The root system of maize consists of the primary root and a variable number of lateral seminal‐, crown‐ and brace roots. Except for the primary root and some minor roots forming at the mesocotyl, all other roots grow out of nodal regions, namely, the embryogenic scutellar node and the underground—as well as the lower above‐ground stem nodes. Besides their role in water and nutrient uptake, some of these roots (crown‐ and brace roots) are essential for the lodging resistance of the plants. This property of the crown roots has now been successfully used for screening a segregating F2 population of a cross between a flint inbred line and an En transposon line. Two allelic root‐deficient mutants have been isolated and have been designated rtcs‐1 and rtcs‐2 for their complete lack of formation of crown‐ and lateral seminal roots. They survive by the ability of the primary root to support the growth of the developing plant. The monogenic and recessive mutants appear to be affected in an early root‐forming function since no primordia are formed either in the case of embryo‐borne lateral seminal or stem‐derived crown roots. The Rtcs locus could be mapped to the short arm of chromosome 1 with the help of a co‐segregating RAPD marker. The effect of the mutation seems to be highly specific since no pleiotropic effects on other parts of the plants have been observed. The formation of adventitious roots can, however, still be induced in the mesocotyl region of the mutant.

An endosperm derived tissue culture of maize (Zea mays L.) variety A636 has been characterised for its ability to synthesize zein protein and respond to a zein gene regulatory element. Western analysis with zein specific antibodies revealed the distinct presence of zein proteins of the 15, 19 and 21 kDa classes in this tissue, in contrast to an embryo-derived Black Mexican Sweet variety tissue culture which exhibited no zein proteins. Transient transformation studies with a cauliflower mosaic virus 35S promoter and luciferase reporter gene construct demonstrate that protoplasts from this tissue culture, but not from the embryo-derived culture, respond positively to the potential enhancer which is located approximately 300 base pairs upstream of the coding region in most zein genes of maize, thus establishing the usefulness of this culture for studies of tissue specific gene regulation.

The high mobility group (HMG) proteins represent a class of chromosomal non‐histone proteins with an assumed influence on transcription. In this context, the effect of the maize HMGa protein on reporter gene expression was examined. Transient co‐transformation experiments in maize protoplasts with plasmid constructs directing the synthesis of the maize HMGa protein and with a luciferase reporter plasmid demonstrated a stimulatory effect of the HMGa protein on the reporter gene expression. Additional experiments with HMGa deletion constructs indicated that the HMG‐Box DNA‐binding motif is important for the observed effect, while the acidic carboxy‐terminal domain of the HMGa protein appears to be dispensable.

Chromosomal non-histone high-mobility-group (HMG) proteins represent essential components of eukaryotic chromatin and have also been isolated from a variety of plants. In maize, studies on structure and function of the two larger of the four major HMG proteins have recently been performed and are now extended by analysis of their in vivo stability using pulse-chase experiments in a cell suspension culture. The half-life of the analyzed HMGa and HMGb proteins was found to be 65 h or more than 78 h, respectively.