Ikuo Furukawa

Radial Variation of Fiber Length Increment in Acacia Mangium

SUMMARY The radial variation of fiber length increment (due to intrusive growth) and its relation with internal and external (climatic) factors were investigated for Acacia mangium trees collected in Indonesia and Malaysia. Wood fiber length and fiber length increment were approximated with respect to the distance from the pith (x) by a logarithmic function and vessel element length by a linear function. The results were y = 0.14 . ln(x) + 0.48, y = 0.0005 . x + 0.20, and y = 0.13 . ln(x) + 0.31, respectively. The radial variation of fiber length was related to the growth rate rather than the age of the cambium. The results of the cross-correlation function between wood fiber length increment and climatic factors showed that fiber lengths responded to changes in precipitation with a time lag of between zero to four months.

Effects of applied gibberellins and uniconazole-P on gravitropism and xylem formation in horizontally positioned Fraxinus mandshurica seedlings

The present study deals with the effects of gibberellins (GA3 GA4) and uniconazole-P, an inhibitor of gibberellin biosynthesis, on negative gravitropism and xylem formation in the stems of horizontally positioned, 2-year-oldFraxinus mandshurica Rupr. var.japonica Maxim. seedlings. Each growth regulator (100 μg) dissolved in 5 μl acetone (50%) was applied to the basal node of the current shoot on May 24, 1995. The same treatment was repeated five times weekly until June 28. Five seedlings were used for each treatment. The seedlings were positioned horizontally 24h after the first application on May 25. Within 5 weeks the horizontal stem of control and GA-treated seedlings exhibited negative gravitropism. In contrast, the application of uniconazole-P inhibited negative gravitropic stem bending. The application of GAs increased the number of gelatinous fibers having thickened cell walls on the upper side of stems. The uniconazole-P application decreased xylem cell formation but did not inhibit the formation of gelatinous fibers. These results indicate that not only the differentiation of gelatinous fibers but also xylem increment is important in the negative gravitropism of horizontally positionedF. mandshurica seedlings. These results also suggest that GAs may be involved in xylem cell :formation rather than the differentiation of gelatinous fibers in this species.

Regulation by uniconazole-P and gibberellins of morphological and anatomical responses of Fraxinus mandshurica seedlings to gravity.

The present study deals with roles of gibberellins (GAs) in gravitropic responses of woody stems of horizontally-positioned, 2-year-old seedling of Fraxinus mandshurica Rupr. var. japonica Maxim. The application of uniconazole-P, an inhibitor of GAs biosynthesis, to stem nodes at various concentrations significantly inhibited not only righting the stems but also wood formation. The application of GAs (GA3 and GA4) in combination with uniconazole-P negated the inhibitory effect of the treatment of uniconazole-P alone. The GAs alone did not affect wood formation, however, both GAs increased wood formation on both the upper and lower sides of horizontal stems with an increase in the concentration of combined uniconazole-P. In all of the seedlings, tension wood was formed on the upper side of stems. The application of uniconazole-P alone at various concentrations did not inhibit the formation of tension wood fibres.

Radial Variation in the size of Axial Elements in Relation to Stem Increment in Quercus Serrata

In Quercus serrata, radial variations of wood fibre length, earlywood vessel element length, and earlywood vessel lumen diameter were investigated and maturation ages of them were estimated using nonlinear segmented regression analysis as proposed by Peszlen (1994). In addition, the age at the maximum point of current annual increment and mean annual increment were estimated by using the Gompertz growth function fitted to the variation of cumulative ring width with ring number from the pith. In the same radial strip, the maturation ages both of wood fibre length and the earlywood vessel element length were similar, and those were close to the ages at the maximum point of current annual increment, whereas the maturation age of earlywood vessel lumen diameter was generally greater, close to the age at the maximum point of mean annual increment. These results indicate that earlywood vessel lumen diameter is the best indicator of the three anatomical properties tested and that a relationship exists between the maturation ages of the size of axial elements and radial stem increment.

Anatomical Variations in the Woody Plants of Arid Areas

Variations in secondary xylem characteristics in 13 xerophytic species growing in an arid sandy region in China are described and compared in detail from an ecological perspective. All species showed similar wood structure (except Haloxylon ammodendron - rayless), obvious growth ring boundaries (except in H. ammodendron, Tamarix mongolica and Zygophyllum xanthoxylon - sometimes discontinuous), ring to semi-ring-porosity, a simple perforation plate, alternate intervessel pitting, non-septate fibres, paratracheal confluent axial parenchyma, helical thickenings and heterocellular rays. However, some quantitative differences in rays and vessels between species were observed. Rays are uniseriate in Salix psammophila, one- to two-seriate in Tamarix mongolica and Hippophae rhamnoides, two- to five-seriate in Ammopiptanthus mongolicus, Lespedeza bicolor, Z. xanthoxylon, Nitraria tangutorum, Elaeagnus angustifolia, and Calligonum mongolicum, and generally four- to ten-seriate in the other three species. This quantitative study of anatomical characteristics revealed that secondary xylem cells have high adaptability to desert conditions. Vessels with small diameter, either solitary or grouped in multiples, very short elements and minute pits are among the responses to demand for greater water transport capacity, and the appearance of such features in the xylem of arid zone species is interpreted as a strategy for conductive safety. T. mongolica and A. mongolicus had narrower vessels and higher vessel frequency than the other 11 species, which could lead to lowered vulnerability and mesomorphy value. Thus it was considered that the anatomical features of T. mongolica and A. mongolicus were more likely to suffer from water stress than those of other species. Fibre length and vessel element length were measured and analysed, with their horizontal variations showing either decreasing, increasing, considerable fluctuation or constant tendency with age. Fibre length is less than 900 µm, which is defined as “short range” according to IAWA Committee classification. There was significant difference both in among-tree and within-tree fibre length and vessel element length except in A. mongolicus.

Relationship between the radial variation of ray characteristics and the stages of radial stem increment in Zelkova serrata

We used ten discs from two Zelkova serrata trees - five discs from each tree at sampling heights of 1, 4, 7, 10, and 13 m above the ground - and investigated the radial variation in ray characteristics, i.e., ray area (cross-sectional area of rays on a tangential section), ray density (number of rays/mm2 on a tangential section), and ray proportion (the percentage of the area occupied by rays on a tangential section) and analyzed the pattern of variation with respect to the three stages (early, middle, and late) of radial stem increment as estimated using the Gompertz growth function. A juvenile-mature pattern of variation was observed in ray area and ray density. Ray area increased in the inner part of stem and fluctuated around a certain value in the outer part of the stem, and ray density decreased in the inner part of stem and tended to be constant in the outer part of the stem. The maturation age of ray density was similar to the age at the boundary between the early and the middle stages of radial stem increment, but ray area and ray proportion did not relate to the stages of radial stem increment.

Synchronized maturation of vessel diameter and ray width in Zelkova serrata.

This study describes radial variation in fibre length, vessel element length, vessel lumen diameter, and ray width (number of cells) in relation to the developmental stages in radial stem increment in Zelkova serrata trees. Maturation age (the age at which the size of the wood elements is stabilized) was compared to the ages at the boundary between the early and middle stages (age t1), and the middle and late stages (age t2) of radial stem increment. The maturation age was estimated by nonlinear segmented regression analysis. Ages t1 and t2 were estimated by the Gompertz growth function. The maturation age for the length of axial elements (wood fibres and vessel elements) was not related to either age t1 or age t2. However, the maturation ages for vessel lumen diameter and ray width were close, and both were related to age t2. This indicates that the maturation of vessel lumen diameter and ray width was synchronized and both were related to the stage of radial stem increment.