Fractionating of Calcium in Tuber and Leaf Tissues Explains the Calcium Deficiency Symptoms in Potato Plant Overexpressing CAX1

STOP1 regulates CCX1-mediated Ca2+ homeostasis for plant adaptation to Ca2+ deprivation

Calcium (Ca) is essential for plant growth and stress adaptation, yet its availability is often limited in acidic soils, posing a major threat to crop production. Understanding the intricate mechanisms orchestrating plant adaptation to Ca deficiency remains elusive. Here, we show that the Ca deficiency-enhanced nuclear accumulation of the transcription factor SENSITIVE TO PROTON RHIZOTOXICITY 1 (STOP1) in Arabidopsis thaliana confers tolerance to Ca deprivation, with the global transcriptional responses triggered by Ca deprivation largely impaired in the stop1 mutant. Notably, STOP1 activates the Ca deprivation-induced expression of CATION/Ca2+ EXCHANGER 1 (CCX1) by directly binding to its promoter region, which facilitates Ca2+ efflux from endoplasmic reticulum to cytosol to maintain Ca homeostasis. Consequently, the constitutive expression of CCX1 in the stop1 mutant partially rescues the Ca deficiency phenotype by increasing Ca content in the shoots. These findings uncover the pivotal role of the STOP1-CCX1 axis in plant adaptation to low Ca, offering alternative manipulating strategies to improve plant Ca nutrition in acidic soils and extending our understanding of the multifaceted role of STOP1.

CAX control: multiple roles of vacuolar cation/H+ exchangers in metal tolerance, mineral nutrition and environmental signalling

Plant vacuolar transporters, particularly CAX (Cation/H+ Exchangers) responsible for Ca2+/H+ exchange on the vacuole tonoplast, play a central role in governing cellular pH, ion balance, nutrient storage, metal accumulation, and stress responses. Furthermore, CAX variants have been employed to enhance the calcium content of crops, contributing to biofortification efforts. Recent research has uncovered the broader significance of these transporters in plant signal transduction and element partitioning. The use of genetically encoded Ca2+ sensors has begun to highlight the crucial role of CAX isoforms in generating cytosolic Ca2+ signals, underscoring their function as pivotal hubs in diverse environmental and developmental signalling networks. Interestingly, it has been observed that the loss of CAX function can be advantageous in specific stress conditions, both for biotic and abiotic stressors. Determining the optimal timing and approach for modulating the expression of CAX is a critical concern. In the future, strategically manipulating the temporal loss of CAX function in agriculturally important crops holds promise to bolster plant immunity, enhance cold tolerance, and fortify resilience against one of agriculture's most significant challenges, namely flooding.

Genome-Wide Identification of BrCAX Genes and Functional Analysis of BrCAX1 Involved in Ca2+ Transport and Ca2+ Deficiency-Induced Tip-Burn in Chinese Cabbage (Brassica rapa L. ssp. pekinensis)

Calcium (Ca2+) plays essential roles in plant growth and development. Ca2+ deficiency causes a physiological disorder of tip-burn in Brassiceae crops and is involved in the regulation of cellular Ca2+ homeostasis. Although the functions of Ca2+/H+ exchanger antiporters (CAXs) in mediating transmembrane transport of Ca2+ have been extensively characterized in multiple plant species, the potential roles of BrCAX genes remain unclear in Chinese cabbage. In this study, eight genes of the BrCAX family were genome-widely identified in Chinese cabbage. These BrCAX proteins contained conserved Na_Ca_ex domain and belonged to five members of the CAX family. Molecular evolutionary analysis and sequence alignment revealed the evolutionary conservation of BrCAX family genes. Expression profiling demonstrated that eight BrCAX genes exhibited differential expression in different tissues and under heat stress. Furthermore, Ca2+ deficiency treatment induced the typical symptoms of tip-burn in Chinese cabbage seedlings and a significant decrease in total Ca2+ content in both roots and leaves. The expression changes in BrCAX genes were related to the response to Ca2+ deficiency-induced tip-burn of Chinese cabbage. Specially, BrCAX1-1 and BrCAX1-2 genes were highly expressed gene members of the BrCAX family in the leaves and were significantly differentially expressed under Ca2+ deficiency stress. Moreover, overexpression of BrCAX1-1 and BrCAX1-2 genes in yeast and Chinese cabbage cotyledons exhibited a higher Ca2+ tolerance, indicating the Ca2+ transport capacity of BrCAX1-1 and BrCAX1-2. In addition, suppression expression of BrCAX1-1 and BrCAX1-2 genes reduced cytosolic Ca2+ levels in the root tips of Chinese cabbage. These results provide references for functional studies of BrCAX genes and to investigate the regulatory mechanisms underlying Ca2+ deficiency disorder in Brassiceae vegetables.

