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Karabourniotis G, Horner HT, Bresta P, Nikolopoulos D, Liakopoulos G. New insights into the functions of carbon-calcium inclusions in plants. THE NEW PHYTOLOGIST 2020; 228:845-854. [PMID: 32583442 DOI: 10.1111/nph.16763] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 06/10/2020] [Indexed: 06/11/2023]
Abstract
Carbon-calcium inclusions (CCaI) either as calcium oxalate crystals (CaOx) or amorphous calcium carbonate cystoliths are spread among most photosynthetic organisms. They represent dynamic structures with a significant construction cost and their appearance during evolution indicates an ancient origin. Both types of inclusions share some similar functional characteristics providing adaptive advantages such as the regulation of Ca levels, and the release of CO2 and water molecules upon decomposition. The latter seems to be essential under drought conditions and explains the intense occurrence of these structures in plants thriving in dry climates. It seems, however, that for plants CaOx may represent a more prevalent storage system compared with CaCO3 due to the multifunctionality of oxalate. This compound participates in a number of important soil biogeochemical processes, creates endosymbiosis with beneficial bacteria and provides tolerance against a combination of abiotic (nutrient deprivation, metal toxicity) and biotic (pathogens, herbivores) stress factors. We suggest a re-evaluation of the roles of these fascinating plant structures under a new and holistic approach that could enhance our understanding of carbon sequestration at the whole plant level and provide future perspectives.
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Affiliation(s)
- George Karabourniotis
- Laboratory of Plant Physiology and Morphology, Faculty of Crop Science, Agricultural University of Athens, Athens, 11855, Greece
| | - Harry T Horner
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA, 50011, USA
| | - Panagiota Bresta
- Laboratory of Plant Physiology and Morphology, Faculty of Crop Science, Agricultural University of Athens, Athens, 11855, Greece
| | - Dimosthenis Nikolopoulos
- Laboratory of Plant Physiology and Morphology, Faculty of Crop Science, Agricultural University of Athens, Athens, 11855, Greece
| | - Georgios Liakopoulos
- Laboratory of Plant Physiology and Morphology, Faculty of Crop Science, Agricultural University of Athens, Athens, 11855, Greece
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Decomposition of Calcium Oxalate Crystals in Colobanthus quitensis under CO 2 Limiting Conditions. PLANTS 2020; 9:plants9101307. [PMID: 33023238 PMCID: PMC7600318 DOI: 10.3390/plants9101307] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/19/2020] [Accepted: 09/21/2020] [Indexed: 12/23/2022]
Abstract
Calcium oxalate (CaOx) crystals are widespread among plant species. Their functions are not yet completely understood; however, they can provide tolerance against multiple environmental stress factors. Recent evidence suggested that CaOx crystals function as carbon reservoirs since its decomposition provides CO2 that may be used as carbon source for photosynthesis. This might be advantageous in plants with reduced mesophyll conductance, such as the Antarctic plant Colobanthus quitensis, which have shown CO2 diffusion limitations. In this study, we evaluate the effect of two CO2 concentrations in the CaOx crystals decomposition and chlorophyll fluorescence of C. quitensis. Plants were exposed to airflows with 400 ppm and 11.5 ppm CO2 and the number and relative size of crystals, electron transport rate (ETR), and oxalate oxidase (OxO) activity were monitored along time (10 h). Here we showed that leaf crystal area decreases over time in plants with 11.5 ppm CO2, which was accompanied by increased OxO activity and only a slight decrease in the ETR. These results suggested a relation between CO2 limiting conditions and the CaOx crystals decomposition in C. quitensis. Hence, crystal decomposition could be a complementary endogenous mechanism for CO2 supply in plants facing the Antarctic stressful habitat.
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Giannopoulos A, Nikolopoulos D, Bresta P, Samantas A, Reppa C, Karaboiki K, Dotsika E, Fasseas C, Liakopoulos G, Karabourniotis G. Cystoliths of Parietaria judaica can serve as an internal source of CO2 for photosynthetic assimilation when stomata are closed. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:5753-5763. [PMID: 31270538 DOI: 10.1093/jxb/erz316] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Accepted: 06/25/2019] [Indexed: 06/09/2023]
Abstract
The recently reported 'alarm photosynthesis' acts as a biochemical process that assimilates CO2 derived from the decomposition of calcium oxalate crystals. This study examined whether CaCO3 cystoliths could also serve as CO2 pools, fulfilling a similar role. Shoots of Parietaria judaica were subjected to carbon starvation, abscisic acid (ABA), or bicarbonate treatments, and the volume of cystoliths and the photochemical parameters of photosystem II (PSII) were determined. The size of cystoliths was reduced under carbon starvation or ABA treatments, whereas it was restored by xylem-provided bicarbonate. Under carbon starvation, ABA, or bicarbonate treatments, the photochemical efficiency of PSII was higher, while non-photochemical quenching, representing the safe dissipation of excess PSII energy due to lack of electron sinks, was lower in treated samples compared with controls. This observation suggests the involvement of ABA or other carbon starvation cues in the release of subsidiary CO2 for photosynthesis, inevitably from an internal source, which could be the cystoliths. Carbon remobilized from cystoliths can be photosynthetically assimilated, thus acting as a safety valve under stress. Together with alarm photosynthesis, these results show a tight link between leaf carbon deposits and photosynthesis.
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Affiliation(s)
- Andreas Giannopoulos
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Dimosthenis Nikolopoulos
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Panagiota Bresta
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Aris Samantas
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Chrysavgi Reppa
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Kalliopi Karaboiki
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Elissavet Dotsika
- Stable Isotope Unit, Institute of Material Science, National Centre for Scientific Research 'Demokritos', Athens, Greece
| | - Constantinos Fasseas
- Laboratory of Electron Microscopy, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - Georgios Liakopoulos
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
| | - George Karabourniotis
- Laboratory of Plant Physiology, Faculty of Crop Science, Agricultural University of Athens, Athens, Greece
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