Masayuki Oda

Anatomy and physiology of graft incompatibility in solanaceous plants

Summary Graft incompatibility in solanaceous plants was investigated using representative cultivars of tomato (Solanum lycopersicum L.), eggplant (Solanum melongena L.), and pepper (Capsicum annuum L.). Evaluations of the extent of graft (in)compatibility were made by examining survival percentages, fruit yields, and fruit quality in grafted plants. Tomato/pepper (scion/rootstock) and pepper/tomato grafts were considered severely incompatible, and the tomato/eggplant and eggplant/tomato grafts were considered moderately incompatible, when compared with the compatible homo-specific graft combinations of tomato/tomato, eggplant/eggplant, and pepper/pepper.Three, or 3 and 6 weeks after grafting, the dry weights of scions and rootstocks, carbohydrate concentrations in stems above and below the graft unions, scion mineral nutrient concentrations, water potentials of scions, and xylem hydraulic conductivities were measured in the grafted plants. The anatomy of the graft unions was also observed. Growth inhibition and high mortality in tomato/pepper and pepper/tomato grafts (i.e., severe graft incompatibility) was due to discontinuities in the vascular bundles at the graft union, which prevented the translocation of assimilates, mineral nutrients, and water between scions and rootstocks. Reductions in fruit yield and/or fruit quality of tomato/eggplant and eggplant/tomato grafts (i.e., moderate graft incompatibility) may have been due to differences in the requirements for assimilates and mineral nutrients between tomato and eggplant. Plant responses to graft incompatibility varied in solanaceous plants depending on the scion and rootstock combination.

Freezing tolerance and soluble sugar contents affected by water stress during cold-acclimation and de-acclimation in cabbage seedlings

The effect of water stress on freezing tolerance during cold-acclimation and de-acclimation in cabbage seedlings were studied. The seedlings were subjected to water stress by withholding water. The treatment wilted the seedlings and decreased the water content of their shoots. Exposure of seedlings to low temperatures (5°C) for 7 days induced freezing tolerance. Water stress promoted the increase in freezing tolerance during cold-acclimation. However, the interruption of water stress by rewatering decreased freezing tolerance rapidly to the same level as for continually watered seedlings. Exposure of cold-acclimated seedlings to normal growth temperature (20°C/15°C) reduced freezing tolerance within a day. Water stress during the de-acclimation period prevented the loss of freezing tolerance. Changes in glucose, fructose and sucrose contents were related to variations in freezing tolerance of seedlings. These results suggest that water stress affects freezing tolerance and is accompanied by changes in sugar contents during cold-acclimation and de-acclimation.

Strict de novo methylation of the 35S enhancer sequence in gentian.

A novel transgene silencing phenomenon was found in the ornamental plant, gentian (Gentiana triflora × G. scabra), in which the introduced Cauliflower mosaic virus (CaMV) 35S promoter region was strictly methylated, irrespective of the transgene copy number and integrated loci. Transgenic tobacco having the same vector did not show the silencing behavior. Not only unmodified, but also modified 35S promoters containing a 35S enhancer sequence were found to be highly methylated in the single copy transgenic gentian lines. The 35S core promoter (−90)-introduced transgenic lines showed a small degree of methylation, implying that the 35S enhancer sequence was involved in the methylation machinery. The rigorous silencing phenomenon enabled us to analyze methylation in a number of the transgenic lines in parallel, which led to the discovery of a consensus target region for de novo methylation, which comprised an asymmetric cytosine (CpHpH; H is A, C or T) sequence. Consequently, distinct footprints of de novo methylation were detected in each (modified) 35S promoter sequence, and the enhancer region (−148 to −85) was identified as a crucial target for de novo methylation. Electrophoretic mobility shift assay (EMSA) showed that complexes formed in gentian nuclear extract with the −149 to −124 and −107 to −83 region probes were distinct from those of tobacco nuclear extracts, suggesting that the complexes might contribute to de novo methylation. Our results provide insights into the phenomenon of sequence- and species- specific gene silencing in higher plants.

