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

Journal Article · · Annals of Botany
DOI:https://doi.org/10.1093/aob/mcad017· OSTI ID:2282173
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 CO2. Growing recognition of a key role for starch degradation in C3 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 CO2 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 CO2 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.

Research Organization:
University of Nevada, Reno, NV (United States)
Sponsoring Organization:
Biotechnology and Biological Sciences Research Council (BBSRC); USDOE; USDOE Office of Science (SC)
Grant/Contract Number:
SC0008834
OSTI ID:
2282173
Alternate ID(s):
OSTI ID: 2471985
OSTI ID: 1958637
Journal Information:
Annals of Botany, Journal Name: Annals of Botany Journal Issue: 4 Vol. 132; ISSN 0305-7364
Publisher:
Oxford University PressCopyright Statement
Country of Publication:
United Kingdom
Language:
English

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