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CROP PHYSIOLOGY & METABOLISM

Gene Expression of Metallothioneins in Barley during Senescence and Heavy Metal Treatment

^a Institute of Plant Physiology, Martin-Luther Univ. Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Germany
^b Institute of Biochemistry, Martin-Luther-Univ. Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle, Germany

^* Corresponding author (klaus.humbeck{at}pflanzenphys.uni-halle.de).

Despite their ubiquitous distribution, the exact functions of metallothioneins (MTs) are still not known. We analyzed the expression of four novel barley (Hordeum vulgare L.) genes coding for MTs, comparing two different situations: (i) leaf senescence, and (ii) heavy metal stress. Physiological analysis of chlorophyll content and photosystem II efficiency revealed similar stress response during natural leaf senescence and short-term heavy metal treatment with toxic concentrations of Cu and Cd. Gene expression patterns of the newly identified MTs (HvMT-1a, HvMT-2a, HvMT-2b and HvMT-3a) clearly vary under these different conditions, suggesting specific roles for the barley MTs during leaf senescence and heavy metal stress. While HvMT-1a is induced during leaf senescence and after heavy metal treatment but not during metal deficiency, expression of HvMT-2a is not affected under any of conditions tested. The MT HvMT-3a is only induced in response to Cu deficiency and HvMT-2b is downregulated in response to Cd stress.

Abbreviations: aa, amino acids • bp, base pairs • EST, expressed sequence tag • MS, Murashige–Skoog • MT, metallothionein • PS, photosystem • RT-PCR • reverse transcription polymerase chain reaction.