Biosynthesis of ethylene in sweet potato root tissue

The biosynthetic pathway of ethylene in freshly cut and blackrot-diseased tissues of sweet potato roots was investigated.Glucose-U-¹⁴C administration gave labeled ethylene in both freshand diseased tissues, but at the early stage of infection, therewas ethylene production which was not derived from the fed ¹⁴C-glucose.Acetate-1-¹⁴C and acetate-2-¹⁴C were equally incorporated intoethylene produced from fresh tissue, but acetate-2-¹⁴C was preferentiallyincorporated into ethylene from diseased tissue. Pyruvate-3-¹⁴Cwas more efficient as a precursor than was acetate or glucosein fresh tissue, while its efficiency was the same as that ofacetate in diseased tissue. Monofluoroacetate promoted pyruvate-3-¹⁴Cincorporation in fresh tissue but inhibited incorporation indiseased tissue. We concluded that the TCA cycle is involvedin the case of diseased tissue but not in fresh tissue; thus,showing different pathways for ethylene production in each tissue.In addition, in diseased tissue, ethylene is assumed to be producedfrom some cellular component(s), not easily synthesized fromglucose through fungus infection, but is degraded as soon asinfection commences. ¹This paper constitutes Part 85 of the Phytopathological Chemistryof Sweet Potato with Black Rot and Injury ²Present address: The Institute for Biochemical Regulation,Faculty of Agriculture, Nagoya University, Chikusa, Nagoya 464,Japan (Received April 20, 1970; )     

Transgenic rice hybrids that carry the Rf-1 gene at multiple loci show improved fertility at low temperature

By using a genomic fragment that carries the rice (Oryza sativa L.) fertility restorer gene, Rf-1, rice restorer lines harbouring multiple Rf-1 genes on different chromosomes were developed by genetic engineering and crossing. Hybrid lines that were obtained by crossing the restorer lines having two and three Rf-1 genes with a cytoplasmic male sterile (CMS) line had nearly 75 and 87.5% pollen fertility rates under a normal condition, respectively, whereas a conventional hybrid line showed a 50% pollen fertility rate. Furthermore, the seed set percentage under low temperature conditions was much higher in the hybrid lines with multiple Rf-1 genes than the conventional hybrid line. These results indicate that multiplication of the Rf-1 gene conferred cold tolerance at the booting stage to hybrid rice through increasing the potentially fertile pollen grains. This strategy to improve fertility at low temperature of hybrids could be applied to any grain crops that are developed based on CMS and its gametophytic restorer gene, let alone rice.     

Auxin-induced ethylene production by mungbean hypocotyl segments

Auxin induced an increase in the rate of ethylene productionby hypocotyl segments of etiolated mungbean seedlings aftera 1 hr lag period. The increase in the production rate was greatestwith segments immediately below the cotyledonary hook. Effectiveconcentrations of indoleacetic acid ranged from 1 µm to0.5 mM. Length of the lag period was the same regardless ofthe interval between segment excision and the addition of auxin.Auxin-induced ethylene production was inhibited by cycloheximidebut not by chloramphenicol. Auxin removal from, or cycloheximideaddition to, segments actively producing ethylene in responseto auxin caused a rapid decrease in the rate of ethylene production.These results suggest that the ethylene producing system inducedby auxin is rapidly turning over and that auxin acts at twosites to increase ethylene production ¹This work was supported in part by grant No. 0802 from Ministryof Education, Japan (Received November 30, 1970; )     

Production of ethylene by sweet potato roots infected by black rot fungus

Ethylene production by sweet potato roots infected by the blackrot fungus, Ceratocystis fimbriata, increased strikingly afterinfection. The fungus grown on potato extract containing 1%sucrose or steamed sweet potato produced no ethylene. Thus,ethylene was proven to be produced from the host tissue affectedby fungus invasion. The ethylene production seemed to be stimulatedby carbon dioxide. Oxygen was essential for production, butexcess oxygen, probably over 80%, was found to be inhibitory.Apparent fungus growth on sweet potato was reduced under a hightension of oxygen, but this was not a cause of reduced ethyleneproduction in excess oxygen. When tissue plugs of infected sweet potato which were activelyproducing ethylene were sliced into thin discs, ethylene productionwas abolished with the exception that the first 1 mm discs atthe 1st and 2nd day stages produced a significant amount ofethylene. Similarly, plugs which were removed from fungus-invadedparts did not produce an appreciable amount of ethylene. Theproduction of ethylene was observed only by tissue plugs whichconsisted of both fungus invaded and noninvaded parts. Infected sweet potato tissue produced ethylene at a rate comparableto that in apples and may provide a goodsystem for the studyof ethylene biosynthesis. ¹Part 72 of the Phytopathological Chemistry of Sweet Potatowith Black Rot and Injury.     

