Characteristics of Tracheids Produced in Gamma and Gamma-Neutron Environment

Modification in the environment of trees in normal ecosystems, particularly with regard to ionizing radiation, can result in significant changes in xylem tissue characteristics of two Pinus species. Tracheid dimensions were reduced in P. rigida by 17.9 percent in length, 10.0 percent in lumen diameter, and 17.0 percent in wall thickness during an 8-year chronic exposure. Similar reductions were observed in P. echinata after a 1-month exposure to radiation. Disorganization of secondary tissue produced during exposure and a suppression of cell multiplication were observed. Ionizing radiation did not cause permanent cytological damage. Resumption of normal cell multiplication and xylem organization during the time that apical meristems exhibited some external damage from radiation indicates the existence of other controlling mechanisms in addition to auxin. Tree vigor was found to influence susceptibility to ionizing radiation. In the event that great quantities of ionizing radiation are released to the atmosphere, damage to secondary tissues and modification of the normal “within tree” pattern of variation in anatomical characteristics would occur at levels of radiation considerably below that required for mortality.

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