Discovery of senescence associated metabolites in Juglans regia leaves by the use of principal component analysis (PCA)

During the last few years, the development of analytical methods has made great progress. Especially analytical methods such as UPLC-MS, being very fast and accurate and thus allowing the generation of a great amount of data at high speed have become more and more popular. In order to cope with the quantity of data being generated, methods of multivariate statistical analysis (MVA) can be used to minimize a complex data matrix and to extract the most relevant data.

In this project, principal component analysis (PCA) was used to discover differences in the LC-MS fingerprint chromatograms between samples of green and senescent leaves of Juglans regia L. Plant senescence describes the complex process of changes taking place in the plant metabolome, for example during autumn. Not only are substances decomposed and nutrients regained but also new substances can be generated. Regarding the discovery of new and possibly bioactive substances, plant senescence is seen as a promising new source. Examples are known where new substances are generated exclusively during plant senescence.

23 different samples were taken from Juglans regia green and yellow leaves throughout the year. Samples were either freeze dried or air dried and extracted with methanol in the ultrasonic bath. Fingerprint chromatograms were taken with UHPLC-ESI-qTOF-MS and the data was analysed with PCA.

It was discovered that senescence processes are responsible for changes in the metabolome of Juglans regia leaves. Additionally, the treatment of plant material plays a role regarding the fingerprint. In senescent leaves, for instance, sesquiterpenes were found that are absent in green leaves.