Suppression of growth and death of meristematic tissues in Abies sachalinensis under strong shading: comparisons between the terminal bud, the terminally lateral bud and the stem cambium.

The suppression of apical growth and radial trunk growth in trees under shade is a key factor in the competition mechanism among individuals in natural and artificial forests. However, the timing of apical and radial growth suppression after shading and the physiological processes involved have not been evaluated precisely. Twenty-one Abies sachalinensis seedlings of 5-years-old were shaded artificially under a relative light intensity of 5% for 70 days from August 1, and the histological changes of the terminal bud and terminally lateral bud of terminal leader and the cambial zone of the trunk base were analyzed periodically. In shade-grown trees, cell death of the leaf primordia in a terminal bud of terminal leader was observed in one of the three samples after 56 and 70 days of shading, whereas the leaf primordia in a terminal bud of terminal leader in all open-grown trees survived until the end of the experiment. In addition, the leaf primordia of the terminally lateral buds of terminal leader retained their cell nuclei until the end of the experiment. No histological changes were observed in the cambial cells after shading, but the shade-grown trees had less cambial activity than the open-grown trees through the experiment. Strong shading appeared to inhibit the formation and survival of cells in the terminal bud of terminal leader rather than the terminally lateral buds of terminal leader and the cambium. The suppression of the terminal bud growth and elongation of the surviving lateral buds would result in an umbrella-shaped crown under shade.

Cessation of annual apical growth and partial death of cambium in stem of Abies sachalinensis under intensive shading.

This study evaluated variation in the height at which absent rings and internodes were detected along stem of Abies sachalinensis trees grown under shade for 39 years. Eight sample trees planted in 1974 under a secondary forest in Japan were felled in 2013 and analyzed. A. sachalinensis is a monopodial species in which it is possible to measure annual apical growth using the distinct internodes. We applied microscopic analysis on 154 stem disks from the stem base to the top to evaluate the cessation of apical and radial growth caused by intensive shading. Cessation of apical stem growth for one or more years was found in 6 out of 8 sample trees. We termed this phenomenon as "absent internode". In addition, the absent growth rings were detected more frequently in the lower part of sample stems, and the number of absent rings at the stem base did not correspond with the number of absent internodes in the six trees. From cellular level observation, the five suppressed trees had no living cambial cells at the stem base but had living cells at the stem top. The cessation of the apical and radial growth did not occur synchronously but did occur independently under a shade environment in A. sachalinensis.

Access to Chiral Silicon Centers for Application to Circularly Polarized Luminescence Materials.

Asymmetric arylation of secondary silanes catalyzed by a Pd-chiral phosphoramidite complex was developed for application to low-molecular-weight circularly polarized luminescence (CPL) materials. The asymmetric arylation provided a convenient, efficient synthetic method for a variety of chiral tertiary silanes (2-21), which were key intermediates for preparing the quaternary silicon center. A stepwise, one-pot procedure was used to transform the appropriate aryl iodide to the quaternary silane (22) with good yield and enantioselectivity. Among compounds synthesized in this work, four optically pure tertiary silanes (18-21) were selected to investigate the relationship between the structure and optical properties. Optically pure (S,S)-21 displayed the highest CPL emission with a high fluorescence quantum yield (glum: +0.008, ΦF: 0.42). This simple molecular design provides new strategies for developing small organic CPL dyes.

Differences in drought- and freeze-induced embolisms in deciduous ring-porous plant species in Japan.

MAIN CONCLUSION: Deciduous ring-porous species in Japan shed all of their leaves under severe water stress before large vessels in earlywood are embolized, and embolization take place during winter. Water in deciduous ring-porous species is mainly conducted upward via large earlywood vessels of the current year. Water columns in large vessels are vulnerable to drought-induced and freeze stress-induced embolisms. Although a vulnerability curve can be created to estimate the hydraulic capacity of plants, it remains unclear why the loss of conductivity in potted plants of ring-porous species does not reach 100 % under severe drought stress. In this study, two deciduous ring-porous species in Japan (Kalopanax septemlobus and Toxicodendron trichocarpum) were used to explain the species-specific pattern in the water-conducting pathway of the stem. We monitored and visualized the spatial distribution of xylem embolisms in the stem of K. septemlobus saplings under drought stress and freeze stress using compact magnetic resonance imaging and cryo-scanning microscopy. In addition, we evaluated the water ascent in the stems of both species using a dye uptake method. Although embolisms of large vessels were observed under drought stress and in winter, all leaves were dropped to avoid fatal water loss after embolization of some large vessels. In contrast, all large vessels were embolized in winter. Larger-diameter vessels of latewood in T. trichocarpum tended to function in trees growing in the warm temperate zone. Thus, our results suggest that the unclear curve may be derived from a discrepancy between leaf water potential and actual water potential in the xylem under severe drought stress. The frequency of xylem embolisms in deciduous ring-porous species in Japan mainly depends on the number of freeze-thaw cycles.

Improvement of heme oxygenase-1-based heme sensor for quantifying free heme in biological samples.

We recently reported a novel heme sensor using fluorescently labeled heme oxygenase-1; however, its inherent enzyme activity would be a potential obstacle in quantifying heme in biological samples. Here, we found that mutation of the catalytically important residue, Asp140, with histidine in the sensor not only diminished the heme degradation activity but also increased heme binding affinity. The sensor with a visible fluorophore was also found to be beneficial to avoid background emission from endogenous substance in biological samples. By using the improved heme sensor, we succeeded in quantifying free heme in rat hepatic samples for the first time.

Development of a heme sensor using fluorescently labeled heme oxygenase-1.

Free heme, the protein-unbound form of heme, has both toxic and regulatory effects on cells. To detect free heme at low concentrations, we developed a heme sensor using fluorescently labeled heme oxygenase-1 (HO-1), an enzyme that catalyzes oxidative heme degradation and has a high affinity for heme. The response of the heme sensor is based on the fluorescence quenching that occurs when heme binds to the enzyme. Each of the three fluorescently labeled HO-1s exhibits a 1:1 binding stoichiometry and an absorption spectrum similar to that of the heme complex of the wild-type HO-1. Titration of the labeled proteins with hemin resulted in fluorescence quenching in a hemin concentration-dependent manner, presumably due to an energy transfer from the fluorophore to the heme bound to HO-1. The sensor showed a potent affinity for heme with a dissociation constant in the low nanomolar range and a high selectivity for heme. Based on the linear response of the sensor to heme, we performed a fluorometric microplate assay. The sensor was able to selectively detect free heme but did not respond to heme bound to native hemoglobin. This assay will be a useful tool for determination of free heme in biological samples containing protein-bound heme.

Optimal conditions for visualizing water-conducting pathways in a living tree by the dye injection method.

To elucidate the water-conducting pathways in living trees by the dye injection method, suitable sample preparation procedures are needed. We evaluated quantitatively the properties and concentrations of three dyes (acid fuchsin, basic fuchsin and safranin) widely used for this purpose, and determined the optimal conditions required to avoid artifacts after dye injection into the sap stream of Pieris japonica D. Don. Among the dyes tested, an aqueous solution of acid fuchsin at a concentration of 0.1% or more was the most useful for delineating water movement. In non-transpiring stem segments, the vertical movement of acid fuchsin by capillarity and diffusion from the dye injection site was limited. However, acid fuchsin moved rapidly in the horizontal direction by capillarity and diffusion, and most xylem cells were stained within 2 h. A delay of more than 2 h between dye injection and examination of the tissues greatly reduces the precision of the method. Use of the dye injection method without appropriate, well-defined experimental procedures may give rise to misleading information about the functional water-conducting pathway in living trees.