User talk:IsadoraofIbiza/Chloroplast/Sandbox

—Proposed rewrite of "Pathogen defense" section——Kelvinsong (talk) 23:09, 6 April 2013 (UTC)

Pathogen defense (old)

Plants have no mobile immune cells, so disease fighting takes place largely at the cellular level. Chloroplasts are key players in plant innate immunity, along with the nucleus, cell membrane, and endoplasmic reticulum. Due to its role in a plant cell's immune response, pathogens frequently target the chloroplast.

Chloroplasts serve as cellular sensors, and after detecting a stress situation within the cell (which may be due to a pathogen), chloroplasts begin producing defense-signaling molecules like salicylic acid, jasmonic acid, nitric oxide and reactive oxygen species which are produced by the chloroplast by inhibiting the function and repair of its photosynthetic system. These molecules trigger retrograde signaling molecules—signals from the chloroplast that regulate gene expression in the nucleus.

Depending on how many reactive oxygen species are produced, the plant cell can enter programmed cell death. High levels of reactive oxygen species will kill the infected cell and any pathogens in it. With lower levels of reactive oxygen species, the cell will start systemic acquired resistance—triggering defense-molecule production in the rest of the plant. As cellular signals, reactive oxygen species are unstable molecules, so they probably don't leave the chloroplast, but instead pass on their signal to an unknown second messenger molecule.

In addition to defense signaling, chloroplasts, with the help of the peroxisomes, also help synthesize an important defense molecule, jasmonate. Chloroplasts synthesize all the fatty acids in a plant cell—linoleic acid, a fatty acid, is a precursor to jasmonate.

Role in plant immunity (new)

Plants lack specialized immune cells—all plant cells participate in the plant immune response. Chloroplasts, along with the nucleus, cell membrane, and endoplasmic reticulum, are key players in pathogen defense. Due to its role in a plant cell's immune response, pathogens frequently target the chloroplast.

Plants have two main immune responses—the hypersensitive response, in which infected cells seal themselves off and undergo programmed cell death, and systemic acquired resistance, where infected cells release signals warning the rest of the plant of a pathogen's presence. Chloroplasts stimulate both responses by producing reactive oxygen species, by purposely damaging their photosynthetic system. High levels of reactive oxygen species will cause the hypersensitive response. The reactive oxygen species also directly kill any pathogens within the cell. Lower levels of reactive oxygen species initiate systemic acquired resistance, triggering defense-molecule production in the rest of the plant.

In some plants, chloroplasts are known to move closer to the infection site and the nucleus during an infection.

Chloroplasts can serve as cellular sensors. After detecting stress in a cell, which might be due to a pathogen, chloroplasts begin producing molecules like salicylic acid, jasmonic acid, nitric oxide and reactive oxygen species which can serve as defense-signals. As cellular signals, reactive oxygen species are unstable molecules, so they probably don't leave the chloroplast, but instead pass on their signal to an unknown second messenger molecule. All these molecules initiate retrograde signaling—signals from the chloroplast that regulate gene expression in the nucleus.

In addition to defense signaling, chloroplasts, with the help of the peroxisomes, help synthesize an important defense molecule, jasmonate. Chloroplasts synthesize all the fatty acids in a plant cell—linoleic acid, a fatty acid, is a precursor to jasmonate.