In a transgenic plant, a housekeeping gene could be expressed under the control of the CAB promoter or similar promoter expressed prior to senescence. It is well es- tablished that the CAB promoter drives expression in photosynthetic leaves and is rapidly attenuated once senescence begins (Fig. 2 and Lohman et al. 1994). Thus, RAN1 or an- other gene could be expressed before senescence begins possibly allowing normal development of a mutant. Once se- nescence begins, the expression of the gene would decrease allowing researchers to study the progression of senescence in the absence of the gene to be studie