Potassium flux in the pollen tubes was essential in plant sexual reproduction

A Compendium of in vitro Germination Media for Pollen Research

The correct choice of in vitro pollen germination media (PGM) is crucial in basic and applied pollen research. However, the methodological gaps (e.g., strong focus of current research on model species and cultivated plants along with the lack of general rules for developing a PGM) makes experimenting with pollen difficult. We closed these gaps by compiling a compendium of optimized in vitro PGM recipes from more than 1800 articles published in English, German, and Russian from 1926 to 2019. The compendium includes 1572 PGM recipes successfully used to germinate pollen grains or produce pollen tubes in 816 species representing 412 genera and 114 families (both monocots and dicots). Among the 110 components recorded from the different PGM recipes, sucrose (89% of species), H₃BO₃ (77%), Ca²⁺ (59%), Mg²⁺ (44%), and K⁺ (39%) were the most commonly used PGM components. PGM pH was reported in 35% of all studies reviewed. Also, we identified some general rules for creating PGM for various groups of species differing in area of research (wild and cultivated species), phylogenetic relatedness (angiosperms vs. gymnosperms, dicots vs. monocots), pollen physiology (bi- and tri-cellular), biochemistry (starchy vs. starchless pollen grains), and stigma properties (dry vs. wet), and compared the component requirements. Sucrose, calcium, and magnesium concentrations were significantly different across most categories indicating that pollen sensitivity to sugar and mineral requirements in PGM is highly group-specific and should be accounted for when composing new PGM. This compendium is an important data resource on PGM and can facilitate future pollen research.

Calcium-Regulated Phosphorylation Systems Controlling Uptake and Balance of Plant Nutrients

Essential elements taken up from the soil and distributed throughout the whole plant play diverse roles in different tissues. Cations and anions contribute to maintenance of intracellular osmolarity and the formation of membrane potential, while nitrate, ammonium, and sulfate are incorporated into amino acids and other organic compounds. In contrast to these ion species, calcium concentrations are usually kept low in the cytosol and calcium displays unique behavior as a cytosolic signaling molecule. Various environmental stresses stimulate increases in the cytosolic calcium concentration, leading to activation of calcium-regulated protein kinases and downstream signaling pathways. In this review, we summarize the stress responsive regulation of nutrient uptake and balancing by two types of calcium-regulated phosphorylation systems: CPK and CBL-CIPK. CPK is a family of protein kinases activated by calcium. CBL is a group of calcium sensor proteins that interact with CIPK kinases, which phosphorylate their downstream targets. In Arabidopsis, quite a few ion transport systems are regulated by CPKs or CBL-CIPK complexes, including channels/transporters that mediate transport of potassium (KAT1, KAT2, GORK, AKT1, AKT2, HAK5, SPIK), sodium (SOS1), ammonium (AMT1;1, AMT1;2), nitrate and chloride (SLAC1, SLAH2, SLAH3, NRT1.1, NRT2.4, NRT2.5), and proton (AHA2, V-ATPase). CPKs and CBL-CIPKs also play a role in C/N nutrient response and in acquisition of magnesium and iron. This functional regulation by calcium-dependent phosphorylation systems ensures the growth of plants and enables them to acquire tolerance against various environmental stresses. Calcium serves as the key factor for the regulation of membrane transport systems.

Constituent analysis and proteomic evaluation of ovular secretions in Ginkgo biloba: not just a pollination medium

Pollination drop (PD) is a characteristic feature of major wind-pollinated gymnosperms and plays a vital role during the course of pollination, however, the composition and proteomic profile of PDs in Ginkgo biloba remain unclear. Through inductively coupled plasma mass spectrometry, we detected mineral elements in PDs, including calcium (Ca), sulfur (S), magnesium, boron, and potassium (K), among which S, Ca, and K were found at high levels. The total sugar concentration was approximately 5.908 mg/mL, which accounted for approximately 5.9% (mass ratio) of the PD. The sugars primarily consisted of fructose, glucose, and sucrose, of which the glucose level was highest, accounting for 57.6%, followed by fructose (37.1%) and sucrose (5.3%). We also used FTIR to validate the presence of sugars and proteins in PDs. Further proteomic analysis revealed that the PD contained calmodulin, α-L-arabinofuranosidase, β-D-xylosidase, superoxide dismutase, α-L-arabinosidase, glutathione S-transferase, histones, glycine-rich family protein, methionine synthase, and arabinogalactan, suggesting that proteins present in PDs of G. biloba play a critical role in the defense against external bacteria and facilitate germination and growth of the pollen tube. Our results suggest that PDs are not merely a medium to receive and transport pollen but may also play a more complex biological role in pollination and fertilization.