Some enzymes present in the walls of mesophyll cells of tobacco leaves.
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ABSTRACT:
SUBMITTER: Yung KH
PROVIDER: S-EPMC1172335 | biostudies-other | 1975 Oct
REPOSITORIES: biostudies-other
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Project description:The overall metabolism of purines was studied in tobacco (Nicotiana tabacum) mesophyll protoplasts. Metabolic pathways were studied by measuring the conversion of radioactive adenine, adenosine, hypoxanthine and guanine into purine ribonucleotides, ribonucleosides, bases and nucleic acid constituents. Adenine was extensively deaminated to hypoxanthine, whereupon it was also converted into AMP and incorporated into nucleic acids. Adenosine was mainly hydrolysed to adenine. Inosinate formed from hypoxanthine was converted into AMP and GMP, which were then catabolized to adenine and guanosine respectively. Guanine was mainly deaminated to xanthine and also incorporated into nucleic acids via GTP. Increased RNA synthesis in the protoplasts resulted in enhanced incorporation of adenine and guanine, but not of hypoxanthine and adenosine, into the nucleic acid fraction. The overall pattern of purine-nucleotide metabolic pathways in protoplasts of tobacco leaf mesophyll is proposed.
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Project description:Background and aimsIt is commonly accepted that the leaf of a crassulacean acid metabolism (CAM) plant is thick, with large mesophyll cells and vacuoles that can accommodate the malic acid produced during the night. The link between mesophyll characteristics and CAM mode, whether obligate or C3/CAM, was evaluated.MethodsPublished values of the carbon isotopic ratio (δ 13C) as an indicator of CAM, leaf thickness, leaf micrographs and other evidence of CAM operation were used to correlate cell density, cell area, the proportion of intercellular space in the mesophyll (IAS) and the length of cell wall facing the intercellular air spaces (Lmes/A) with CAM mode.Key resultsBased on 81 species and relatively unrelated families (15) belonging to nine orders, neither leaf thickness nor mesophyll traits helped explain the degree of CAM expression. A strong correlation was found between leaf thickness and δ 13C in some species of Crassulaceae and between leaf thickness and nocturnal acid accumulation in a few obligate CAM species of Bromeliaceae but, when all 81 species were pooled together, no significant changes with δ 13C were observed in cell density, cell area, IAS or Lmes/A.ConclusionsAn influence of phylogeny on leaf anatomy was evidenced in a few cases but this precluded generalization for widely separate taxa containing CAM species. The possible relationships between leaf anatomy and CAM mode should be interpreted cautiously.
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Project description:Considering that Actinidia kolomikta bears abundant white leaves on reproductive branches during blossoming, we hypothesized that the white leaves may maintain photosynthetic capacity by adjustments of leaf anatomy and physiological regulation. To test this hypothesis, leaf anatomy, gas exchange, chlorophyll a fluorescence, and the transcriptome were examined in white leaves of A. kolomikta during flowering. The palisade and spongy mesophyll in the white leaves were thicker than those in green ones. Chloroplast development in palisade parenchyma of white leaves was abnormal, whereas spongy parenchyma of white leaves contained functional chloroplasts. The highest photosynthetic rate of white leaves was ~82% of that of green leaves over the course of the day. In addition, the maximum quantum yield of PSII (F v/F m) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas F v/F m and quantum yield for electron transport were significantly higher in the spongy mesophyll of white leaves. Photosynthetic capacity regulation of white leaf also was attributed to upregulation or downregulation of some key genes involving in photosynthesis. Particularly, upregulation of sucrose phosphate synthase (SPS), glyeraldehyde-3-phosphate dehydrogenase (GAPDH) and RuBisCO activase (RCA) in white leaf suggested that they might be involved in regulation of sugar synthesis and Rubisco activase in maintaining photosynthetic capacity of white leaf. Conclusions: white leaves contained a thicker mesophyll layer and higher photosynthetic activity in spongy parenchyma cells than those of palisade parenchyma cells. This may compensate for the lowered photosynthetic capacity of the palisade mesophyll. Consequently, white leaves maintain a relatively high photosynthetic capacity in the field.
