Experiment Station Record, Volume 92, January-June, 1945 Page: 28
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28 EXPERIMENT STATION RECORD [Vol. 92
127-132, illus. 16; Eng. abs., p. 132).-P. infestans appeared to require thiamine,
maximum effects being obtained with 2 gg. to 1 cc. of the liquid mineral-dextrose
medium containing asparagine and organic acids. In contrast to Phycomyces
blakesleeanus, used as a control, Phytophthora infestans failed to respond to the
pyrimidine and thiazole derivatives of thiamine. Inositol in combinations with
thiamine at certain concentrations appeared to inhibit somewhat the effect of this
substance. A yeast extract preparation, almost ineffective alone, appeared to increase
the effect of thiamine.
Bleeding and sap movement, H. LUNDEGARDH (Arkiv Bot., 31 (1944), No. 1,
[Art. 2], pp. 1-56, illus. 6).-Bleeding experiments were conducted with vigorous 15day-old
wheat seedlings grown in nutrient solutions in photothermostats under
special care to maintain good aeration and fresh bleeding surfaces. The bleeding
sap contained no carbohydrates or proteins. The inorganic anions and cations
predominated and were present in about equivalent amounts, but under special conditions
(e. g., anaerobiosis) the metallic cations considerably exceeded the anions.
It is concluded that under these conditions CO2 and HCO3 invade the sap, which
has a pH of about 6. The composition of the sap was influenced by that of the
medium; e. g., in nutrient solutions containing nitrate, NO3 and K predominated
in the sap, in phosphate solutions the P04 in the sap rose, and in solutions without
nitrate Cl was present. The average intensity of bleeding in dilute solutions was
about proportional to the concentration of anions in the sap. The nitrate concentration
in the sap exceeded the average nitrate concentration in the total root system;
on the contrary, the average content of K was much greater in the tissue. When
the bleeding was retarded by osmotic counterpressure in the medium or by choking
of the vessels at the place of decapitation the osmotic value of the sap rose. The
bleeding is an aerobic process but does not stop immediately after exclusion of 02 or
poisoning with HCN. The time course of bleeding varied with different solutions;
it is concluded that the presence or absence of certain ions or of 02 influenced the
permeability of the cortex to the movement of water. Chemical analysis of the
guttation fluid of 15-day-old plants indicated a lower NO3 concentration than in
the bleeding sap, but a large content of sugar and other organic compounds. No
close proportionality was found between the rates of ion absorption and exudation.
Exudation into the sap occurred independently of absorption as long as the excess
of salts (nitrate) in the tissue persisted.
As regards theoretical conclusions, it is believed that bleeding is primarily an
osmotic phenomenon. Owing to the great permeability to water and the complete
saturation of the roots investigated, the cells of the parenchyma fail to develop
any free suction force. In the central vessels of a decapitated plant the suction
force is equal to the osmotic pressure of the sap minus that of the medium, and
independently of the osmotic value of the parenchyma. In an intact plant the
vessels are more or less closed in their upper extremities and a certain turgidity
arises. The exudation is believed to be a counterpart to the absorption process in
the surface of the root. Both processes are linked up with aerobic processes
sensitive to HCN. The high efficiency of the osmotic transport of water is believed
due to a localization of the exudation process in a protoplasmic membrane of special
structure. Anions and water will then be simultaneously moved. The cations are
secondarily released from the surrounding tissue. This mechanism would also be
able to maintain a limited nonosmotic transport of water, viz, a transport against
an osmotic gradient.
There are over two pages of references.
Water relations of root cells of Beta vulgaris, H. B. CURRIER (Amer. Jour. Bot.,
31 (1944), No. 7, pp. 378-387, illus. 1).-Through use of methods described, the
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/41/: accessed November 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.