The fiming of maize leaf senescence and characferisaiion oi setieseence-related cDNAs. -Physiol. Plant. 93: 67.V682.Leaf seneseenee was eharaeferised in fwo Zea mays lines, earlier senescence (ESl and later senescence (LSi. Loss of chlorophyll was delayed in LS compared with ES, but the decline in photosynthesis occurred simultanetiusly in fhe two lines. Western analysis defected transition points during senescence of both lines when major quantitative and qualitati\e changes oeeutTed in a number of leaf proteins. Differences in fhe pattern ol translatable mRNAs were apparenf earlier fhan alterations in pigtTient or protein levels. , A cDN.A library was constructed using mRNA from ES leaves early in senescence and differenfial screening was employed to isolate senescence-relafed clones. Two seneseence-enhaneed cDNAs showed sequenee homology with cDNAs for seed profeins -a eysteine protease and a protein-processing enzyme. These findings suggest fhat there are similarities between gene expression during seed maturation, germinafion and leaf senescence. Other senescence-enhanced eDN.As were related to genes implieated In glueoneogenesis and chlorophyll breakdown.

The fiming of maize leaf senescence and characferisaiion oi setieseence-related cDNAs. -Physiol. Plant. 93: 67.V682.Leaf seneseenee was eharaeferised in fwo Zea mays lines, earlier senescence (ESl and later senescence (LSi. Loss of chlorophyll was delayed in LS compared with ES, but the decline in photosynthesis occurred simultanetiusly in fhe two lines. Western analysis defected transition points during senescence of both lines when major quantitative and qualitati\e changes oeeutTed in a number of leaf proteins. Differences in fhe pattern ol translatable mRNAs were apparenf earlier fhan alterations in pigtTient or protein levels. , A cDN.A library was constructed using mRNA from ES leaves early in senescence and differenfial screening was employed to isolate senescence-relafed clones. Two seneseence-enhaneed cDNAs showed sequenee homology with cDNAs for seed profeins -a eysteine protease and a protein-processing enzyme. These findings suggest fhat there are similarities between gene expression during seed maturation, germinafion and leaf senescence. Other senescence-enhanced eDN.As were related to genes implieated In glueoneogenesis and chlorophyll breakdown.

Sequence analysis of a 1.4 kb clone from a cDNA library of senescing Zea mays leaves reveals an open reading frame for a 360 amino acid protein. Both the DNA and deduced amino acid sequences are highly homologous to the cysteine proteinases oryzain gamma and aleurain. Northern analysis demonstrates that the corresponding RNA level increases during natural leaf senescence, seedling germination and in chilling of tolerant maize lines, but decreases in a sensitive line. The mRNA level also decreases in regreening leaves, in dark-induced senescence and in nutrient or water stress. Southern and RFLP analysis provide evidence that the gene has two copies, on chromosomes 2 and 7.