Iojap (ij) is a recessive striped mutant of maize affecting the development of plastids in a local and position‐dependent manner on the leaves. The ij‐affected plastids are transmitted to some of the progeny even when the function of the nuclear gene is restored. Developmental defects during embryogenesis and leaf proliferation are other phenotypic characteristics of ij. The extent of striping and the degree of developmental arrest in ij depend upon genetic background. To understand the diverse and unique phenotypic expression of ij, a transposon tagging experiment has been conducted using Robertson's Mutator (Mu). A new ij mutant was obtained from crosses of the reference allele of (ij‐ref) to Mu lines. Subsequent genetic and molecular studies showed that the mutant carried a new ij allele (ij‐mum1) from the Mu lines and contained a Mu1 element that cosegregated with the iojap phenotype. A 6.0 kb EcoRI genomic DNA fragment containing the Mu1 element was cloned. ij‐ref is unstable, and revertants (Ij‐Rev) have been obtained. Using the flanking DNA from the genomic clone as a probe, DNA polymorphisms were detected between ij‐ref and these revertants. Further, transcripts were restored to the normal level in Ij‐Rev seedlings. Comparison of genomic DNA clones from ij‐ref, ij‐mum1 and Ij indicated that the ij‐ref allele contained 1.5 kb of additional DNA related to a transposable element, Ds. Germinal and somatic revertant alleles were derived by excision of this 1.5 kb element from ij‐ref. The structure of the Ij gene and the DNA sequence of its transcribed region were determined. The Ij gene encodes a 24.8 kDa protein that showed no significant sequence similarity with proteins listed in databases.

Herbaceous peony (Paeonia lactiflora Pall.) is an important ornamental plant which contains different flower colors. In this paper, eight genes encoding phenylalanine ammonialyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3'-hydroxylase (F3'H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), UDP-glucose: flavonoid 3-o-glucosyltransferase (UF3GT) were isolated. Moreover, the expression patterns of these eight genes and UF5GT in the flowers were investigated in three cultivars, that is, 'Hongyanzhenghui', 'Yulouhongxing' and 'Huangjinlun' with purplish-red, white and yellow flower respectively. Furthermore, flavonoid accumulation in the flowers was also analyzed. The results showed that in different organs, most of genes expressed higher in flowers than in other organs. During the development of flowers, all genes could be divided into four groups. The first group (PlPAL) was highly expressed in S1 and S4. The second group (PlCHS and PlCHI) was at a high expression level throughout the whole developmental stages. The third group (PlF3H, PlF3'H, PlDFR, PlANS and PlUF5GT) gradually decreased with the development of flowers. The fourth group (PlUF3GT) gradually increased during the flower development. In addition, anthoxanthins and anthocyanins were detected in 'Hongyanzhenghui' and 'Yulouhongxing', chalcones and anthoxanthins were found in 'Huangjinlun'. When different color flowers were concerned, low expression level of PlCHI induced most of the substrate accumulation in the form of chalcones and displaying yellow, changing a small part of substrates to anthoxanthins, and there was no anthocyanin synthesis in 'Huangjinlun' because of low expression level of DFR. In 'Yulouhongxing', massive expressions of upstream genes and low expression of DFR caused synthesis of a great deal of anthoxanthins and a small amount of colorless anthocyanins. In 'Hongyanzhenghui', a large number of colored anthocyanins were changed from anthoxanthins because of PlDFR, PlANS and PlUF3GT high expressions. These results would provide us a theoretical basis to understand the formation of P. lactiflora flower colors.

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Herbaceous peony (Paeonia lactiflora Pall.) is a traditional famous flower, but its poor inflorescence stem quality seriously constrains the development of the cut flower. Mechanical strength is an important characteristic of stems, which not only affects plant lodging, but also plays an important role in stem bend or break. In this paper, the mechanical strength, morphological indices and microstructure of P. lactiflora development inflorescence stems were measured and observed. The results showed that the mechanical strength of inflorescence stems gradually increased, and that the diameter of inflorescence stem was a direct indicator in estimating mechanical strength. Simultaneously, with the development of inflorescence stem, the number of vascular bundles increased, the vascular bundle was arranged more densely, the sclerenchyma cell wall thickened, and the proportion of vascular bundle and pith also increased. On this basis, cellulose and lignin contents were determined, PlCesA3, PlCesA6 and PlCCoAOMT were isolated and their expression patterns were examined including PlPAL. The results showed that cellulose was not strictly correlated with the mechanical strength of inflorescence stem, and lignin had a significant impact on it. In addition, PlCesA3 and PlCesA6 were not key members in cellulose synthesis of P. lactiflora and their functions were also different, but PlPAL and PlCCoAOMT regulated the lignin synthesis of P. lactiflora. These data indicated that PlPAL and PlCCoAOMT could be applied to improve the mechanical strength of P. lactiflora inflorescence stem in genetic engineering.

