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

Abstract

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.

International Biological Flora:Ginkgo biloba

“…A mature male tree can produce 12,000–17,000 pollen grains per year (Xing et al, 1998). Mature pollen is shed from microsporangia and floats in the air until it is trapped by the pollination drop which can transport pollen to the nucellar surface (Cheng et al, 2018; Jin, Jiang, et al, 2012; Jin, Wang, et al, 2012). Once inside the ovule, the male gametophyte commences a 4‐month long development period that culminates in the production of a pair of multi‐flagellated spermatozoids, one of which fertilises a waiting egg cell (Friedman, 1987).…”

The role of pollination in controlling Ginkgo biloba ovule development

“…The possible degradation of sucrose was further suggested by increasing glucose‐6‐phosphate and fructose‐6‐phosphate content, which are the main products derived from glucose during glycolysis, guaranteeing a carbon flux towards the Krebs cycle. The modulated regulation of genes connected with sugars and amino acid metabolism is also consistent with studies on Ginkgo pollination drop composition, which demonstrated that the drop is mainly composed of sugars (at a high level) and amino acids (at a lower level) (Nepi et al ., 2017 ; von Aderkas et al ., 2018 ; Cheng et al ., 2018 ; Prior et al ., 2019 ; Lu et al ., 2020 ).…”

“…Lastly, genes required for the defence against abiotic and biotic stresses are always expressed at high levels in the stages under consideration. This is probably because the micropyle and the pollination drop represent an open way and a vehicle for putative pathogens that could enter the ovule (von Aderkas et al ., 2018 ; Cheng et al ., 2018 ; Lu et al ., 2020 ). Indeed, protection from potential bacterial and fungal pathogens is essential.…”

Phytohormone requirements for pollination drop secretion in Ginkgo biloba ovules

“…Furthermore, the secretory mechanisms for both PDs and nectar may also be similar (Nepi et al 2009(Nepi et al , 2012Lu et al 2020). In addition, several substances other than sugars and amino acids have been found in nectar, and some affect the foraging behavior of insects and potentially increase the benefits to the plant (Nepi et al 2018;Cheng et al 2018). JA is a phytohormone that is involved in plant flower development as well as plant defense (Wasternack and Hause 2013).…”