Sucrose suppression of chlorophyll synthesis in carrot tissue cultures: The role of invertase

Summary Free space invertase activities were determined in carrot callus strains CRT1 and CRT2 grown under conditions in which sucrose suppression of chlorophyll synthesis occurred in CRT1 but not CRT2. CRT2 possessed a high free space acid invertase activity (pH optimum 5.0 K_m for sucrose 3.1×10^-3M) while CRT1 lacked this enzyme. [U-¹⁴C] sucrose introduced into the free space of calluses was rapidly inverted by CRT2, but not by CRT1.Despite their different invertase levels, CRT1 and CRT2 showed similar sucrose uptake rates and took up [U-¹⁴C-glucosyl] sucrose and [5-T-glucosyl] sucrose from external bathing media essentially without prior inversion.It is concluded that acid invertase in callus tissue relieves the suppression of chlorophyll synthesis caused by sucrose in the free space. The invertase may in some circumstances hydrolyse sucrose before uptake, but is not an essential part of the sucrose uptake mechanism in carrot tissue cultures.     

Sucrose Suppression of Chlorophyll Synthesis in Carrot-Tissue 2: THE EFFECT OF COMPOSITION OF THE CULTURE MEDIUM

Sucrose (but not other sugars) suppresses chlorophyll synthesisin a carrot-callus strain grown on a medium on which free-spaceinvertase does not develop (Heller's mineral elements, thiamine0.1 mg/1, IAA 0.01 mg/1, sucrose 3 per cent). This suppression was not caused by trace contaminants in sucroseor by the lack of available iron in the medium. Suppressionof chlorophyll synthesis by sucrose was reversed by transferof growing tissue to a medium on which high free-space invertaseactivity developed (Murashige and Skoog mineral elements, White'svitamins, 2, 4-D 0.05 mg/1, sucrose 3 per cent). Feeding of porphyrin precursors, and tests of Krebs cycle function,were employed in an attempt to locate the sucrose-inhibitedstep in chloroplast biogenesis.     

Sucrose Suppression of Chlorophyll Synthesis in Tissue Culture: Changes in the Activity of the Enzymes of the Chlorophyll Biosynthetic Pathway

Chlorophyll synthesis in carrot root tissue cultures grown ona medium containing sucrose is inhibited. Examination of theactivities of the first enzymes in the chlorophyll biosyntheticpathway shows that the major effect of sucrose upon chlorophyllsynthesis occurs at the stage controlling 5-aminolevulinic acid(ALA) synthesis. The toxic nature of ALA in this tissue precluded its use toalleviate the sucrose inhibition effect but the utilizationof various other precursors for chlorophyll synthesis was consistentwith a block occurring at the level of ALA synthesis. The activities of other enzymes involved in chlorophyll synthesisdecreased in activity paralleling decreases in chlorophyll amount.These latter changes are thought to result as a consequenceof chloroplast degeneration rather than representing a primecause in the loss of greening.     

Influence of exogenous sucrose on the greening of oat

The greening of roots and leaves has been studied in whole oat seedlings grown on White's medium either with or without 2% sucrose. The added nutrient promotes chlorophyll synthesis and chloroplast differentiation in the roots. Yet it manifests a negative effect in the foliar tissues where it accelerates the decline in chlorophyll as well as the chloroplast ultrastructural alterations usually associated with senescence. The negative effect of the nutrient in the leaves is probably a consequence of the addition of exogenous sucrose to the endogenous sugars produced by photosynthesis. The foliar tissues would therefore be in the presence of high sucrose concentrations, which are known to be harmful for the photosynthetic apparatus. SDS-PAGE analysis of thylakoid polypeptides from root and leaf chloroplasts has revealed organ-specific differences in the electrophoretic patterns.     

Characteristics of Photosynthate Partitioning during Chloroplast Development in Avena Leaves

The first leaves (40 millimeters long) of 4-day-old light-grown Avena sativa L. cv Victory I seedlings contained a complete age sequence of cells from the base to the tip, and within these tissues all stages of chloroplast development could be observed. Although chloroplasts underwent progressive development, a marked increase in number of thylakoids per granum, in chloroplast volume, and in chlorophyll content occurred in the region between 20 and 30 millimeters from the base. Photosynthetic CO₂ fixation (per unit chlorophyll) increased markedly during chloroplast development and closely followed structural changes in chloroplasts. It was also found that the partitioning of photosynthates differed greatly in the segment from 30 to 40 millimeters (at the tip of the leaf) compared with the segment nearer to the leaf base, although both total ¹⁴CO₂ fixation and chlorophyll content per segment did not change significantly along the length of the leaves. As the thylakoid system reached full maturation, partitioning of photosynthates into sucrose increased but partitioning decreased into starch, lipids, and phosphorylated intermediates.     

