the red alga Prionitis

Galls

Prionitis covered with tons of galls (circled in blue). See below for better close-ups of the galls.

Galls have been observed on Prionitis since Prionitis itself was first described. They were originally thought to be a parasitic red alga called Lobocolax deformans. They are most commonly found on individuals in the low intertidal and subtidal in areas subject to high wave action. Gall formation has been reported on Prionitis lanceolata from Washington, Oregon, California, Peru, and Chile. The galls are light pink to red tumorous domes that protrude from the thallus* of Prionitis and can be 1-15 mm in size. They exhibit uncontrolled growth, are undifferentiated, and the cells are very irregular in shape and structure.

Close-up of a magnificent gall

More recently, it has been determined that the galls are produced when a specific bacterium comes in direct contact with the medulla* of Prionitis. This can only occur when Prionitis has been previously wounded. The bacterium can then enter through the wound to induce gall formation. The bacterium has not yet been isolated, but there is evidence that it is a close relative to Roseobacter denitrificans, a parasite that has been isolated from Ulva in Japan. These bacteria can be found between the gall cells but not in the normal host tissue. There is evidence of coevolution between Prionitis and the bacteria, since a specific bacterium induces galls in Prionitis lanceolata, while another specific bacterium induces galls in Prionitis lyallii, etc. Another interesting angle on this tumorous conundrum is the presence of elevated levels of indole-3-acetic acid (IAA) in the infected tissue. IAA is an important growth hormone in terrestrial plants; however, it is normally only present in low levels, if at all, in algae. Experiments have shown a 3-fold increase in the concentration of IAA in the infected tissue versus uninfected tissue from the same individual. The physiological importance of this has not yet been investigated. It is uncertain if IAA is secreted by the bacteria to induce gall formation (in which case, does the gall benefit the bacteria in some way?), or if the alga secretes it as a response to the bacteria (wound healing, perhaps? but then why not in response to wounds when bacteria are not present?). As you can see, Prionitis is still a very mysterious character, especially when it comes to its interactions with bacteria.

Cross section of the outgrowth. The gall is clearly derived from medullary tissue, which then disrupts the cortex to emerge.

Created by Alice Chiu, 2003. Images may be used with permission.

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		Marine Botany
MARINE BOTANY Monterey Bay Flora Seagrasses Green algae Red algae Brown algae Phytoplankton Lichens Methods Habitats Bibliography Glossary Syllabus Students PHYCOLOGICAL SOCIETY OF AMERICA	Prionitis lanceolata Home Taxonomy Morphology Life History Ecology Gallery Glossary Galls Prionitis covered with tons of galls (circled in blue). See below for better close-ups of the galls. Galls have been observed on Prionitis since Prionitis itself was first described. They were originally thought to be a parasitic red alga called Lobocolax deformans. They are most commonly found on individuals in the low intertidal and subtidal in areas subject to high wave action. Gall formation has been reported on Prionitis lanceolata from Washington, Oregon, California, Peru, and Chile. The galls are light pink to red tumorous domes that protrude from the thallus* of Prionitis and can be 1-15 mm in size. They exhibit uncontrolled growth, are undifferentiated, and the cells are very irregular in shape and structure. Close-up of a magnificent gall More recently, it has been determined that the galls are produced when a specific bacterium comes in direct contact with the medulla* of Prionitis. This can only occur when Prionitis has been previously wounded. The bacterium can then enter through the wound to induce gall formation. The bacterium has not yet been isolated, but there is evidence that it is a close relative to Roseobacter denitrificans, a parasite that has been isolated from Ulva in Japan. These bacteria can be found between the gall cells but not in the normal host tissue. There is evidence of coevolution between Prionitis and the bacteria, since a specific bacterium induces galls in Prionitis lanceolata, while another specific bacterium induces galls in Prionitis lyallii, etc. Another interesting angle on this tumorous conundrum is the presence of elevated levels of indole-3-acetic acid (IAA) in the infected tissue. IAA is an important growth hormone in terrestrial plants; however, it is normally only present in low levels, if at all, in algae. Experiments have shown a 3-fold increase in the concentration of IAA in the infected tissue versus uninfected tissue from the same individual. The physiological importance of this has not yet been investigated. It is uncertain if IAA is secreted by the bacteria to induce gall formation (in which case, does the gall benefit the bacteria in some way?), or if the alga secretes it as a response to the bacteria (wound healing, perhaps? but then why not in response to wounds when bacteria are not present?). As you can see, Prionitis is still a very mysterious character, especially when it comes to its interactions with bacteria. Cross section of the outgrowth. The gall is clearly derived from medullary tissue, which then disrupts the cortex to emerge. Created by Alice Chiu, 2003. Images may be used with permission. Marine Flora Habitats Glossary Syllabus Students
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