Introduction

Flowering in plants is a complex process involving the co-ordinated expression of many genes essential for the differentiation of specialised tissues. Whilst many of these genes may also be expressed in other tissues during growth of the plant, an important group of essential genes will be developmental- and tissue-specific, expressed only at critical stages and in defined tissues during the flowering process. In tobacco flowers for example, there are approximately 10000 ovary-specific and 11000 anther-specific mRNAs representing 40% and 42% of all diverse mRNAs present in the respective organs (Kamalay & Goldberg, 1980, 1984).

We are interested in genes which are expressed specifically in the male flowers of maize. In this monoecious plant the male flowers are borne in the tassel which terminates the main stem and the female flowers on ear branches which arise from nodes midway on the main stem. We have used differential screening of cDNA libraries made from whole tassels to isolate six male flower-specific (MFS) cDNAs from maize. Differential screening has also been used to clone floral-specific cDNAs from tomato (McCormick et al., 1987; Gasser et al., 1989), tobacco (Goldberg, 1988), pollen-specific cDNAs from maize (Stinson et al, 1987) and style-specific cDNAs from Brassica oleracea (Nasrallah et al., 1985) and Nicotiana alata (Anderson et al., 1985).

Whilst conventional Northern and dot blotting techniques using whole organ RNA preparations can be used to establish the organ specificity of the cDNA clones, it is clear that these techniques do not localise expression to particular tissues within the organ.