Tuesday, November 14, 2006

Roles of Auxin and Cytokinin in Pod Set of Soybean.

Kaori Nonokawa, Takayuki Nakajima, Teiji Nakamura, and Makie Kokubun. Grad. Schl. Agric. Sci., Tohoku Univ., Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai, 981-8555, Japan

  Soybean plants differentiate abundant floral buds, but a majority of the buds fail to grow pods and abort during development. Many of previous studies indicate promotive effects of exogeneously-applied cytokinin on pod set while effects of auxin application on pod set are not consistent. The objectives of the present study are to know the endogenous change of auxin and cytokinin in racemes and to examine the effects of application to racemes of the two hormones, and thereby to clarify the role of auxin and cytokinin in pod set of soybean. The long-raceme soybean genotype IX93-100 was grown in field for two years and in pots for a year. The auxin (IAA) concentration in racemes of field-grown plants was high during a relatively longer period from pre-anthesis to 9 days after anthesis of the first flower on a raceme (DAA), whereas the concentration of cytokinin was high for a relatively shorter period with its peak at 9 DAA. The auxin application to racemes did not affect floweirng and podding in field-grown plants, but in pot-grown plants it tended to increase the number of flowers when applied before 0DAA while it tended to reduce the number of flowers and pods when applied after 0DAA. The exogeneous cytokinin (BA) reduced the number of flowers and pods when applied to racemes before 0DAA, whereas it increased pod set percentage resulting in an increase in the number of pods. The results show that the concentration of endogenous auxin and cytokinin in racemes changes in a different manner, and that cytokinin application has a positive but auxin application has a negative effect on pod set.