles with mono-, sesqui- and homoterpenes. … jasmonic acid (JA) showed the activation … following herbivory. Further evidence that airborne interplant communication may be important in the response of alder trees to beetle attack came from container experiments, In airtight chambers, unattacked leaves significantly increased the activity of proteinase inhibitors when they were associated with leaves previously attacked by beetle larvae. … the relative importance of airborne and possible soil-borne signals as well as unknown effects of intensified nutrient absorption of defoliated trees, possibly reducing foliage quality of undamaged neighbours, remains to be shown. Tscharntke et al.

27. Tobacco, cotton and maize plants each produce distinct volatile blends in response to damage by two closely related herbivore species, Heliothis virescens{tobacco budworm} and Helicoverpa zea {corn earworm}. The specialist parasitic wasp Cardiochiles nigriceps exploits these differences to distinguish infestation by its host, H. virescens, from that by H. zea. Herbivore-infested plants selectively attract parasitoidsDe Moraes et al. 1998. NATURE 393:570-573. Abstract: In response to insect herbivory, plants synthesize and emit blends of volatile compounds from their damaged and undamaged tissues, which act as important host-location cues for parasitic insects. Here we use chemical and behavioural assays to show that these plant emissions can transmit herbivore-specific information that is detectable by parasitic wasps (parasitoids). The production by phylogenetically diverse plant species and the exploitation by parasitoids of highly specific chemical signals, keyed to individual herbivore species, indicates that the interaction between plants and the natural enemies of the herbivores that attack them is more sophisticated than previously realized.

28. from deBuron & Beckage, 1992. Polydnavirus-mediated suppression of insect immunity.Shelby KS, Webb BA. 1999. Journal Of Insect Physiology 45: 507-514. bstract:Polydnaviruses are symbiotic proviruses of some ichneumonid and braconid wasps that modify the physiology, growth and development of host lepidopteran larvae. Polydnavirus infection targets neuroendocrine and immune systems, altering behavior, stunting growth, and immobilizing immune responses to wasp eggs and larvae. Polydnavirus-mediated disruption of cellular and humoral immunity renders parasitized lepidopteran larvae suitable for development of wasp larvae as well as more susceptible to opportunistic infections. …the unique genomic organization of polydnaviruses may have evolved to amplify the synthesis of immunosuppressive viral proteins. …