Herbaceous peony (Paeonia lactiflora Pall.) is an important ornamental plant that has different flower types. However, the molecular mechanism underlying its floral organ development has not been fully investigated. This study isolated six floral organ development-related genes in P. lactiflora, namely, APETALA1 (PlAP1), APETALA2 (PlAP2), APETALA3-1 (PlAP3-1), APETALA3-2 (PlAP3-2), PISTILLATA (PlPI) and SEPALLATA3 (PlSEP3). The expression patterns of these genes were also investigated in the three cultivars 'Hangshao', 'Xiangyangqihua' and 'Dafugui'. Furthermore, gene expression during floral development was also analyzed in different organs. The results showed that PlAP1 was mainly expressed in the sepals, and PlAP2 was mainly expressed in the carpels and sepals. PlAP3-2 and PlPI had the highest expression levels in the stamens, followed by the petals. The expression levels of PlAP3-1 (from highest to lowest) were in the following order: petals, stamens, carpels and sepals. PlSEP3 was mainly expressed in sepals and carpels. With the depth of stamen petaloidy, the expression levels of PlAP1, PlAP2 and PlSEP3 increased, whereas those of PlAP3-1, PlAP3-2 and PlPI decreased, which showed that PlAP1 mainly determined sepals and petals of P. lactiflora. The PlAP2 not only determined the sepals and petals, and it participated in carpel formation. PlAP3-1, PlAP3-2 and PlPI mainly determined stamens and petals. PlSEP3 determined the identities of sepals and petals. This study would help determine the molecular mechanism underlying floral organ development in P. lactiflora.

To clarify the theoretical basis of the differences in high temperature stress tolerance among herbaceous peony (Paeonia lactiflora Pall.), we investigated the heat injury index of twelve P. lactiflora cultivars. Of these, heat-tolerant 'Zifengyu' and moderately heat-tolerant 'Hongyanzhenghui' were selected to study the biochemical and molecular responses to high temperature stress. 'Zifengyu' had reduced malondialdehyde (MDA) content, increased soluble sugar, chlorophyll (Chl) a, Chl b, Chl a + b. and carotenoid contents, as well as elevated antioxidant enzymes activities, photosynthetic rate (Pn), transpiration rate (Tr) and relatively intact cellular structures compared with 'Hongyanzhenghui', especially when the temperature was the highest. Additionally, we isolated partial cDNAs of two heat shock protein genes (HSP60 and HSP90) from P. lactiflora, which were 880-bp and 1077-bp nucleotides in length, respectively. The expression levels of PlHSP60, PlHSP70 and PlHSP90 were lower in 'Zifengyu' than in 'Hongyanzhenghui' for the first three of four developmental stages examined. These results indicated that heat-tolerant P. lactiflora cultivar could effectively scavenge reactive oxygen species (ROS), protect cellular structures, reduce thermal damage and delay the death of plants by enhancing antioxidant enzymes activities and HSP expression under high temperature stress. These findings provide a theoretical basis for breeding heat-tolerant P. lactiflora cultivars.Key words: herbaceous peony, high temperature stress, physiological mechanism, heat shock protein.Résumé : Afin d'éclaircir les fondements théoriques expliquant la tolérance variable des pivoines de Chine (Paeonia lactiflora Pall.) au stress thermique, les chercheurs ont examiné l'indice des dommages causés par la chaleur de douze cultivars. Parmi ceux-ci, on a retenu les variétés Zifengyu, résistante à la chaleur, et Hongyanzhenghui, modérément tolérante à la chaleur, pour approfondir les réactions biochimiques et moléculaires au stress thermique. Comparativement à Hongyanzhenghui, la variété Zifengyu se caractérise par une plus faible teneur en malondialdéhyde (MDA), une concentration plus élevée de sucres solubles, de chlorophylle (Chl) a, de Chl b, de Chl a + b et de caroténoïdes, ainsi qu'une hausse de l'activité des enzymes antioxydants, du taux de photosynthèse (Pn), du taux de transpiration (Tr) et de la quantité d'organites cellulaires relativement intacts, surtout quand la température atteint un maximum. Par ailleurs, les auteurs ont isolé une partie de l'ADNc des gènes codant deux protéines de choc thermique (HSP60 et HSP90) chez P. lactiflora, dont lalongueur respective est de 880-bp et de 1,077-bp nucléotides. Le taux d'expression des gènes PlHSP60, PlHSP70 et PlHSP90 était plus faible chez Zifengyu que chez Hongyanzhenghui au cours des trois premiers stades de développement sur les quatre examinés. Ces résultats indiquent que le cultivar de P. lactiflora résistant à la chaleur pourrait neutraliser les dérivés réactifs de l'oxygè...