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A new viviparous mutant of maize (Zea mays L.), associated with genetic instability and designated viviparous-12 (vp12), was identified in a synthetic Tuxpeño adapted to tropical regions. In the present work, the linkage group of this new locus was determined. Progenies of inbred line L477 segregating for the vp12 mutant were crossed with waxy-marked reciprocal translocation stocks. The phenotypic frequencies of the wx and vp12 mutants were analyzed in F2 progenies. The results demonstrated that the Viviparous-12 locus of maize is located on the long arm of chromosome 6.

Photosynthetic efficiency is considered one of the traits potentially suitable to differentiate hybrids from their inbred lines. Previous evaluations concerning photosynthetic efficiencies of maize (Zea mays L.) plants in the field have shown inconsistent and contradictory data. In this work, we attempted to study photosynthetic O2 evolution through photoacoustic spectroscopy in intact undetached leaves of dark-adapted seedlings of inbreds and their hybrids. The results indicate that photosynthetic efficiencies of inbreds and hybrids can be differentiated by photoacoustic measurements of oxygen evolution, providing a parameter that might prove useful in evaluating plant genotypes.

A new and highly sensitive method, based on the photoacoustic effect, is described for in vivo and in situ studies of photosynthetic activity of undetached leaves. The general utility of this simple photothermal method is demonstrated by examining the spectroscopy and photosynthetic activity of green, striped, and albino plants of maize (Zea mays L.).

We have shown that the open reading frame orf221 is an active mitochondrial gene which encodes a novel mitochondrial polypeptide. The orf221 sequence is common to higher plants but absent in animal and fungal mitochondria. A mitochondrial polypeptide with an apparent molecular weight of 21,000 was detected with a polyclonal antibody raised against an ORF221 fusion protein. In organello translation followed by immunoprecipitation with the anti-ORF221 antibody demonstrated that this polypeptide is encoded by the orf221 gene in plant mitochondria. The ORF221 was found to be a mitochondrial membrane protein in normal (N), cms-T, and cms-C cytoplasms of several inbred lines of maize (Zea mays L.) and in other plant species.

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.

Germplasm sources from the Maydea Tribe are being utilized for maize improvement. Several species of this Tribe have been introduced into a research program and are being exploited through conventional breeding, tissue culture, and techniques of molecular biology, with the aim of gaining access to new corn genotypes. Teosinte species, as well as isogenic lines and commercial hybrids of Zea mays, are being used for tissue culture screening for regeneration capacity. Among teosinte materials, Zea diploperennis seems very attractive due to its perennial habit, whereas the annual Zea mexicana is the closest relative to domesticated corn. Interspecific hybrids from corn and teosinte species are also being utilized in this program.