Biosynthesis of Sulfoquinovosyldiacylglycerol in Higher Plants: The Incorporation of SO(4) by Intact Chloroplasts in Darkness

Intact spinach chloroplasts incorporated ³⁵SO₄²⁻ into sulfoquinovosyldiacylglycerol in the dark at rates equivalent to those previously reported for illuminated chloroplasts provided that either ATP itself or an ATP-generating system was added. No additional reductant was necessary for SQDG synthesis by chloroplasts. The optimal concentration of ATP was between 2 and 3 millimolar. Rates of synthesis up to 2.6 nanomoles per milligram chlorophyll per hour were observed. UTP, GTP, and CTP could not substitute for ATP. Incubation of UTP with ATP (1:1) stimulated synthesis of sulfoquinovosyldiacylglycerol. No additional stimulation of the reaction was observed upon addition of other nucleoside triphosphates with ATP. For the generation of ATP in the chloroplast, addition of dihydroxyacetone phosphate alone did not promote synthesis of sulfoquinovosyldiacylglycerol, but in combination with inorganic phosphate and oxaloacetate, rates of synthesis up to 3.2 nanomoles per milligram chlorophyll per hour were observed. Dark synthesis was optimal in the presence of 2 millimolar dihydroxyacetone phosphate, 2 millimolar oxaloacetate, and 1 millimolar KH₂PO₄.     

Identification of the primary lesion in a protoporphyrin accumulating mutant of Chlamydomonas reinhardtii

Summary A group of chlorophyll deficient mutants (br _s mutants) of Chlamydomonas accumulates protoporphyrin and has poorly developed chloroplast membrane systems (Wang et al. 1974). In order to determine whether a poorly developed chloroplast membrane system is the reason for, or the result of, the inability of the br _s mutants to metabolize protoporphyrin to chlorophyll, a second mutation was selected which restored chlorophyll synthesis in br _s mutants. One such double mutant (br _s-2 g-4) was analyzed. The double mutant br _s-2 g-4 has partially restored chlorophyll synthesis, but has defective photosystem II and photosystem I electron transport as well as abnormal chloroplast ultrastructure. Since these defects are not present in cells carrying only the g-4 mutation, they are presumed to be caused by the br _s-2 mutation. It is concluded that a defect in chloroplast membrane development resulting from the br _s-2 mutation causes an apparent defect in magnesium chelation by protoprophyrin. This is consistant with evidence that chlorophyll biosynthesis from magnesium protoporphyrin to chlorophyll takes place on the chloroplast membranes.     

Chloroplast Integrity and ATP-Dependent CO(2) Fixation in Spinacia oleracea

Washed whole chloroplasts of Spinacia oleracea isolated and assayed in a tris (hydroxymethyl aminomethane)-HCl buffered sucrose solution exhibited low dark CO₂ fixing activity, whereas washed whole chloroplasts isolated in the same buffer but assayed in that buffer without sucrose exhibited much greater dark CO₂ fixing activity. The lowered activity could be attributed to the impermeability of the chloroplast membrane to ribose-5-phosphate or adenosine triphosphate. The preservation of the integrity of the chloroplast membrane, as reflected by its impermeability to either or both of the abovementioned compounds, was measured by the fixation of ¹⁴CO₂ into acid-stable products in the presence of ribose-5-phosphate and adenosine triphosphate by the whole chloroplast as compared with fixation by the chloroplast extract. An effect (i.e., apparent resistance to the passage of ribose-5-phosphate or adenosine-5-triphosphate into the chloroplast) similar to, but less pronounced than, that produced by the presence of sucrose in the isolation medium was observed upon the addition of MnCl₂ or CaCl₂ to the buffered sucrose isolation medium. The addition of KCl enhanced slightly the effect produced by addition of sucrose alone to the isolation medium. The presence of MgCl₂ in the isolation medium, however, either caused the chloroplasts to become leaky or more fragile since more of the activity of the carboxylative phase enzymes appeared in the cytoplasm. When a mixture of all of the metal ions was added to the buffered sucrose suspending medium, the chloroplasts exhibited the same response observed with MgCl₂ alone. The addition of ethylene diaminetetraacetate or dithiothreitol appeared to alter the permeability of the chloroplast membrane nonspecifically when the assay was conducted in the absence of sucrose. Specific activities (μmoles CO₂ fixed/mg chlorophyll × hr) as high as 329.6 have been observed for dark fixation by chloroplasts. The phosphoenolpyruvate carboxylase activity in the chloroplasts was only one-seventh that of ribulose diphosphate carboxylase. The phosphoenolpyruvate carboxylase activity in the cytoplasm was 5 times that of the chloroplasts.     

