In Lake Haruna (mesotrophic lake) the oxygen and chlorophyll maxima were found in the metalimnion. Dominant species of phytoplankton in the low layer of the euphotic zone wasCryptomonassp. and it showed a characteristic shade type in the photosynthesis-light curve. The photosynthetic activity ofCryptomonassp. at low light intensities and low temperature was remarkably higher than that of other phytoplankters. From the photosynthesis-light curve ofCryptomonassp. obtained in the laboratory and depth-light profile observed in the lake, the depth-photosynthesis relation of the alga was calculated and it was found to be in good accordance with the relation measuredin situ. It was thus concluded that the oxygen maximum in the metalimnion of Lake Haruna is due to the special photosynthetic characteristics ofCryptomonassp. living in that lake which is adapted to the environment of low light intensity and low temperature prevailing at the foot of the euphotic zone. The lake was found to show the chlorophyll maximum in the deeper layer. This was attributed to the intensive growth ofCryptomonasand not to the accumulation of the deteriorated phytoplankton sedimented from the surface layer.
Ovules ofPinus resinosafrom 1 and 2 year-old cones were collected periodically during July to August in 1963 and 1964. The embryo-gametophyte complex containing embryos at different stages of development were irradiated by a 60Co source with doses from 0.25 to 2 kilorads. The effects of radiation on the embryo and the gametophytes were determined on the basis of abnormal differentiation and abortion of embryos and the cytological anomaly in the gametophytic cells. There was less abnormal differentiation in the embryos irradiated at stage I in comparison to other stages whereas the percentage of aborted embryos was a maximum in stage I. A possible explanation of the varying radiation effect was attempted on the basis of the average nuclear volume of embryonic cells at each stage of development. In stage I, the average nuclear volume was increased about 11 to 14-fold over those in the other stages with a concomitant peak in the percentage of aborted embryos. In contrast, higher radiation effect in root apices than that in the shoot apices could not be explained through a difference in nuclear volume. The changes in the average nuclear volume in the embryonic cells at various stages of differentiation could not be explained on the basis of an increase in the DNA content alone.
The sporeling of a Thailand liverwort, Pleurozia acinosa, was observed and discussed. During the earlier stage of its spore germination a few-celled globose protonema is formed inside the stretched exospore. After a rupture of the exospore, the protonema develops by further divisions into a many-celled ovoid mass. Such pattern of spore germination may be a new type in the leafy liverworts and seems to be transitional from the protonema formed outside the exospore to that formed inside the stretched exospore.
Photosynthesis and respiration in 3 yellow-green tobacco variants, “Consolation 402”. “Bright Consolation”. “Aurea” and a green variant, “Bright Yellow”. were measured at various stages of leaf growth, using an infra-red carbon dioxide analyzer. In four variants examined, photosynthetic activity per unit leaf area first increased during leaf growth and reached a maximum before the leaves had fully expanded. The activity then decreased slowly (Bright Consolation and Bright Yellow) or rapidly (Consolation and Aurea) along with leaf maturation. As to the maximum value of the activity, no significant difference was found among these four variants. Respiration per unit leaf area showed similar varietal trends, i.e., the activity decreased rather rapidly before the leaves had fully expanded, and slowly after that stage. Remarkable differences in chlorophyll (a+b) content per unit leaf area were observed among these variants. In the leaves of “Aurea” and “Bright Yellow”. the chlorophyll content changed parallel with the activity of photosynthesis, but in “Consolation 402” and “Bright Consolation” such a correlation was not observed. The relationship between photosynthetic activity and chlorophyll (a+b) content in growing tobacco leaves was also discussed.
A new bioassay is described which is based upon the elongation response of the second leaf sheath of rice plants to gibberellins. Rice seedlings, at their first leaf stage, were treated by applying gibberellins to coleoptils in a 1μl drop of 50% acetone using a micropipette. Agar blocks can be used in place of test solution. By means of this method, five cultivars of rice, including one normal and four dwarfs of different simple recessives, were tested for their response to gibberellins A1 to A5. Gibberellins A1 and A3 are of high potency in these cultivars. The dwarfs differ in the specificity of their response to gibberellins. For example, 'Tan-ginbozu' responses well but 'Waito-C' much less to Gibberellin A5. These dwarfs can be used as a 'mutiple plant assay' to detect gibberellins with similar structures. Gibberellin A3can be bioassayed in the range from 0.05 up to 100mμg using the 'Tan-ginbozu' dwarf. The rice test using microdrop application was less susceptible to inhibiting substances such as Abscisin II, fusarinic acid, and indoleacetic acid than the test using the application in growing media. Because of this and because of the rapidity and high sensitivity of the test, it has been successfully applied to the estimation of gibberellin-like substances in extracts from small quantities of rice shoots and Pharbitis nilseeds. The chromatographic behavior of the active zone of rice shoot material was similar to that of gibberellin A3. Bioassays on extracts ofPharbitis nilseeds using the 'Tan-ginbozu' and 'Waito-C' dwarfs indicated the presence of gibberellin-like substances with differential effects on the two dwarfs.