A mutation in a Chlamydomonas inositol kinase sensitizes cells to inhibition of TOR kinase signaling in a carbon source-dependent manner and uncouples lipid acc

The photoprotective role of anthocyanin remains controversial. In this study, we explored the effects of anthocyanin on photosynthesis and photoprotection using transgenic ‘Galaxy Gala’ apple plants overexpressing MdMYB10 under high light stress. The overexpression of MdMYB10 dramatically enhanced leaf anthocyanin accumulation, allowing more visible light to be absorbed, particularly in the green region. However, through post-transcriptional regulation, anthocyanin accumulation lowered leaf photosynthesis in both photochemical reaction and CO₂ fixation capacities. Anthocyanin accumulation also led to a decreased de-epoxidation state of the xanthophyll cycle and antioxidant capacities, but this is most likely a response to the light-shielding effect of anthocyanin, as indicated by a higher chlorophyll concentration and lower chlorophyll a/b ratio. Under laboratory conditions when detached leaves lost carbon fixation capacity due to the limitation of CO₂ supply, the photoinhibition of detached transgenic red leaves was less severe under strong white, green, or blue light, but it became more severe in response to strong red light compared with that of the wild type. In field conditions when photosynthesis was performed normally in both green and transgenic red leaves, the degree of photoinhibition was comparable between transgenic red leaves and wild type leaves, but it was less severe in transgenic young shoot bark compared with the wild type. Taken together, these data show that anthocyanin protects plants from high light stress by absorbing excessive visible light despite reducing photosynthesis.

C₄ photosynthesis in grasses requires the coordinated movement of metabolites through two specialized leaf cell types, mesophyll (M) and bundle sheath (BS), to concentrate CO₂ around Rubisco. Despite the importance of transporters in this process, few have been identified or rigorously characterized. In maize (Zea mays), DCT2 has been proposed to function as a plastid-localized malate transporter and is preferentially expressed in BS cells. Here, we characterized the role of DCT2 in maize leaves using Activator-tagged mutant alleles. Our results indicate that DCT2 enables the transport of malate into the BS chloroplast. Isotopic labeling experiments show that the loss of DCT2 results in markedly different metabolic network operation and dramatically reduced biomass production. In the absence of a functioning malate shuttle, dct2 lines survive through the enhanced use of the phosphoenolpyruvate carboxykinase carbon shuttle pathway that in wild-type maize accounts for ∼25% of the photosynthetic activity. The results emphasize the importance of malate transport during C₄ photosynthesis, define the role of a primary malate transporter in BS cells, and support a model for carbon exchange between BS and M cells in maize.

Summary: Central metabolism produces amino and fatty acids for protein and lipids that establish seed value. Biosynthesis of storage reserves occurs in multiple organelles that exchange central intermediates including two essential metabolites, malate, and pyruvate that are linked by malic enzyme. Malic enzyme can be active in multiple subcellular compartments, partitioning carbon and reducing equivalents for anabolic and catabolic requirements. Prior studies based on isotopic labeling and steady‐state metabolic flux analyses indicated malic enzyme provides carbon for fatty acid biosynthesis in plants, though genetic evidence confirming this role is lacking. We hypothesized that increasing malic enzyme flux would alter carbon partitioning and result in increased lipid levels in soybeans. Homozygous transgenic soybean plants expressing Arabidopsis malic enzyme alleles, targeting the translational products to plastid or outside the plastid during seed development, were verified by transcript and enzyme activity analyses, organelle proteomics, and transient expression assays. Protein, oil, central metabolites, cofactors, and acyl‐acyl carrier protein (ACPs) levels were quantified overdevelopment. Amino and fatty acid levels were altered resulting in an increase in lipids by 0.5–2% of seed biomass (i.e. 2–9% change in oil). Subcellular targeting of a single gene product in central metabolism impacts carbon and reducing equivalent partitioning for seed storage reserves in soybeans.

Calcium (Ca) plays a key role in cell wall stabilization and various physiological processes. Ca fertilizers are widely used in agriculture to meet crop demands and improve yield and quality. However, traditional Ca fertilizers often suffer from low solubility, poor absorption, and mobility issues. Chelated Ca fertilizers offer enhanced efficiency and uptake. In this study, we compared the effects of lignosulfonate-chelated Ca (LS–Ca), EDTA-chelated Ca (EDTA–Ca), Ca(NO₃)₂, and alcohol sugar-chelated Ca (AS–Ca) with a Ca concentration of 15 mg/L on tomato growth. The results showed that LS–Ca increased the contents of chlorophyll a and b contents in leaves by 26% and 46%, respectively. The application of Ca fertilizers significantly enhanced Ca²⁺ uptake and transport, with the LS–Ca treatment achieving the highest utilization efficiency. Without altering fruit weight, the LS–Ca treatment increased the firmness of mature tomato fruits by 29%. Furthermore, the LS–Ca treatment improved fruit sweetness by 33%, with the total sugar content increasing by 45%, sucrose by 80%, reducing sugars by 64%, and titratable acidity by 18%. This study aims to compare the effects of different chelated Ca fertilizers on tomato cultivation and to explore optimal Ca supplementation strategies, thereby contributing to improvements in tomato cultivation practices and fruit quality.