Iron nutrition-mediated chloroplast development

Membrane development in chloroplasts was explored by resupplying iron to iron-deficient sugar beet (Beta vulgaris L. cv F58-554H1) and monitoring changes in lamellar components during regreening. The synthesis of chlorophyll a, chlorophyll b, and Q, the first stable electron acceptor of photosystem II, exhibited a lag phase during the first 24 to 48 hours of resupply. In contrast, the per area amounts of P₇₀₀ and cytochrome f increased linearly over the first 48 hours. During the early regreening period, the Q to P₇₀₀ ratio was 2.6 and decreased to 0.7 after 96 hours of regreening. The rate of photosynthesis (net CO₂ uptake) per chlorophyll increased during the first 48 hours of resupply, then by 96 hours decreased to values typical of control plants. The results suggest that there was preferential synthesis of the measured photosystem I components during the first 24 to 48 hours, while from 48 to 96 hours there was rapid synthesis of all components. The iron nutrition-mediated chloroplast development system provides a useful experimental approach for studying biomembrane synthesis and structural-functional relations of the photosynthetic apparatus.     

Quantitative and structural characteristics of lipids in Chlorobium and Chloroflexus

Exposure of dark grown resting Euglena to light induced the synthesis of chloroplast valyl-tRNA synthetase. Ethanol, a specific inhibitor of Euglena chloroplast development had little effect on chloroplast valyl-tRNA synthetase induction during the first 12 h of light exposure. Ethanol, however, completely inhibited enzyme synthesis between 12–72 h of light exposure. Malate, an alternative carbon source, had little effect on the photoinduction of valyl-tRNA synthetase. When dark grown resting cells were exposed to 2 h of light and returned to the dark, chloroplast valyl-tRNA synthetase continued to accumulate for 8–12 h at a rate which was less than the rate in cells maintained continuously in the light. The mutant strain W₃BUL lacks detectable chloroplast DNA and phototransformable protochlorophyllide, but retains a plastid remnant. Exposure of strain W₃BUL to light induced the synthesis of chloroplast valyl-tRNA synthetase and enzyme induction was not inhibited by ethanol. After 72 h of light exposure in the presence or absence of ethanol, enzyme levels in strain W₃BUL were comparable to the levels found in the wildtype strain after 8–14 h of light exposure. These results suggest that the nonchloroplast photoreceptor regulates the initial phase of enzyme synthesis. Mutant strain W₁₀BSmL differs from strain W₃BUL in that the plastid remnant if present, is greatly reduced. Chloroplast valyl-tRNA synthetase was undetectable in the strain W₁₀BSmL suggesting that the levels of active, cytoplasmically synthesized, chloroplast localized enzymes may be related to the developmental status of the chloroplast through the extent to which the enzyme precursor can be accumulated and or posttranslationally processed into an active enzyme within the chloroplast or chloroplast remnant.This research was supported by National Institutes of Health Grant GM26994, Biomedical support grant RR-0755 and funds from the Research Council, University of Nebraska     

Accumulation of Trehalose and Sucrose in Cyanobacteria Exposed to Matric Water Stress

The drought-resistant cyanobacteria Phormidium autumnale, strain LPP₄, and a Chroococcidiopsis sp. accumulated trehalose, sucrose, and both trehalose and sucrose, respectively, in response to matric water stress. Accumulated sugar concentrations reached values of up to 6.2 μg of trehalose per μg of chlorophyll in P. autumnale, 6.9 μg of sucrose per μg of chlorophyll in LPP₄, and 4.1 μg of sucrose and 3.2 μg of trehalose per μg of chlorophyll in the Chroococcidiopsis sp. The same sugars were accumulated by these cyanobacteria in similar concentrations under osmotic water stress. Cyanobacteria that did not show drought resistance (Plectonema boryanum and Synechococcus strain PCC 7942) did not accumulate significant amounts of sugars when matric water stress was applied.     

