The relationship between the growth of flower clusters of Delaware grape and endogenous cytokinin activities in the flower cluster was studied. The rates of both photosynthesis and respiration of the clusters were measured during their development.
(1) The fresh weight of the flower clusters increased rapidly from their early growth stage to the anthesis stage. Water content of the flower clusters was high in the early stage of their development, and then gradually decreased till full bloom.
(2) Reducing sugars in the flower clusters increased gradually during their development, but amino acids and organic acids in the clusters were high in the early stage of their growth and then decreased rapidly.
(3) Cytokinin activities in the flower clusters were present in both n-butanol and aqueous phases during the development of the flower clusters, and cytokinin activities in the n-butanol phase increased gradually from the early stage of growth to anthesis. On the other hand, cytokinin activities in the aqueous phase were very high at the early stage of growth, and thereafter decreased, but again increased rapidly at the time of full bloom.
(4) Chlorophyll content in the flower clusters, expressed on 100mg fresh weight basis, was very high in the early stage of their growth and then decreased up to anthesis.
(5) Photosynthetic activity of the flower clusters increased with light intensity and reached a saturation point 10Klx, and the compensation point was very high. The rate of respiration increased with raising temperature. The rate of netphotosynthesis reached a maximum at 20°C.
(6) Respiration rate of the flower clusters was high at the early stage of their growth, which decreased gradually until a few days before full bloom. At full bloom it increased markedly when the gross-assimilation rate was also fairly high.