Ling-Long Kuo-Huang

Bizonoplast, a unique chloroplast in the epidermal cells of microphylls in the shade plant Selaginella erythropus (Selaginellaceae).

Study of the unique leaf anatomy and chloroplast structure in shade-adapted plants will aid our understanding of how plants use light efficiently in low light environments. Unusual chloroplasts in terms of size and thylakoid membrane stacking have been described previously in several deep-shade plants. In this study, a single giant cup-shaped chloroplast, termed a bizonoplast, was found in the abaxial epidermal cells of the dorsal microphylls and the adaxial epidermal cells of the ventral microphylls in the deep-shade spike moss Selaginella erythropus. Bizonoplasts are dimorphic in ultrastructure: the upper zone is occupied by numerous layers of 2-4 stacked thylakoid membranes while the lower zone contains both unstacked stromal thylakoids and thylakoid lamellae stacked in normal grana structure oriented in different directions. In contrast, other cell types in the microphylls contain chloroplasts with typical structure. This unique chloroplast has not been reported from any other species. The enlargement of epidermal cells into funnel-shaped, photosynthetic cells coupled with specific localization of a large bizonoplast in the lower part of the cells and differential modification in ultrastructure within the chloroplast may allow the plant to better adapt to low light. Further experiments are required to determine whether this shade-adapted organism derives any evolutionary or ecophysiological fitness from these unique chloroplasts.

Altitudinal variation of resin ducts in Pinus taiwanensis Hayata (Pinaceae) needles

The variation of resin ducts in needles of Pinus taiwanensis along an altitude gradient (700 m- 3,100 m) in central Taiwan is revealed for the first time in this study, including position type, number, size, arrangement pattern and anatomical structural variation. Three types of resin ducts-medial, external and septal-were found according to their relative positions in the mesophyll. All needles sampled showed combinations of these three resin duct types. Mostly, 3-7 resin ducts were found in the mesophyll per needle, and the number of resin ducts was significantly greater at mid altitudes than at high and low altitudes. Septal ducts decreased in number with an increase in altitude; however, needles from mid altitudes had more external ducts. Eight patterns (basic and patterns I-VII) of resin ducts in the mesophyll of needles were delineated to present the arrangement variations. In addition to the primary ducts found in the mesophyll, we found the rare bundle sheath ducts in some needles, and their frequencies decreased obviously with an increase in altitude. The consistent combination feature of medial, external, and septal ducts in needles of P. taiwanensis from Taiwan could be easily distinguished from those with medial ducts from mainland China. However, this difference has unrecognized before, and it should be considered in future taxonomic work.

Deep simple epicotyl morphophysiological dormancy in seeds of two Viburnum species, with special reference to shoot growth and development inside the seed

BACKGROUND AND AIMS In seeds with deep simple epicotyl morphophysiological dormancy, warm and cold stratification are required to break dormancy of the radicle and shoot, respectively. Although the shoot remains inside the seed all winter, little is known about its growth and morphological development prior to emergence in spring. The aims of the present study were to determine the temperature requirements for radicle and shoot emergence in seeds of Viburnum betulifolium and V. parvifolium and to monitor growth of the epicotyl, plumule and cotyledons in root-emerged seeds. METHODS Fresh and pre-treated seeds of V. betulifolium and V. parvifolium were incubated under various temperature regimes and monitored for radicle and shoot emergence. Growth of the epicotyl and cotyledons at different stages was observed with dissecting and scanning electron microscopes. KEY RESULTS The optimum temperature for radicle emergence of seeds of both species, either kept continuously at a single regime or exposed to a sequence of regimes, was 20/10 °C. GA(3) had no effect on radicle emergence. Cold stratification (5 °C) was required for shoot emergence. The shoot apical meristem in fresh seeds did not form a bulge until the embryo had grown to the critical length for radicle emergence. After radicle emergence, the epicotyl--plumule and cotyledons grew slowly at 5 and 20/10 °C, and the first pair of true leaves was initiated. However, the shoot emerged only from seeds that received cold stratification. CONCLUSIONS Seeds of V. betulifolium and V. parvifolium have deep simple epicotyl morphophysiological dormancy, C(1b)B (root)-C(3) (epicotyl). Warm stratification was required to break the first part of physiological dormancy (PD), thereby allowing embryo growth and subsequently radicle emergence. Although cold stratification was not required for differentiation of the epicotyl--plumule, it was required to break the second part of PD, thereby allowing the shoot to emerge in spring.

