Genotypic differences in thermotolerance are dependent upon prestress capacity for antioxidant protection of the photosynthetic apparatus in Gossypium hirsutum

Numerous studies have illustrated the need for antioxidant enzymes in acquired photosynthetic thermotolerance, but information on their possible role in promoting innate thermotolerance is lacking. We investigated the hypothesis that genotypic differences in source leaf photosynthetic thermostability would be dependent upon prestress capacity for antioxidant protection of the photosynthetic apparatus in Gossypium hirsutum. To test this hypothesis, thermosensitive (cv. ST4554) and reportedly thermotolerant (cv. VH260) G. hirsutum plants were exposed to control (30/20°C) or high‐day temperature (38/20°C) conditions during flowering and source leaf gas exchange, chlorophyll content and maximum photochemical efficiency (F_v/F_m) were measured for each treatment. The relationship between source leaf thermostability and prestress antioxidant capacity was quantified by monitoring the actual quantum yield response of photosystem II (PSII) (Φ_PSII) to a range of temperatures for both cultivars grown under the control temperature regime and measuring antioxidant enzyme activity for those same leaves. VH260 was more thermotolerant than ST4554 as evidenced by photosynthesis and F_v/F_m being significantly lower under high temperature for ST4554 but not VH260. Under identical growth conditions, VH260 had significantly higher optimal and threshold temperatures for Φ_PSII and glutathione reductase (GR; EC 1.8.1.7) activity than ST4554, and innate threshold temperature was dependent upon endogenous GR and superoxide dismutase (SOD; EC 1.15.1.1) activity. We conclude that maintaining a sufficient antioxidant enzyme pool prior to heat stress is an innate mechanism for coping with rapid leaf temperature increases that commonly occur under field conditions.     

Biosynthesis of the iridoid glucoside,lamalbid, in Lamium barbatum

The biosynthesis of the iridoid glucoside lamalbid in Lamium barbatum, a plant species in the Lamiaceae, was investigated by administrating ¹³C-labeled intermediates of MVA and MEP pathways, respectively. The results demonstrated that [3,4,5-¹³C₃]1-deoxy-d-xylulose 5-phosphate could be incorporated into lamalbid, whereas the incorporation of [2-¹³C₁]mevalonolactone was not observed. Based on the ¹³C labeling pattern of lamalbid and the incorporation data, we deduce that the iridoid glucoside in L. barbatum is biosynthesized through the MEP pathway, whereas the classic MVA pathway is not utilized.     

Evidence That High Activity of Vacuolar Invertase Is Required for Cotton Fiber and Arabidopsis Root Elongation through Osmotic Dependent and Independent Pathways,Respectively

