DROUGHT TOLERANCE MECHANISMS IN PLANTS AND THEIR GENETIC BASE IN WHEAT

Tolerantnost na sušu je kompleksno svojstvo nekih vrsta i genotipova biljaka, a određeno je različitim morfološkim i/ili fiziološkim odlikama. Tolerantni genotipovi sušu mogu prevladati na više načina: (1) ranim dozrijevanjem (mehanizam izbjegavanja suše), (2) zatvaranjem puči što spriječava preveliku transpiraciju, ali reducira i fotosintezu (mehanizam smanjenja dehidracije), ili (3) pojačanim nakupljanjem različitih osmolita koji održavaju turgor biljke i omogućavaju normalan metabolizam i u uvjetima vodnog stresa (mehanizam tolerantnosti na dehidraciju). Vrlo važna sposobnost tolerantnih biljaka je obrana od oksidativnog stresa kao sastavnog dijela vodnog stresa. Većina gena odgovornih za tolerantnost na sušu ima inducibilne promotore, a hormon abscizinska kiselina (ABA) je signal koji ih u dosta slučajeva aktivira. Kod pšenice je identificirano više lokusa za kvantitativna svojstva (QTL-a) povezanih sa svojstvom tolerantnosti, a nalaze se na različitim kromosomima. Osim u klasičnu selekciju tolerantnih genotipova, veliki napori se ulažu i u genetičke modifikacije biljaka za bolju tolerantnost. Genetički modificirana pšenica pokazala je veliku tolerantnost na sušu u poljskim pokusima.Drought tolerance is a complex trait of some plant species and genotypes determined by different morphological and/or physiological traits. Tolerant genotypes can circumvent drought in different ways: (1) by early maturity (mechanism of drought escape), (2) by closing stomata that prevents excessive transpiration, but also reduces photosynthesis (mechanism of drought avoidance), or (3) by enhanced accumulation of different osmolites that maintain plant turgor and enable normal metabolism in water stress conditions (mechanism of drought tolerance). The very important is also the ability of tolerant plants to defend against oxidative stress as part of water stress. Most of the genes responsible for tolerance to drought have inducible promotors, and abscisic acid (ABA) is a signal that induces many of them. Many loci for quantitative traits (QTL-s) that control drought tolerance in wheat have been identified and mapped on different chromosomes. Apart from conventional selection for drought tolerance, great efforts have been made to produce genetically modified plants tolerant to drought. Genetically modified wheat showed high drought tolerance in field conditions