Inflorescence development in tomato plants (Lycopersicon esculentum Mill., cv. King Plus) grown under a low‐light regime is promoted by exogenous applications of a mixture of N6‐benzyladenine (BA) and gibberellins A4+7 (GA) directly on the inflorescence. The photosynthetic rate of the young mature leaf, which feeds the developing inflorescence, and the proportion of 14C‐assimilates exported from the source leaf are not affected by the growth substance treatment, but the pattern of 14C‐assimilate distribution is altered. Assimilate supply to the treated inflorescence increases concomitantly with a decrease in the 14C import into the apical shoot, reflecting a competition between these two plant parts. The increased assimilate accumulation in the treated inflorescence is apparent 1 day after the first application of BA+GA, and precedes any morphological changes in the reproductive structure. These results are discussed in relation to nutritional hypotheses that regard assimilate supply as limiting for reproductive development.
Vegetative plants of Xanthium strumarium L. grown in long days were induced to flower by exposure to one or several 16-hour dark periods. The distribution of male and female inflorescences on the flowering shoot was described, and a scoring system was designed to assess the development of the female inflorescences. The time of movement of the floral stimulus out of the induced leaf and the timing of action of high temperature were shown to be similar for both the apical male and lateral female inflorescences.Strong photoperiodic induction of the plants favored female sex expression, while maleness was enhanced by exogenous gibberellic acid. The problem of the control of sex expression in Xanthium is discussed in relation to the distribution pattern of male and female inflorescences on the flowering shoot and to the state of the meristem at the time of the arrival of the floral stimulus.Flowering in the Chicago strain of Xanthium strumarium L., an absolute short-day plant, has been extensively investigated (16,18). However, most studies were devoted to the initiation and development of the terminal staminate inflorescence, and little is known about the formation of the lateral pistillate inflorescences. Their gross morphological and anatomical development has been described in a few studies (4,8,9,12), and fragmentary physiological aspects have been considered in some other reports (12,13,19,20).The available information on factors that affect sex expression in cocklebur is also very scarce. Effects of photoperiod (12) and nutrition (13) have been described, and it was reported that exogenous GA3 decreased the male to female ratio in a dayneutral strain (21).The aim of the present work was to start a comparative physiological study of the initiation and development of the male and of the female inflorescences in the Chicago strain of cocklebur. Since GA is known generally to increase the tendency to maleness when applied to monoecious and dioecious plants (5) Application of GA3. GA3 was applied in aqueous 0.3 mm solution by spraying the whole plants to run off with a hand atomizer. In preliminary experiments, this concentration was found to give the optimal effect on sex expression, and this application method was found to be superior to spraying only the sole, half-expanded leaf or treatment of the roots by watering or of the shoot apex by application with a small cotton plug. Control plants were sprayed with distilled H20. Tween 20 (polyoxyethylene-sorbitan monolaurate; 0.1%) was present in all solutions as surfactant.Recording Methods. The main axis and side axes of the plant were considered. The side axes were numbered acropetally from the induced leaf (Fig. 1). On the basis of the sex of the terminal inflorescence of the side axes, the whole flowering shoot can be divided into three zones ( Fig. 1) In studies of initiation and development of the female inflorescence, the terminal bud of the side axes 8 and 9, which generally produced a pistillate inflorescence, were dissected 40 days after the start ...
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