Cytokinin treatment of embryos inhibits the synthesis of chloroplast proteins in Norway spruce

A pulse treatment of Norway spruce (Picea abies (L.) Karst) embryos with the cytokinin N⁶-benzyladenine induces the formation of adventitious buds from subepidermal cells in the hypocotyl and cotyledons. In addition the treatment also inhibits elongation growth, a key process during germination. In this report we demonstrate that these effects on development of the plant are associated with a suppression of the accumulation of several major chloroplast proteins during germination. These proteins include the large subunit of ribulose bisphosphate/carboxylase oxygenase, two subunits of the chloroplast ATPase, protochlorophyllide reductase and a 23000-M_r component of photosystem II. For two nuclear-encoded proteins, the small subunit of ribulose bisphosphate carboxylase/oxygenase and the light-harvesting chlorophyll a/b-binding protein, a corresponding suppression of the increase in the steady-state amounts of mRNA is recorded. The suppression of chloroplast protein synthesis is consistant with the previously documented delay in greening that results from cytokinin treatment, but the effect is opposite to that found in other plants, where cytokinins promote the synthesis of chloroplast proteins, and stimulate chloroplast biogenesis. We believe that this difference is explained by the cytokinin primarily suppressing organ development, and a strict dependance of chloroplast biogenesis on the developmental state of the organs.Abbreviations Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - CF1 coupling-factor 1 of chloroplast ATPase - LHCP light-harvesting chlorophyll a/b-binding protein - LSU large subunit of Rubisco - NADPH-protochlorophyllide oxidoreductase Pchlide reductase - SDS sodium dodecyl sulfate - SSU small subunit of Rubisco We thank K. Hutchison (Dept. of Biochemistry, University of Maine, Orono, Maine, USA) and P. Gustafsson (Dept. of Plant Physiology, University of Umeå, Sweden) for providing the Larix and Pinus clones, and M. Ryberg (Dept. of Plant Physiology, University of Göteborg, Sweden), R. Ölmüller (Botanisches Institut, Universität München, FRG) and W. Lockau (Institut für Botanik, Universität Regensburg, FRG), for the gift of antisera towards Pchlide reductase, RuBPCase and LHCP, and ATPase, respectively. Supported by the Swedish Council for Forestry and Agricultural Research and the Swedish Natural Sciences Research Council.     

Action of Myxin on the Chloroplast System of Euglena gracilis

SYNOPSIS. Myxin (1-hydroxy-6-methoxy-phenazine-5,10-dioxide), a wide spectrum antibiotic, inhibits chloroplast replication in Euglena gracilis strain Z at concentrations which have no effect upon growth or survival. Myxin also inhibits the synthesis of chlorophyll when etiolated Euglena are illuminated in resting medium. By analogy with its action on bacteria, it is suggested that myxin may cause selective inhibition of chloroplast nucleic acid synthesis.     

Effects of sucrose and kinetin on growth and chlorophyll synthesis in tobacco tissue cultures

Investigations were carried out on the effects of various combinations of sucrose and kinetin concentrations on growth and chlorophyll production in a green and a nongreen clone of pith callus of Nicotiana tabacum L. It was found that 2 milligrams per liter or higher amounts of kinetin induced greening in the nongreen tissue. The observations suggested that growth of the callus and synthesis of chlorophyll and soluble protein are controlled by relative concentrations of sucrose and kinetin in the medium. Kinetin was found to be inhibitory for chlorophyll synthesis in the green callus.     