Production of ethylene by injured sweet potato root tissue

Ethylene production by sweet potato root tissue was examinedwith special emphasis on tissue injury. The root tissue producedethylene in response to cut injury. Increasing the cut surfacearea increased ethylene production, and the amount was proportionalto logarithm of the surface area. Tissue discs washed with waterbefore incubation produced less ethylene than unwashed discs. When the tissue was treated with chemicals that might destroythe cells, ethylene production remarkably increased. Monoiodoacetamide,trichloroacetic acid and sodium ethylmercurithiosalicylate wereparticularly effective in inducing ethylene production. Here,again, ethylene production was related to the degree of injury.Treatment of the tissue with increasing concentrations of thesechemicals resulted in increasing ethylene production, but concentrationsover a certain limit rather decreased the ethylene production.This may be due to the rapid destruction of the whole tissueused before ethylene production commenced. For thylene production,the presence of injured but still living cells was necessary. Relationship of the injury-induced ethylene production to metabolicactivation is discussed. ¹Part 67 of the Phytopathological Chemistry of Sweet Potatowith Black Rot and Injury. ²Fulbright grantee of 1967. Present address: Department of Biochemistry,University of Wisconsin, Madison, Wisconsin, U.S.A.     

The effect of ethylene on auxin-induced growth of excised rice coleoptile segments

Elongation growth induced by exogenous auxin of apical coleoptilesegments of etiolated rice seedlings was promoted by ethylene.In the absence of exogenous auxin, growth promotion was notobserved. The highest promotion by ethylene was obtained at10^–6 M of indole-3-acetic acid, a suboptimal concentrationfor auxin-induced elongation. Level of ethylene which achievedthe effect was less than 1 µl per liter of an incubationatmosphere. ¹Present address: The Ocean Research Institute, University ofTokyo, Nakano, Tokyo, Japan (Received May 27, 1970; )     

IPOMEAMARONE ACCUMULATION AND LIPID METABOLISM IN SWEET POTATO INFECTED BY THE BLACK ROT FUNGUS I. IDENTIFICATION OF STEROL AND CHANGES IN LIPID METABOLISM DURING INFECTION PROCESS

Changes in lipid contents during infection process in the non-infectedtissue adjacent to the infected region of diseased sweet potatoroots with black rot were examined in comparison with cut controltissue. Incorporation of 2 ¹⁴C-acetate and ³²P-phosphate intolipid fraction was also investigated. Although there was nosignificant change in lipid ester groups in both tissues, increasein phospholipids was found in diseased tissue. Sterol isolatedfrom fresh material was identified with ß-sitosterol.Chromatographic patterns of non-phospholipid fraction of diseasedtissue suggested that some metabolic alteration of this fractionmight occur in response to infection. ¹This paper constitutes Part 40 of Phytopathological Chemistryof Sweet Potato with Black Rot.     

IPOMEAMARONE ACCUMULATION AND LIPID METABOLISM IN SWEET POTATO INFECTED BY THE BLACK ROT FUNGUS II. ACCUMULATION MECHANISM OF IPOMEAMARONE IN THE INFECTED REGION WITH SPECIAL REGARD TO CONTRIBUTION OF THE NON-INFECTED TISSUE

Tracer studies with the use of 2-¹⁴C-acetate revealed that theinfected tissue of diseased sweet potato roots with black rotwas incapable of synthesizing ipomeamarone from acetate, butwas capable of synthesizing it from some intermediate(s) whichwas produced from acetate by the non-infected tissue in a shortperiod. It is very likely that migration of the intermediate(s)from the non-infected tissue to the infected region occurs duringinfection process. Significance of the intermediate(s) in ipomeamaroneaccumulation was discussed. ¹This paper constitutes Part 41 of Phytopathological Chemistryof Sweet Potato with Black Rot.