Effect of Harvesting in Different Ripening Stages on the Content of the Mineral Elements of Rosehip (Rosa spp.) Fruit Flesh

Studies on the mineral content of different rosehip species/cultivars during the ripening period are very limited. Therefore, the objective of this research was to evaluate the content and composition of the mineral elements of two species and two rosehip cultivars growing on an organic farm. The rosehip fruits were harvested at different ripening stages, five time per season. Mineral composition (K, Ca, Mg, P, Fe, Na, Ti, Cu, B, Mn, Al, Zn, Cr, Co, Ni, As, Mo, Cd and Pb) was analyzed by means inductively coupled plasma mass spectrometry (ICP–MS). The results showed that the ripening stage and species/cultivars had an effect on the contents of the mineral elements. Significantly, the highest content of mineral elements was determined at ripening stage I (Ca, Mg, Ti, Mn, Al and Cr) and IV (K, P, Fe, Cu and B). Species of the Rosa canina accumulated the highest content of mineral elements. Correlation analysis showed that the hue angle had a positive and very strong relationship with six mineral elements: K (r = 0.909), Ca (r = 0.962), Mg (r = 0.965), P (r = 0.945), Fe (r = 0.929) and Ti (r = 0.944).

Effects of Plant Hormones, Metal Ions, Salinity, Sugar, and Chemicals Pollution on Glucosinolate Biosynthesis in Cruciferous Plant

Cruciferous vegetable crops are grown widely around the world, which supply a multitude of health-related micronutrients, phytochemicals, and antioxidant compounds. Glucosinolates (GSLs) are specialized metabolites found widely in cruciferous vegetables, which are not only related to flavor formation but also have anti-cancer, disease-resistance, and insect-resistance properties. The content and components of GSLs in the Cruciferae are not only related to genotypes and environmental factors but also are influenced by hormones, plant growth regulators, and mineral elements. This review discusses the effects of different exogenous substances on the GSL content and composition, and analyzes the molecular mechanism by which these substances regulate the biosynthesis of GSLs. Based on the current research status, future research directions are also proposed.

Understanding calcium functionality by examining growth characteristics and structural aspects in calcium-deficient grapevine

This study characterized growth characteristics and cellular details employing microscopy techniques in hydroponically-grown Ca²⁺-sufficient and Ca²⁺-deficient grapevines (Vitis vinifera) in a glasshouse. The Ca²⁺-deficient vines exhibited significant reductions in shoot length, shoot and trunk fresh weights, leaf area, chlorophyll, which eventually led to drooping, yellowing, and chlorosis of leaves. Roots were less dense and primarily dark and necrotic. Furthermore, their xylem vessels were small, polygonal, and appeared to be collapsed yet increased in number and developed lateral roots. Despite such alterations, the anatomical organization of leaves was not affected, yet they developed with more xylem vessels with thick walls and lignin in their mesophyll and vascular tissues. The chloroplasts in internodes’ chlorenchyma, phloem, and cambium underwent significant ultrastructural modifications. The concentrations of macro and micronutrients varied significantly among the roots, trunk, canes, and leaves, including the growth characteristics. These structural and growth modifications of calcium deficiency enable us to understand better the link between the symptoms and functions and for a holistic understanding of Ca²⁺ functionalities.