Dynamic modelling of limitations on improving leaf CO2 assimilation under fluctuating irradiance

A dynamic model of leaf CO₂ assimilation was developed as an extension of the canonical steady‐state model, by adding the effects of energy‐dependent non‐photochemical quenching (qE), chloroplast movement, photoinhibition, regulation of enzyme activity in the Calvin cycle, metabolite concentrations, and dynamic CO₂ diffusion. The model was calibrated and tested successfully using published measurements of gas exchange and chlorophyll fluorescence on Arabidopsis thaliana ecotype Col‐0 and several photosynthetic mutants and transformants affecting the regulation of Rubisco activity (rca‐2 and rwt43), non‐photochemical quenching (npq4‐1 and npq1‐2), and sucrose synthesis (spsa1). The potential improvements on CO₂ assimilation under fluctuating irradiance that can be achieved by removing the kinetic limitations on the regulation of enzyme activities, electron transport, and stomatal conductance were calculated in silico for different scenarios. The model predicted that the rates of activation of enzymes in the Calvin cycle and stomatal opening were the most limiting (up to 17% improvement) and that effects varied with the frequency of fluctuations. On the other hand, relaxation of qE and chloroplast movement had a strong effect on average low‐irradiance CO₂ assimilation (up to 10% improvement). Strong synergies among processes were found, such that removing all kinetic limitations simultaneously resulted in improvements of up to 32%.     

Over-expression of gsh1 in the cytosol affects the photosynthetic apparatus and improves the performance of transgenic poplars on heavy metal-contaminated soil

Recent studies of transgenic poplars over‐expressing the genes gsh1 and gsh2 encoding γ‐glutamylcysteine synthetase (γ‐ECS) and glutathione synthetase, respectively, provided detailed information on regulation of GSH synthesis, enzymes activities and mRNA expression. In this experiment, we studied quantitative parameters of leaves, assimilating tissues, cells and chloroplasts, mesophyll resistance for CO₂ diffusion, chlorophyll and carbohydrate content in wild‐type poplar and transgenic plants over‐expressing gsh1 in the cytosol after 3 years of growth in relatively clean (control) or heavy metal‐contaminated soil in the field. Over‐expression of gsh1 in the cytosol led to a twofold increase of intrafoliar GSH concentration and influenced the photosynthetic apparatus at different levels of organisation, i.e., leaves, photosynthetic cells and chloroplasts. At the control site, transgenic poplars had a twofold smaller total leaf area per plant and a 1.6‐fold leaf area per leaf compared to wild‐type controls. Annual aboveground biomass gain was reduced by 50% in the transgenic plants. The reduction of leaf area of the transformants was accompanied by a significant decline in total cell number per leaf, indicating suppression of cell division. Over‐expression of γ‐ECS in the cytosol also caused changes in mesophyll structure, i.e., a 20% decrease in cell and chloroplast number per leaf area, but also an enhanced volume share of chloroplasts and intercellular airspaces in the leaves. Transgenic and wild poplars did not exhibit differences in chlorophyll and carotenoid content of leaves, but transformants had 1.3‐fold fewer soluble carbohydrates. Cultivation on contaminated soil caused a reduction of palisade cell volume and chloroplast number, both per cell and leaf area, in wild‐type plants but not in transformants. Biomass accumulation of wild‐type poplars decreased in contaminated soil by more than 30‐fold, whereas transformants showed a twofold decrease compared to the control site. Thus, poplars over‐expressing γ‐ECS in the cytosol were more tolerant to heavy metal stress under field conditions than wild‐type plants according to the parameters analysed. Correlation analysis revealed strong dependence of cell number per leaf area unit, chloroplast parameters and mesophyll resistance with the GSH level in poplar leaves.     

The influence of high levels of brief or prolonged supplementary far-red illumination during growth on the photosynthetic characteristics, composition and morphology of Pisum sativum chloroplasts

Abstract. Peas were grown in controlled environments (12h white fluorescent light. ∼47 μmol photons m^-2 s 1/12 dark, 25 °C), using (1) 15-min far-red illumination at the end of each photoperiod (brief FR) to simulate the increase in the far-red/red ratio near the end of the day, and (2) high levels of supplementary far-red light (red:far-red ratio=0.04) during the entire photoperiod (long-term FR) to simulate extreme shade conditions under a plant canopy. Brief FR illumination led to marked morphological effects attributable to phytochrome regulation, namely, an increase in internodal length, but a decrease in leaflet area, chloroplast size and chlorophyll content per chloroplast compared with the control. Significantly, brief FR illumination had little or no effect on the amounts of the major chloroplast components (ribulose 1.5-biphosphate carboxylase, adenosine triphosphate synthase, cytochrome b/f complex and Photosystem II) relative to chlorophyll or Photosystem I, and the leaf photosynthetic capacities per unit chlorophyll were similar. In contrast, supplementing high levels of far-red light during the entire photoperiod not only led to the phytochrome effects above, but there was also a marked increase in leaf photosynthetic capacity per unit chlorophyll. due to increased amounts of the major chloroplast components relative to chlorophyll or Photosystem I. We hypothesize that supplementary far-red light, absorbed by Photosystem I, induced an increase in the major chloroplast components by a photosynthetic feedback mechanism. In fully greened leaves, we propose that the two photosystems themselves, rather than phytochrome, may be the predominent sensors of light quantity in triggering modulations of the stoichiometries of chloroplast components, which in turn lead to varying photosynthetic capacities.     

