A study of the ultrastructure of leaf tissues of Chinese mustard shows that there is a progressive degeneration of the membrane structure of the grana of the chloroplast accompanied with the appearance of globules of lipid material and loss of chlorophyll during leaf senescence. A controlled atmosphere of 5% CO2 plus 3% O2 maintained chloroplast grana membrane structure for up to 4 weeks storage at 10°C. Both 5% CO2 (in air) and 5% CO2 plus 3% O2 maintained the highest chlorophyll content compared to 3% O2 alone or in air (control).
Hong Wang and Robert C. Herner
Liping Wang, Guoping Wang, Ni Hong, Rongrong Tang, Xiaoyun Deng, and Hong Zhang
Apple stem grooving virus (ASGV) and apple chlorotic leaf spot virus (ACLSV) are two major viruses of pear. In this study, in vitro thermotherapy was carried out at 37°C for 25, 30 and 35 days followed by subculturing of meristem tips of different sizes to eliminate ASGV and ACLSV from pear plants. Virus titers in heat-treated shoot tips were evaluated by ELISA testing of regenerated plants. Results showed that thermotherapy for 35 days significantly decreased the titer of ASGV and ACLSV in cultures regenerated from tips of main and axillary shoots, especially in those from explants 1 mm in length from the tip of meristems. Dot-blot hybridization of biotinylated cDNA probes derived from ACLSV and ASGV was used to detect these viruses in crude tissue extracts of in vitro-grown pear plants. Intense signals were consistently detected in untreated plant samples equivalent to less than 0.5 mg tissue. Comparison of signals from dot-blot hybridization and ELISA absorbance values (A405) confirmed that dot-blot hybridization had a higher sensitivity than PAS-ELISA. Dot-blot hybridization could detect viruses with a titer below the threshold level of ELISA. These results indicate that dot-blot hybridization is a useful tool for large-scale surveys of viruses, which facilitates the production of virus-free propagation materials in certification and sanitation programs. Results of PAS-ELISA and dot-blot hybridization showed that high virus elimination efficiency was achieved by a combination of thermotherapy for 35 days and in vitro culture of 1 mm meristem tips.
Shiow Y. Wang, Miklos Faust, and Hong J. Jiao
The effects of thidiazuron on changes in superoxide dismutase (SOD) activity in apple (Malus domestica Borkh cv. York Imperial) buds during dormancy break were determined. Dormant buds had low SOD activity. Increased SOD activity was correlated with budbreak induced by thidiazuron. Buds contained three distinct forms of SOD: Cu, Zn-SOD; Mn-SOD; and Fe-SOD. Most of the SOD activity in apple buds was attributed to Cu and Zn-SOD, followed by Mn-SOD. Iron-SOD was not present in dormant buds, and only a trace amount was found as buds started rapid expansion. Chemical name used: N-phenyl-N′-1,2,3,-thidiazol-5-ylurea (thidiazuron).
Mohamed S. Elmongy, Xiuyun Wang, Hong Zhou, and Yiping Xia
Auxins and humic acid (HA) were investigated for their roles in adventitious root induction in azalea microshoots in our previous study. To reveal the regulatory mechanisms of auxins and HA in this process, measurements of the levels of reactive oxygen species (ROS), carbohydrates, and phenolic compounds and gene expression during in vitro root development were performed. During the adventitious root induction process, ROS levels in shoots treated with auxins and HA increased compared to untreated shoots, especially during the earliest period after transfer to the media. Media supplemented with NAA experienced increases in H2O2 contents by 480%and 250%, respectively, after 7 and 14 days of culture. The phenolic compound levels were also enhanced in the shoots treated with auxins and HA, reflecting the different rooting-promoting abilities of both auxins and HA. The highest levels of total phenolic [68.6 mg·g−1 fresh weight (FW)], polyphenolic acids (121.72 μg caffic acid/g FW), and total flavonols (162.42 μg quercetin/g FW) were recorded after 21 days for NAA media, but the maximum levels of anthocyanins (49.76 μg cyanindin/g FW) were recorded after 21 days for IBA medium. Soluble carbohydrate, starch, and soluble protein levels were increased in the shoots treated with all treatments; however, the influence of NAA treatments was stronger than that of other treatments for most investigated parameters. The NAA significantly enhanced soluble carbohydrates by 30%, 37%, and 25%, respectively, at 14, 21, and 28 days compared with untreated microshoots. Expression of the POD1 gene increased in the shoots submitted to HA treatment media. Expression levels of auxin response factors (ARFs) increased with IBA- and NAA-treated explants, suggesting that ARFs may have diverse regulatory roles in adventitious root induction in evergreen azalea. Moreover, the profiles of the IAA1, IAA9, IAA14, and IAA27 transcripts were analyzed to reveal their roles in the adventitious rooting of evergreen azalea microshoots. These results indicate that auxins and HA promote adventitious root induction in Rhododendron plants through their impact on ROS, carbohydrate contents, phenolic compound levels, and expression levels of different genes related to root development in evergreen azalea plants.
