No abstract

In observing the growth phases of a plant’s many structures, a paraphrasing of J.L. Harper (7), and later Sussman and Douthit (13), comes to mind: “Some structures are born dormant, some achieve dormancy, and some have dormancy thrust upon them”. Indeed, the dormancy phenomena can be associated with essentially all meristematic regions of the plant. Accordingly, a wealth of terminology has arisen to describe various plant dormancy phenomena. While recently discussing seasonal growth processes, our use and misuse of current and historic dormancy terms led us to conclude that a simplified, descriptive dormancy terminology would be of benefit to the plant science community. Our purpose here is to review briefly the terminology now in use, critically examine dormancy phenomena and reduce terminology to a minimal number of descriptive terms, and consequently to stimulate discussion of this terminology scheme by our peers.

A series of experiments were conducted to determine the sensitivity of radish to four light alcohols (ethanol, methanol, 2-propanol, and t-butanol) identified as atmospheric contaminants on manned spacecraft. Radish (Raphanus sativus L. `Cherry Bomb' Hybrid II) seedlings were exposed for 5 days to concentrations of 0, 50, 100, 175, 250, and 500 ppm of each alcohol and the effect on seedling growth was used to establish preliminary threshold response values. Results show a general response-pattern for the four alcohol exposures at threshold responses of 10% (T10), 50% (T50) and 90% (T90) reduction in seedling length. There were differences in the response of seedlings to the four alcohols, with the T10 for t-butanol and ethanol (25 to 40 ppm) being 3 to 5× lower than for methanol or 2-propanol (110 to 120 ppm). Ethanol and t-butanol exhibited similar T50 values (150 to 160 ppm). In contrast, T50 for methanol (285 ppm) and 2-propanol (260 ppm) were about 100 ppm higher than for ethanol or t-butanol. Chronic exposures to 400 ppm t-butanol, ethanol or 2-propanol were highly toxic to the plants. Radish was more tolerant of methanol, with T90 of 465 ppm. Seeds did not germinate at the 500 ppm treatment of t-butanol, 2-propanol, or ethanol. There were significant differences in projected performance of plants in different environments, dependent upon the regulatory guidelines used. The use of exposure guidelines for humans is not applicable to plant systems.

Experiments were designed to alter the carbohydrate status of olive (Olea europaea L.) leaves during the presumed flower induction period. Bearing and nonbearing ‘Oblonga’ olive trees were exposed to either 850 μmol s-1n-2 PAR for 14 hr daily in a 1000 ppm CO2-enriched atmosphere, 150 μmol s-1m-2 PAR for 14 hr daily in 340 ppm CO2, or maintained in a lathhouse at ambient winter conditions of about 350 μmol s-1m-2 PAR and daily temperature fluctuations from 5° to 20°C. The trees exposed to 850 μmol s-1m-2 had 3 to 5 times the starch concentrations of either the 150 μmol s-1m-2 PAR or lathhouse treatments. There were few and inconsistent differences in sucrose, fructose or mannitol concentrations between treatments. The high levels of starch in the 850 μmol s-1m-2 PAR treatment had no effect on the flowering pattern of bearing or nonbearing trees. Gross levels of carbohydrates do not appear to limit flower induction of olive.

Membrane lipids and cellular water states were studied in endodormant and paradormant apple buds. Paradormancy was overcome by thidiazuron while endodormant buds were forced to break after a certain period of chilling. Nuclear magnetic resonance imaging was used to determine water states in buds of different stages of dormancy. In endodormant buds, the changes in water states from a more tightly-bound to a more free form were correlated with changes in membrane fatty acid composition. The ratio of saturated/unsaturated fatty acids decreased with chilling, especially in C18:l/C18:3 molecular species of phosphatidylcholine and phosphatidylethanolamine. Bud lipase activity, which was assayed by in vitro hydrolysis of triglycerides, showed an abrupt increase after chilling treatments.