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Drought does not induce crassulacean acid metabolism (CAM) but regulates photosynthesis and enhances nutritional quality of Mesembryanthemum crystallinum.

ABSTRACT: Physiology and nutritional quality of a facultative CAM plant Mesembryanthemum crystallinum under drought stress alone are poorly understood. To induce drought, M. crystallinum was cultured aeroponically with different nutrient spraying intervals such as 5, 30, 60 and 240 min. The long spraying interval such as 240 min resulted in lower mass of root and shoot, shorter total root length with less tips and smaller surface area, compared to short interval of 5 min. Grown under the longest spraying interval of 240 min, M. crystallinumalso had significantly higher leaf dry matter content but lower leaf succulence. However, CAM acidity was undetectable for any plants. Although M. crystallinum grown under extended spraying intervals had higher photosynthetic pigments, they utilized lesser light energy and did not dissipate heat as effectively as those grown under 5 min. Compare to other shorter spraying intervals, photosynthetic gas exchange rates were significantly reduced under 240 min spraying interval, indicating signs of water deficit stress. Shoot nitrate, total reduced nitrogen, total soluble protein and Rubisco concentrations were similar for all plants. For phytochemicals and dietary minerals, plants grown under 240 min spraying interval had significantly higher values than the other plants. Therefore, drought does not result in the induction of CAM but regulates photosynthetic performance and enhances nutritional quality of M. crystallinum.

SUBMITTER: He J

PROVIDER: S-EPMC7059918 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:C3 or crassulacean acid metabolism (CAM)-induced Mesembryanthemum crystallinum plants perform nocturnal starch degradation which is linear with time. To analyse the composition of metabolites released by isolated leaf chloroplasts during starch degradation we developed a protocol for the purification of starch-containing plastids. Isolated chloroplasts from C3 or CAM-induced M. crystallinum plants are also able to degrade starch. With respect to the endogenous starch content of isolated plastids the rate of starch degradation in intact leaves. The combined presence of Pi, ATP, and oxaloacetate is identified to be the most positive effector combination to induce starch mobilization. The metabolic flux through the oxidative pentose-phosphate pathway in chloroplasts isolated from CAM-induced M. crystallinum is less than 3.5% compared with other metabolic routes of starch degradation. Here we report that starch-degrading chloroplasts isolated from CAM-induced M. crystallinum plants use exogenously supplied oxaloacetate for the synthesis of malate. The main products of starch degradation exported into the incubation medium by these chloroplasts are glucose 6-phosphate, 3-phosphoglyceric acid, dihydroxyacetone phosphate and glucose. The identification of glucose 6-phosphate as an important metabolite released during starch degradation is in contrast to the observations made on all other types of plastids analysed so far, including chloroplasts isolated from M. crystallinum in the C3 state. Therefore, we analysed the transport properties of isolated chloroplasts from M. crystallinum. Surprisingly, both types of chloroplasts, isolated from either C3 or CAM-induced plants, are able to transport glucose 6-phosphate in counter exchange with endogenous Pi, indicating the presence of a glucose 6-phosphate translocator as recently demonstrated to occur in other types of plastids. The composition of metabolites released and the stimulatory effect of oxaloacetate on the rate of starch degradation are discussed with respect to the acidification observed for CAM leaves during the night.

Project description:Mesembryanthemum crystallinum (common ice plant), as a nutritious ready-to-eat salad in Singapore, has become popular in recent years. However, basic data about the impacts of NO3 - supply on its NO3 - accumulation and nutritional quality are lacking. In this study, all plants were first grown indoor hydroponically in 10% artificial seawater (ASW) with modified full-strength Netherlands Standard Composition nutrient solution for 11 days, before transferring them to different reduced NO3 - solutions. All plants grew well and healthy after 7 days of treatment. However, plants grown with 3/4 N and 1/2 N were bigger with higher shoot and root fresh weight (FW), greater leaf number, and total leaf area (TLA) than those grown with full nitrogen (N), 1/4 N, and 0 N. Mesembryanthemum crystallinum grown with full N, 3/4 N, and 1/4 N had similar specific leaf area (SLA), while 0 N plants had significantly lower SLA. All plants had similar leaf succulence (LS). However, leaf water content (LWC) was lower, while leaf dry matter accumulation (LDMC) was higher in 0 N plants after 7 days of treatment. Compared with plants grown with full N, shoot NO3 - concentrations in 3/4 N, 1/2 N, and 1/4 N plants were constant or slightly increased during the treatments. For 0 N plants, shoot NO3 - concentration decreased significantly during the treatment compared with other plants. Shoot NO3 - accumulation was associated with nitrate reductase activity (NRA). For instance, after 7 days of treatment, shoot NO3 - concentration and NRA on a FW basis in 0 N plants were, respectively, 45 and 31% of full N plants. After transferring full N to 0 N for 7 days, all M. crystallinum had higher chlorophyll (Chl) content coupled with higher electron transport rate (ETR) and higher effective quantum yield of PSII, while full N plants had higher non-photochemical quenching (NPQ). The 0N plants had much higher concentrations of proline, total soluble sugar (TSS), and total ascorbic acid (ASC) than other plants. In conclusion, totally withdrawing NO3 - from the growth media prior to harvest could be one of the strategies to reduce shoot NO3 - concentration. Reduced NO3 - supply further enhanced nutritional values as concentrations of proline, TSS, and ASC were enhanced markedly in M. crystallinum plants after transferring them from full N to 0 N.

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Drought does not induce crassulacean acid metabolism (CAM) but regulates photosynthesis and enhances nutritional quality of Mesembryanthemum crystallinum.

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