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.

'Personalisation' of droplet-vitrification protocols for plant cells: a systematic approach to optimising chemical and osmotic effects.

Although an appropriate cryopreservation protocol is a prerequisite for basic studies and large-scale implementation as well as further cryopreservation studies, the process relies on trial and error. Among the vitrification-based cryopreservation techniques, droplet-vitrification produces high post-cryopreservation recovery. However, the protocol itself cannot solve the problems engaged in plant cryopreservation, prominently due to dehydration with cytotoxic vitrification solutions. This paper proposes a set of treatments to develop droplet-vitrification using a standard procedure associated with additional treatments and alternative vitrification solutions. The proposed standard protocol consists of a progressive preculture with 0.3 M sucrose for 31 h and with 0.7 M for 17 h, loading with vitrification solution C4-35% (17.5 percent glycerol + 17.5 percent sucrose, w/v) for 20 to 40 min, dehydration with vitrification solutions A3-90 percent (37.5 percent glycerol + 15% DMSO + 15 percent EG + 22.5 percent sucrose) for 10 to 30 min or B1-100 percent (PVS3) for 40 to 120 min at room temperature, cooling the samples using aluminum foil strips, rewarming by plunging into pre-heated (40 degree C) unloading solution (0.8 M sucrose) and further unloading for 20 to 60 min, depending on size and permeability of the materials. Using this systematic approach we can identify whether the material is tolerant or sensitive to chemical toxicity and to the osmotic stress of dehydration with vitrification solutions, thus revealing which is the main barrier in solution-based vitrification methods. Based on the sensitivity of samples we can design a droplet-vitrification procedure, i.e. preculture, loading, dehydration with vitrification solutions, cooling and rewarming. Using this approach, the development of appropriate droplet-vitrification protocol is facilitated.

Leaf anatomy and light acclimation in woody seedlings after gap formation in a cool-temperate deciduous forest.

The photosynthetic light acclimation of fully expanded leaves of tree seedlings in response to gap formation was studied with respect to anatomical and photosynthetic characteristics in a natural cool-temperate deciduous forest. Eight woody species of different functional groups were used; two species each from mid-successional canopy species (Kalopanax pictus and Magnolia obovata), from late-successional canopy species (Quercus crispula and Acer mono), from sub-canopy species (Acer japonicum and Fraxinus lanuginosa) and from vine species (Schizophragma hydrangeoides and Hydrangea petiolaris). The light-saturated rate of photosynthesis (Pmax) increased significantly after gap formation in six species other than vine species. Shade leaves of K. pictus, M. obovata and Q. crispula had vacant spaces along cell walls in mesophyll cells, where chloroplasts were absent. The vacant space was filled after the gap formation by increased chloroplast volume, which in turn increased Pmax. In two Acer species, an increase in the area of mesophyll cells facing the intercellular space enabled the leaves to increase Pmax after maturation. The two vine species did not significantly change their anatomical traits. Although the response and the mechanism of acclimation to light improvement varied from species to species, the increase in the area of chloroplast surface facing the intercellular space per unit leaf area accounted for most of the increase in Pmax, demonstrating the importance of leaf anatomy in increasing Pmax.

Reproductive success and distance to conspecific adults in the sparsely distributed tree Kalopanax pictus.

To understand how a sparsely distributed species can maintain viable populations, and with a particular interest in distance-dependent reproductive success, we investigated the ovule survival and the factors that determine the survival for sparsely distributed Kalopanax pictus (Araliaceae) in a temperate forest landscape around the Ogawa Forest Reserve, central Japan. We found 154 potentially mature trees (>20 cm diameter at breast height) in a 600-ha site. The year 2000 was a mass flowering year for K. pictus; 96.8% of the trees examined flowered in that year; however, this was less than half of the trees that flowered in other years. The flowers of K. pictus include protandrous inflorescences, which bloom on individual tress in midsummer when few other tree species bloom. We conducted pollination experiments with out-crossed, self-pollinated, bagged, and control inflorescences. Results suggest that self-pollination is limited, partially by low self-compatibility and partially by protandry. Ovule survival from the flower to the seed stages was not dependent on the temporal flowering density of conspecific adults. The flowering habit and presence of effective pollinators may allow K. pictus to avoid the negative effects of sparse distribution on pollination efficiency. However, ovule survival during the ovary development stage depended on infection by a species-specific fungus, Mycosphaerella acanthopanacis. The fungus damages leaves, and the infection intensity depends on the distance between conspecific K. pictus adults. Thus, an advantage of sparse distribution in K. pictus is disease avoidance, whereas its disadvantages are overcome by pollination efficiency.