A cytogenetic study of bilateral sexual polyploidization in cassava (Manihot esculenta Crantz)

Microsporogenesis and megasporogenesis were cytogenetically and histologically analysed in three cassava clones:‘Rayong 1′,‘Rayong 60′,‘M. mga’ and two hybrid lines,‘OMR 3641‐1’ and ‘OMR 3641‐1’ to elucidate the evolution of sexual polyploids in cassava. At telophase II, formation of 17‐21 micronuclei per pollen cell plate was observed in 16 out of 351 cell plates in ‘M. mga’. Micronuclei were observed at low (0.3‐2.3%) frequencies, at the sporad stage in all clones. Monads, dyads, triads and tetrads, which are established sources of high ploidy levels were observed at low (2.6%) and high (22.2%) frequencies. Megasporogenesis in ‘Rayong 1’ and ‘Rayong 60’ showed a lack of second meiotic divisions after a successful first division that resulted in partly unreduced embryo sacs with 2n eggs, suggesting another unrecognized and, as yet, unreported source of sexual polyploid formation in cassava. Meiotic abnormalities during microsporogenesis and megasporogenesis are implicated as being responsible for the formation of mixoploids (triploids and tetraploids) in cassava breeding programmes. A cytogenetic mechanism resulting in bilateral sexual polyploids through different gametic fertilization pathways in cassava is suggested and its role in breeding is briefly discussed.     

Histological analysis of embryo-sac formation and detection of meiotic diplospory in cassava (Manihot esculenta Crantz)

Summary Embryo-sac formation in six cultivated Asian cassava clones and one unknown wild type, was histologically investigated to determine apomictic potential in the genus Manihot. All the 6 clones were found to possess one single sexual embryo-sac containing 6–8 nuclei at maturity. However, one clone, Rayong 3 possessed two functional embryo-sacs at 12 hours after controlled pollination (HACP). The larger embryo-sac was 6-nucleate (all 3 nuclei of the egg apparatus, 1 polar and 2 antipodal cells) and located towards the false micropylar or the nucellar beak region. The smaller embryo-sac also contained a total of 6 nuclei and approximately 10 m³ or 1/2 the volume of the former and located towards the chalazal pole. Percentage sexuality estimates indicated a 100% sexual reproduction in embryo-sacs of all the clones analysed. However, apomeiotic relationships indicate a low (0.3%) degree of meiotic diplosporous embryo-sac formation, thus suggesting facultative apomixis in cv. Rayong 3. This is the first embryological identification and evidence of apomeiosis and apomictic potential in cassava.Contribution from Plant Breeding Laboratory, Applied Genetics & Biotechnology Division, Faculty of Agriculture, Miyazaki University, No. 91.     

In vitro propagation of Japanese garden iris,Iris ensata Thunb.

Summary Explants of young scapes of Iris ensata were cultured on MS medium with 1 mg/l NAA, 1 mg/l 6-BA, 30 g/l sucrose and 10 g/l agar, and this species was characterized by high variety specificity for callus, shoot and root induction. Among 23 varieties and one wild form tested, Okichidori, Miyukisudare and Meiji-l exhibited a considerable rate of shoot induction, although these induced poorly rooted shoots. In addition, two types of callus induction such as green and white calli were observed, and the induction of green-type calli was significantly correlated with that of shoots. Surprisingly, the only modification, half-strength MS inorganic salts, for the above medium proved to be very effective for shoot induction in the scape culture. For shoots obtained from the scape culture, effects of sucrose concentrations and activated charcoal on root induction were examined by using 1/2 MS with 1 mg/l NAA, 1 mg/l 6-BA, 30 g/l sucrose and 10 g/l agar as the basic medium. The addition of 1% activated charcoal to the media had a marked effect for root induction independent of sucrose concentrations and varieties tested. The in vitro propagation technique of I. ensata is discussed.     

