The starch-deficient plastidic PHOSPHOGLUCOMUTASE mutant of the constitutive crassulacean acid metabolism (CAM) species Kalanchoe fedtschenkoi impacts diel regulation and timing of stomatal CO₂ responsiveness

Hurtado-Castano, Natalia, Atkins, Elliott, Barnes, Jerry, Boxall, Susanna F ORCID: 0000-0002-8753-101X, Dever, Louisa V, Knerova, Jana, Hartwell, James ORCID: 0000-0001-5000-223X, Cushman, John C and Borland, Anne M (2023) The starch-deficient plastidic PHOSPHOGLUCOMUTASE mutant of the constitutive crassulacean acid metabolism (CAM) species Kalanchoe fedtschenkoi impacts diel regulation and timing of stomatal CO₂ responsiveness ANNALS OF BOTANY, 132 (4). pp. 881-894. ISSN 0305-7364, 1095-8290

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Abstract

• Background and Aims Crassulacean acid metabolism (CAM) is a specialized type of photosynthesis characterized by a diel pattern of stomatal opening at night and closure during the day, which increases water-use efficiency. Starch degradation is a key regulator of CAM, providing phosphoenolpyruvate as a substrate in the mesophyll for nocturnal assimilation of CO<inf>2</inf>. Growing recognition of a key role for starch degradation in C<inf>3</inf> photosynthesis guard cells for mediating daytime stomatal opening presents the possibility that starch degradation might also impact CAM by regulating the provision of energy and osmolytes to increase guard cell turgor and drive stomatal opening at night. In this study, we tested the hypothesis that the timing of diel starch turnover in CAM guard cells has been reprogrammed during evolution to enable nocturnal stomatal opening and daytime closure. • Methods Biochemical and genetic characterization of wild-type and starch-deficient RNAi lines of Kalanchoë fedtschenkoi with reduced activity of plastidic phosphoglucomutase (PGM) constituted a preliminary approach for the understanding of starch metabolism and its implications for stomatal regulation in CAM plants. • Key Results Starch deficiency reduced nocturnal net CO<inf>2</inf> uptake but had negligible impact on nocturnal stomatal opening. In contrast, daytime stomatal closure was reduced in magnitude and duration in the starch-deficient rPGM RNAi lines, and their stomata were unable to remain closed in response to elevated concentrations of atmospheric CO<inf>2</inf> administered during the day. Curtailed daytime stomatal closure was linked to higher soluble sugar contents in the epidermis and mesophyll. • Conclusions Nocturnal stomatal opening is not reliant upon starch degradation, but starch biosynthesis is an important sink for carbohydrates, ensuring daytime stomatal closure in this CAM species.

Item Type:	Article
Uncontrolled Keywords:	Crassulacean acid metabolism, Kalanchoe fedtschenkoi, CO2 uptake, stomatal conductance, starch, phosphoglucomutase
Divisions:	Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Systems, Molec & Integrative Biology > Inst. Systems, Molec & Integrative Biology
Depositing User:	Symplectic Admin
Date Deposited:	27 Jan 2023 10:26
Last Modified:	16 Jun 2026 11:40
DOI:	10.1093/aob/mcad017
Open Access URL:	https://doi.org/10.1093/aob/mcad017
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3167932
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