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In the past ten years considerable progress has been made on plant regeneration from tissues, cells, and protoplasts of various Gramineae species. In maize, plant regeneration was first described in 19751. After the initial reports on somatic embryogenesis in maize in 19822,3, plant regeneration from embryo-derived callus was extended to numerous other genotypes4,5,6. Genetic variability for plant regeneration has been reported within maize germplasms adapted to temperate7,8,9,10,11 and tropical6 regions. Further studies on the genetic control of somatic embryogenesis are still needed to better understand and manipulate this trait. Considerable attention has also been directed at studying the genetic variability observed among plants derived from maize callus for use in genetics and breeding12,13,14,15. The possibility of regenerating plants from maize cell suspension and protoplast cultures has opened new perspectives for direct gene transfer. Nevertheless, reports on the establishment of maize cell suspension and protoplast cultures capable of regenerating plants remain limited to a few genotypes16,17,18,19.

We report plant regeneration from maize (Zea mays L.) protoplasts with recovery of fertile plants from a Cateto inbred line adapted to tropical regions. Protoplasts were isolated from embryogenic cell suspension cultures capable of regenerating fertile plants. Cell colonies and embryogenic calli were obtained at high frequencies when protoplasts were cultured either in a thin layer of liquid medium or on cellulose-nitrate filters placed on a feeder layer of maize cells. High plating efficiencies were obtained with both culture methods using either a modified KM-8p or a modified N6 culture media. The results confirmed that maize protoplasts maintain the regeneration capacity of donor cells. We also demonstrated that high plating efficiencies and plant regeneration from maize protoplasts can be achieved with different culture methods. Furthermore, we recovered fertile plants with viable progenies from maize protoplasts.

High frequency and reliable plant regeneration from somatic cells of Zea mays is the key step in allowing the tools of soma-clonal variation, somatic cell hybridization, and recombinant DNA to be used in the development of improved breeding lines. This communication describes high frequency plant regeneration from somatic stem donor tissue of field-grown Zea diploperennis. Reliable plant regeneration has now been achieved in a perennial diploid relative of corn (Zea diploperennis), which, like perennials in general, is highly tillered. This species is being used in our maize improvement program as a source of germplasm for the unique trait of high tillering and its associated capacity for plantlet regeneration. After 3–4 subcultures of cultured somatic tissues on a primary medium, small callus fragments are transferred to secondary medium devoid of the auxin, 2,4-D. After a few days, numerous shoots regenerate and develop into normal plantlets which are then separated and transferred to a tertiary medium for root development. The selection of somaclonal variants from cultured somatic cells of interspecific hybrids between corn and teosinte holds promise for the synthesis of breeding lines suited for the development of improved corn varieties.

Photoacoustic spectroscopy is an efficient tool for the non-destructive assessment of chlorophyll and carotenoid deficient mutants of Zea mays L. Intact leaf samples taken from the mutants Albina, Luteus I and Luteus II were compared with those from the corresponding isogenic normals. The results are compared with those obtained applying some commonly used destructive techniques.

High frequency plant regeneration is described for Zea diploperennis callus from somatic tissues. Small callus fragments were excised after 3-4 passages on primary medium (MS salts containing 2,4-D) and transferred to regeneration medium (without 2,4-D). After 10-15 days, numerous shoots were observed which grew to normal plantlets following separation and transfer to a rooting medium. Presently, ca. 500 plants have been recovered from which approximately 80 plants are growing in small pots in a nursery and ca. 50 plants have already produced normal flowers and seeds under field conditions. The culture of somatic tissues of interspecific hybrids between cultivated corn and teosinte may offer new success for in vitro plant regeneration.