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Project description:In several taxa, increasing leaf succulence has been associated with decreasing mesophyll conductance (g M) and an increasing dependence on Crassulacean acid metabolism (CAM). However, in succulent Aizoaceae, the photosynthetic tissues are adjacent to the leaf surfaces with an internal achlorophyllous hydrenchyma. It was hypothesized that this arrangement increases g M, obviating a strong dependence on CAM, while the hydrenchyma stores water and nutrients, both of which would only be sporadically available in highly episodic environments. These predictions were tested with species from the Aizoaceae with a 5-fold variation in leaf succulence. It was shown that g M values, derived from the response of photosynthesis to intercellular CO2 concentration (A:C i), were independent of succulence, and that foliar photosynthate ?(13)C values were typical of C3, but not CAM photosynthesis. Under water stress, the degree of leaf succulence was positively correlated with an increasing ability to buffer photosynthetic capacity over several hours and to maintain light reaction integrity over several days. This was associated with decreased rates of water loss, rather than tolerance of lower leaf water contents. Additionally, the hydrenchyma contained ~26% of the leaf nitrogen content, possibly providing a nutrient reservoir. Thus the intermittent use of C3 photosynthesis interspersed with periods of no positive carbon assimilation is an alternative strategy to CAM for succulent taxa (Crassulaceae and Aizoaceae) which occur sympatrically in the Cape Floristic Region of South Africa.
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Project description:Leaf epidermal micromorphology and mesophyll structure during the development of Populus euphratica heteromorphic leaves, including linear, lanceolate, ovate, dentate ovate, dentate rhombic, dentate broad-ovate and dentate fan-shaped leaves, were studied by using electron and light microscopy. During development of heteromorphic leaves, epidermal appendages (wax crystals and trichomes) and special cells (mucilage cells and crystal idioblasts) increased in all leaf types while chloroplast ultrastructure and stomatal characters show maximum photosynthetic activity in dentate ovate and rhombic leaves. Also, functional analysis by subordinate function values shows that the maximum adaptability to adverse stress was exhibited in the broad type of mature leaves. The 12 heteromorphic leaf types are classified into three major groups by hierarchical cluster analysis: young, developing and mature leaves. Mature leaves can effectively obtain the highest stress resistance by combining the protection of xerophytic anatomy from drought stress, regulation of water uptake in micro-environment by mucilage and crystal idioblasts, and assistant defense of transpiration reduction through leaf epidermal appendages, which improves photosynthetic activity under arid desert conditions. Our data confirms that the main leaf function is differentiated during the developing process of heteromorphic leaves.
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Project description:Purpose: To further identify the genes and pathways involved in the necrotic phenotype of NtCBL5A-OE lines, the leaf transcriptome profiling of WT and OE-2 lines grown under control conditions and salt stress (100 mM NaCl) at 4 DAT were sequenced and compared. Methods: Two datasets of differentially expressed genes (DEGs) were made in which we identified the genes that were differentially expressed as a result of the overexpression of NtCBL5A: Control-WT vs Control-OE2 (C-WT/C-OE2), Salt-WT vs Salt-OE2 (S-WT/S-OE2). Another two datasets were also used to identify the transcripts that were responsive to the salt treatments: Control-WT vs Salt-WT (C-WT/S-WT) and Control-OE2 vs Salt-OE2 (C-OE2/S-OE2). DEGs from C-WT/C-OE2 and S-WT/S-OE2 were compared to select the transcripts affected by NtCBL5A overexpression only under salt stress. We also compared DEGs from C-WT/S-WT and C-OE2/S-OE2 to identify the specific transcripts affected by salt stress and only in NtCBL5A-OE lines. This procedure was done for two independent experiments, and only DEGs that were identified in both experiments were considered. Results: The OE-affected DEGs and salt-affected DEGs together resulted in 2079 up-regulated DEGs and 1154 down-regulated DEGs, strongly affected by the combination of NtCBL5A overexpression and salt stress.
2021-08-17 | GSE181164 | GEO