1. Plant Nutrients. 2. The Soil as a Plant Nutrient Medium. 3. Nutrient Uptake and Assimilation. 4. Plant Water Relationships. 5. Plant Growth and Crop Production. 6. Fertilizer Application. 7. Nitrogen. 8. Sulphur. 9. Phosphorus. 10. Potassium. 11. Calcium. 12. Magnesium. 13. Iron. 14. Manganese. 15. Zinc. 16. Copper. 17. Molybdenum. 18. Boron. 19. Further Elements of Importance. 20. Elements with More Toxic Effects. General Readings. References. Index.

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Principles of plant nutrition

PATHWAY OF ETHYLENE BIOSyNTHESIS 156 Methionine as an Intermediate ....... 157 S-Adenosylmethionine as an Intermediate 158 I-Aminocyclopropanecarboxylic Acid as an Intermediate . ......... 158 Methionine Cycle ........ 161 Conversion of l-Aminocyclopropanecarboxylic Acid to Ethylene 164 REGULATION OF ETHYLENE BIOSYNTHESIS 167 Regulation in Ripening Fruits and Senescing Flowers ...... 167 Auxin-Induced Ethylene Production 169 Regulation of Ethylene Biosynthesis by Ethylene 169 Stress-Induced Ethylene Production . . . . . . . . 171 Regulation by Light and Carbon Dioxide 173 Inhibitors of Ethylene Biosynthesis : 174 Conjugation of l-Aminocyclopropanecarboxylic Acid to l-(Malonylamino) cyclopropanecarboxylic Acid 178 CONCLUDING REMARKS 180

Ethylene biosynthesis and its regulation in higher plants

Seed dormancy is an innate seed property that defines the environmental conditions in which the seed is able to germinate. It is determined by genetics with a substantial environmental influence which is mediated, at least in part, by the plant hormones abscisic acid and gibberellins. Not only is the dormancy status influenced by the seed maturation environment, it is also continuously changing with time following shedding in a manner determined by the ambient environment. As dormancy is present throughout the higher plants in all major climatic regions, adaptation has resulted in divergent responses to the environment. Through this adaptation, germination is timed to avoid unfavourable weather for subsequent plant establishment and reproductive growth. In this review, we present an integrated view of the evolution, molecular genetics, physiology, biochemistry, ecology and modelling of seed dormancy mechanisms and their control of germination. We argue that adaptation has taken place on a theme rather than via fundamentally different paths and identify similarities underlying the extensive diversity in the dormancy response to the environment that controls germination.

/pdf/seed-dormancy-and-the-control-of-germination-4tdhm2985s.pdf

Seed dormancy and the control of germination

The variation in growth rate with temperature of unicellular algae suggests that an equation can be written to describe the maximum expected growth rate for temperatures less than 40°C. Measured rates of phytoplankton growth in the sea and in lakes are reviewed and compared with maximum expected rates. The assimilation number (i.e., rate of photosynthetic carbon assimilation per weight of chlorophyll a) for phytoplankton photosynthesis is related to the growth rate and the carbon/chlorophyll a ratio in the phytoplankton. Since maximum expected growth rate can be estimated from tempera­ ture, the maximum expected assimilation number can also be estimated if the carbon/ chlorophyll a ratio in the phytoplankton crop is known. Many investigations of phytoplankton photosynthesis in the ocean have included measures of the assimilation number, while fewer data are available on growth rate. Assimilation numbers for Antarctic seas are low as would be expected from the low ambient temperatures. Tropical seas and temperate waters in summer often show low assimilation numbers as a result of low ambient nutrient concentrations. However, coastal estuaries with rapid nutrient regeneration processes show seasonal variations in the assimilation number with temperature which agree well with expectation. The variation in maximum expected growth rate with temperature seems a logical starting point for modeling phytoplankton growth and photosynthesis in the sea.

Temperature and phytoplankton growth in the sea

Auxin: regulation, action, and interaction.

The paper chromatography of indole compounds and some indole-containing auxins of plant tissues.

The evolution of ethylene, both from the endogenous source and from added 1-aminocyclopropane-1-carboxylic acid (ACC), has been followed in close relationship with the senescent loss of chlorophyll from seedling oat leaves. In white light, where chlorophyll loss is slow, the ethylene evolution increases slowly at first, but when the loss of chlorophyll becomes more rapid, ethylene evolution accelerates. CoCl 2 inhibits this increase and correspondingly maintains the chlorophyll content, with an optimum concentration of 10 micromolar. The rapid rate of chlorophyll loss in the dark is slightly decreased by 3-aminoethoxyvinyl glycine (AVG), by cobalt, and slightly stimulated by ACC. The slower chlorophyll loss in white light, however, is almost completely inhibited by silver ions, greatly decreased by cobalt and by AVG, and strongly increased by ACC. Since the chlorophyll loss is accompanied by proteolysis, it represents true senescence. Chlorophyll loss in light is also strongly antagonized by CO 2 , 1% CO 2 giving almost 50% chlorophyll maintenance in controls, while in the presence of added ACC or ethylene gas, the chlorophyll loss is 50% reversed by about 3% CO 2 . The ethylene system in leaves is thus more sensitive to CO 2 than that in fruits. Indoleacetic acid also clearly decreases the effect of ACC. It is shown that kinetin, CO 2 , Ag + , and indoleacetic acid, all of which oppose the effect of ethylene, nevertheless increase the evolution of ethylene by the leaves, and it is suggested that ethylene evolution may, in many instances, mean that its hormonal metabolism is being prevented. Abscisic acid somewhat increases ethylene evolution also, but its action in promoting senescence in light is antagonized only partially by Ag + , Co 2+ , or AVG. For this and a number of other reasons it is concluded that ethylene and abscisic acid both independently control leaf senescence in the light.

Kenneth V. Thimann

Papers

The paper chromatography of indole compounds and some indole-containing auxins of plant tissues.

The role of ethylene in the senescence of oat leaves.

The role of the seed-coats in germination of photosensitive lettuce seeds

The physiology of ethylene formation in apples

Auxins and the growth of roots