一种具有高β-葡聚糖酶活性的几丁质外切酶基因的克隆、表达和性质鉴定

【目的】表达并鉴定来源于维氏气单胞菌的几丁质酶Chi92并研究其作为水产饲用酶的有效性。【方法】自A.veronii B565中克隆chi92基因并在Pichia pastoris GS115中进行表达,对表达成功的Chi92进行分离纯化和生化鉴定。最后将Chi92添加到含有毕赤酵母粉的饲料中饲喂斑马鱼2周,研究Chi92添加对斑马鱼生长、饲料利用率、肠道微绒毛形态和抗病性能的影响。【结果】chi92基因编码具有864个氨基酸残基的多肽。Chi92在p H 6.0和40°C时表现最佳酶活。Chi92对蛋白酶有抗性,同时酶活不受金属离子显著影响。Chi92具备高几丁质酶活(69.4 U/m L)。以胶体几丁质和β-1,3-1,4-葡聚糖作为底物时,比活力分别为809.2 U/mg和235.6 U/mg。薄层层析和电喷雾电离质谱联用技术均表明N-乙酰葡糖胺二聚体是Chi92酶解胶体几丁质的主要产物。Chi92在对酵母细胞壁的降解方面比其他几丁质酶性能更加优良。经过2周饲喂,添加有Chi92的饲料显著提高了斑马鱼肠道微绒毛的高度和密度,同时斑马鱼的生长,饲料利用率,以及抗病性能均得到了一定提高。【结论】Chi92具有p H稳定性、抗逆性和高酵母细胞壁降解功能,能较好地作为饲用酶用于温水水产养殖。     

Metabolic regulation of ammonia emission in different senescence phenotypes of Nicotiana tabacum

In order to reveal the character of ammonia emission in senescent tobacco (Nicotiana tabacum), the content of NH₄⁺, total nitrogen, and soluble protein, and the activities of nitrogen metabolism-related enzymes were measured in leaves of a quick-leaf-senescence phenotype ZY90 and a slow-leaf-senescence phenotype NC89. Compared with NC89, ZY90 had a higher NH₄⁺ accumulation, a lower glutamine synthetase activity, and a significantly higher stomatal ammonia compensation point, and ammonia emission during 40 to 60 d after leaf emergence. During senescence, the quick-leafsenescence phenotype was characterized by nitrogen re-transfer by ammonia emmission, whereas the slow-leafsenescence phenotype by nitrogen re-assimilation. The ammonia emission was primarily regulated by glutamine synthetase activity, apoplastic pH, and NH₄⁺ content.     

Genomic constitution and taxonomy of the Chinese hexaploids Elymus cylindricus and E. breviaristatus (Poaceae: Triticeae)

Elymus cylindricus (2n = 6x = 42) and E. breviaristatus (2n = 6x = 42) are distributed in grasslands and deserts of northern and north‐western China. Their genomic constitution and taxonomic status are unclear. Elymus cylindricus was crossed with E. wawawaiensis J.R.Carlson & Barkworth ( StH ), Roegneria grandis Keng ( StY ) and Campeiostachys dahurica (Turcz. ex Griseb.) B.R.Baum, J.L. Y ang & C. Y en var. dahurica ( StYH ). Meiotic pairing in the hybrids E. cylindricus × E. wawawaiensis ( StH ), E. cylindricus × R. grandis ( StY ) and E. cylindricus × C. dahurica var. dahurica ( StYH ) showed on average 10.00, 11.30 and 20.92 bivalents per cell, respectively. Elymus breviaristatus was crossed with C. dahurica var. dahurica ( StYH ) and E. cylindricus. Chromosome pairing in the hybrids of E. breviaristatus × C. dahurica var. dahurica and E. breviaristatus × E. cylindricus showed on average 19.60 and 19.27 bivalents, respectively. Genomic in situ hybridization (GI SH ) revealed the presence of St , Y and H genomes in E. cylindricus and E. breviaristatus. An intergenomic rearrangement was observed in E. cylindricus using GI SH . Meiotic pairing data and GI SH indicated that both E. cylindricus and E. breviaristatus are allohexaploids containing the StYH genomes. Elymus cylindricus and E. breviaristatus should be treated as Campeiostachys dahurica var. cylindrica and Campeiostachys breviaristata, respectively.     

Functional androdioecy in the rare endemic tree Tapiscia sinensis

Tapiscia sinensis, a rare endemic woody plant with both male and hermaphrodite individuals, is distributed in southern China. Whether T. sinensis is functionally androdioecious is unknown. In this study, we compare the male fitness between male and hermaphrodite individuals and perform pollination experiments in different habitats, identify the ability of actual siring of pollen from hermaphrodites and males under natural pollination, and discuss the evolution and maintenance of androdioecy in T. sinensis. Research suggests that flowers and fruits grow synchronously on hermaphrodite plants of T. sinensis from April to June. The males of T. sinensis had more than twice the genetic contribution of hermaphrodites through their male function and the fruit set from male pollination and cross‐pollination was the highest in all of the treatments, whereas that from self‐pollination was the lowest. Additionally, paternity analysis showed that the hermaphroditic pollen could result in siring success under natural pollination. The results showed that T. sinensis is a functionally androdioecious tree, that male individuals might evolve from a hermaphroditic ancestor and that the synchronous growth of flowers and fruit in hermaphrodites might facilitate the evolution and maintenance of androdioecy in T. sinensis.