SummaryThe changes of the activity of growth inhibitors in the latter half of the development of strawberry fruits and the interaction of cytokinin and growth inhibitors on fruit development were investigated.1. Fruits grown at day/night temperature of 30°C/25°C matured earlier than those at 20°C/17°C. The activity of growth inhibitors in the fruits increased with their maturing, and inhibitor activity in the fruits grown at high temperature appeared earlier than that at low temperature.In chromatography of inhibitors on a Sephadex column, peak of inhibitory activity in a bioassay using rice seedling was found in fractions 5 and 6 corresponding with those of authentic ABA.2. Number of days to maturity of fruits in vitro decreased as the concentration of ABA increased in the medium. Number of days to maturity was definitely affected by the concentration of ABA independently of BA concentration when fruits were cultured on the medium with BA and ABA. Fruit maturing was suppressed and inhibitor activity in them decreased when fruits were cultured on the medium with BA.Based on these results, following conclusion can be induced. In the latter half of the development of strawberry fruits, ABA synthesized actively owing to lowering of cytokinin activity in fruits promotes fruit maturing.
Low temperature-induced fruit malformation in tomato was studied from plant hormonal view point. Treatment of TIBA (2, 3, 5-triiodobenzoic acid) and NAP (sodium N-1-naphthylphthalamic acid), auxin-transport inhibitors, increased locule numbers and induced severe malformation including catfaced and strawberry fruits with ovary splits, and oblate and fasciated fruits. Bendroquinone (2-benzimidoyl-3hydroxyl-1, 4-napthoquinone), which is considered to have the similar action mechanism to TIBA and NPA, also showed the same effects. Auxins, PCPA (p-chlorophenoxyacetic acid), 2, 4-D (2, 4-dichlorophenoxyacetic acid) and 2, 4, 5-T (2, 4, 5-trichlorophenoxyacetic acid) reduced oblate and triangular types of malformation by decreasing locule numbers. Gibberellin (GA3) induced ovary split but CCC [(2chloroethyl) trimethylammonium chloride] and SADH (succinic acid-2, 2-dimethylhydrazide), which are considered to inhibit gibberellin synthesis, could not reduce low temperature-induced fruit malformation.
Fruits of strawberry, Fragaria x ananassa (Duch), cv. `Hohkoh-wase', one day prior to anthesis, were cultured in vitro to determine the roles of seeds in fruit development in relation to plant growth regulators .1. Fruits from which carpels were removed enlarged normally as intact fruits with carpels on the medium with a-naphthaleneacetamide (NAAm) . The ripening of intact fruits with carpels on the NAAm medium was suppressed in comparison to that of fruits without carpels.2. When fruits with or without carpels were cultured on the medium with gibberellic acid (GA3), in either fruit, only the basal portion, which was originally devoid of carpels, swelled, but the upper portion, where there were carpels originally, showed no growth.With addition of GA3 to the NAAm medium, fruits with carpels enlarged into normal shape and their growth and ripening were promoted in comparison to those of fruits on the NAAm medium.3. When fruits with or without carpels were cultured on the medium with Nsbenzyladenine (BA) and NAAm, the growth and ripening were suppressed in either fruit as the concentration of BA increased.4. When fruits with carpels were cultured on the medium with maleic hydrazide (MH) and NAAm, the browning of the carpels became severe as the concentration of MH increased, and the growth and ripening were promoted .Based on these results, it is suggested that auxin is more essential for the growth of strawberry fruits than gibberellin, and the carpel is the production site of cytokinin, which suppresses the growth and ripening of strawberry fruits.
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