Ling Yu, Hongwei Chen, Peipei Hong, Hongli Wang, and Kefeng Liu
Salvia splendens is a widely used ornamental bedding plant; however, the limited propagation method has decreased its quality and yield. Through years of selection, we have obtained a new variety of S. splendens with weak apical dominance and named it as ‘Cailinghong’. To establish an effective method for regeneration of S. splendens ‘Cailinghong’, different explants, including leaves, receptacles, petioles, stem nodes, and stem segments were used for adventitious bud induction. Next, various combinations of plant growth regulators (PGRs) were selected for bud and root induction, which were assessed by adventitious bud initiation rate and proliferation rate, as well as root induction rate. Meanwhile, the survival rate of transplanted plantlets was also calculated. As a result, stem nodes were found easy to be induced to form buds, and the optimum medium component was 1/2 Murashige and Skoog (MS) medium supplemented with 0.45 µM naphthalene acetic acid (NAA), 8.88 µM 6-benzylaminopurine (6-BA), and 2.46 µM 3-indolebutyric acid (IBA) for plantlets induction, whereas 1/4 MS medium supplemented with 2.23 µM NAA for root induction. Furthermore, the survival rate of transplanted plantlets was up to 80%, and all regenerated plantlets were normal in phenotype. Therefore, cultured in 1/2 MS medium with combined PGRs, whole plantlet of S. splendens ‘Cailinghong’ could be regenerated directly from stem node.
Fengxia Shao, Sen Wang, Juan Chen, and Rongyan Hong
To investigate whether reproductive disorders exist in the sexual reproduction of Ziziphus jujuba Mill. ‘Zhongqiusucui’ and to understand the reproductive biology of ‘Zhongqiusucui’ and genetic improvements in jujube trees, we used ‘Zhongqiusucui’ flowers at different developmental stages as materials and conducted field and microscopic observations on the developmental pattern of mega- and microsporogenesis, as well as on the development of male and female gametophytes. The results show the following. 1) From the inflorescence development stage to flowering, the grade 0 bud on the inflorescence exhibited an increase in horizontal diameter, longitudinal diameter, peduncle length, and bud weight, but the rates of increase were different. From day 1 to day 5 after the inflorescence had developed, floral buds mostly grew horizontally. Day 5 was the floral bud flattening stage. From day 6 to day 8 after the inflorescence had developed, floral buds mostly grew longitudinally, and day 8 was the floral bud enlarging stage. 2) The stamens of ‘Zhongqiusucui’ had five anthers, and there were four locules per anther. The anther wall consisted of epidermis, endothecium, one- to two-layered middle layer, and a secretory-type tapetum. In addition, the development of the anther wall belonged to the basic type. The cytokinesis of the microsporocytes was synchronous, the tetrads mostly arranged as a tetrahedron, and the mature pollen had three germ pores, three grooves, and was bicellular pollen. During meiosis, the microsporocytes in each locule were at the same phase and therefore exhibited synchrony. Among the different anthers in the same floral bud, as well as the four locules in the same anther, the microsporocytes had asynchronous meiosis. 3) The pistils in the ‘Zhongqiusucui’ had two ovaries, two anatropous ovules, inner and outer integument, crassinucellate tetrads formed by the meiosis of megasporocytes aligned linearly along the nucellus, megaspore at the chalazal end that developed into the functional megaspore, which underwent mitotic division three times and developed into the mature embryo sac containing seven cells and eight nuclei, and embryo sac development of the Polygonum type. 4) The external morphology of the ‘Zhongqiusucui’ floral buds correlated with the internal developmental stage of the male and female gametophyte. Therefore, the internal developmental progress of the stamen and pistil can be determined by the external morphological characteristics of the floral buds.
