MODIFICATION OF FLORAL INITIATION WITH AUXINS AND TEMPERATURES

Abstract

THE FACT that auxins are capable of modifying floral initiation has been known since 1937 when Dostal and Hosek demonstrated an inhibition of flowering in Circaea. It appears from the experiments of Cholodny (1936) and Thimann and Lane (1938) that auxins may have an effect on flowering as a function of vernalization, and the work of Leopold and Thimann (1948) and Bonner and Thurlow (1949) indicate that auxins can modify flowering as a function of photoperiodism. Up to the present time promotive effects of auxins upon photoperiodic induction have been reported only for long-day plants (Leopold and Thimann, 1948; Leopold and Thimann, 1949; Klein, 1951; Claes, 1952; Liverman and Lang, 1952) . Studies of floral initiation in this laboratory have indicated a strong interaction between auxin effects and temperatures experienced by pea plants (Leop6ld and Guernsey, 1953a). A similar interaction has been found between auxin and vernalization of barley (Leopold, 1952). These results suggest the possibility that an auxin-temperature interaction might be general among plants, and might offer a new method of altering floral initiation. Knowledge of such a phenomenon would be of considerable interest both physiologically and agriculturally. METHODS.-Seeds of diverse types of plants were soaked in solutions of auxin (naphthaleneacetic acid) for 24 hr. at room temperature. After removal from the solution, the seeds were placed in moist vermiculite and transferred to dark controlled temperature rooms where they remained for a period of 2 wk. At the end of the temperature treatment they were transplanted into gravel beds in the greenhouse and permitted to develop under photoperiods which were favorable for flowering. Ten plants from each treatment were then dissected under a microscope and the numbers of flower primordia, their location and stage of development were recorded. This procedure is essentially the same as that described by Leopold and Guernsey (1953a) for peas, with the exception that a longer temperature control period was used. Long photoperiods were obtained by extension of natural daylight hours with 100 ft.-c. of incandescent light. Short photoperiods were obtained by use of black cloth curtains. The stage of development of the various grain species was recorded in each experiment upon dissection. A simple scoring method was used as follows: 0 vegetative; 1 simple spikelet primordia; 2 floret parts differentiated; 3 pre-boot stage; 4 boot stage; 5 flag stage; 6 heading out.