Plant tissues, aging

As a plant tissue ages, the solubility of the polysaccharides decreases to some extent. Decreased solubility is most pronounced when the tissue material is dried. Insolubilization is not inherent in the drying process itself because it is possible to dry plant material in such a way as to prevent loss of solubility or chemical reactivity. Optimum drying... 

Before we can predict the response of a plant variety to a specific pollutant or group of pollutants, we must understand the following factors genetic variability (both between and within species), climatic and edaphic factors, interactions with other pollutants, interactions with biotic pathogens and insects, and the growth and physiologic age of susceptible plant tissue. The overall conceptualization of relationships between pollutant exposure and ultimate effects is shown simplistically (Figure 11-1) in an adaptation from van Haut and Stratmann. ... 

Werck-Reichhart, D., Jones, O.T.G., and Durst, F., Heme synthesis during cytochrome P-450 induction in higher plants. 5-Aminolevulinic acid synthesis through a five-carbon pathway in Helianthus tuberosus tuber tissues aged in the dark, Biochem. J., 249, 473 -80, 1988. 

The extraction of DNA from mummified and fossilized plant tissue is one of the most exciting developments in molecular systematics. Mummified plant tissues up to 44,600 years old have yielded analyzable DNA.13-19 The recent publications of rbcL sequences from Miocene fossils (17-20 million years old) of Magnolia20 and Taxodium21 and the amplification of similar-aged DNA from Platanus and Pseudofagus21 open a new source for land plant tissue and offer enormous possibilities for research in molecular systematics and evolution. The latter report clearly invalidates the objections22 to the authenticity of the Miocene fossil plant DNA and hence of their systematic utility. 

If not grazed, or if the pasture is not burned, most of the P absorbed in plant tops will be immobilized by plant tissue and, thus, will be unavailable in the soil. Transfer of P and N by nutrient resorption in forage plants and in the weedy vegetation prior to leaf fall induces low nutrient concentration in litter (Table 6.6) and may in part explain the decreasing amount of available soil P often associated with an increase in the weed biomass of a degrading pasture or with pasture age. Without this biological immobilization, however, these nutrients would be more vulnerable to loss through runoff and erosion. 

Critical sodium levels in plants depend on species and on the age of the leaves or plant tissue. Sodium contents of l.Sgkg in wheat and lucerne are considered toxic. 

Some plant species are zinc accumulators, but the extent of the accumulation in plant tissues varies with soil properties, plant organ and tissue age. New studies have shown that the uptake of zinc by terrestrial plants is significantly increased at a low soil pH, but reduced when there is a high content of organic matter (Jones and Burgess 1984, Chaney etal. 1987). A comprehensive overview of the absorption of zinc by plants is to be found in Lindsay (1972). 

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