Vacuolar invertase (VIN) has long been considered as a major player in cell expansion. However, direct evidence for this view is lacking due, in part, to the complexity of multicellular plant tissues. Here, we used cotton (Gossypium spp.) fibers, fast-growing single-celled seed trichomes, to address this issue. VIN activity in elongating fibers was approximately 4-6-fold higher than that in leaves, stems, and roots. It was undetectable in fiberless cotton seed epidermis but became evident in initiating fibers and remained high during their fast elongation and dropped when elongation slowed. Furthermore, a genotype with faster fiber elongation had significantly higher fiber VIN activity and hexose levels than a slow-elongating genotype. By contrast, cell wall or cytoplasmic invertase activities did not show correlation with fiber elongation. To unravel the molecular basis of VIN-mediated fiber elongation, we cloned GhVIN1, which displayed VIN sequence features and localized to the vacuole. Once introduced to Arabidopsis (Arabidopsis thaliana), GhVIN1 complemented the short-root phenotype of a VIN T-DNA mutant and enhanced the elongation of root cells in the wild type. This demonstrates that GhVIN1 functions as VIN in vivo. In cotton fiber, GhVIN1 expression level matched closely with VIN activity and fiber elongation rate. Indeed, transformation of cotton fiber with GhVIN1 RNA interference or overexpression constructs reduced or enhanced fiber elongation, respectively. Together, these analyses provide evidence on the role of VIN in cotton fiber elongation mediated by GhVIN1. Based on the relative contributions of sugars to sap osmolality in cotton fiber and Arabidopsis root, we conclude that VIN regulates their elongation in an osmotic dependent and independent manner, respectively.Suc is the principal end product of photosynthesis in higher plants and the major carbohydrate translocated from source to sink tissues through phloem. Suc cleavage, serving as a starting point for various carbohydrate metabolic pathways, is catalyzed by Suc synthase (EC 2.4.1.13) and invertase (β-fructofuranosidase; EC 3.2.1.26). In contrast to the reversible reaction of Suc synthase, invertase irreversibly hydrolyzes Suc to Fru and Glc. This hydrolysis step is required for the development of many sink tissues and their responses to various stresses (Sturm, 1999; Weschke et al., 2003; Roitsch and González, 2004; Huang et al., 2007; Essmann et al., 2008; Jin et al., 2009; for a recent review, see Ruan et al., 2010).Based on their pH optimums and subcellular localizations, invertases are classified into three isoforms: a nonglycosylated cytosolic invertase (CIN), with an optimal pH of 7.0 to 7.8, and highly glycosylated acid invertases with an optimum pH of 3.5 to 5.5 either tightly bound to cell wall (CWIN) or appearing as a soluble form inside the vacuole (VIN; Roitsch and González, 2004). Mutational and transgenic studies have established the critical roles of CWIN in the development of seed (Cheng et al., 1996; Ruan et al., 2003), pollen (Roitsch et al., 2003), root (Tang et al., 1999), and leaf and fruit (Jin et al., 2009). By contrast, much less is known about the function of VIN or CIN (Ruan et al., 2010).High VIN expression or activity has been observed in a range of expanding tissues, including maize (Zea mays) ovaries (Andersen et al., 2002; McLaughlin and Boyer, 2004), grape (Vitis vinifera) berry (Davies and Robinson, 1996), carrot (Daucus carota) taproot (Tang et al., 1999), and sugar beet (Beta vulgaris) petioles (González et al., 2005). It is hypothesized that VIN may play a major role in plant cell expansion, a key step in plant cell development (González et al., 2005). However, progress in determining the roles of VIN in cell expansion suffers from several experimental limitations. Most notably, the multicellular nature of plant tissues makes it difficult to quantitatively evaluate the contribution of VIN in specific cell types. For example, decrease of VIN expression is associated with maize ovary abortion or reduction in its expansion (Andersen et al., 2002; McLaughlin and Boyer, 2004). The VIN gene Ivr2, however, is expressed in nucellus and vascular bundles of the pedicel deeply embedded within the pericarp (Andersen et al., 2002). This inherent anatomical feature makes it challenging to experimentally assess the role of invertase in these cells.In this context, developing cotton (Gossypium hirsutum) fiber offers a tractable experimental system to study the role of invertase in cell expansion for the following reasons. First, after initiation from the ovule epidermis at anthesis, the single-celled cotton fibers undergo rapid and synchronized unidirectional expansion to several centimeters long by approximately 18 d after anthesis (DAA; Ruan et al., 2001). Hence, a large quantity of homogenous single cells can be readily harvested for studying the control of cell expansion (Ruan, 2007). Second, compelling evidence has indicated a major role of osmotically active solutes in fiber elongation through the generation of cell turgor (Ruan et al., 2004). To this end, Suc moves into fibers symplasmically early in elongation (Ruan et al., 2001), and hexoses accumulated in the vacuole are major osmotically active solutes in the fiber sap (Dhindsa et al., 1975; Ruan et al., 1997), where VIN activity has been reported (Wäfler and Meier, 1994). These observations raise the possibility that VIN may be a central player in osmotically driven fiber expansion (Andersen et al., 2002; Ruan, 2005). Finally, elucidating the role of VIN in cotton fiber could help us not only better understand the control of rapid cell expansion but also identify novel ways to increase fiber length, a key quality and yield determinant of cotton, the most important textile crop worldwide (Ruan, 2005).This study aims to examine the role of VIN in cell expansion by using cotton fiber as a model, coupled with integrative analyses on elongating root of Arabidopsis (Arabidopsis thaliana). A combination of cellular, biochemical, and molecular genetic analyses show that (1) rapid fiber expansion requires high activity of VIN, which is probably exerted by the expression of GhVIN1, and (2) the impact on cotton fiber and Arabidopsis root elongation by VIN is most likely achieved through an osmotic dependent and independent manner, respectively.     

