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Interaction of Gas Composition and Salinity upon Root Cell Division of Vicia faba L.¹

The responses of Vicia faba L. seedlings to treatments consisting of combinations of O₂, CO₂, and N₂ gases in the root environment were determined by microscopic examination of root tips at several times during and after treatment. Superimposed on the gaseous treatments were three nutrien solution salinity levels of 2.95, 5.95, and 8.95 mmho/cn. The plants were grown in an artificially lighted, controlled environment room with roots in airtight chambers. Roots in the chambers were sprayed intermittently (1 min/5 min) with one of the nutrient solutions.

When roots were continually in air, the number of dividing cells in secondary root tips decreased linearly as the salinity level increased. The N₂, treatment drastically reduced the number of dividing cells at all salinity levels, but during the recovery period, the numbers of dividing cells were 70,80, and 100% of the controls at low, medium, and high salinity, respectively. Carbon dioxide levels of 3.5% and 6.0% with O₂ at 17.5% and 15.0%, respectively, considerably reduced the number of dividing cells at a low salinity level and the number of diving cells did not return to normal during recovery. At a medium salinity level 6.0% CO₂ plus 15.0% O₂ reduced the number of dividing cells, but 3.5% CO₂ plus 17.5% O₂ did not. During recovery following treatment with 6.0% CO₂ plus 15% O₂ at the medium salinity level, the number of dividing cells returned to that of the control. At the highest salinity level mitotic divisions in root tips were stimulated by CO₂ treatments. These daa suggest that short periods of inundation or overirrigation may be less injurious to roots in saline than in nonsaline soil.

Key Words: Drainage • Aeration • Oxygen deficiency • Excess carbon dioxide

² Graduate Assistant and Research Plant Physiologist, respectivcly. Botany Department and SWCRD, Agricultural Research Service, US Department of Agriculture, Raleigh, N. C. 27607.

Received for publication May 15, 1969.