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Drought-Affected Mitochondrial Processes as Related to Tissue and Whole Plant Responses¹

The purpose of this study was to correlate the respiratory rates of whole seedlings, excised shoots, and isolated mitochondria of Zea mays L. (Wf9 x M14) water stressed to various degrees. Drought stress was imposed by two different methods and monitored with a Peltier psychrometer. Respiration was determined in whole plants with an infrared gas analyzer and in excised shoots and mitochrondrial suspensions with an oxygen electrode. Substrate oxidation rates by mitochondria isolated from water-stressed tissue decreased with increased stress. Similar decreased respiration rates were observed with excised shoots and whole seedlings when stressed on paper toweling. When the seedlings were stressed with carbowax 6000 in vermiculite, the respiration of excised shoots increased to a potential of about —16 bars and then decreased as stress was increased. The water content of these seedlings also appeared to increase and then decrease in a manner analogous to respiration. When water stress was alleviated by rewatering, the seedling water potentials soon returned to prestress levels in all but severely stressed samples. Respiration rates of excised shoots and mitochondrial suspensions and mitochondrial swelling-contraction responses recovered more slowly. The results showed that in vitro mitochondrial processes were altered by water stress and that these alterations persist even when the mitochondria were isolated from the growing tissue. These results suggest that the decrease in the rate of whole plant respiration with increased stress may be due to membrane alterations that effect the ability of mitochondria to oxidize substrate.

Key Words: Water stress • Drought recovery • Zea mays • Respiration • Phosphorylation • Membranes

² Assistant Professor, Professor, and Research Associate, respectively, Department of Agronomy, University of Illinois, Urbana.

Received for publication July 1, 1972.