Biomechanical modeling of gravitropic response of branches: roles of asymmetric periphery growth strain versus self-weight bending effect

Bending movement of a branch depends on the mutual interaction of gravitational disturbance, phototropic response, and gravitropic correction. Four factors are involved in gravitropic correction: asymmetric growth strain, eccentric growth increment, heterogeneous longitudinal elasticity (MOE), and initial radius which are associated with reaction wood production. In this context, we have developed a simplified model to calculate the rate of curvature change by combination of these factors. Experimental data from Taiwan red cypress were used to test the validity of the model. Our results show clearly that asymmetric growth strain is the main factor involved in correction. Eccentric growth increment has positive efficiency and increases correction in addition to growth strain, while the total effect of longitudinal MOE variation has negative efficiency and decreases correction. Spring-back strain measurement is found to be useful for the measurement of self-weight bending moment of branch. The branches studied are essentially close to a biomechanical equilibrium which maintains branches in horizontal positions. In the case of a deciduous dicotyledonous tree, flamegold, the effect of defoliating behavior on measured growth strain and curvature change was formulated by a modified model. Growth strain is the sum of measured growth strain after defoliation and spring-back strain during defoliation. The curvature change can be calculated by using measured growth strain and spring-back strain after defoliation. These results show that full-leaf branches of flamegold have a tendency to bend downward, but defoliated branches have a tendency for upward bending. The efficiency of correction increased after defoliation due to weight loss.

Growth stresses and related anatomical characteristics in coconut palm trees

The surface growth strains and the distribution of internal stresses in woody palms, coconut (Cocos nucifera L.), were determined by measuring the strains released by the kerf method using strain gauges. Measurements of the surface strains showed that longitudinal tensile stresses existed at the cortex, while longitudinal compressive stresses existed at the periphery of the central cylinder. These stresses may be generated from the fibers located in the scattered fiber and vascular bundles. In the central cylinder of narrow and wide trunks, both positive and negative stresses were observed, indicating the existence of some tensile and compressive stresses in the trunks. The amount of stress varied from base to top and from periphery to core because of the variation in proportion of the vascular bundles and the fibers, and the cell wall layers of fibers along these points. Furthermore, changes in the angle of vascular bundles and of the fiber microfibrils were correlated with the various tensile and compressive stresses located in the central cylinder of the trunks.

GROWTH STRAINS AND RELATED WOOD STRUCTURES IN THE LEANING TRUNKS AND BRANCHES OF TROCHODENDRON ARALIOIDES - A VESSEL-LESS DICOTYLEDON

Leaning trunks and branches of Trochodendron aralioides Sieb. & Zucc., a primitive vessel-less dicotyledon, show increased radial growth and gelatinous fibers on the upper side similar to the features found in dicotyledons with vessels. The patterns of peripheral longitudinal growth strain are variable among trees but similar at different heights within the same leaning trunk. Growth strains on the lower side of the trunks are very small but they are relatively large on the lower side of the branches. Growth stress in the branches is partly affected by the gravitational bending stress, which would be exerted mostly on the lower side. Large spring back strains of branches are associated with large surface strains. Both the microfibril angle (MFA) and the percentage area of gelatinous fiber show positive relationships with the measured strains. The MFA of the S2 wall layer in tracheids in the opposite wood is 24.6 ± 2.2°, whereas the MFA of gelatinous layer in the tension wood is only 14.2 ± 2.7°. The difference of MFA between the gelatinous fibers and the opposite wood is one of the factors accounting for the large contracting force for reorientation.

Deep simple morphophysiological dormancy in seeds of the basal taxad Cephalotaxus

Although mature seeds of the monogeneric conifer family Cephalotaxaceae sensu stricto have underdeveloped embryos, no definitive studies have been done to classify dormancy in this family. Our primary purpose was to determine the kind of dormancy in seeds of Cephalotaxus wilsoniana and to put the results into a broad phylogenetic context for gymnosperms. The species is of horticultural and medicinal value, and information is needed on how to propagate it efficiently from seeds. Embryo growth and germination were monitored for seeds at warm, cold and warm plus cold temperatures, and germination was monitored for seeds subjected to: (1) cold rn warm rn cold rn warm; and (2) warm rn cold rn warm rn cold rn warm temperature sequences. The effects of gibberellic acids GA3 and GA4 were tested on radicle emergence in ungerminated seeds and on shoot emergence in root-emerged seeds. Germination was promoted byngn36 weeks of warm stratification followed byngn8 weeks of cold stratification, but only if seeds were returned to high temperatures. The underdeveloped embryo must increase in length by g120% before the radicle emerges. Neither GA3 nor GA4 was effective in promoting radicle emergence; however, both plant growth regulators increased rate (but not percentage) of shoot emergence in root-emerged seeds. We conclude that seeds of C. wilsoniana have the deep simple level of morphophysiological dormancy (MPD), C1b-C3-B1b; thus, warm stratification followed by cold stratification and then warm-temperature incubation are required for germination. In gymnosperms, MPD is known in cycads, Ginkgo and now in three families of conifers.

