Differential regulation of enzyme activities and physio-anatomical aspects of calcium nutrition in grapevine

•Consequences of calcium sufficiency and deficiency were examined in grapevine.•Photosynthesis declined paralleling with altered chloroplast ultrastructure in calcium- deficient vines.•The enzymes of sugar metabolism were both elevated and reduced in calcium-deficient vines. It remains true that through its signaling mechanisms, Ca2+ also has specific, direct effects on plant metabolic activities, which are poorly understood due to the currently trendy pursuit of Ca2+ signaling studies. This paucity triggered us to examine the virtues of calcium nutrition by investigating carbohydrate metabolism using combinations of physiological and microscopy techniques in Ca2+ sufficient and Ca2+ starved grapevines (Vitis vinifera L.). Net photosynthesis was severely down-regulated in Ca2+ deficient vines, which paralleled with altered chloroplast ultrastructure and reduced chlorophyll concentration. Interestingly, the activities of Rubisco, sucrose phosphate synthase (SPS), sucrose synthase (SS), and fructose-1, 6-bisphosphatase (FBPase) were elevated in Ca2+ deficient vines, while ADP-glucose pyrophosphorylase (AGPase) and phosphoribulose kinase (PRK) activities were reduced. Since plants evolved adaptive mechanisms to cope up with lack or excess of nutrients, these metabolic changes in Ca2+ deficient and sufficient grapevines could be interpreted as acclimation reactions to establish optimal homeostasis. However, given the controversial nature of calcium’s multifunctionality, we need concrete evidence for this radical new paradigm.