Báo cáo lâm nghiệp: "Compartmentation of storage compounds in peach leaves"

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Compartmentation of storage compounds in peach leaves A. Lamant M. Brison 2 2 J.P. Gaudillère A. 1 Moing J. Schaeffer 2chaeffer 2 I Station de Centre de Bordeaux, BP’ 131, 33140 Pont-de-la-Maye, Physiologie V6g6tale, JNRA, and Laboratoire 2 de Biologie et de Physiologie Vegetale, CNRS UA568, Université de Bordeaux /, 33405 Talence Cedex, France Introduction Materials and Methods High leaf photosynthesis is achieved when Plant material Green or red seedlings of Prunus persica L. primary photosynthetic products are ac- Batsch (var. ’G!F305’, green; var. ’Rubira’, red) tively metabolized to avoid inhibition of the were grown in ;a growth chamber (15 h photo- carbon reduction cycle. Two main condi- period, high pressure Na lamps (800 tions must be fulfilled: mineral phospha- 1) J.lM.m- and 25/20°C day-night tempera- 1 s- ’ 2 te must be available (Sivak and Walker, ture). For protoplast preparation, expanding leaves (about 25% of final area) were collected 1986); and 2) osmotic pressure must be 5 h after the beginning of the light period. The regulated at a physiological level (Kaiser first mature leaves used for sugar analysis were et al., 1981Many strategies are found collected at the beginning and at the end of the amount plants. Carbon can be stored as light period. starch in the chloroplast. Sucrose can be stored in the vacuole and soluble polysac- Biochemical analyses charides can be synthesized as fructans. Glucose, sucrose, sorbitol, inositol and a cyano- Sugar transfer from the mesophyll cells genic glucoside, prumasin, were extracted with be very efficient. It can fill storage hot (60°C) ethanol/water (1J1, v/v) and analyzed can by gas-liquid chromatography (Moing et al., compartments in the leaf or be loaded into 1988). Starch was assayed enzymatically the phloem and exported to other parts of (Boehringer, Mannheim). In situ starch was the plant. The study of interactions be- located by iodine staining in intact leaves tween photosynthesis and sink activity bleached with N,A/-dimethyiformamide. (growth and storage) requires detailed information about the movement of carbon Preparation and purification of protoplasts among different chemical fractions and The partially expanded leaves were harvested among different cell types of the leaf. In and surface sterilized. Main veins were re- this way, we examined the distribution of moved. Leaf strips were put into the digestion medium and incubated for 15 h and 25°C on a carbon in peach leaves.
gyratory shaker (Ochatt et al., 1987). The par- The preparation of protoplasts resulted tially digested leaves were filtered through a in 2 main cell types. The smaller proto- nylon net (26 pm). Protoplasts were purified on plasts (diam. !1 pm) came from meso- a Percoll gradient (Robinson and Loveys, phyll tissue, as they contained chlorophyll 1986), after staining of the vacuoles with neutral pigments. They were poorly vacuolated red for protoplasts prepared from green leaves. Large protoplasts were collected at the 80/60% and had large starch granules in chloro- Ficoll interface; small protoplasts bearing chlo- plasts. The large protoplasts (diam. =20 rophyll were collected at the 50/30% Percoll JIm) came from epiderm, as they con- interface. tained anthocyanin pigments if they were isolated from the red peach seedlings. Anthocyanin pigments are typically local- Results ized in leaf epiderm (Thayer and Conn, 1981).Microscopic observation did not reveal chloroplasts or amyloplasts. Pruna- Chemical characterization of storage sin was exclusively contained in epidermal compounds in mature peach leaves cells (Table 111). Conversely, inositol was found in mesophyll cells. Sucrose was The quantitatively most important com- mainly accumulated in epidermal cells and pounds of adult peach leaves are present- sorbitol in mesophyll cells. The number of ed in Table I. These compounds repre- epidermal cells relative to mesophyll cells sented about 40% of the total leaf dry was estimated to be 13% by counting on weight at the end of the light period. Com- leaf cross-sections. Based on this percent- pounds which significantly decreased in age, it was possible to calculate the rela- concentration during the night, have a sto- tive amount of storage compounds be- rage function. Starch and sorbitol were the tween epiderm and mesophyll (Table IV). main carbon storage compounds in these Sucrose and prunasin accumulated in epi- leaves. Sucrose concentration also dermal cells, while starch seemed to be decreased during the night but to a lesser equally distributed. This last result was extent. The other surveyed compounds surprising because electron microscopic had no storage function during this time. observation did not reveal a significant amount of starch in large protoplasts. This cell fraction might have been contam- Distribution of storage compounds inside inated by free starch grains liberated growing leaf a during leaf digestion. By electron micro- scopy, we observed large lipid deposition In growing leaf tissue after 5 h of light, the in both types of cells. But is was not pos- chemical fractions in mature leaf same as sible to quantify specifically this carbon tissue present (Table II). were compartment.
The iodine starch staining of intact phloem loading and translocated as sorbi- tol. The modelling of the distribution of leaves showed that bundlesheath cells stored a large amount of starch which was carbon in these leaves is a difficult task. It must consider the size and the turnover of not taken into account in our analysis. all these compartments. Conclusions References In photosynthetic cells, carbon can be Butt A.D. (1985) A, general method for the high stored as sorbitol, starch and lipids. Car- yield isolation of mesophyll protoplasts from bon can be exported to epiderm and deciduous tree species. Plant Sci. 42, 55-59 stored as prunasin, sorbitol, sucrose and Kaiser W.M., Kaiser G., Prachuab P.K., Wild- lipids or to the bundlesheath and stored man S.G. & Heber U. (1981) Photosynthesis under osmotic stress. Inhibition of photosynthe- mainly as starch. Prunasin, mainly stored sis of intact chloroplasts, protoplasts and leaf in peach leaf epiderm, like dhurrin in sor- slices at high osmotic potential. Planta 153, ghum leaf epiderm (Thayer and Conn, 416-422 1981), decreases in concentration during Matile P. (1987) The sap of plant cells. New leaf growth. It is probably reassimilated as Phytol. 105, 1-26 in seedlings of Hevea (Selmar et al., Moing A., Salessc!s G. & Saglio P.H. (1987) Growth and the composition and transport of 1988). Lastly, carbon can be exported by
Selmar D.R., Lieberei R. & Biehl B. (1988) carbohydrate in compatible and incompatible Mobilization and utilization of cyanogenic glyco- peach/plum grafts. Tree Physiol. 3, 345-354 sides. Plant Physiol. 86, 711-7166 Ochatt S.J., Cocking E.C. & Power J.B. (1987) Sivak M.N. & Walker D.A. (1986) Photosynthe- Isolation, culture and plant regeneration of colt sis in vivo can be limited by phosphate supply. cherry (Prunus avium x laurocerasus) proto- 2 New PhytoL 102, 499-512 plasts. Planta 50, 139-143 S.S. & Conn E.E. (1981) Subcellular Robinson S.P. & Loveys B.R. (1986) Uptake Thayer localization of dhurrin P-glucosidase and and retention of external solutes from the digest hydroxynitrile lyase in the mesophyll cells of medium during preparation of protoplasts. sorghum leaf blades. Plant Physiol. 67, 617-622 Plant Sci. 46, 43-51