Multiple roles of proline in plant responses to abiotic stress

Biljke u prirodnom okolišu vrlo su često izložene različitim stresnim uvjetima i preživljavanje u takvim uvjetima omogućuju im brojne prilagodbe. Prolin, osim što je jedna od proteogenih aminokiselina, ima više važnih uloga u biljkama. U ovom su radu opisani metabolički putovi prolina te mehanizmi njegovog djelovanja u stresnim uvjetima. Brojne uloge prolina najčešće su rezultat njegovog nakupljanja u biljnoj stanici koje izravno ovisi o samom metabolizmu prolina, tj. biosintezi, transportu i razgradnji. Brojna istraživanja potvrdila su ulogu prolina u uvjetima visoke ili niske temperature, manjka vode, povišenog saliniteta i prisutnosti teških metala. Najviše je istraživana uloga prolina kao kompatibilnog osmolita, no on ima i brojne druge uloge. Prolin je molekularni šaperon koji stabilizira brojne enzime mnogih metaboličkim putova, a također sudjeluje u neutralizaciji ROS. Metabolizam prolina važan je i za održavanje NADP+/ NADPH ravnoteže tijekom stresnih uvjeta, a nakupljeni prolin može biti izvor energije za biljku po završetku djelovanja stresnih uvjeta. Otkrića o ulogama prolina i njegovom metabolizmu moguće je primijeniti za stvaranje novih, poboljšanih sorti koje će biti rodnije i lakše za uzgoj, a daljnja istraživanja detaljnije će razjasniti uloge prolina. Postoji mogućnost otkrića i novih uloga prolina u biljkama izloženim kako abiotičkom, tako i biotičkim stresnim uvjetima.Plants in natural habitat are very often exposed to different stressful conditions and their survival in such conditions is enabled by many adjustments. Proline, except being one of proteinogenic amino acids, has many important functions in plants. In this article are described metabolic pathways of proline and mechanisms by which it acts during stressful conditions. Many functions of proline are mainly the result of its accumulation in plant cell that depends directly on its metabolism, i.e. biosynthesis, transport and catabolism. Many researches have confirmed function of proline in conditions of high or low temperature, water deficit, high salinity and heavy metals. The most studied proline function is the one of proline as compatible osmolyte, but it has many other functions as well. Proline is molecular chaperone able to stabilize numerous enzymes of many metabolic pathways and it also takes part in ROS scavenging. Proline metabolism also plays role in maintaining NADP+/ NADPH balance during stressful conditions, while accumulated proline serves as energy source for plant once the stressful conditions are over. Discoveries of24 proline functions and its metabolism can be used for creation of new, improved cultivars that will have higher yields and will be easier to grow and further researches will clarify exact functions of proline. There is also a possibility of discovering new, yet unknown proline functions in plants exposed to different stressful conditions, both biotic and abiotic