BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF BORON TOXICITY IN WHEAT AND BARLEY

Mahboobi, Homa Ph.D., in Biochemistry

Supervisor: Prof. Dr. Hüseyin A. Öktem

Co-supervisor: Prof. Dr. Meral Yücel

June 2000, 111 pages

In this work, several aspects of boron toxicity were investigated with the aim of identifying mechanism(s) that contribute to B-toxicity tolerance in wheat and barley. Studies were conducted on wheat (Triticum aestivum) cultivars named Bolal (B-tolerant) and Atay (B-sensitive) and barley (Hordeum vulgare) cultivars named Anadolu (B-tolerant) and Hamidiye (B-sensitive),

Firstly, changes in protein profiles were investigated in roots and leaves. Boron stress caused quantitative and qualitative changes in protein patterns of root and leaf. A newly synthesised protein (Mr: 35kDa, pI 7.8) in root of B-tolerant barley cultivar and a novel protein in root of B-tolerant wheat cultivar (Mr: 27kDa, pI 7.1) were detected. Leaf tissue electrophoretic patterns of B-stressed seedlings revealed induction of numerous proteins upon boron toxicity especially in tolerant cultivars. It suggests the possibility that these proteins might play a role in B-resistance mechanism in these species.

Secondly, changes in cell wall uronic acid contents upon boron toxicity were studied. The results suggested that cell wall uronic acid content does not contribute to detoxification of excess boron in wheat and barley.

Finally, changes in activity of key enzymes of nitrogen assimilation, namely nitrate reductase and glutamate dehydrogenase upon boron toxicity were investigated. Total activity of nitrate reductase tended to decrease following boron toxicity in root and leaf tissues of all cultivars and this decrease was more pronounced in sensitive cultivars. Reduction of total activity of nitrate reductase in roots was more than in leaf tissues. Total activity of glutamate dehydrogenase, increased upon boron toxicity in roots and leaves of all cultivars, especially in leaves of tolerant cultivars. This could be an adaptive mechanism in these species and possibly plays a protective role under boron stress conditions.