Effets du recépage sur les réserves glucidiques et lipidiques du «faux-vernis du Japon» (Ailanthus glandulosa Desf, Simarubacées)

Les jeunes plants de l'Ailanthus glandulosa sont remarquables par leur précocité à rejeter de souche et à drageonner. L'enlèvement des parties aériennes provoque l'apparition de brins néoformés de diverses origines. Ils peuvent être issus de bourgeons préexistants dans l'hypocotyle, de bourgeons adventifs apparus sur la section de coupe et de bourgeons axillaires des cataphylles présentes sur la base des brins néoformés. Ces brins cataphyllaires s'affranchissent très facilement. Les recépages successifs pratiqués en conditions contrôlées sur des plants de 8 mois provoquent globalement une stimulation de la production de matière sèche du compartiment racinaire. Ce traitement favorise les racines latérales plagiotropes par rapport au pivot. Contrairement à certaines observations réalisées à propos d'autres feuillus, les recépages successifs ont un effet positif sur l'accumulation de réserves glucidiques dans le système souterrain. Ceci est mis en relation avec l'efficacité photosynthétique et les capacités de colonisation de cette essence. Le compartimentage et la qualité des réserves glucidiques et lipidiques sont également modifiés sous l'effet de coupes répétées. Dans ce cas, les racines latérales vont constituer la zone principale d'accumulation de l'amidon, alors que le pivot joue ce rôle chez les plants témoins. La souche devient une zone d'accumulation de sucres solubles. Pour les plants recépés 3 fois, la souche représente également une zone privilégiée d'accumulation de lipides. A 90 j, les brins développés après 3 coupes sont plus riches en lipides que les tiges des plants témoins. Le recépage provoque aussi une augmentation du degré d'insaturation des acides gras totaux. Ceci est particulièrement sensible dans les racines latérales et est dû à une plus grande importance des acides linoléique et linolénique. Après le recépage, le pivot, qui reste toujours pauvre en lipides, montre une prédominance des acides palmitique et stéarique.Effects of cutting back on the carbohydrate and lipid reserves In the tree of heaven (Ailanthus glandulosa Desf, Simaroubaceae). Seedlings of Ailanthus glandulosa show a remarkably early development of stump shoots and suckers. The removal of aerial parts induced the development of shoots of different origins (fig 3). They may originate from pre-existing buds in the hypocotyl, adventitious buds on a cut section, or axillary buds of cataphylls present at the base of the new shoots. These cataphyllary shoots separated from seedlings very easily. After 2 or 3 cuts, seedlings also produced adventitious buds on roots and some started to develop suckers (tables I, II). The 8-month-old seedlings raised under controlled greenhouse conditions were cut back 1, 2 or 3 times (fig 1). Dry weights and nutrient reserves of cut and intact seedlings were determined at 30-d intervals from the first cut. The root system of the seedlings increased in dry weight throughout the successive cuts and the dry weight increase was higher in the lateral roots than in the taproot. At 90 d, the largest increase in the total dry weight was observed in seedlings after 3 cuts. Growth of the collar which then became a stump only occurred in seedlings after 3 cuts (table III). Contrary to some observations concerning deciduous trees, repetitive cutting back had a positive effect on the carbohydrate accumulation in the subterranean system. This result was related to the photosynthetic efficiency and the colonization of this species. The distribution and the quality of the carbohydrate and lipid reserves were also modified by repetitive cuts. At 90 d, the carbohydrates were distributed in similar quantities between the aerial and subterranean parts of intact seedlings (table IV). After 2 or 3 successive cuts, the greater proportion of the starch reserve was then located in the root system. In this case, the lateral roots represented the principal site of starch accumulation whereas the taproot played this role in intact seedlings. The stump mainly accumulated soluble sugars (table IV). In intact seedlings, the level of lipids was higher in the root system than in stems (table V). Cutting back induced a significant decrease in total lipids which occurred in shoots developed after 3 cuts at 30 and 90 d. At the same time, the stump also represented the site of lipid accumulation for cut seedlings (table V). In other areas, cutting back caused an increase in the desaturation of the total fatty acids of the lateral roots, expressed as an increase in linoleic and linolenic acids (table V, fig 4). In contrast, the most important fatty acids in the taproot were palmitic and stearic acids (fig 4)

Testing the branch autonomy theory: a 13C/14C double-labelling experiment on differentially shaded branches

36 ref.absen

Influence of frost damage on the sugars and sugar alcohol composition in quince (Cydonia oblonga Mill.) floral nectar

Cold stress adversely affects growth and productivity, and triggers a series of morphological, physiological, biochemical and molecular changes in plants. Since sugars are present in all floral nectars in greater amounts than any other constituent, the aim of this study was to examine how frost exposure changes sugar metabolism and how it affects on the content of sugar components in the nectar of quince. Three quince cultivars ('Vranjska', 'Triumph' and 'Leskovac. ka') were investigated in this study. The contents of sugars (glucose, fructose, sucrose, trehalose, maltose, isomaltose, rhamnose, arabinose, ribose, melezitose, raffinose, and panose) and sugar alcohols (sorbitol, erythritol, mannitol and galactitol) were analyzed by high performance anion exchange chromatography (HPAEC) with amperometric detection. The results showed that after late spring frosts and irreversible damage of flower parts, the nectar of the three quince cultivars contained elevated levels of fructose, trehalose, arabinose, ribose, rhamnose, raffinose, galactitol and mannitol, indicating an impairment of central carbohydrate metabolism. The ratios between individual sugars, such as the glucose/fructose ratio, were changed in the nectar of damaged flowers in all three quince cultivars. The examined cultivars showed similar sugar response to cold stress. The only exception was 'Leskovac. ka' for the glucose and melezitose pathway, which means that composition of those two sugars changed significantly according to the genotype. The larger are the carbohydrates reserves in different parts of a fruit tree, the higher is the tolerance to any form of frost damage, the results of this study could help in the understanding of how different quince cultivars react to this kind of stress and how they modulate their sugar metabolism