Dissertations and Theses @ UNI


Thesis (UNI Access Only)


Barley--Effect of drought on; Barley--Metabolism;


Drought is the single most important stress that reduces crop yield. Plants are particularly vulnerable to drought at the reproductive stage. The photosynthetic organs of the barley spike are largely responsible for grain filling and are considered to be drought tolerant. In barley and other cereal crops, drought response has been largely characterized in the vegetative organs. In this study, barley plants were exposed to drought stress for four days at the grain filling stage to compare differences in the response between the inflorescence (spike) organs (lemma, palea, and awn) and the fifth leaf. We have three objectives. First, determine differences in the water status of the spike and the fifth leaf during drought stress. For this, we measured relative water content and osmotic potential. Second, determine differences in the rate of gas exchange (photosynthesis and stomatal conductance) between the spike and the leaf in response to drought stress. Third, analyze changes in the metabolome of the spike and the leaf during drought stress. Metabolites were extracted and modified using a derivatization technique. This was necessary to identify and quantify non-volatile compounds using gas chromatography-mass spectrometry (GC/MS) between control and drought-stressed samples. Relative water content (RWC) and osmotic potential decreased significantly during drought with some difference between organs. However, compared to the flag leaf, the decrease in the RWC of the lemma and the palea was very small and that of osmotic potential was greater. This suggests that the lemma and the palea maintain better water status during drought, most likely through osmotic adjustment. Photosynthesis and stomatal conductance measurements from the awn and the fifth leaf also showed that these processes are depressed significantly during the four day drought treatment. This suggests that the awn and the fifth leaf contribute very little photosynthate for grain filling during drought stress. In total, 18 metabolites were positively identified and quantified. The number and types of metabolites accumulated varied between organs. The flag leaf had many metabolites accumulated followed by the awn. Both the lemma, awn, and flag leaf accumulated sugars (glucose, fructose, and sucrose) and awn and flag leaf also showed higher amounts of amino acids. Proline was the only metabolite that accumulated in all organs during drought stress, and the only metabolite that accumulated in the palea.

Year of Submission


Degree Name

Master of Science


Department of Biology

First Advisor

Tilahun Abebe, Chair

Date Original


Object Description

1 PDF file (xi, 92 pages)



File Format


Off-Campus Download