John Skok

Accumulation of scopoletin glucoside in boron-deficient tobacco leaves

Abstract Isopropyl alcohol-water extracts of tobacco leaves yielded a blue-fluorescent compound that was identified as the glucoside of scopoletin (6-met hoxy-7-hydroxycoumarin). Leaves of boron-deficient plants produced a twenty-fold increase of this material over leaves of normal plants. The possible role of boron in lignin biosynthesis is pointed out on the basis that certain phenolic compounds that may serve as lignin precursors accumulate in boron-deficient plants.

Boron Requirement of Chlorella vulgaris

1. Chlorella vulgaris (Columbia strain) was subcultured in a boron-deficient medium contained in Corning boron-free flasks to bring the level of this element in the cells to a low level; such Chlorella cells were then inoculated into a medium containing 0, 0.5, 1, or 5 p.p.m. boron. 2. Chlorella cultures in a medium containing no boron but maintained in Pyrex flasks exhibited a greater concentration of cells after 24 days than did those grown in vessels of boron-free glass. This response undoubtedly resulted from a leaching of boron from Pyrex glass. 3. When compared with Chlorella cultured in boron-free medium, those in 0.5-p.p.m. boron exhibited a 60% increase in cell number and 137% increase in dry weight per cell. 4. The 1- and 5-p.p.m. boron levels resulted in less growth in comparison with the 0.5-p.p.m. cultures.

Boron Nutrition and Lignification in Sunflower and Tobacco Stems

Sunflower plants (Helianthus annuus L.) decapitated above the third node and tobacco plants (Nicotiana tabacum L.) decapitated above the tenth node were grown in plus- and minus-boron solutions in an attempt to determine whether boron plays a role in tissue lignification. After 18 days the stems of sunflower and after 82 days those of tobacco were harvested and analyzed for lignin. The percentage lignin in the stems of the minus-boron sunflower plants was higher, although there was no significant difference between the two series in total quantity of lignin. The percentage and total quantity of lignin in the seventh and eighth internodes of tobacco stems were lowest in the minus-boron plants; in the ninth internode these values were highest in the minus-boron plants. The present results seem to indicate that boron has some function in lignin production, but it was not established whether this is a direct role. Some of the factors which have resulted in the apparent discrepancies in the literature with respect to the effect of boron on lignification are discussed.

Characteristics and Movement of the Flowering Stimulus from the Induced Leaf of Xanthium

1. A technique was used of photoinducing single-leaved Xanthium plants for the production of floral primordia, followed by removal of the leaf after various time intervals and under different dark and light conditions. This provided a method for studying (a) the time required for formation and translocation of the flowering stimulus from its site of synthesis, the leaf, and (b) the effect of light on its movement and lability. 2. The substance moves out of the leaf shortly after it is formed, and under certain conditions a total period of about 24 hours is adequate for formation and translocation of sufficient amounts of the floral stimulus to induce the formation of floral primordia at the apical meristem. 3. This flower-inducing substance is not destroyed by light while still in the leaf, and, in fact, the final effective amount normally does not move out of the leaf until the following light period. 4. Xanthium can be induced to produce flower primordia by subjection to a long continuous dark period not followed by a light period, but a light period following the dark period greatly enhances flowering, presumably by its effect on hastening the movement of the flower-inducing substance out of the leaf to the terminal meristem.

Growth of Chlorella in Relation to Boron Supply

Growth of Chlorella vulgaris Beijerinck (Columbia strain) was measured by final cell number, growth rate, and dry weight per cell in relation to boron supply. Growth in low-boron media was neither stimulated nor inhibited by the addition of boron in amounts up to 10 mg/liter, nor was growth affected in purified media in which boron had been reduced to 1 μg/liter. Boron was not detected in the inocula. The amount of boron present in nutrient solutions was the same at the start and at the end of the growth period when the cells were cultured in 2-liter polypropylene bottles. The trace amounts of boron found in the cells did not correlate with the concentration of boron in the nutrient media. Boron concentrations in culture media from 0.001 to 10 0 mg/liter did not affect growth of C. vulgaris.

Uptake of CO2 by Roots of Xanthium Plants

1. The magnitude of CO2 uptake and fixation by Xanthium plant roots was reinvestigated in an attempt to explain unexpectedly low C14/C12 ratios of tree leaves with regard to fixation of radiocarbon of nuclear-test origin. 2. It was found that plants derive relatively insignificant amounts of carbon from CO2 via the roots, and the minute amounts that are incorporated are approximately one hundred times less than the amount lost by root respiration. 3. The results permit the conclusion that the previously noted C14/C12 ratios of the tree leaves were most likely obtained by incorporation of carbon from sources stored in the tree.

Photoperiodic Responses of Sequoia gigantea Seedlings

1. Marked differential growth responses were exhibited by Sequoia gigantea seedlings grown under various photoperiods. A single observed case of cone formation by an 11-month-old seedling was apparently not a response to photoperiod, since none of the experimental treatments subsequently tested resulted in further fruiting. 2. Growth as measured by main axis heights, number and total length of primary branches, and stem diameters was depressed by short photoperiods and stimulated by long photoperiods, while intermediate photoperiods produced intermediate amounts of growth. 3. Certain photoperiodic effects on bud characteristics, including the size and shape of bud leaves and degree of node and internode compaction within the bud, were also noted.

Nature of the Photoperiodic Responses of Buckwheat

1. Photoperiod had no effect on floral initiation in Tartary buckwheat, Fagopyrum tataricum Gaertn., but markedly influenced the regulation of vegetative growth, floral development, and fruiting. 2. Short photoperiods promoted floral development, fruiting, and lateral-shoot production, but depressed main-axis elongation. Long photoperiods favored main-axis growth and an increase in total plant weight but depressed lateral-shoot growth, floral development, and fruit production. 3. Although both floral and vegetative development are photoperiodically controlled, their control operates through separate mechanisms, as indicated by the results of experiments involving dark- or light-period interruption. Floral development is chiefly associated with a dark-dependent mechanism, which appears to be similar to the one controlling floral initiation of a typical short-day plant. Main-axis elongation is chiefly associated with a light-dependent mechanism.

Determination of Boron in Water, Nutrient Media, and Chlorella Cells

Methods are presented for determining submicrogram amounts of boron in distilled water, nutrient media, and in Chlorella cells Boron is determined colorimetrically as a boron-curcumin complex after the sample is either dried or ashed in the presence of calcium hydroxide Boron is removed from distilled water by passing it through a column of Dowex-1 ion exchange resin in the hydroxl form Ions which interfere with the boron analysis are removed on small columns of Dowex-1 and Dowex-50 in the formate and sodium forms, respectively. Neither of the columns retains boron. Approximately 80% of a 1-μg boron standard added to Chlorella cells is recovered when calcium hydroxide is used to trap the boron during the evaporation and ashing steps Regardless of the amount of boron supplied to Chlorella during its growth, only trace amounts of boron were found in the cells

Further Aspects of the Photoperiodic Responses of Sequoia gigantea

1. The stimulatory growth effects of long photoperiods and the depressive effects of short photoperiods in Sequoia gigantea are apparently operative through a dark-dependent mechanism. 2. The short-day effects may be largely nullified by daily interruptions of the long dark period with short light breaks. 3. Significant increases in primary-branch growth were attained in plants growing on long photoperiods when the long light period was interrupted with daily 1-hour periods of either darkness or low-intensity light.