獐牙菜小孢子发生及雄配子体发育(英文)

用石蜡切片法对獐牙菜小孢子发生及雄配子体发育过程进行首次观察研究。主要结果如下:花药四室,药壁发育为基本型;绒毡层异型起源,属于腺质型绒毡层,药室内具有的退化绒毡层核是早期该层细胞有丝分裂凸入药室中央并原位退化形成的;中层细胞2层;药室内壁同表皮同时宿存,细胞柱状伸长,纤维状加厚。小孢子母细胞减数分裂为同时型,四分体排列方式主要为四面体形,少数为左右对称形和十字交叉形;成熟花粉多为2-细胞类型,偶见3-细胞型,具三萌发孔。     

美洲黑杨×小叶杨杂种多倍体诱导研究

用不同浓度秋水仙素处理美洲黑杨(Populus deltoides)与小叶杨(Populus simonii)杂种后代以诱导产生多倍体,并采用流式细胞术(FCM)对初选的多倍体材料进行DNA含量分析.结果表明:小于0.1%秋水仙素浓度处理对诱导多倍体无作用;0.3%及其以上浓度处理对诱导产生多倍体效果较好,但随处理浓度增加秋水仙素对杨树的毒害作用增大, 0.5%浓度处理可使顶芽死亡率高达71.43%,且在顶芽死亡的植株中未发现多倍体单株.应用气孔性状对388株扦插苗进行多倍体初选后,采用流式细胞术对初选的5株拟多倍体进行DNA含量分析,鉴定到2株四倍体材料.获得的四倍体材料与二倍体植株在株高和叶绿素含量上差异显著,但在SOD和POD活性上无显著性差异.     

The kinesin of the flagellum attachment zone in Leishmania is required for cell morphogenesis,cell division and virulence in the mammalian host

Leishmania parasites possess a unique and complex cytoskeletal structure termed flagellum attachment zone (FAZ) connecting the base of the flagellum to one side of the flagellar pocket (FP), an invagination of the cell body membrane and the sole site for endocytosis and exocytosis. This structure is involved in FP architecture and cell morphogenesis, but its precise role and molecular composition remain enigmatic. Here, we characterized Leishmania FAZ7, the only known FAZ protein containing a kinesin motor domain, and part of a clade of trypanosomatid-specific kinesins with unknown functions. The two paralogs of FAZ7, FAZ7A and FAZ7B, display different localizations and functions. FAZ7A localizes at the basal body, while FAZ7B localizes at the distal part of the FP, where the FAZ structure is present in Leishmania. While null mutants of FAZ7A displayed normal growth rates, the deletion of FAZ7B impaired cell growth in both promastigotes and amastigotes of Leishmania. The kinesin activity is crucial for its function. Deletion of FAZ7B resulted in altered cell division, cell morphogenesis (including flagellum length), and FP structure and function. Furthermore, knocking out FAZ7B induced a mis-localization of two of the FAZ proteins, and disrupted the molecular organization of the FP collar, affecting the localization of its components. Loss of the kinesin FAZ7B has important consequences in the insect vector and mammalian host by reducing proliferation in the sand fly and pathogenicity in mice. Our findings reveal the pivotal role of the only FAZ kinesin as part of the factors important for a successful life cycle of Leishmania.