Lemna paucicostata Hegelm. 6746

Abstract

The sequence of frond emergence and the intervals required for daughter colony separation have been determined for L. paucicostata Hegelm. 6746 growing under standardized conditions. After separation of a new mother colony, the 1st daughter colony is produced from the left meristematic pocket and separates after approximately 60 h, the 2nd daughter, produced from the right pocket, separates after a further 30 h, and the 3rd daughter, again from the left, after a further 40 h. The pattern of alternating longer and shorter intervals for separation of daughters continues throughout the life of the mother colony. Protein contents of fronds and whole colonies were determined either by chemical methods or by labeling to isotopic equilibrium with 35SO42-. The smallest fronds measured were 5-6% of the final area they would attain when fully expanded and contained 10% of the protein they would finally contain. Thus, most protein accumulation occurred during the phase of rapid frond expansion rather than in an earlier primordial stage. The specific rates of protein accumulation were 0.027-0.030 .mu.g/.mu.g protein per h during rapid frond expansion and relatively constant thereafter at 0.014-0.019 for whole colonies until at least 4 daughter colonies had separated. A substantial amount of 35S is transferred directly from the mother frond to its attached daughter fronds. The results are consistent with the transfer of soluble compounds arising through turnover of protein in the mother frond. Tree diagrams and a mathematical treatment were utilized to relate the distribution of colony types and the over-all doubling time in a large population of Lemna colonies to the doubling times and modes of division of the individual colonies within that population. A population with the growth properties described increases exponentially and that within a relatively few generations reaches an equilibrium population distribution which is independent of the initial proportions of the members of the population. The measured distribution of colony types producing odd-numbered as compared to those producing even-numbered daughters was the same as that predicted by the theoretical analyses. Once a mass culture of L. paucicostata has attained its equilibrium distribution of colony types, under standard conditions the proportions of colonies in which the indicated daughter will be next to separate will be: 60%, 1st; 15%, 2nd; 11%, 3rd; 5%, 4th; 8% 5th or higher. Thus, about 91% of colonies will have produced no more than 4 daughter colonies. For at least this period the specific rate of protein accumulation is relatively constant and senescent changes in mother fronds are rare. In the equilibrium distribution, 39% of colonies will themselves be 1st daughters, 25% will be 2nd daughters, 14% will be 3rd daughters, 9% 4th, and 13% greater than 4th daughters. Apparently, obtaining representative samples of colonies from such a population for biochemical studies should be relatively simple.