Christian Jay-Allemand

Formation of heartwood substances in the stemwood of Robinia pseudoacacia L. II. Distribution of nonstructural carbohydrates and wood extractives across the trunk

SummaryThe distributions of reserve carbohydrates and of three dominant heartwood extractives were determined in the trunkwood of Robinia pseudoacacia L. The trees were cut at different times of the year (September, November, January, and April). With the exception of the tree felled in January, all trunks exhibited highest contents of nonstructural storage carbohydrates (glucose, fructose, sucrose, and starch) in the youngest, outermost sapwood zone. With increasing depth of the trunk, the levels of carbohydrates decreased. At the sapwood-heartwood transition zone, only trace amounts of nonstructural carbohydrates were present. The heartwood itself contained no storage material. The wood zones of different ages of the trees cut in September, November, and January exhibited glucose/fructose ratios of approximately 1. In April, however, there was a shift to glucose. In the youngest sapwood the amounts of soluble sugars were higher in the earlythan in the latewood. Older zones of the sapwood and the sap-wood-heartwood transition zone showed the opposite behaviour. Three main wood extractives of Robinia were characterized and quantified: the flavanonol dihydrorobinetin (DHR), the flavonol robinetin (ROB) and a hydroxycinnamic acid derivative (HCA). Only DHR was present — in very low amounts — in the younger sapwood of all trunks investigated. Higher amounts (>1 μmol/g dry weight) of this compound and the HCA were present in the sapwood-heartwood transition zone. DHR augmented within the heartwood up to a more or less constant level. HCA increased towards the heartwood and decreased again in the inner heartwood parts. ROB appeared in the innermost parts of the sapwood-heartwood transition zone and reached maximum values in older parts of the heart-wood. The results indicate that starch is hydrolyzed at the sapwood-heartwood boundary and thus represents a primary major source of hydroxycinnamic acid and flavonoid synthesis.

Natural wood colouring process in Juglans sp. (J. nigra, J. regia and hybrid J. nigra 23 ×J. regia) depends on native phenolic compounds accumulated in the transition zone between sapwood and heartwood

Abstract Radial distribution of soluble phenolics was investigated at different heights in stems of Juglans nigra, J. regia and hybrids J. nigra 23 × J. regia. Four major phenolic compounds were studied: hydrojuglone glucoside (HJG), quercitrin (QUER) and two unknown compounds characterized as two ellagic acid derivatives E1 and E2. HJG and E1 content increased gradually in the sapwood, peaked in the sapwood-heartwood transition zone, and decreased drastically in the heartwood. QUER was accumulated preferentially around the transition zone, and its content was relatively low in the outer part of the sapwood and in the inner part of the heartwood. E2 content was low in the sapwood and increased in the heartwood. The heartwood formation was marked by the accumulation of new soluble compounds. The relationship between wood extractives and wood colour were evaluated and discussed. HJG was considered to be a major precursor of heartwood colour providing chromophores through hydrolysis (deglucosylation), oxidation and polymerization processes.

Root development of in vitro hybrid walnut microcuttings in a vermiculite-containing gelrite medium

Abstract Quantitative and qualitative improvements in root development have been obtained in six clones of hybrid walnut trees propagated by tissue culture and selected for multiplication and rooting abilities. A mixture of diluted gelified medium (DKW, macroelements 1 4 ) and vermiculite, used in the proportions 250 200 (v/v), strongly promoted root elongation (two to seven-fold) and the development of secondary roots of induced shoots (IBA 24.6 μM) after 2 weeks of culture. Furthermore, rooting rates were enhanced (from 15 to 50%) and the number of primary roots per rooted explant was from two to six-fold higher. Distilled water added to vermiculite always gave the poorest rooting. Vermiculite promoted penetration and aeration of the roots more than gelrite alone, and its effect was better than that of perlite. This procedure resulted in 80–100% rooting for five hybrid clones.

Transcription Factor Networks. Pathways to the Knowledge of Root Development

Plants are bipolar organisms in which the apical part generates vegetative and reproductive organs and the basal part generates the root system. Roots perform a variety of biological functions. They keep the plant upright but are also the site of nutrient and water uptake and constitute important

Expression of antisense chalcone synthase RNA in transgenic hybrid walnut microcuttings. Effect on flavonoid content and rooting ability

Walnut somatic embryos (Juglans nigra × Juglans regia) were transformed with a vector containing a neomycin phosphotransferase II, a β-glucuronidase and an antisense chalcone synthase (chs) gene. This antisense construct included a 400 bp cDNA fragment of a walnut chs gene under the control of the duplicated CaMV-35S promoter. Molecular, biochemical and biological characterizations were performed both on transformed embryos propagated by secondary somatic embryogenesis and on microshoots developed by in vitro culture of embryonic epicotyls from somatic embryos. Thirteen transformed lines with the vector containing the antisense chs gene, one line with only the gus and nptII genes and one untransformed line were maintained in tissue culture. Six of the antisense lines were shown to be flavonoid-deficient. They exhibited a strongly reduced expression of chs genes, very low chalcone synthase activity and no detectable amounts of quercitrin, myricitrin, flavane-3-ols and proanthocyanidins in stems. Rooting tests showed that decreased flavonoid content in stems of antisense chs transformed lines was associated with enhanced adventitious root formation. Free auxin and conjugated auxin contents were determined during the latter phase of the micropropagation, and no variations were detected between control and antisense chs transformed lines. The in vitro plants developed a large basal callus and apical necrosis upon auxinic induction and the transformed lines highly deficient in flavonoids were more sensitive to exogenous application of indolebutyric acid (IBA).

