In the present investigation, organic acids as metabolic products in the culture filtrates of Phytophthora infestans were examined by the method of paper chromatography and microchemistry.
1. As a non-volatile organic acid, oxalic acid and succinic acid are recognized in the filtrate of asparagine-glucose medium and potato decoction, and oxalic acid in that of Waksman's medium.
2. As a volatile organic acid, no organic acid has been detected by the method of paperchromatography, whereas the existence of a small quantity of acetic acid and formic acid has been confirmed by the microchemical method in the filtrates of asparagine-glucose medium and potato decoction.
3. The principal acid of these organic acids produced by Phytophthora infestans was found to be oxalic acid.

View full abstract

In the previous reports^{17, 18, 19)}, it was shown that in the Phytophthora infestans infected tuber tissue of resistant potato varieties, remarkable increase in respiration, water soluble protein, starch, and polyphenol compounds content occurred at an early stage of infection (15-20hrs. after inoculation), while in susceptibles no such a remarkable increase took place, and it was concluded that the resistance of potato tuber to P. infestans accompanies the activation of metabolism in the infected tissue. In the present paper studies on the physiological changes in the potato tuber tissue, and the susceptibility to P. infestans under the influence of ethanol narcosis, are reported.
Tuber of highly resistant seedling “41089-8” was cut in halves; one half was immersed in 10% ethanol for 10 minutes, and the other half was immersed in water. After washing for a short time, tubers in each plot were divided into two groups, then the cut surface of tuber of one group was inoculated by zoospore suspension of P. infestans (common strain H₁) and that of the other group was left noninoculated. Twenty or 44 hours after inoculation, blockets of tissue were stamped out of the tuber at a right angle to the cut surface by means of a cork borer having a diameter of 2cm. Superficial layer of these blockets was then worked up into slices 0.45mm thick with microtome. After washing the slices in running water, the O₂ uptake and the CO₂ output were determined by means of Warburg's “direct method”. Slices were also used for determination of water soluble protein-N, total water soluble-N, and polyphenol compounds content.
Results obtained are shown in Tables 1, 2, 3 and 4. Twenty hours after treatment, the respiratory rate in the non-anaesthetized tissue both inoculated and non-inoculated, was remarkably accelerated, while in the ethanol-treated tissue of potato tuber such a remarkable increase in respiration was not observed in either inoculated or noninoculated tubers. The RQ value of ethanol-treated tissue of cut surface was lowered slightly in comparison with that of non-anaestized tissue (Table 5). Accompanying the inhibition of respiratory increase, the amounts of water soluble protein and polyphenol content in the ethanol-treaded cut surface of potato tuber were less than those of non-treated tissue 20hrs. after treatment. When non-anaesthetized cut surface of potato tuber was infected by P. infestans, rate of increase in respiration, water soluble protein and polyphenol content was greater in the infected tissue than in the non-infected one. In the ethanol-treated tissue, however, increase in such physiological reactions induced by infection of P. infestans was not so great as that in non-narcotized tissue (shown in Table 4). It was. stated in the previous report that the changes in hyphal substance in inoculated tissue may be negligible in comparison with the physiological changes in host tissue within the period of about 20hrs. On the contrary, 44hrs after inoculation, the content of hyphal substance in the infected tissue may play an important role in the changes of chemical compounds contained in the tissue. Forty-four hours after inoculation, moreover, the content of polyphenol compounds decreases in infected resistant tissue, possibly due to the deposition of the compounds in collapsed cells (Table 3).
Above described results show that the excited metabolism in tissue of resistant potato tuber induced by P. infestans may be inhibited by the pre-infectional ethanol narcosis. It may be possible to presume that such an inhibition of metabolic acceleration may result in the reduction of resistance of interspecific hybrids to the infection by common strain of P. infestans.

View full abstract

This paper reports some observations on the death of mesophyll-cells in barley leaves infected with the powderly mildew, which is an epidermal cell invading parasite.
1. In the case of the resistant varieties of barley, (a) a few days after inoculation, some of the mesophyll-cells beneath the epidermal cell, in which the first haustorium is formed, are observed to be dead. As the days go on, death of the mesophyll-cells extends sometimes to those which are not directly in contact with the haustorium-bearing cell.
(b) The chloroplasts in the dying mesophyll-cell become smaller in size and in number, often all of the chloroplasts and the nucleus becoming unrecognizable. Then the mesophyll-cell loses turgidity. The dead mesophyll-cells may be strongly browned or remain unchanged.
(c) Death of the mesophyll-cells occurs while the epidermal cell above them is living and being absorbed nutriments by the haustoria. When the epidermal cell dies soon after the penetration hypha of the fungus intrudes or swells into a primordial haustorium, no mesophyll-cells beneath the dead epidermal cell are collapsed.
(d) When a greater percentage of the mesophyll-cell beneath a haustorium-bearing epidemal cell die, the fungal development is checked, giving an impression that death of the mesophyll-cell is the cause of resistance of the barley leaf to the powdery mildew. The hyphal cells are, however, not rarely observed to be dead or dying, while no mesophyll-cells are dead or only a few mesophyll-cells among many ones attaching to a haustorium-bearing epidermal cell are dead. In such cases the haustorium may be in difficulties to absorb nutriments from the epidemal cell, antecedent to the death of the mesophyll cells underneath.
2. In the case of the susceptible varieties, the mesophyll-cells apart from the pustule portion become chlorotic, while those beneath the pustule are green and apparently not so much disturbed. And the mesophyll-cells begin to die from the farthest ones from the pustule.
3. There is an opinion that mesophyll-cell death of the resistant barley leaf is due to a toxin secreted by the haustorium, but such a substance is not yet proved. It may be possible to suppose that the mesophyll cell dies as a result of being suddenly deprived of its nutriments by the haustorium-containing epidermal cell. The phenomenon that the mesophyll-cells distant from the pustule portion, in the case of the susceptible varieties, die while those under the pustule are alive, may be also interpreted by one-sided translocation of nutriments toward the pustule-bearing part.
4. Both in susceptible and resistant varieties of barley, the first haustorium is developed far more easily in the auxiliary cell than in the common epidermal cell. It is worthy of mentioning that the the auxiliary cell is not directly in contact with the mesophyll-cell.

View full abstract