A Case Study on Estimation of Dry Deposition of Sulfur and Nitrogen Compounds by Inferential Method

In order to estimate dry deposition, deposition velocity calculation and concentration measurement were carried out in Niigata, Japan. Deposition velocities of SO₂ and HNO₃ for some surfaces such as coniferous forest, deciduous forest, agricultural land, and water were calculated taking into account diurnal variations of meteorological elements using routine meteorological data. Deposition velocities of fine and coarse aerosols were also estimated respectively. Concentrations of SO₂, HNO₃, sulfate and nitrate in fine and coarse aerosols respectively were measured from July to December in 1998 using filter pack and denuder methods. The results indicate that HNO₃ dry deposition for the high aerodynamic roughness surfaces such as forests is quite large. It is suggested that sulfate and nitrate aerosols depositions as well as the gases depositions should be taken into account to estimate dry deposition of sulfur and nitrogen compounds. It is also indicated that dry depositions of sulfur and nitrogen compounds are unable to ignore compared with their wet depositions.     

In vitro development of equine oocytes from preserved ovaries after intracytoplasmic sperm injection

In this study, we evaluated the meiotic competence of equine oocytes from ovaries preserved for one day. We also investigated fertilization, cleavage rate, developmental competence and freezability of equine embryos after intracytoplasmic sperm injection (ICSI). After collection from ovaries, the oocytes were classified into two groups comprised of those having compact cumulus layers (Cp) or those having expanded cumulus layers (Ex). Oocytes with a first polar body were subjected to fertilization by ICSI using frozen-thawed stallion spermatozoa and were then cultured in CR1aa medium. The rates of metaphase II-stage oocytes, normal fertilization and cleavage were not significantly different between the two oocyte categories (38.5, 70.0 and 48.7% for CP and 43.5, 60.0 and 58.8% for Ex, respectively). However, the blastocyst development rate of Ex was significantly (P<0.05) higher than that of Cp (25.5 vs. 7.7%). Three Cp-derived and 12 Ex-derived early blastocysts were cryopreserved using the slow cooling protocol, and all of them developed to hatching blastocysts after thawing. These results suggest that equine oocytes fertilized by ICSI can develop to the preimplantation stage in culture conditions similar to those used in the bovine. Furthermore, the Ex oocytes had higher developmental competence than the Cp oocytes, and the in vitro-produced blastocysts had high viability after freezing and thawing.     

Phosphorus Stress-Induced Differential Growth,and Phosphorus Acquisition and Use Efficiency by Spring Wheat Cultivars

ABSTRACT

Phosphorus (P) is a finite, non-renewable, and natural resource and a vital major nutrient for plant metabolic and developmental processes. However, adverse soil biogeochemical characteristics of alkaline-calcareous soils (especially Aridisols) and highly weathered acid soils (i.e., Ultisols and Oxisols) render orthophosphate (Pi) as the least available major nutrient due to P complexation, sorption, and/or fixation. In such soil environments, plant bioavailable P is only a small fraction of total soil P, seriously limiting crop growth and production. Different plant species, and even cultivars of the same species, may display a suite of growth responses that enable them to solubilize and scavenge soil P either by enhancing external Pi acquisition or reprioritizing internal Pi use under P-stress soil environments. This paper reports relative growth responses, P acquisition and P-use efficiency characteristics by 14 cultivars of spring wheat (Triticum aestivum L.) grown in solution culture with high/low P supply induced by applying soluble NH₄H₂PO₄, sparingly soluble rock phosphate, and Ca₃(PO₄)₂. The wheat cultivars exhibited considerable genetic diversity in biomass accumulation, P concentrations, P contents, factor (PSF) and P efficiency characteristics [i.e., P utilization efficiency (PUE), P efficiency (PE), and PE ratio (PER)]. Plant growth and PE parameters were significantly correlated, while P uptake was linearly related with biomass increase and solution pH decrease. The wheat cultivars with high PUE, PER and P uptake, and low PSF, and plant P concentration were more efficient in utilizing P and, hence, more tolerant under P-stress environment. Biomass and P contents of “P efficient/low-P tolerant” wheat cultivars were superior to “P inefficient/low-P sensitive” cultivars at all P-stress levels. Hence, “P efficient/low-P tolerant” cultivars are the most desirable wheat genotypes for P-stress environments because they are able to scavenge more P from sparingly soluble P sources or soil-bound P forms.     

