Plant genome values: how much do we know?

Abstract

Plants are the basis of life on earth. We cannot overemphasize their importance. The value of plant genome initiatives is self-evident. The need is to identify priorities for action. The angiosperm genome is highly variable, but the extent of this variability is unknown. Uncertainties remain about the number of genes and the number of species living. Many plants will become extinct before they are discovered. We risk losing both genes and vital information about plant uses. There are also major gaps in our karyotypic knowledge. No chromosome count exists for >70% of angiosperm species. DNA C values are known for only approximately 1% of angiosperms, a sample unrepresentative of the global flora. Researchers reported new relationships between genome size and characters of major interest for plant breeding and the environment and the need for more data. In 1997, a Royal Botanic Gardens Kew workshop identified gaps and planned international collaboration to fill them. An electronic version of the Angiosperm DNA C value database also was published. Another initiative, which will make a very significant contribution to the conservation of plant genetic diversity on a global scale is Kew's Millennium Seed Bank, partly funded by the U.K. Millennium Commission, celebrating the year 2000. Costing up to 80 million (1 = $1.62), its main aims are to collect and conserve the seed of almost all of the U.K. spermatophyte flora by the year 2000, to collect and conserve a further 10% of the world spermatophyte flora principally from the drylands by 2009, and to provide a world class building as the focus of this activity by 2000.

Figure 1

Root-tip mitotic metaphases in (A) the grass Z. biebersteiniana (2n ≈ 4) and (B) the palm V. gerardii (2n ≈ 600), new chromosome counts that increased the range of chromosome numbers known for monocots over fourfold since 1960 (11, 16). Chromosomes are C-banded by using a fluorochrome (A) or stained with Feulgen and aceto-orcein (B).

Figure 2

Relationships between genome size and four developmental or environmental characters in angiosperms: (a) minimum root-tip mitotic cycle time in six diploids grown at 23°C (redrawn from ref. 20); (b) the duration of meiosis in 18 diploid species (including three grass species) grown at 20°C (replotted from ref. 21); (c) response in the absolute growth rate of the shoot in a mixture of five herbaceous species (including three grass species) to elevated temperature—winter warming of +5°C above ambient (replotted from ref. 27); and (d) enhanced growth (responsiveness in final biomass to elevated CO₂) in eight annual grass species (replotted from ref. 25).