Plant reproduction

photos by Meredith Moore

38.2: Plants reproduce sexually, asexually, or both

• many angiosperm species reproduce both asexually and sexually
• sexual reproduction results in offspring that are genetically different from their parents --> diversity!
• asexual reproduction results in a clone of genetically identical organisms --> good if environment is favorable
• stamen = filament + anther
• carpel = stigma + style
• asexual reproduction does not need pollinates because of clone ---> pollination takes on a different meaning (like what? comment)

Mechanisms of Asexual Reproduction

• fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction
• in some species, a parent plant's root system gives rise to adventitious shoots that become separate shoot systems
• Ex: Aspen trees clones, all connected with root systems and if one dies the others die. All "rooted" in vascular mechanisms

Advantages and Disadvantages of Asexual versus Sexual Reproduction

• asexual reproduction is also vegetative reproduction
• asexual reproduction can be beneficial to a successful plant in a stable environment
• however, a clone of plants is vulnerable to local extinction if there is an environmental change
• sexual reproduction generates genetic variation that makes evolutionary adaptation possible
• however, only a fraction of seedlings survive

Self-incompatibility

• the most common type is self-incompatibility, a plant's ability to reject its own pollen
• researchers are unraveling the molecular mechanisms involved in self-incompatibility
• some plants reject pollen that has an s-gene matching an allele in the stigma cells
• recognition of self pollen triggers a signal transduction pathway leading to a lock in growth of a pollen tube

*REVIEW*

• functioning xylem tissue, both vessel members and tracheids, consists only of cell walls.
• the cork cambium procudes the cork of woody plants.
• transpiration is the driving force for the cohesion-tension mechanism responsible for the movement of water through xylem. Capillary action and rot pressure contribute little, if at all, to water movement. Carbohydrate utilization and plasmosdesmata refer to the movment of sugars through phloem.
• The Casparian strip prevents water and minerals from entering the stele through the apoplast.
• passage through selective channels, aided by the membrane potential created by proton pumps, facilitates the movement of k + into epidermal cells of the root.