Synthesis and Turnover of the Chloroplast Coupling Factor 1 in Chlamydomonas reinhardi

Studies on the biosynthesis of the chloroplast coupling factor 1 (CF₁) in Chlamydomonas reinhardi have been initiated. The ratio of CF₁ to chlorophyll in the cell was shown to be independent of the density of the culture. No turnover of assembled CF₁ could be detected, thus suggesting that CF₁ was synthesized at a rate equivalent to that of net chlorophyll synthesis. A lag of between 5 to 7 minutes in the incorporation of radioactive precursor sulfate into assembled CF₁ was measureable. This puts an upper limit on the pool size of any precursor to the assembled CF₁ complex. The pool size is estimated to be equivalent to 1% of the total CF₁ in the cell.     

Studies on the entry of fructose-2,6-bisphosphate into chloroplasts

The regulatory metabolite fructose-2,6-bisphosphate (Fru-2,6-P₂) has an important function in controlling the intermediary carbon metabolism of leaves. Fru-2,6-P₂ controls two cytosolic enzymes involved in the interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate (fructose-1,6-bisphosphatase and pyrophosphate, fructose-6-phosphate 1-phosphotransferase) and thereby controls the partitioning of photosynthate between sucrose and starch. It has been demonstrated that Fru-2,6-P₂ is present mainly in the cytosol. Here we present evidence that Fru-2,6-P₂ can be taken up by isolated intact chloroplasts but at a very slow rate (about 0.01 micromoles per milligram of chlorophyll per hour). This uptake is time and concentration dependent and is inhibited by PPi. When provided a physiological concentration of Fru-2,6-P₂ (10 micromolar), chloroplasts accumulated up to 0.6 micromolar Fru-2,6-P₂ in the stroma. Elevated plastid Fru-2,6-P₂ levels had no effect on overall photosynthetic rates of isolated chloroplasts. The results indicate that, while Fru-2,6-P₂ enters isolated chloroplasts at a sluggish rate, caution should be exercised in ascribing physiological importance to effects of Fru-2,6-P₂ on chloroplast enzymes.     

水杨酸和茉莉酸甲酯对丹参幼苗叶片显微结构、光合及非结构糖积累的影响

研究了水杨酸(SA)和茉莉酸甲酯(MeJA)处理对丹参(Salvia miltiorrhiza Bunge)幼苗叶片显微结构、叶片光合能力及幼苗中非结构糖积累的影响.结果显示:SA处理增加了丹参幼苗叶片气孔密度;叶肉细胞排列紧密、体积减小,叶肉细胞内叶绿体数目减少,但叶绿体体积增大,叶绿体基粒片层结构的数目增加;叶片中叶绿素a、b含量、叶气孔导度、蒸腾速率以及净光合速率均增加;同时,幼苗根中和叶片中酸性转化酶活性降低,幼苗地上部分蔗糖含量及可溶性糖总量显著高于对照.MeJA处理减少了叶片气孔密度,气孔发育畸形;叶肉细胞间隙增大,栅栏细胞层数减少,叶肉细胞内叶绿体数目减少,叶绿体体积减小,叶绿体基粒片层结构被破坏;叶片中叶绿素a及类胡萝卜素含量、叶片的净光合速率低于对照,叶气孔导度、蒸腾速率增强;同时,幼苗根中及叶中酸性转化酶活性增加,幼苗根中蔗糖含量及可溶性糖总量显著低于对照.可见,SA处理能促进植物叶片显微结构发育,增强叶片光合能力,抑制蔗糖降解并促进蔗糖积累;而MeJA处理则破坏了植物叶片显微结构,降低了叶片光合能力,促进了蔗糖降解并减少蔗糖积累.