Maize seedlings show cell-specific responses to heat shock as revealed by expression of RNA and protein.

The cellular localization of heat-shock proteins has been described in a number of experimental animal systems but is not well defined in plant systems. Sense and antisense RNA transcripts from the open reading frame (ORF) of 18-kDa maize heat-shock protein genes were employed in in situ hybridizations of inbred Oh43 radicles and plumules to reveal the locations of their mRNAs. Localization of the specific mRNAs to the younger meristematic cells of the root-tips and shoot-tips and also to the densely cytoplasmic cells of the vasculature was observed routinely. The ORF of one of our 18-kDa genes was cloned into an expression vector, and the 161-amino acid polypeptide was used to raise antibodies. Using a Fast Red procedure, the cellular positions of the heat-shock protein-antibody conjugates were observed in sections similar to those employed in the antisense RNA in situ hybridizations. The localization of the antibody appears to parallel closely the patterns of distribution of the mRNAs.

Production of normal, germinable and viable pollen from in vitro-cultured maize tassels.

Immature tassel meristems (1.0-1.5 cm long) of Zea mays L. inbred, Oh43, and single cross hybrid, Se60, cultured on a nutrient liquid medium underwent extensive development through to maturity and produced normal, mature, trinucleate pollen grains. The grains germinated on nutrient agar and on receptive silks and also produced viable kernels. No differences were observed between in vitro-produced pollen and in vivo pollen (pollen from greenhouse-grown plants) in characteristics such as pollen size, in vitro and in situ germination, and pollen tube growth in vitro. The kernels produced with in vitro pollen grew into mature plants (in vitro plants) which were similar to in vivo plants (plants produced with in vivo pollen), with no significant differences for all the morphological characteristics measured, and no phenotypic and cytological abnormalities. Gel electrophoresis of polypeptides revealed no major differences between in vitro and in vivo seedlings. This demonstration of fertilization and production of normal, uniform plants with pollen from cultured tassels has significant potential in basic and applied research studies.

Fertilization and seed production with pollen from in-vitro-cultured maize tassels.

Immature tassel meristems (1-1.5 cm) of maize (Zea mays L.) explanted to a defined nutrient medium underwent further growth and floral development. Microsporogenesis, gametogenesis and pollen maturation were completed within 25 d in vitro. The pollen, recovered from the cultured tassel, germinated on nutrient agar and also on receptive silks. Viable seed produced from controlled pollinations germinated and grew into mature, normal plants. Thus, a significant component of the life cycle of maize can be completed in vitro where analyses and manipulations are possible for both basic and applied research.