TiO 2 photocatalytic decomposition and detoxification of phytotoxic compounds released by the roots of asparagus ( Asparagus officinalis L.) were investigated from the viewpoint of conservation-oriented cultivation. The phytotoxically active fraction was extracted either from dried asparagus roots or from the recycled nutrient solution of an asparagus hydroponic cultivation system. We found that the phytotoxic activity gradually decreased in the fraction with TiO 2 powder under irradiation with ultraviolet (UV) light at an intensity of 1.0 mW/cm (2). The growth of asparagus plants under actual cultivation conditions was also investigated by comparing asparagus grown in a hydroponic system where recycled waste nutrient solution was photocatalytically treated with solar light and a system with untreated recycled waste nutrient solution. The results showed, as measured by growth indices such as stem length and stem thickness, that asparagus growth in the photocatalytically treated system was superior to the untreated one. Furthermore, the yield of asparagus spears was 1.6-fold greater in the photocatalytically treated system, demonstrating the detoxification effect on the phytotoxic compounds and also the killing effect on pathogenic microorganisms.
From the viewpoint of conservation-oriented agriculture, a closed soilless cultivation using an organic substrate is desirable. We found that photocatalytic treatment efficiently decomposed phytotoxic compounds from rice hull, and the growth and yield of tomatoes in a closed system with the treatment were superior to a system without it. To enhance disease control in the system, this study investigated the suppression of bacterial wilt disease in a simulated waste nutrient solution with photocatalytic and silver treatments. The untreated waste nutrient solution had a high total organic carbon (TOC) concentration, and silver in the untreated solution had no antibacterial activity. By contrast, silver in the photocatalytically treated solution showed a high antibacterial effect via the low TOC of the treated solution. A similar trend of disease onset was observed when pathogenic bacteria were inoculated into the solutions used to cultivate tomato seedlings. These results suggest that, even if the concentration of organic species in waste nutrient solution from a closed system is high, lowering the TOC by photocatalytic treatment promotes the suppression of bacterial wilt disease through the antibacterial activity of silver. It is anticipated that combining photocatalytic and silver treatments will help to stabilize crop production in closed soilless cultivation.
Deficiency in meiotic recombination leads to aberrant chromosome disjunction during meiosis, often resulting in the lethality of gametes or genetic disorders due to aneuploidy formation. Budding yeasts lacking Spo11, which is essential for initiation of meiotic recombination, produce many inviable spores in meiosis, while very rarely all sets of 16 chromosomes are coincidentally assorted into gametes to form viable spores. We induced meiosis in a spo11∆ diploid, in which homolog pairs can be distinguished by single nucleotide polymorphisms and determined whole‐genome sequences of their exceptionally viable spores. We detected no homologous recombination in the viable spores of spo11∆ diploid. Point mutations were fewer in spo11∆ than in wild‐type. We observed spo11∆ viable spores carrying a complete diploid set of homolog pairs or haploid spores with a complete haploid set of homologs but with aneuploidy in some chromosomes. In the latter, we found the chromosome‐dependence in the aneuploid incidence, which was positively and negatively influenced by the chromosome length and the impact of dosage‐sensitive genes, respectively. Selection of aneuploidy during meiosis II or mitosis after spore germination was also chromosome dependent. These results suggest a pathway by which specific chromosomes are more prone to cause aneuploidy, as observed in Down syndrome.
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