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Title: | Maltose Processing and Not β-Amylase Activity Curtails Hydrolytic Starch Degradation in the CAM Orchid Phalaenopsis | Authors: | Ceusters, Nathalie Frans, Mario Van den Ende, Wim CEUSTERS, Johan |
Issue Date: | 2019 | Publisher: | FRONTIERS MEDIA SA | Source: | Frontiers in plant science, 10 (Art N° 1386) | Abstract: | Crassulacean acid metabolism (CAM) is one of the three photosynthetic pathways in higher plants and is characterized by high water use efficiency. This mainly relies on major nocturnal CO2 fixation sustained by degradation of storage carbohydrate such as starch to provide phosphoenolpyruvate (PEP) and energy. In contrast to C3 plants where starch is mainly degraded by the hydrolytic route, different observations suggested the phosphorolytic route to be a major pathway for starch degradation in CAM plants. To elucidate the interplay and relevant contributions of the phosphorolytic and hydrolytic pathways for starch degradation in CAM, we assessed diel patterns for metabolites and enzymes implicated in both the hydrolytic route (beta-amylase, DPE1, DPE2, maltase) and the phosphorolytic route (starch phosphorylase) of starch degradation in the CAM orchid Phalaenopsis "Edessa." By comparing the catalytic enzyme activities and starch degradation rates, we showed that the phosphorolytic pathway is the major route to accommodate nocturnal starch degradation and that measured activities of starch phosphorylase perfectly matched calculated starch degradation rates in order to avoid premature exhaustion of starch reserves before dawn. The hydrolytic pathway seemed hampered in starch processing not by beta-amylase but through insufficient catalytic capacity of both DPE2 and maltase. These considerations were further corroborated by measurements of enzyme activities in the CAM model plant Kalanchoe fedtschenkoi and strongly contradict with the situation in the C3 plant Arabidopsis. The data support the view that the phosphorolytic pathway might be the main route of starch degradation in CAM to provide substrate for PEP with additional hydrolytic starch breakdown to accommodate mainly sucrose synthesis. | Notes: | Ceusters, J (reprint author), Katholieke Univ Leuven, Div Crop Biotech, Res Grp Sustainable Crop Prod & Protect, Dept Biosyst, Campus Geel, Geel, Belgium.; Ceusters, J (reprint author), UHasselt, Environm Biol, Ctr Environm Sci, Diepenbeek, Belgium. johan.ceusters@kuleuven.be |
Keywords: | hydrolytic starch degradation;phosphorolytic starch degradation;DPE2;maltase;crassulacean acid metabolism;Phalaenopsis | Document URI: | http://hdl.handle.net/1942/31413 | ISSN: | 1664-462X | e-ISSN: | 1664-462X | DOI: | 10.3389/fpls.2019.01386 | ISI #: | WOS:000499492700001 | Rights: | Open Access. 2019 Ceusters, Frans, Van den Ende and Ceusters. This is an openaccess article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. | Category: | A1 | Type: | Journal Contribution | Validations: | ecoom 2020 |
Appears in Collections: | Research publications |
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fpls-10-01386.pdf | Published version | 1.91 MB | Adobe PDF | View/Open |
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