This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Drought tolerance is an important quantitative trait with multipart phenotypes that are often further complicated by plant phenology. Different types of environmental stresses, such as high irradiance, high temperatures, nutrient deficiencies, and toxicities, may challenge crops simultaneously; therefore, breeding for drought tolerance is very complicated. Interdisciplinary researchers have been attempting to dissect and comprehend the mechanisms of plant tolerance to drought stress using various methods; however, the limited success of molecular breeding and physiological approaches suggests that we rethink our strategies.
However, little is known about the metabolites associated with drought tolerance. The objectives of this study were to elucidate changes in metabolite levels in wheat under drought, and to identify potential metabolites associated with drought stress through untargeted metabolomic profiling using a liquid chromatography-high resolution mass spectrometry LC-HRMS -based technique called Isotopic Ratio Outlier Analysis.
Metabolomic analysis was performed on flag leaves of drought-stressed and control well-watered plants after 18 days of post-anthesis drought stress at three-hour intervals over a hour period.
Out of peaks detected in leaves, were identified as known metabolites. The most pronounced accumulation due to drought stress was demonstrated by tryptophan, proline, pipecolate and linamarin, whereas the most pronounced decrease was demonstrated by serine, trehalose, N-acetyl-glutamic acid, DIBOA-glucoside etc.
Three different patterns of metabolite accumulation were observed over hour period. The increased accumulated metabolites remained higher during all 8 time points in drought stressed leaves. On the contrary, metabolites that showed decreased level remained significantly lower during all or the most time points.
However, the levels of some decreased metabolites were lower during the day, but higher during night in drought stressed leaves. Both univariate and multivariate analyses predicted that N-acetyl-glutamic acid, proline, pipecolate, linamarin, tryptophan, and DIBOA-glucoside could be potential metabolite biomarkers, and their levels could serve as indicators of drought tolerance in wheat.
Introduction Wheat is one of the most widely produced and consumed cereal grains worldwide and global wheat demand is expected to rise in excess of million metric tons by . Production of major crops, including wheat, is declining in some regions of the world due to climate change, especially progressive drought stress, induced by either declining rainfall or higher water stress allied with a hot climate   .
Water stress during the flowering stage and onwards in wheat typically interrupts photosynthesis and increases translocation of carbohydrates from source to sink, reduces grain number, weight and yield, accelerates phasic development, reduces grain filling duration and enhances senescence     .
Genetic improvement is the most effective and sustainable method to reduce the detrimental effect of water stress. However, the genetic improvement of traits that confer stress tolerance can only be achieved when we have a better understanding of the biochemical mechanism controlling those traits.
The analyses of biologically important molecules are necessary to understand which molecules are influencing stress tolerance mechanisms in wheat plants. Under water-stress, plants produce an array of biomolecules including different metabolites . Plants can modify their physiology to acclimate to abiotic conditions through metabolic changes  .
Changes in the metabolic level in an organism are likely correlated with the phenotype, as metabolites are the end-products of biological systems . Other than the changes in the level of metabolites, little is known about their complex metabolic regulation under water stress or potential role in developing climate resilient wheat.
Crop yield has shown significant correlation with metabolites under drought . Metabolic composition is highly variable in a wide variety of plants including major crops like wheat rice maize and cassava .Genetic analysis of heat tolerance will help breeders produce rice (Oryza sativa L.) varieties adapted to future climates.
An F6 population of recombinant inbred lines of Bala (tolerant) × Azucena (susceptible) was screened for heat tolerance at anthesis by measuring spikelet fertility at 30°C (control) and 38°C (high temperature) in experiments conducted in the Philippines and the.
responsible for heat tolerance, heat-tolerant and -sensitive culti- vars or variable natural accessions can be compared at the physiological, molecular, and genetic levels.
Genetic analysis of heat tolerance will help breeders produce rice (Oryza sativa L.) varieties adapted to future climates. An F6 population of recombinant inbred lines of Bala (tolerant) × Azucena (susceptible) was screened for heat tolerance at anthesis by measuring spikelet fertility at 30°C.
Pollen viability represents sporo-gametophytic tolerance to the heat stress. Therefore, pollen fertility index under heat stress can be exploited to differentiate resistant and susceptible genotypes. In rice, QTLs for heat tolerance at flowering stage have been mapped on almost all rice chromosomes, improving heat tolerance in rice varieties using the identified genetic resources (Ye et al.
Ye C, Tenorio FA, Argayoso MA, Laza MA, Koh HJ, Redoña ED, Jagadish KSV, Gregorio GB. In the current research, the CSSLs were used for genetic analysis of heat tolerance at anthesis in rice for the first time.
Compared to other permanent mapping populations, such as RILs and DH, using CSSLs to map QTLs can eliminate the interference of genetic background, thus QTLs with minor effects could be detected (Ebitani.
et al. ).