Differences in lamina joint anatomy cause cultivar differences in leaf inclination angle of rice

ABSTRACT

Leaf erectness is an important agronomic trait for improving canopy photosynthesis in rice. It is well known that leaf inclination angle (LIA) decreases after expansion during ripening. However, the high-yielding indica cultivar ‘Takanari’ retains a greater LIA during ripening than the high-quality japonica cultivar ‘Koshihikari’. To clarify the cause of the cultivar difference in LIA, we investigated anatomical characteristics of the lamina joint of a flag leaf. We found a close linear correlation between LIA at the centre and at the base of the leaf blade in both cultivars during ripening. The length of the lamina joint increased significantly more on the adaxial side of a leaf (the margin of the collar) than on the abaxial side (the abaxial side of the central part of the collar) in ‘Koshihikari’ after leaf expansion, but there was no clear difference in ‘Takanari’. We found a close linear correlation between the ratio of lamina joint length on the adaxial to abaxial sides and LIA in ‘Koshihikari’ and ‘Takanari’ during ripening. In ‘Koshihikari’, the average length of cells on the adaxial side increased significantly after leaf expansion, with no significant increase in that on the abaxial side and no significant change in cell number on either side. In ‘Takanari’, cell length and cell number showed no significant changes on either side of the lamina joint. We conclude that the cultivar difference in LIA during ripening is caused mainly by cell elongation on the adaxial side of the lamina joint.

List of Abbreviations: k: light extinction coefficient; LIA: leaf inclination angle; QTL: quantitative trait locus     

Internal fruit rot of netted melon caused by <Emphasis Type="Italic">Pantoea ananatis</Emphasis> (=<Emphasis Type="Italic">Erwinia ananas</Emphasis>) in Japan

An internal fruit rot with a malodor was found in netted melons (Cucumis melo L.) in commercial greenhouses in Kochi Prefecture, Japan, in 1998, despite their healthy appearance and lack of water-soaking or brown spots on the surface. A yellow bacterium was consistently isolated from the affected fruits. To confirm the pathogenicity of eight representative isolates of the yellow bacterium, we stub-inoculated ovaries (immature-fruits) 5–7 days after artificial pollination, with a pin smeared with bacteria. After the melon fruits had grown for 60 more days, an internal fruit rot resembling the natural infection appeared, and the inoculated bacterium was reisolated. The melon isolates had properties identical with Pantoea ananatis, such as gram-negative staining, facultative anaerobic growth, indole production, phenylalanine deaminase absence, and acid production from melibiose, sorbitol, glycerol, and inositol. Phylogenetic analysis based on 16S rDNA sequences showed that the melon bacterium positioned closely with known P. ananatis strains. The melon bacterium had indole acetic acid (IAA) biosynthesis genes (iaaM and iaaH) and a cytokinin biosynthesis gene (etz). The bacterium could be distinguished from the other ‘Pantoea’ group strains by rep-PCR genomic fingerprinting. From these results, the causal agent of internal fruit rot was identified as a strain of P.ananatis [Serrano in (Philipp J Sci 36:271–305, 1928); Mergaert et al. in (Int J Syst Bacteriol 43:162–173, 1993)]. The nucleotide sequence data reported are available in the DDBJ database under accessions AB297969, AB373739, AB373740, AB373741, AB373742, AB373743 and AB373744.     

Potent cellulase activity in the hepatopancreas of mangrove crabs

Mangrove crabs play a crucial role in the carbon cycle in forests by consuming large amounts of mangrove litter, which is mainly composed of cellulose. However, the detailed mechanism of cellulose digestion remains to be elucidated. We tested endogenous hepatopancreatic cellulase activity in eight species of crabs, including three mangrove sesarmid crabs (Episesarma versicolor, Perisesarma indiarum, and Episesarma palawanense) native to Thailand. Endo-??-1,4-glucanase activity was significantly higher in the enzyme extract from mangrove crabs than in that from Japanese marsh crabs. A ??-glucosidase assay revealed particularly high endo-??-1,4-glucanase activity for E. versicolor, whereas little activity was observed for the Japanese marsh crabs. In a zymogram analysis for endo-??-1,4-glucanase activity, endo-??-1,4-glucanase had a similar molecular mass (30.7?C33.1?kDa) among the mangrove crabs, whereas various sizes (44.3?C84.8?kDa) were found in Japanese crabs depending on the species. These results suggest that mangrove crabs efficiently digest cellulose endogenously.