Steam-girdling of barley (Hordeum vulgare) leaves leads to carbohydrate accumulation and accelerated leaf senescence, facilitating transcriptomic analysis of senescence-associated genes

Leaf senescence can be described as the dismantling of cellular components during a specific time interval before cell death. This has the effect of remobilizing N in the form of amino acids that can be relocalized to developing seeds. High levels of carbohydrates have previously been shown to promote the onset of the senescence process. Carbohydrate accumulation in barley (Hordeum vulgare) plants was induced experimentally by steam-girdling at the leaf base, occluding the phloem, and gene regulation under these conditions was investigated using the Affymetrix Barley GeneChip array and quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR). Transcript levels of plastidial (aminopeptidases, cnd41) and vacuolar (thiol and serine) proteases clearly increase in girdled leaves. Of special interest are cnd41, a plastidial aspartyl peptidase that has been implicated in Rubisco degradation in tobacco; and cp-mIII, a highly upregulated carboxypeptidase. SAG12, hexokinases and other senescence-specific genes are also upregulated under these conditions. Applying a genomic approach to the innovative experimental system described here significantly enhances our knowledge of leaf proteolysis and whole-plant N recycling.