W. A. Beck
1942 Plant Physiology  
It was established previously that light and heat influence pigment production in plants more than any other environmental factors, and that drought plays only a minor role in the cause of the seasonal variation of the pigment present in field plants. The conclusion regarding the influence of soil moisture was arrived at from direct experimental evidence and data furnished by the Abbe Meteorological Observatory in Cincinnati (3). The work of FURLINGER and the conclusions drawn from it caused
more » ... n from it caused reasonable doubt regarding the minor importance of soil moisture. FURLINGER (4) proved that excised sunflower cotyledons fail to become green when they are plasmolyzed in sugar solution and are exposed to light. If the same cotyledons are deplasmolyzed, however, they become green when they remain exposed to the light. The conclusion is drawn that plasmolysis influences the physiological activity of the protoplasm in such a manner that the production of chlorophyll is inhibited. It is the purpose of the present work to study the influence of drought on pigment production more carefully and to determine quantitatively the amount of chlorophyll, xanthophyll, and carotene produced under varying drought conditions. Methods In some of the experiments the soil was permitted to dry naturally but in most of them an artificial or "physiological" drought (SCHIMPER's expression) was induced by saturating the soil with sugar solution. In the control experiments the soil was saturated with water. The greatest concentration of the sugar solution employed was 0.38 mol. The osmotic pressure of this solution is 10.6 atm. (6) which is equivalent to the maximum suction tension found in the hypocotyl of the seedlings employed. The maximum suction tension of the hypocotyl was found in the cortical tissue directly beneath the cotyledons. Sugar solution of this concentration in the soil effectively prevents any water from the soil reaching the cotyledons. Graded sugar solutions of lesser concentrations were also employed. In other experiments the cotyledons were excised and submerged in water or hypertonic sugar solution during the period of irradiation. The amount of pigment present in the seedlings which were not irradiated and not treated was also determined so that the effect of the various factors might be estimated on the basis of the initial amount of pigment present. Sunflower seeds of the same strain and harvest were employed in order to reduce, as much as possible, the individual differences of the test plants. The seeds were planted in pots filled with 487 www.plantphysiol.org on July 23, 2018 -Published by Downloaded from
doi:10.1104/pp.17.3.487 pmid:16653796 pmcid:PMC438044 fatcat:6rj7aou375aa3aedky4ss5odcu