Mechanisms & reversal of gametocide response in cotton.

The property of the gametocide chemicals to induce nondehiscent anthers on cotton plants is utilized by plant breeders in the production of hybrid seed. Of equal importance to the plant physiologist is the utilization of this same property to determine the mechanism of nondehiscent anthers in naturally occurring cotton disorders. Acromania in short-staple and hollow-boll in long-staple cotton are two naturally occurring nondehiscent anther conditions in Arizona (5, 10). Exogenous application of the sodium salts of two closely related chemicals, 2,3-dichloroisobutyric acid (FW-450) and 2,2-dichloropropionic acid (Dalapon), can induce gametocide responses in the treated plant. Eaton (4) was the first to report the selective gametocide response, induction of male sterility, brought about by spray application of FW-450 to Empire cotton plants. King and Cheldelin (9) in yeast studies concluded that unchlorinated propionic acid competes with Beta-alanine and thus prevents coupling of pantothenic acid moieties within the yeast cell. Later Hilton, Jansen, and Gentner (8) found that the addition of Beta-alanine gave varying degrees of protection against the growth inhibitions brought about by the adding of FW-450 or Dalapon. In additional studies, Hilton (6) found that FW-450 is uncompetitive with beta-alanine but competitive with pantoate for a site on the enzyme of pantothenate synthesis. Hilton, Ard, Jansen, and Gentner (7) found that FW-450, Dalapon, and other chloro-substituted aliphatic acids compete with pantoate for a site on the enzyme of pantothenate synthesis. Their data also indicated pantothenate does not completely offset the toxic action of Dalapon. A partial circumvention of Dalapon toxicity occurred by applying pantothenate and pantoate to Dalapon treated plants. Scott and Liverman (17) reported that adenine or compounds closely related to adenine were the final products of the red-light-mediated reaction in leafdisk expansion. The implication of adenine in the biochemistry of flowering was thus indicated since e action spectrum for promotion of etiolated-leaf disk expansion by red light (6,500 A) and for the reversal of this promotive effect by far-red light (7350 A) (11) is analogous to the one controlling flowering ( 14). The implication of pantothenic acid and adenine in the physiology of flowering prompted preliminary studies in which a carbohydrate deficiency was induced by dark-conditioning the plants. Initially the gametocide mechanism was investigated to determine the plant response to gametocide chemicals when ribose, a third constituent of coenzyme A, was deficient (16). The structure of coenzyme A is given in figure 1 for review. It is interesting to know that the plant response to gametocide chemicals is much more drastic when the plants are dark-conditioned (15, 16) than when they are not. In attempts to elucidate still further the interaction of gametocide chemicals with coenzyme A precursor substances, carbonl4 labeled FW-450 was applied to dark-conditioned cotton. The data of McRae and Usdin (12) with radiocarbon-labeled FW-450 indicate that the radiocarbon moves from the leaves to the flowers, and is consistently higher in the anthers than in the ovules, and on a percentage by weight basis the C14 activity was much greater in the anthers than in any other part of the flower. Preliminary studies of the writer with Dalapon also indicate a selective necrosis of reproductive tissues when Dalapon is applied to individual plants on the lower leaf, terminal meristem, or the leaf above the first square. These same results were obtained by applying FW-450. The present studies were undertaken to determine the effect of a dark-induced ribose deficiency on the chemically-induced gametocide response in longand short-staple cotton plants. Radiological studies with carbon14 labeled FW-450 and with chlorine36 labeled Dalapon were carried out to determine their translocation and distribution, and if precursors of coenzyme A alter the distribution of these two gametocides. 1 Received revised manuscript October 18, 1960. 2 Plant Physiologist, Boll Weevil Research Laboratory; Box 748; Starkville, Miss.