Anatomical characteristics of the secondary phloem in branches of Zelkova serrata Makino

The properties and tissue compositions of reaction wood in the leaning trunks or branches of trees have been extensively investigated, but studies on the influence of the related reaction on the secondary phloem are few and incomplete, in this work, formation of the vascular and cork cambium and the secondary phloem in the upper and lower sides of branches of Zelkova serrata Makino were studied. Vascular cambium is formed first in the second internode of shoot. In the third internode, cork cambium began to initiate subepidermally, meanwhile two to four layers of grouped gelatinous fibers were first found in the cortex outside of all the primary phloem. Gelatinous fibers were also found in both the secondary xylem and secondary phloem. The leaning branches exhibited pronounced radial secondary growth promotion to the upper side, and the reaction wood formed eccentrically. The secondary phloem formed layers of conducting sieve elements alternately with gelatinous fibers. Comparing the secondary phloem in the upper side (reaction phloem) of the branches with that in the lower side (opposite phloem), there is no obvious difference in thickness. Nevertheless, it was found that in the cross sections, the gelatinous fibers formed earlier, and there were more continuous cell senates and a much larger area ratio in the upper side. Besides, the sieve tubes in the upper side of secondary phloem were longer and wider and possessed a very horizontally-orientated sieve plate between two sieve elements. These features may imply that, in branches of Zelkova serrata, the secondary phloem of the upper side (reaction phloem) may have a higher translocation efficiency.

Revealing the Functions of the Transketolase Enzyme Isoforms in Rhodopseudomonas palustris Using a Systems Biology Approach

Background Rhodopseudomonas palustris (R. palustris) is a purple non-sulfur anoxygenic phototrophic bacterium that belongs to the class of proteobacteria. It is capable of absorbing atmospheric carbon dioxide and converting it to biomass via the process of photosynthesis and the Calvin–Benson–Bassham (CBB) cycle. Transketolase is a key enzyme involved in the CBB cycle. Here, we reveal the functions of transketolase isoforms I and II in R. palustris using a systems biology approach. Methodology/Principal Findings By measuring growth ability, we found that transketolase could enhance the autotrophic growth and biomass production of R. palustris. Microarray and real-time quantitative PCR revealed that transketolase isoforms I and II were involved in different carbon metabolic pathways. In addition, immunogold staining demonstrated that the two transketolase isoforms had different spatial localizations: transketolase I was primarily associated with the intracytoplasmic membrane (ICM) but transketolase II was mostly distributed in the cytoplasm. Comparative proteomic analysis and network construction of transketolase over-expression and negative control (NC) strains revealed that protein folding, transcriptional regulation, amino acid transport and CBB cycle-associated carbon metabolism were enriched in the transketolase I over-expressed strain. In contrast, ATP synthesis, carbohydrate transport, glycolysis-associated carbon metabolism and CBB cycle-associated carbon metabolism were enriched in the transketolase II over-expressed strain. Furthermore, ATP synthesis assays showed a significant increase in ATP synthesis in the transketolase II over-expressed strain. A PEPCK activity assay showed that PEPCK activity was higher in transketolase over-expressed strains than in the negative control strain. Conclusions/Significance Taken together, our results indicate that the two isoforms of transketolase in R. palustris could affect photoautotrophic growth through both common and divergent metabolic mechanisms.

Insecticidal action of mammalian galectin-1 against diamondback moth (Plutella xylostella).

BACKGROUND Previous studies showed that mammalian galectin-1 (GAL1) could interact with chitosan or chitin, one component of the peritrophic membrane (PM). This finding suggests that the PM could be a target of GAL1, which prompted the authors to explore the effect of GAL1 on larval growth and its potential mechanism. RESULTS The development of Plutella xylostella (L.) larvae was significantly disturbed after they were fed recombinant GAL1. The histochemical structure and immunostaining pattern suggested that GAL1 treatment resulted in dose- and time-dependent disruption of the microvilli and abnormalities in these epithelial cells. Ultrastructural studies showed that the PM was not present in the midgut of GAL1-treated insects; instead, numerous bacteria were found in the lumen area. These results indicate that the protective function of the PM was disrupted by GAL1 treatment. Moreover, in vitro data showed that GAL1 interacts with chitosan/chitin in a dose-dependent manner, and also specifically binds to the PM in vitro. CONCLUSION In view of the fact that the carbohydrate recognition domain of GAL1 recognises the structural motif N-acetyl lactosamine (Gal beta 1-4 GlcNAc), which is similar to that of chitin (beta-1,4 N-acetyl-D-glucosamine), it is proposed that the insecticidal mechanism of GAL1 involves direct binding with chitin to interfere with the structure of the PM.