Researchers Seek Better Understanding of Olive Drupe Development

Newly pub­lished research in Greece is paving the way to a deeper under­stand­ing of olive drupe ripen­ing.

Scientists at the Aristotle University of Thessaloniki inves­ti­gated how the mol­e­c­u­lar and phys­i­o­log­i­cal pro­files of olive dru­pes change as they go through the ripen­ing process.

The researchers hope that a bet­ter under­stand­ing of ripen­ing will help farm­ers make the best deci­sions for plant­ing table olive and olive oil-pro­duc­ing vari­eties. The sci­en­tists explained that one of the project’s main goals is to help develop the Greek coun­try­side while pro­mot­ing the inter­ests of pro­duc­ers and con­sumers.

“At the same time, empha­sis is placed on plant pro­tec­tion and the fight against impor­tant ene­mies of the olive tree,” Evangelos Karagiannis, who led the research team, told Olive Oil Times.

The researchers empha­sized that olive devel­op­ment is a com­plex bio­log­i­cal process that affects the human diet, and their study aimed to under­stand the mol­e­c­u­lar basis of olive qual­ity bet­ter.

“This means that by deploy­ing high-through­put analy­ses, such as liq­uid chro­matog­ra­phy or gas chro­matog­ra­phy-mass spec­trom­e­try tech­niques and oth­ers, we obtain novel pro­teomic [the large-scale study of pro­teins] and metabolomic data,” Karagiannis said.

“This pro­vides new knowl­edge about the mol­e­c­u­lar and phys­i­o­log­i­cal pro­file of the olive dur­ing drupe devel­op­ment,” he added. ​“This knowl­edge paves the way for fur­ther research, for exam­ple with breed­ing pro­grams, and pro­vides new insights into the final qual­ity fea­tures of the fruits.”

According to the researchers, mul­ti­level stud­ies inte­grat­ing olive tran­scrip­tomics (the study of an organism’s RNA), pro­teomics and metabolomics are still lack­ing.

“Such an ana­lyt­i­cal approach will pro­vide an enor­mous amount of data that expands our knowl­edge in the olive devel­op­ment and mat­u­ra­tion process,” the researchers wrote.

The first metabolomic inves­ti­ga­tion con­ducted by the Greek researchers focused on the Chondrolia Chalkidikis cul­ti­var.

“This cul­ti­var is char­ac­ter­ized by its big and green olives that are har­vested by hand,” Karagiannis said. ​“It was selected because it is wide­spread in north­ern Greece. Its dru­pes were mainly picked dur­ing the green-mature stage right before they turned pur­ple.”

Those fruits were then exam­ined in six sub­se­quent stages of ripen­ing. The amount of pri­mary and sec­ondary metabo­lites and pro­teins were iden­ti­fied, and how they changed through­out the ripen­ing process was also observed.

“We obtained a metabolomic and pro­teomic pro­file of Chondrolia Chalkidikis at the green-mature and pur­ple-turn­ing-black stages, which are the stages mostly used for both table olive and olive oil pro­duc­tion,” Karagiannis said. ​“This allowed us to under­stand the rel­e­vant bio­chem­i­cal path­ways asso­ci­ated with the devel­op­ment process.”

“More specif­i­cally, this approach will pro­vide new insights and update our cur­rent knowl­edge on the impor­tant role of pro­teins and metabo­lites in drupe devel­op­ment and ripen­ing, and thus would pro­vide a basis for fur­ther study on olive ripen­ing biol­ogy,” he added.

The olive fruit ripen­ing tran­si­tion from the green-mature to the pur­ple-turn­ing-black stage trig­gers numer­ous phe­no­typ­i­cal and phys­i­o­log­i­cal changes – for exam­ple, the soft­en­ing of the drupe. It also leads to changes at the mol­e­c­u­lar level, such as car­bo­hy­drate reg­u­la­tion.

“According to the results of our study, at the pur­ple-turn­ing-black stage, the main high­lights are car­bo­hy­drate metab­o­lisms, such as cel­lobiose and galac­tose, and oleu­ropein accu­mu­la­tion,” Karagiannis said. ​“On the other hand, at the green-mature stage, sev­eral pho­to­syn­thetic-related pro­teins were sig­nif­i­cantly up-reg­u­lated.”

“This result clearly indi­cates the direct con­nec­tion between the phe­no­typ­i­cal char­ac­ter­is­tics of the olives – for instance, their green color – with changes in the mol­e­c­u­lar-bio­log­i­cal level, such as the increase of the pho­to­syn­thetic pro­teins,” he added.

At the cur­rent research stage, sci­en­tists are inves­ti­gat­ing how much the observed metabolomic shifts dur­ing ripen­ing depend on fac­tors such as the cul­ti­var or the tree’s loca­tion.

“Both metabolomic and pro­teomic shifts depend greatly on dis­tinct para­me­ters such as the eval­u­ated cul­ti­var, grow­ing loca­tion, ter­rain, water sup­ply, stage of devel­op­ment and so on,” Karagiannis said.

“For instance, it is known that oleu­ropein is the most accu­mu­lated com­pound in olive dru­pes,” he added. ​“However, in green-col­ored olive cul­ti­vars at har­vest period, oleu­ropein con­cen­tra­tion could remain at high lev­els or may fall to zero at full mat­u­ra­tion in some pur­ple-black-col­ored cul­ti­vars.”

“Moreover, it is worth men­tion­ing that most of the olive devel­op­men­tal-related stud­ies are mainly focus­ing on the sec­ondary metab­o­lism, with­out pro­vid­ing cer­tain infor­ma­tion about the pri­mary metab­o­lism, which is directly involved in fruit’s nor­mal growth and devel­op­ment,” Karagiannis con­tin­ued.

Overall, the researchers observed sev­eral key changes of the pro­teins and the metabo­lites they believe lay the ground­work for fur­ther stud­ies to under­stand olive fruit devel­op­ment bet­ter.

“This study uncov­ered the impor­tant role of pro­teins and metabo­lites that are asso­ci­ated with drupe devel­op­ment and would pro­vide a basis for fur­ther study on olive biol­ogy,” the researchers con­cluded.

• Food Chemistry
• The Olive Tree Genome