Yifan Jiang, Xinlu Chen, Hong Lin, Fei Wang, and Feng Chen
Volatile chemicals emitted from the flowers of chinese wisteria (Wisteria sinenesis) and japanese wisteria (W. floribunda) were collected using a dynamic headspace technique and identified using gas chromatography–mass spectrometry; 28 and 22 compounds were detected from chinese wisteria and japanese wisteria flowers, respectively. These chemicals can be classified into four major classes, including fatty acid derivatives, benzenoids/phenylpropanoids, terpenoids, and nitrogen-containing compounds. Two monoterpenes, (E)-β-ocimene and linalool, belonging to the class of terpenoids, were the most abundant compounds emitted from both species. Despite strong similarity, the floral volatile profiles of the two species displayed variations in both quality and quantity. Chinese wisteria was selected as a model for further study of volatile emission from different parts of flowers, emission dynamics, and regulation of floral scent production. Although floral volatiles were detected from all flower parts, petals emitted the most. The emission of floral volatiles displayed a diurnal pattern with the maximal emissions occurring during the daytime. This rhythmic pattern was determined to be light-dependent. Regulation of floral volatile emission by exogenous chemicals, including silver thiosulphate (an ethylene inhibitor), salicylic acid, and jasmonic acid, also was analyzed. Generally, jasmonic acid promoted the emission of floral volatiles. In contrast, neither silver thiosulphate nor salicylic acid showed a significant effect on floral volatile emission. The results presented in this article suggest that wisteria can serve as a useful system for exploring novel biochemistry of floral scent biosynthesis. They also build a foundation for the study of the biological/ecological significance of floral volatiles on the reproductive biology of wisteria species.
William R. Woodson, Ky Young Park, Paul Larsen, and Hong Wang
The senescence of carnation (Dianthus caryophyllus L.) flower petals is associated with increased synthesis of the phytohormone ethylene. This ethylene serves to initiate and regulate the processes of programmed cell death. We are using molecular approaches to study the regulation of ethylene biosynthesis in various floral organs during development and senescence of flowers. We have isolated and cloned mRNAs which encode the ethylene biosynthetic pathway enzymes s-adenosylmethionine (SAM) synthetase, 1-aminocyclopropane-1-carboxylate (ACC) synthase and the ethylene forming enzyme (EFE) from carnation flower petals. These cDNAs have been used as molecular probes to determine the steady-state mRNA levels of these transcripts in senescing flowers. The increase in ethylene associated with petal senescence is accompanied by a dramatic increase in the abundance of transcripts for both ACC synthase and EFE. In striking contrast, the level of SAM synthetase mRNA decreases significantly with the onset of petal senescence. Genomic DNA Southern blots reveal both ACC synthase and EFE are encoded by multigene families. We have recently isolated several genomic clones from carnation which represent different ACC synthase genes. The structure and organization of these gene will be presented.
Fengxia Shao, Sen Wang, Zhiming Liu, Rongyan Hong, and Tianjiao Zhao
To explore the reasons for seed abortion in southern China fresh-eating jujube, improve its reproductive biology, and provide a theoretical basis for the crossbreeding of jujube, we carried out self-pollination and cross-pollination experiments with Ziziphus jujuba Mill. ‘Zhongqiusucui’ as the female parent. We observed the process of pollen tube growth in pistil and embryo development by fluorescence microscopy and paraffin section methods. The results show there were self- and cross-incompatibilities during pollination and fertilization, and there were no significant differences in pollen germination and pollen tube growth between self-pollination and cross-pollination. It took at least 4 hours for pollen and stigma to recognize each other, 6 hours for pollen to germinate on the stigma, and 12 hours for the pollen tube to penetrate the mastoid cells of the stigma. After 48 hours of pollination, the pollen tube reached one third of the style. The pollen tube remained stagnant 72 to 120 hours after pollination, and remained at one third of the stylar canal. Simultaneously, the pollen tubes on the stigma twisted and interacted with each other, and expanded into a spherical shape. A few pollen tubes reached the ovary and completed fertilization. However, some early globular embryos degenerated before forming into globular embryos and resulted in the formation of empty embryo sacs, which leads to seed abortion. In conclusion, the poor pollination and fertilization, and the blocked development of the embryo resulted in seed abortion in Z. jujuba ‘Zhongqiusucui’.
Yu Hong, D. Creech, Wang Chuanyong, Gu Yin, and He Shanan
The native species of Vaccinium are distributed in both northeast and south of China but more species are in the South. Ecologically, there is a vast territory in the South with acidic soils and plenty of precipitation and warm weather. On the other hand in the northeast regions temperature in winter is usually a problem for cultivated blueberries and protection from freezing is necessary for young plantations. Based on the result of introduction of cultivars, including rabbiteye, southern highbush and lowbush blueberries, in both northern and southern parts in China during the last 2 decades authors suggested that the most prospective regions for blueberry growing could be mostly in south of China. In the between of the two regions the natural ecological conditions are not appropriate for blueberry growing but plantations under plastic film appeared relatively vigorous. 12 rabbiteye blueberry cultivars have been tested in the south and the performance of growth and fruiting are good. It is expected that the average of yield could reach about 15 t·ha–1. The quality of fruits is similar to that of the natives in North America. Up to now there are less insects and diseases damages. It seems that the regions in the south of Changjiang (Yangtze) River provide good conditions for blueberry commercial growing.