Flower bud opening and senescence in roses (Rosa hybrida L.)

The flower is the most significant and beautiful part of plants. Flowers are very useful organs in plant developmental phenomenon. During flower bud opening, various events takes place in a well defined sequence, representing all aspects of plant development, such as cell division, cellular differentiation, cell elongation or expansion and a wide spectrum of gene expression. The complexity of flower bud opening illustrates that various biological mechanisms are involved at different stages. Senescence represents the ultimate stage of floral development and results in wilting or abscission of whole flower or flower parts. Senescence is an active process and governed by a well defined cell death program. Once a flower bud opens, the programmed senescence of petal allows the removal of a metabolically active tissue. In leaves, this process can be reversed, but in floral tissue it cannot, indicating that a highly controlled genetic program for cell death is operating. The termination of a flower involves at least two, sometimes overlapping, mechanisms. In one, the perianth abscises before the majority of its cells initiate a cell death program. Abscission may occur before or during the mobilization of food reserves to other parts of the plant. Alternatively, the petals may be more persistent, so that cell deterioration and food remobilization occur while the petals are still part of the flower. The overall pattern of floral opening varies widely between plant genera, therefore, a number of senescence parameters have been used to group plants into somewhat arbitrary categories. Opening and senescence of rose flower is still an unsolved jigsaw in the world of floriculture industry and the mechanism behind the onset of the very early events in the sequence still remains to be elucidated. Hence, for advancing the knowledge on the pertinent aspect of bud opening and senescence the literature has been cited under this review.     

Site-specific excisional recombination strategies for elimination of undesirable transgenes from crop plants

A major limitation of crop biotechnology and breeding is the lack of efficient molecular technologies for precise engineering of target genomic loci. While transformation procedures have become routine for a growing number of plant species, the random introduction of complex transgenenic DNA into the plant genome by current methods generates unpredictable effects on both transgene and homologous native gene expression. The risk of transgene transfer into related plant species and consumers is another concern associated with the conventional transformation technologies. Various approaches to avoid or eliminate undesirable transgenes, most notably selectable marker genes used in plant transformation, have recently been developed. These approaches include cotransformation with two independent T-DNAs or plasmid DNAs followed by their subsequent segregation, transposon-mediated DNA elimination, and most recently, attempts to replace bacterial T-DNA borders and selectable marker genes with functional equivalents of plant origin. The use of site-specific recombination to remove undesired DNA from the plant genome and concomitantly, via excision-mediated DNA rearrangement, switch-activate by choice transgenes of agronomical, food or feed quality traits provides a versatile “transgene maintenance and control” strategy that can significantly contribute to the transfer of transgenic laboratory developments into farming practice. This review focuses on recent reports demonstrating the elimination of undesirable transgenes (essentially selectable marker and recombinase genes) from the plant genome and concomitant activation of a silent transgene (e.g., a reporter gene) mediated by different site-specific recombinases driven by constitutive or chemically, environmentally or developmentally regulated promoters. These reports indicate major progress in excision strategies which extends application of the technology from annual, sexually propagated plants towards perennial, woody and vegetatively propagated plants. Current trends and future prospects for optimization of excision-activation machinery and its practical implementation for the generation of transgenic plants and plant products free of undesired genes are discussed.     

Rapid photometric assay of growth of Mycoplasma mycoides subsp. capri

A new spectrophotometric technique for evaluation of early growth in liquid culture of Mycoplasma mycoides subsp. capri has been developed. As turbidity does not appear until after incubation to 18 h the method utilizes the change in absorbance of the medium at 550 nm to monitor growth. The change in absorbance of the medium (which contains phenol red) occurs when the pH changes due to microbial growth. For measurement of growth at later stages when turbidity is proportional to number of colony forming units, two other wavelengths (450 nm and 700 nm) have been suggested.     

Identity cards for patients infected with HIV?

Dr A C Srivastava has written to us to describe a case that raises the suggestion that people infected with the human immuno-deficiency virus (HIV) should carry identity cards. We asked two physicians, a general practitioner working with patients with the acquired immune deficiency syndrome (AIDS), and a general practitioner with a special interest in medical ethics to respond to the broad issues raised by Dr Srivastava''s letter.