Fungi and Plants http://www.wisc-online.com/objects/ViewObject.aspx?ID=BIO304

Fungi

Above: The common mold Rhizopus decomposing strawberries Right: Pilobolus aiming its sporangia. Pilobolus, the hat thrower. Pilobolus is a dung-loving (coprophilous) fungus. Spores are dispersed up to 2 m away and stick to grass blades in the vicinity. The grass and caps are eventually eaten by herbivores.

Zygomycota

Fungi--Nutrition and Habitat - Decomposers/Absorptive heterotrophs - saprobic, parasitic, mutualistic

Structure - hyphae form mycellium

Coenocytic and septate hyphae

Growth and Reproduction

Classification of Fungi Chytridiomycota - uniflagellated spores - link to protists? Zygomycota - zygosporangia - black bread mold (Rhizopus stolonifer) Asomycota - spores produced in asci (sac-like structure) - truffles (Tuber melanosporum) Basidiomycota - spores formed in basidiocarps - mushrooms

Life cycle of bread mold http://bcs.whfreeman.com/thelifewire/content/chp31/31020.html Use these 10 terms to explain the life cycle of a bread mold Hyphae Sporangia Spore Asexual Sexual Pheromones Zygosporangium Nuclei Haploid Diploid

Asomycota

Clockwise: Scarlet cup; the Yellow morel; truffels

Fungal gills, Hypholoma fasciculare (Basidiomycota). The gills hang down from the cap in a tightly packed array. By producing gills in this way the mushroom can increase the surface area of the fertile layer (hymenium) by a factor of 20 or more.

Molds, Yeasts, Lichens and Mycorrhizae - represent unique lifestyles that evolved independently Molds Penicillium on an orange, soft rot of citrus. The name Penicillium comes from penicillus = brush, and this is based on the brush-like appearance of the fruiting structure under the microscope.

Yeasts inhabit moist habitats - Saccharomyces cerevisiae - unicellular fungi that inhabit moist habitats - Saccharomyces cerevisiae - baker/brewer yeast - Candida - inhabit human epithelial tissue - AIDS patients

Lichens b/n fungi and algae - mutual exploitation - symbiotic association b/n fungi and algae - mutual exploitation - tough, resistant; but sensitive to air pollution

Mycorrhizae - increases the absorptive surface area of plant roots - mutualistic associations with plant roots - increases the absorptive surface area of plant roots - exchange of minerals between plant and fungus

Plants

Plant Responses to Internal & External Signals

Plant Hormones Hormones are chemical signals that coordinate the various parts of an organism A hormone is a compound produced in one part of the body which is then transported to other parts of the body, where it triggers responses in target cells and tissues Examples of human hormones: Adrenaline, testosterone, estrogen, epinephrine…

Plant Hormones There are 5 major classes of plant hormones, each with specific functions: Auxin Cytokinins Gibberellins Abscisic acid Ethylene

Auxin Stimulates stem elongation Stimulates development of fruit Involved in phototropism and gravitropism

Cytokinins Stimulate cell division and growth Stimulate cytokinesis Stimulate germination and flowering

Gibberelins Trigger seed and bud germination Promote stem elongation and leaf growth Important in the growth of fruit

Ethylene Promotes fruit ripening Senescence (aging) is a progression of irreversible change that eventually leads to death Caused, at least in part, by ethylene “One bad apple spoils the whole bunch”

Abscisic Acid Induces seed dormancy Inhibits cell growth Anti-gibberellin Inhibits cell growth Anti-cytokinin Inhibits fruit ripening Anti-ethylene Closes stomata during water stress, allowing many plants to survive droughts

Tropisms Tropisms are growth responses that result in curvatures of whole plant organs toward or away from a stimuli There are three major stimuli that induce tropisms Light (Phototropism) Gravity (Gravitropism) Touch (Thigmotropism)

Phototropism Phototropism is the growth of a shoot towards light This is primarily due to the action of auxin Auxin elongates the cells on the non-light side

Biological Clocks/Circadian Rhythms A physiological cycle with a frequency of about 24 hours is called a circadian rhythm Even without external, environmental cues, circadian rhythms persist in humans and in all eukaryotes Example: jet lag in humans

Photoperiodism A physiological response to day length (differs in winter, summer, spring, and fall) is known as photoperiodism Short-day plants Require a shorter light period Flower in later summer/fall/winter Example: poinsettias Long-day plants Require a longer light period Flower in late spring/early summer Example: spinach Day-neutral plants Are unaffected by photoperiod Example: tomatoes But it’s actually the night that matters!!

Plant Defenses Plants defend themselves against herbivores in several ways Physical defenses, such as thorns Chemical defenses, such as producing distasteful/toxic compounds