Hypaphorine accumulation in hyphae of the ectomycorrhizal fungus, Pisolithus tinctorius

Tryptophan betaine or hypaphorine, is the major indolic compound detectable in free-living hyphae of the ectomycorrhizal fungus, Pisolithus tinctorius. Hypaphorine could not be detected in five other ectomycorrhizal species.

Cuttings of the non-rooting rac tobacco mutant overaccumulate phenolic compounds

The auxin and phenolic contents, as well as phenylalanine ammonia-lyase (PAL) activity, were determined in in vitro cultured shoots of the recalcitrant-to-root rac mutant of tobacco, and compared with wild-type shoots. The mutant and wild-type shoots showed similar auxin changes during the culture cycle, but with higher contents for the mutant. A transient peak of auxin (corresponding to the achievement of the rooting inductive phase) occurred at day 14 in both types of shoots, but earlier in the basal parts of the wild-type stems. The rac shoots contained more phenolics, corresponding with an increased PAL activity. The most abundant phenolic compound found in the two types of tobacco was chlorogenic acid, which was more abundant in the rac shoots. Rutin was also detected at a higher concentration in the mutant shoots. Basal parts of wild-type shoots treated with 10-3 M chlorogenic acid reacted by accumulating auxins and, unlike untreated controls, did not form adventitious roots. The relationships between these biochemical analyses in relation to the growth limitation of the rac mutant, and the inhibition of its root development, are discussed.

Mechanisms of primordium formation during adventitious root development from walnut cotyledon explants

Abstract. In walnut (Juglans regia L.), an otherwise difficult-to-root species, explants of cotyledons have been shown to generate complete roots in the absence of exogenous growth regulators. In the present study, this process of root formation was shown to follow a pattern of adventitious, rather than primary or lateral, ontogeny: (i) the arrangement of vascular bundles in the region of root formation was of the petiole type; (ii) a typical root primordium was formed at the side of the procambium within a meristematic ring of actively dividing cells located around each vascular bundle; (iii) the developing root apical meristem was connected in a lateral way with the vascular bundle of the petiole. This adventitious root formation occurred in three main stages of cell division, primordium formation and organization of apical meristem. These stages were characterized by expression of LATERAL ROOT PRIMORDIUM-1 and CHALCONE SYNTHASE genes, which were found to be sequentially expressed during the formation of the primordium. Activation of genes related to root cell differentiation started at the early stage of primordium formation prior to organization of the root apical meristem. The systematic development of adventitious root primordia at a precise site gave indications on the positional and biochemical cues that are necessary for adventitious root formation.

Modifications of hybrid Walnut (Juglans nigra 23 x Juglans regia) wood colour and phenolic composition under various steaming conditions

Summary The effects of steaming were studied on Walnut wood from a hybrid (Juglans nigra 23 × J. regia) tree in terms of wood colour and phenolic composition. Wood samples were subjected to treatments at 75, 100 and 125°C for 4, 8, 16 and 24 hours. Colour changes were measured in the CIELCh colour system and phenolics were characterized and quantified by means of HPLC. Steaming mainly resulted in a darkening of wood tissues. Colour changes increased as temperature increased from 75 to 125°C. Lightness L* gradually decreased from 0 to 24 h at 75°C, whereas with higher temperatures, most of the darkening occurred within the first 4 hours of exposure. Contrast in colour, between sapwood and heartwood in particular, could be reduced by steaming at 125°C. The best steaming treatment, leading to a colour of steamed sapwood close to that of natural heartwood, was at 100°C/16 h. Hydrojuglone glucoside (HJG), ellagic and gallic acid derivatives (E1, E2 and G respectively) were gradually degraded by steaming, whereas a new flavonol (F) and oxidation products (OP) increased. Relationships between wood colour and phenolic content are discussed.

Histological investigation of walnut cotyledon fragments for a better understanding of in vitro adventitious root initiation

SummaryRapid formation of adventitious roots by walnut cotyledon fragments in vitro was traced by light microscopy. It was shown that this plant model is characterized by two major developmental processes: a) confined elongation of the cotyledon petiole caused by a limited number of cell divisions and b) formation of a morphogenetic zone around each initially wounded vascular bundle within 36 h after detachment of the embryonic axis. During the first phase of development, granular storage protein bodies dissolved, and starch grains were deposited mainly in the distal portion of the cotyledon fragments. Rapidly, new globular protein bodies were formed, and phenolic inclusions accumulated in the vacuoles of epidermal and subepidermal cells and of individual cells close to the vascular bundles. Each adventitious root was found to be in continuity with a single vascular bundle of the cotyledon petiole. A short auxin treatment suppressed the formation of large roots and induced numerous tiny rootlets dispersed all over the surface of the cotyledons.