Chapter 32 Pathogens enter plants through damaged tissue or stomata Plant pathogens spread by growing or moving though the plant vascular system o Viruses move in phloem o Bacteria fungi move in xylem Biotrophic pathogens gain resources from living ells o Necrotrophic pathogens kill cells before colonizing them Plants have an innate immune system that allows them to detect and respond to pathogens o one part of the innate immune system acts generally and recognizes highly conserved molecules produced by broad classes of pathogens o second part of innate immune system acts specifically resistance R genes that encode R proteins recognize pathogen derived AVR proteins plants respond to pathogens by actively killing the cells surrounding the infection hypersensitive response and sending a signal to uninfected tissues so they can mount a defense systemic acquired resistance Rhizobium radiobacter bacterium infects plants by inserting some of its genes into the plant s genome results in the formation of a tumor and provides a way to genetically engineer plants Plant defenses against herbivory dense hairs latex chemicals Alkaloids nitrogen bearing compounds that damage the nervous system of animals Terpenes volatile compounds that give rise to many of the essential oils associated with plants deter herbivores Tannins bind with proteins reduce their digestibility Ant plants bullhorn acacia provide food and shelter for ants which defend the host plant Inducible defenses triggered when a plant detects that it is being attacked Constitutive defenses produces whether or not a threat is present Volatile signals attract insects that prey on herbivores Plants growing on nutrient rich environments allocate more resources to growth than to defense Trade off sometimes observed between plant growth and defense plants favor one or the other but can t have both Janzen Connell hypothesis proposes that interactions with pathogens and herbivores increase plant diversity Escape and radiate pattern of plant evolution suggests that plants undergo a burst of diversification following the evolution of a new form of defense against a pathogen or an herbivore Herbirvores and pathogens are a major concern for agriculture Crop protection includes the use of chemical pesticides integrated pest management application of spores or toxins from Bacillus thuringiensis to plants inserting genes that encode for toxins from B thuringiensis to make Bt modified plants Chapter 33 90 of the 400 000 plant species are angiosperms o other 10 are distributed among the 6 other major groups of plants angiosperms first appear in the fossil record 140 million years ago 300 million years after plants moved onto land evolution of angiosperms resulted in rapid and dramatic increase in total plant diversity moist tropical rain forests dominated by angiosperms provided new types of habitat into which other plants could evolve bryophytes diverged before the evolution of vascular plants o they grow in environments where the ability to obtain water from the soil does not provide an advantage bryophytes are a paraphyletic group consisting of mosses liverworts and bryophytes small plants that produce a flattened thallus or an upright leafy hornworts type o don t form roots absorb water through their surfaces o gametophyte generation is dominant o sporophytes can be tiny and non photosynthetic in liverworts or long lived and photosynthetic in hornworts convergent evolution in bryophytes and vascular plants insect dispersal of sports in mosses internal transport cells in mosses and liverworts sphagnum moss is dominant plant of peat bogs o produces water holding ells that allow it to soak up water acidifies the environment help slow decomposition large amounts of organic carbon build up year after year spore dispersing vascular plants small epiphytic plants that usually grow in moist environments o lycophytes ferns and horsetails are seedless vascular plants that have living relatives today o lycophytes used to include large trees dominating swamp forests today they are small plants that grow in the forest understory as epiphytes or occur in shallow ponds ferns produce large leaves that uncoil as they grow horsetails have tiny leaves whisk ferns have no leaves most present day fern species are the result of a radiation that occurred after the rise of the angiosperms gymnosperms produce seeds and woody stems most common in cold or dry regions o have less than 1000 species gymnosperms have 4 groups of woody plants cycads ginkgos conifers and gnetophyes o cycads produce large leaves on stout unbranched stems occur in small fragmented populations mainly in the tropics and subtropics many are insect pollinated form symbiotic associations with nitrogen fixing bacteria o ginkgo single living species of a group that was globally distributed before evolution of angiosperms wind pollinated produces tall branched trees o conifers tallest and longest lived trees on earth found in cool and cold environments wind pollinated largely evergreen widespread before evolution of angiosperms xylem formed entirely of tracheids o gnetophytes small group independently evolved xylem vessels angiosperm diversity partly explained by animal pollination and xylem vessels o may result from low rates of extinction and high rates of species formation o flowering plants can reproduce even if they are far apart rare species can persist and reproduce xylem vessels allow angiosperms to have a diversity of form and to grow toward light angiosperm phylogeny shows a split between monocots and eudicots o monocots grasses coconut palms bananas ginger orchids single cotyledon embryonic seed leaf don t form vascular cambium o eudicots diverse legumes roses cabbage pumpkin coffee tea cacao tube can grow pollen grains with three openings through which the pollen modern agriculture is based on a few plant species with low genetic diversity vulnerable to pests and pathogens Chapter 34 fungi heterotrophs eukaryotes that feed by absorption o depend on preformed organic molecules for carbon and energy o break down their food and then absorb it use the process of growth to find and obtain food in their environment have hyphae branched filaments used to absorb nutrients hyphae form a mycelium network when a rich food source is encountered hyphae form a continuous compartment with many nuclei and no cell walls fungal cell walls made of chitin in early groups in later groups nuclear divisions are