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HvS40 is a marker gene for leaf senescence in barley. It is expressed during dark-induced as well as age-dependent senescence and in response to biotic and abiotic stress factors. Its expression is also induced by hormones involved in the control of stress responses and senescence processes. Run-on-transcription assays with isolated nuclei showed that its expression during dark-induced senescence is regulated at the transcriptional level. Its promoter contains two elicitor response elements (ERE) consisting of two W-boxes. Binding of proteins to these motifs changed during senescence. A 24-kDa protein binding to ERE2 of nonsenescent leaves was identified as WHIRLY1.

Senescence of barley flag leaves has been studied under field conditions. Progression of senescence was monitored by the decrease in photosystem II efficiency (measured as F v /F m ) and chlorophyll content of the flag leaves. To identify genes upregulated during natural senescence of barley leaves, a cDNA library prepared from RNA of senescent flag leaves collected in the field, was differentially screened, and three cDNA clones were isolated. Enhanced expression of the corresponding genes was studied either in barley leaves of different developmental stages or in barley leaves induced to senesce by darkness. While transcripts represented by the cDNA clones HvSF6 and HvSF42 accumulated during senescence of flag leaves as well as during dark-induced senescence of attached primary foliage leaves, the transcript of HvSF2 accumulated exclusively during natural senescence. Based on sequence homologies the cDNA clone HvSF2 encodes the first senescence-related glycosyltransferase. The sequence of the cDNA clone HvSF42 is highly homologous to cysteine protease sequences. The protein encoded by the cDNA HvSF6 resembles the wheat geminivirus repA binding protein GRAB2.