Crop Production and Global Warming

Crop production will be affected by global warming, resulting in world-wide food shortages and starvation. Increased concentrations of carbon dioxide (CO2), one of the main substances responsible for global warming, will promote plant growth through intensified photosynthesis. Some reports indicate that a rise in the levels of CO2 would actually benefit plants, rather than harm them. The growth rates of C3 plants increase in response to elevated concentrations of carbon dioxide. Thus, global warming might increase plant growth, because of higher temperatures and higher levels of atmospheric CO2. High atmospheric temperatures caused by elevated concentrations of CO2 will induce heat injury and physiological disorders in some crops, which will decrease the incomes of farmers and agricultural countries. Photosynthesis is one of the most sensitive physiological processes to high temperature stress. Reproductive development is more sensitive than vegetative development to high temperatures, and heat-sensitivity differs among crops. In tomato, the optimal temperature for fruit set was reported as 21–24°C (Geisenberg and Stewart, 1986) or 22–25°C (Peet and Bartholomew, 1996), while pollen viability and release are adversely affected by high temperatures, and become major limiting factors for fruit set. Thus, global warming can have opposite effects on plant growth. From a long-term viewpoint, however, high atmospheric temperatures will drive the main sites of crop production further north, establishing new rules for the ‘right crop for right land’. Water shortages caused by global warming will be the greatest problem for crop production. Plants fundamentally rely on adequate fresh water, and agricultural water accounts for 70% of water use world-wide. As higher temperatures increase evaporation from water sources and decrease precipitation, arid regions will become further desertified. Particularly in semiarid regions, the cultivatable area will decrease because of drought, and this could result in famines and mass migration. As well, it is likely that there will be human conflicts over irrigation water and food. Global warming is thought to be related to strong hurricanes, cyclones, and typhoons. These extreme weather events can seriously damage crop production, and destabilize farm management and the lives of consumers. However, these agricultural problems are most likely to occur in the medium and long-term future. In this chapter, we summarize some of the agricultural problems and crop damage that result from global warming, and present some technical countermeasures (not political and administrative countermeasures) that could be used to ameliorate the effects of global

Absorption, translocation, and assimilation of foliar-applied urea compared with nitrate and ammonium in tomato plants

Abstract To evaluate the use of foliar application of N fertilizer and the occurrence of leaf injury in tomato plants (Lycopersicon esculentum Mill., cv. Momotaro), the effects of the form and concentration of N and solution pH on the leaf injury were studied in the first experiment (Expt. 1). The effects of solution pH and leaf surface on the absorption, translocation, and assimilation of urea were compared with those of nitrate and ammonium in the second experiment (Expt. 2). In Expt. 1, no leaf injury was observed regardless of N sources applied at the N concentration of 1.0 g L-1. Compared with nitrate or ammonium, the index of leaf injury was the lowest in the leaf to which urea had been applied (hereafter referred to as “urea-applied leaf”), when the N level increased from 2.0 to 10.0 g L-1. Leaf injury was not affected by the solution pH in the case of urea, but it increased in the case of ammonium and decreased when nitrate was applied with increasing solution pH. In Expt. 2, the absorption of nit...

Shoot regeneration of tomato (Lycopersicon esculentum Mill.) in tissue culture using several kinds of supporting materials

Cotyledon segments of tomato were cultured on several kinds of supporting materials made from polyester, ceramic, wood pulp and cotton fiber. A liquid medium which contained MS salts and vitamins, 10 g/l myo-inositol, 3% sucrose, 0.1 mg/l IAA and 1.0 mg/l zeatin was supplied to explants through the medium supports. Adventitious buds were induced and phenotypically normal plantlets grew using pulp and cotton fiber supports. Explants formed mainly callus tissue, and normal adventitious shoots were rarely obtained using polyester or ceramic supports. When pulp and polyester supports were placed side by side in a culture vessel, shoot regeneration on the polyester support was markedly stimulated. Shoot regeneration was stimulated by a water extract from the pulp support when explants were cultured on the polyester support. When the pulp extract was partitioned with organic solvents into acidic, basic and the remaining fractions, shoot regeneration was stimulated by the remaining fraction. When the pulp extract was fractionated on a Sephadex G-25 gel column, the regeneration stimulating activity was found in the low molecular weight fraction. These results suggest that effective shoot regeneration of tomato on a pulp support is attributable to an extractable substance which was a thermostable, hydrophilic compound of low molecular weight.

Identification of Nicotiana tabacum linkage group corresponding to the Q chromosome gene(s) involved in hybrid lethality.

