- Department of Plant Biology, Swedish University of Agricultural Sciences
Temperature response of pollen mother cells in Larix and its importance for pollen formation
In the present paper the meiotic development in the PMC of the three larch species Larix: decidua, L. leptolepis, and L. sibirica was studied. Emphasis was paid to the analysis of the conditions of importance for breaking the dormancy of the diplotene stage as well as the factors responsible for the initiation of further development from diplotene. On the basis of a detailed analysis of meiosis in a few clones 1966-67 as well as in larger number of clones in 1967-68, the following characteristics of the meiotic development of the three species were observed: L. decidua: Diplotene is reached relatively early. The initiation of the further development from diplotene takes place late. L. leptolepis: Diplotene is reached relatively late. The initiation of the further development takes place somewhat earlier than in L. decidua. L. sibirica: Diplotene is reached early. The initiation of the further development from diplotene takes place early, even during the autumn. During the course of the investigation irregularities appeared frequently. For an understanding of the origin of the irregularities a distinction was made between different categories. Chromosomal irregularities and irregularities in cell division were the two main categories. The appearance of the various irregularities was demonstrated by photomicrographs. In L. decidua and L. leptolepis stickiness and degeneration predominated, whereas polyspory, stickiness and degeneration occurred most frequently in L. sibirica. It was shown that irregularities did not appear until sensitive cells were exposed to low temperatures. All phases of active division during meiosis were believed to be highly sensitive to low temperatures. An attempt was made to obtain quantitative relations between low temperatures and sensitive cells on one hand and irregularities on the other hand. Good approaches for such relations were observed in several cases. However, the exact temperature response could not be revealed, owing to the impossibility of achieving an artificial control of the outdoor temperature conditions. From this investigation, as well as previous ones, the prerequisites for proper pollen formation could be stated in the follom-ing way: 1. Reaching of diplotene before frost appears during autumn. 2. Stability of the resting diplotene stage to short temperature fluctuations around O°C (-5 - +5°C). 3. Rapid reaching of the tetrad stage when development from diplotene is initiated. On this basis it could be concluded that the probability of obtaining proper pollen formation was not promising as L. leptolepis did not fulfil any of these requirements, whereas L. sibirica only fulfilled the first one. For the Stockholm area the best chance of obtaining a high pollen fertility should be given by L. decidua.
Larix; meiosis; pollen formation; temperature
Studia Forestalia Suecica
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