Experimental conditions for efficient callus initiation from mangrove plants were investigated. As a source explant, leaf ofBruguiera sexangula was used. Mangrove plant is one of the most famous woody plants which can grow at the salty area. The initiated callus can be a suitable material for the investigation of salt tolerant mechanisms of mangrove plants.Leaf pieces cultured in an Amino Acid medium supplemented with 2 μM 2,4-dichlorophenoxyacetic acid and 2 μMN-(2-chloro-4-pyridyl)-N'-phenylurea at 30 C developed calluses. Microscopic observation suggested that the callus was initiated from the tissue in the vascular bundles in the leaf.We also examined the effect of NaCl on callus initiation and short-term culture of the calluses on the leaves. Callus initiation rate decreased with increasing NaCl concentration higher than 100 mM in the culture media. The medium containing 100 mM NaCl produced the largest callus on the leaf, compared with higher or lower concentrations of NaCl.

Five superior clones of Eucalyptus camaldulensis from in vitro propagation or tissue culture at the Sra Keaw plantation site in the eastern part of Thailand were selected for examining radial variations of anatomical characteristics and specific gravity. The age of the clones was 5 years at harvest. A 9-year-old tree grown from seed in the same site was also investigated. Results were as follows: 1) Mean specific gravity showed significantly different values among the 5 clones and the seedling. 2) Vessel density rapidly decreased in the first 2–4 cm from the pith in the clones and in 5 cm from the pith in the seedling. 3) Fiber lengths of the clones slowly increased from the pith outwards, while that of the seedling rapidly increased. 4) Each clone and the seedling had a different specific gravity and anatomical characteristics. 5) Clones had a narrower juvenile wood zone than the seedling due to the older cambial age of the clones.

We measured radial variation of carbon isotope composition and vessel traits in tree species in seasonally dry forests of Northeast Thailand to explore a more reliable and amenable method of tropical dendrochronology for trees that lack visually detectable and consistent growth rings. Six Dipterocarpaceae species (3 Shorea, 2 Dipterocarpus, and 1 Hopea species) with indistinct or irregular growth rings and teak (Tectona grandis), a species which forms distinct growth rings, were examined. The d 13 C value variations in all species showed annual cyclicity. Dipterocarpaceae species usually marked the lowest values of d 13 C in the middle of the growing season, whereas teak had the lowest values at nearly the end of the growing season. Since the growing season of the species examined almost corresponds to the rainy season in the study area, the d 13 C variation was likely caused by the change in moisture availability. The different variation pattern of teak was attributable to its stronger dependence on 13 C-enriched reserved material early in the growing season. Changes in tree vessel traits for all species examined also showed annual cyclicity. Dipterocarpaceae species showed significant correlation between d 13 C values and vessel measurements. Vessel lumen (mean area, tangential and radial diameter, and proportion of total area) had a negative correlation, whereas vessel frequency showed a positive correlation. The correlations indicated that changes in vessel traits were caused by the seasonal variation of moisture available to the trees. Thus, we concluded that methods using wood anatomy, as well as d 13 C, have great potential for use as tools in tropical dendrochronology within the context of seasonal climate.

Seasonal characteristics of wood formation were investigated using the pinning method in Hopea odorata and Shorea henryana in a natural dry evergreen forest of eastern Thailand. The position of cells having initiated S1-layer formation at the time of pinning was estimated in the zone where cells were directly injured by the pinning and consequently destroyed. The position of cambial initials at the time of pinning was estimated in the zone where cells were indirectly affected by the pinning and continued their physiological activity resulting in the formation of aberrant cells. Traumatic resin canals were occasionally formed in Shorea. These canals were formed after pinning and could, therefore, not record the exact time of the pinning. Diameter growth of both species was greatest in the rainy season and decreased in the dry season.

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