Takao Ichii

In vitro flowering of Japanese pear and the effect of GA4+7

Abstract Flower formation of some Japanese pear cultivars, differing in the extent of apical dominance, was studied in relation to young-leaf removal (removing apical dominance) and in vitro vegetative apex culture. In all cultivars, removal of young leaves and disbudding promoted flowering in the remaining axillary buds on the long shoots as compared with only disbudding. The degree of promotion, however, remained within their flowering capacities, indicating that this capacity is inherent in the bud itself. Explants cultured in vitro formed flowers in the bract axils of their main shoot, regardless of whether they were prepared from the shoot apex or the axillary leaf bud. Occurrence of flowering in the explants was closely related to the flowering capacity characteristic of the cultivar from which they were derived. Flowering occurred predominantly in the explants with a particular range of node number, above or below which it decreased rapidly. The presence of gibberellin GA 4+7 in the medium tended to decrease flowering of explants, but had no effect on their node number.

Hydroxyproline-containing diketopiperazines inducing drought resistance in rice

Abstract Hydroxyproline-containing diketopiperazines (HPCDs), including natural l -hydroxyprolyl- l -proline anhydride [cyclo( l -Hyp- l -Pro): D-104] and l -hydroxyprolyl- l -leucine anhydride [cyclo( l -Hyp- l -Leu): D-301], induce significant resistance in rice ( Oryza sativa ) against water stress caused by sodium chloride or mannitol, when the seeds are treated with the HPCDs during the initial four days of the germination period. The possibility that tricyclic HPCDs such as D-104 can be plant hormone candidates is discussed, based upon structure-activity relationships obtained by using D-104, D-301 and six derivatives thereof.

The effect of gibberellins and growth retardants on in vitro flowering of the vegetative apex of Japanese pear

Effects of gibberellins GA3 and GA4 and of growth retardants succinic acid-2,2-dimethylhydrazide (B-9), (2-chlorethyl)trimethylammonium chloride (CCC) and (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (S-3307) on flowering of Japanese pear cultivars ‘Kosui’ and ‘Chojuro’ were investigated. Explants were prepared from the shoot apex or the axillary bud. The presence of GA4 but not GA3 in the culture medium tended to decrease flowering of ‘Chojuro’ explants, although inhibition was less clear in ‘Kosui’ explants which showed low flowering percentages. S-3307 effectively promoted flowering, particularly for ‘Kosui’ explants. The promotive effect of CCC was slight or none, and B-9 reduced flowering. GA4 (but not GA3) or the growth retardants had a tendency to increase or decrease shoot and internode length of the explants; these morphological changes were not always associated with flowering behavior. The growth regulators had little or no effect on node number of the explants, which was closely related to flowering. Successive subculture of the vegetative apex in the adult form resulted in a rapid loss of flowering ability with an increase in shoot or internode length in the resulting explants, shifting to juvenile characteristics.

Naturally occurring heterocycles inducing drought resistance in plants

During screening of animal metabolites which induce drought resistance in plants, two diketopiperazines, cyclo(L-Hyp-L-Pro) (1) and cyclo(L-Hyp-L-Leu) (2), emerged as effective. When rice seeds were pretreated with the cyclic dipeptides (1 and2) during their germination period, the resulting seedlings showed significant resistance to water-stress caused by 0.5–1.5% NaCl solution or 2.5–5.0% mannitol solution.

Ultrastructural study on the stylar transmitting tissue in Japanese pear

SummaryThe stylar transmitting tissue in the mature pistil of the Japanese pear consists of its component cells and intercellular heterogeneous secretions. The cytoplasm of the periplasmic region contains two different organelles that are characteristic of floral bud development. One of these is the vesicle, which is derived from rough ER and transferred to the periplasmic region of the cell during an early stage of the floral bud. The other one is the lipid droplet, which reacts to polysaccharidic staining and is seen throughout floral bud development. The lipid droplets are closely associated with the Golgi bodies and seem to be dissolved in the vacuole. The materials found in the vacuoles appear to diffuse and pass through the cell walls as intercellular substances.

Effects of bud scales and gibberellins on dormancy of in vitro cultured Japanese pear leaf buds

Abstract Leaf buds of Japanese pear were collected in early June and early November and regarded as summer and winter dormant buds, respectively. Bud explants with and without scales were prepared from each of them, and cultured in vitro for 75 days at 25°C with 14 h photoperiod, on a medium either without growth regulators, or supplied with BA and GAs (GA 3 and GA 4+7 ), singly or in combination. When either BA or GA 4+7 was contained in the medium, bud expansion occurred. Thereafter, summer dormant buds grew into shoots in the presence of BA, while winter dormant buds, although they swelled profusely, remained in a rosette. In the presence of BA, GA 4+7 markedly stimulated shoot elongation of summer dormant buds, but GA 3 did not. In winter dormant buds, GA 4+7 not only failed to stimulate shoot elongation, but also interfered with the BA-induced swelling described above. The presence of bud scales delayed expansion of summer dormant buds, while it had little effect on winter dormant buds. The delaying effect of scales on expansion of summer buds was effectively removed by application of GA 4+7 to the medium.