Background A linkage map consisting of 24 linkage groups has been constructed using simple sequence repeat (SSR) markers in Nicotiana tabacum. However, chromosomal assignments of all linkage groups have not yet been made. The Q chromosome in N. tabacum encodes a gene or genes triggering hybrid lethality, a phenomenon that causes death of hybrids derived from some crosses. Methodology/Principal Findings We identified a linkage group corresponding to the Q chromosome using an interspecific cross between an N. tabacum monosomic line lacking the Q chromosome and N. africana. N. ingulba yielded inviable hybrids after crossing with N. tabacum. SSR markers on the identified linkage group were used to analyze hybrid lethality in this cross. The results implied that one or more genes on the Q chromosome are responsible for hybrid lethality in this cross. Furthermore, the gene(s) responsible for hybrid lethality in the cross N. tabacum × N. africana appear to be on the region of the Q chromosome to which SSR markers PT30342 and PT30365 map. Conclusions/Significance Linkage group 11 corresponded to the Q chromosome. We propose a new method to correlate linkage groups with chromosomes in N. tabacum.

球根ベゴニアの葉片挿しにおける不定芽形成に及ぼす BA および葉片の置床方向の影響

We studied the effects of the type of leaf cuttings, 6-benzylaminopurine (BA) application, and the section position and orientation of leaf pieces on adventitious bud formation in leaf cuttings inserted in rockwool beds, using expanded young leaf blades of Begonia Tuberhybrida Group ‘Tenella’. In BA absence, 73% of whole leaf blades with petioles formed adventitious buds, whereas none of the 2 × 1.5 cm leaf pieces did at all. The percentages of surviving and adventitious bud formation of 2 × 1.5 cm leaf pieces without petioles were 47% and 0%, respectively. When these small leaf pieces were inserted in rockwool beds containing 0.25–2 ppm BA, the percentages of surviving and adventitious bud formation were 100% and 80%, respectively. In BA presence, the percentage of adventitious bud formation became lower from the base towards the tip of the leaf, and the leaf pieces at positions 2 cm away from the leaf bases did not form adventitious buds at all. When they were placed horizontally and vertically inverted, the percentages of adventitious bud formation were 60% and 80%, respectively.

Effects of temperature and moisture content of the substrate during storage on embryo development and germination in seeds of Musa velutina Wendl. & Drude

Summary Many wild plants in the Musa genus are diploid and form many seeds. However, their seeds rarely germinate after sowing. This non-germination phenomenon makes the breeding of Musa difficult. A method to promote seed germination for breeding and mass propagation has long been awaited. There are many reports on tissue culture or embryo culture, but the procedures are very cumbersome. In this study, we investigated embryo development during the seed germination process and examined optimal seed storage conditions. Germinability of the seeds of Musa velutina immediately after harvest and optimal seed storage conditions for embryo development and germination were investigated. Most seeds harvested in January and August did not germinate within 10 weeks after sowing at 10˚–30˚C. These seeds had immature mushroom-shaped embryos. When seeds with mushroom-shaped embryos were stored after harvest in vermiculite with different moisture contents, under various temperatures, a 75% (w/w) moisture content (–0.01 MPa) and 25˚C promoted embryo development and germination. Seeds stored for 2 months took 7 weeks to germinate, but seeds stored for 4–8 months germinated in 2–3 weeks.

Seed and embryo germination in Ardisia crenata.

Ardisia crenata is an evergreen shrub with attractive bright red berries. Although this species is usually propagated by seed, the seeds take a long time to germinate with conventional sowing methods. We investigated the germination capacity of seeds and embryos collected in different months and the effects of seed storage conditions, germination temperature, water permeability of the seed coat, and the endosperm on seed germination. Seeds and embryos collected in late September or later showed good germination rates. Seeds germinated more rapidly after longer periods of storage at low temperature (approximately 5°C), and those stored in dry conditions showed lower emergence frequency than those stored in wet conditions. Seeds germinated at 15–30°C, but not at 5–10°C. Removal of the seed coat enhanced water uptake and seed germination. Seeds with various proportions of the removed seed coat were sown on a medium supplemented with sucrose. The germination frequency increased as the size of the remaining endosperm decreased. However, the opposite results were obtained when seeds were sown on a medium without sucrose. We concluded that the optimal temperature of 25°C is the most critical factor for seed germination in A. crenata.