Ch 38 Plant Nutrition By Team GS Nitrogen

Ch 38 - Plant Nutrition By: Team GS

Nitrogen Fixation • A process performed by certain bacteria found in the nodules of leguminous plants, which make the resulting nitrogenous compounds available to their host plants. • Important because plants need ammonia to build amino acids, but most of the nitrogen in the atmosphere is in the form of Nitrogen gas • Most plants lack the biochemical pathways (which includes the enzyme nitrogenase) necessary to convert nitrogen gas to ammonia

• Bacteria have the capacity to convert nitrogen gas to ammonia live close to plant roots. Others are located in plant tissues called nodules • Hosting these bacteria costs the plant to lose energy • To conserve energy, legume root hairs will not respond to bacterial signals when nitrogen levels are high A root hair of Alfalfa is invaded by Rhizobium

• Extensive signaling between bacteria and the legume lets each organism know the other is present and checks whether the bacteria is the correct species for the specific legume • These highly evolved symbiotic relationships depend on exact species matches • Different legumes have their own specific symbiotic Rhizobium

Carnivorous Plants • Carnivorous plants have the ability to obtain nitrogen directly from other animals • They often grow in acidic soils that lack organic nitrogen (bogs) • By capturing and digesting small animals directly, these plants obtain adequate nitrogen supplies • Carnivorous plants have modified leaves to lure and trap insects and other small animals • The plants digest their prey with enzymes secreted from various types of glands

• Pitcher plants attract insect by the bright colors within their leaves and their sugar-rich secretions • Once inside, insects slide into the cavity of the leaf, which is filled with water and digestive enzymes • Asian pitcher plant, Nepenthes • Complex communities of invertebrates and protists inhabit the pitchers Pitcher Plant

Venus Flytrap • The Venus flytrap has three sensitive hairs called trichomes on each side of each leaf that, when touched, trigger the two halves of the leaf snap together. The enzymes secreted from the leaf surfaces digest the prey • These use a growth mechanism to close and open • As a result, they can only open and close a limited amount of times

Ancestry • The Venus flytrap and the Sundew share a common ancestor that lacked the snap-trap mechanism characteristics of flytraps • Glandular trichomes secrete both sticky mucilage (traps small animals) and digestive enzymes. They close slowly. • Molecular phylogenic studies indicate that Venus flytraps are sister species to of the Sundews, forming a sister clade • The snap-trap mechanism evolved only once in decedents of the Sundew ancestor

Aquatic waterwheel • An even closer ancestor to the flytrap is the Aldrovanda vesicular, the Aquatic waterwheel • The waterwheel is a rootless plant that uses trigger hairs and a snap trap mechanism like the flytrap to capture and digest small aquatic animals • The waterwheels ancestor must have been a terrestrial plant that made its way back into the water

Mycorrhizae • While symbiotic relationships with nitrogen-fixing bacteria are rare, symbiotic associations with mycorrhizal fungi are found in about 90% of vascular plants • The fungi in mycorrhizae associations function as extensions of the root system • This dramatically increases the amount of soil contact and total surface area for absorption • When mycorrhizae are present, they aid in the direct transfer of phosphorous, copper, zinc and other nutrients from the soil into the roots • The plant supplies organic carbon to the fungus. The system is an example of mutualism

Parasitic Plants • Parasitic plants come in photosynthetic and nonphotosynthetic varieties • At least 3000 types of plants are known to tap into the nutrient resources of other plants • Adaptations include structures that tap into the vascular tissue of the host plant so that nutrients can be siphoned into the parasite

• The Dodder is a parasitic plant which looks like brown twine wrapped around its host • The Dodder lacks chlorophyll and completely relies on its host for all its nutritional needs. • The Indian pipe, Hypopitys uniflora also lacks chlorophyll and hooks into host trees through the fungal hypae of the hosts mycorrhizae • This is called a saprophyte because it lacks chlorophyll and depends completely on decaying organic matter for all its nutrients. Indian pipes are found in forests of the northeastern United States

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