Reanalysis of filter-feeding behavior of caddis fly (Brachycentrus) larvae reveals masking and circadian rhythmicity.

Data published on the subjectively determined presence or absence of circadian periodicity in feeding of Brachycentrus occidentalis Banks, an aquatic insect belonging to the order Trichoptera, were reanalyzed by statistical methods based on the cosine model. The 4h data for 5 days of synchronized environmental conditions followed by 5 days of constant conditions (using original values and purified values after removal of an 8h component attributed to the feeding schedule) were quantified for rhythm characteristics by the least-squares fit of cosines. A circadian rhythm was highly significant during synchronized conditions (light-dark and cycling water temperature) and in continuous light when water temperature continued to cycle. A circadian rhythm in the percentage of larvae feeding during continuous light and constant water temperature, which had not been observed by visual inspection in the original data, was detected in the unmasked data with a "free-running" period not overlapping 24.0h (95% confidence limits from 18.95h to 21.66h). Effects of masking brought about by manually feeding the larvae every 8h were statistically significant under both synchronized and constant environmental conditions.

Ultradian movements of shoots of two species of soybeans Glycine soja (Sieb. and Zucc.) and Glycine max (L.) Merr.

Circumnutation movements of shoot tips of two species of soybean were studied. Shoot tips of Glycine soja (Sieb. and Zucc.) moved in a counterclockwise direction with a mean period (+/- SD) of 108 +/- 9 minutes when the shoots were not handled prior to monitoring (n = 17). Effects of mechanical stress or stimulation (thigmomorphogenesis) resulted in the lengthening of the mean period by 15% when shoot lengths were measured (handled) prior to monitoring movements (124 +/- 18 minutes, n = 49) or handled and restaked prior to monitoring movements (124 +/- 14 minutes, n = 11). Shoot tips of G. max cultivars moved counterclockwise, and, depending on the cultivar, periods ranged from 112 minutes to 133 minutes, with an overall average period of 124 +/- 21 minutes (n = 21). This period was identical to the mean period of comparably handled G. soja shoot tips. Amplitudes for the four G. max cultivars were much smaller (0.12 cm to 1.43 cm) than for G. soja (2.9-8.7 cm). Factors that may have contributed to differences in rhythm characteristics between species and among cultivars included the presence of a distinguishable bending zone in G. soja, but not in G. max, and morphological features associated with shoot development.

Movement of a bean shoot: an introduction to chronobiology.

An active learning exercise that focuses on movements (circumnutations) of climbing bean plants (Phaseolus vulgaris L.; cv. Kentucky Wonder, pole bean) has been successfully incorporated into the curriculum of educational institutions to introduce the subject of chronobiology to students. This didactic activity, which involves an ultradian rhythm, can be completed within a span of 2-4 h, fits into the schedule of various courses, uses materials commonly found in classrooms, requires a time commitment of only a few minutes from each student, and can be modified to include a circadian rhythm project. Ultimately, students develop a better understanding about parameters and characteristics of rhythms, analytical procedures, and the temporal organization of life.

Phase shift in leaf movements of xanthium attributed to age and rhythm patterns.

Leaves of cockelbur (Xanthium strumarium L.) have been reported to be in either an upright or downward position during the dark span (night) of a 24-hour cycle. Results from our studies clearly indicate that such differences in leaf position are not related to differences in ecotypes but can be attributed to age of the leaf, pattern of the waveform of the rhythm at various stages of the light-dark synchronizer regimen, and the statistical model used for the analysis of the waveform. Younger leaves reached a maximum upright position closer to the middle of the dark span, whereas older leaves reached this position closer to the end of the dark span. A phase shift of up to 6 to 10 hours may occur as the leaf ages. Results from the examination of the pattern of the waveform at four different times showed that the pattern of a younger leaf was different from that of an older leaf during the middle of the dark span, during the light-to-dark transition, and during the middle of the light span, but not during the dark-to-light transition. Linear regression, statistical analyses, and the fitting of harmonics clearly indicate that it is the trough, more than the peak, that differs with the age of the leaf.

Ultradian oscillations of three variables in the circumnutation movements of shoots.

During the processes of growth and development of climbing Phaseolus vulgaris L. shoots, 3 parameters or variables of movement consisting of a horizontal component, a vertical component, and speed display ultradian rhythms. Generally, they have periods in the range of 80 to 110 min. Shoot elongation is reflected in the chronograms of the vertical component by an increasing trend in the pattern of the oscillations. Characteristics of the rhythmic movements of the shoot, such as circulating phase differences among cells, may provide a useful tool in exploring interactions between temporal and structural components of biological organization, synchronization, and communication.

Masking in plants.

Circadian rhythms in plants are liable to masking, i.e. alterations by environmental influencing agents. Experiments have been reported for both positive and negative masking, attributed to a Zeitgeber which may either increase or decrease the amplitude of a circadian rhythm (CR). In some instances, the CR may even be unexpressed. This inhibition, however, may be alleviated by synchronizing agents. Reports are also available for changes in the shape or pattern of an oscillation. The latter may be prevented, at least in Acetabularia in certain conditions, by a phytohormone antagonist. Masking may also be brought about by water stress, relative humidity, bacterial infection and alteration in the relative direction of the gravitational force. Finally, subjecting plants to constant conditions, particularly continuous light, alters the physiological state of the organism.

An experimental analysis and comparison of three rhythms of movements in bean (Phaseolus vulgaris L.).

Three types of rhythmic movements of Phaseolus vulgaris L. (pole beans) were examined collectively and their characteristics compared. Although the ultradian rhythms of shoot circumnutation and leaf movement, as well as the circadian rhythm of leaf movement, occurred simultaneously, each rhythm could be expressed independently of the other two. Shoot circumnutation and ultradian leaf movements displayed the same period (80 min at 25 degrees C and Q10 congruent to 2), while the period of the circadian leaf movements was not temperature dependent (Q10 congruent to 1). Interaction into the plant between two ultradian rhythms (shoot circumnutation and ultradian leaf movement) with the same period and coexistence in the pulvinus of an ultradian with a circadian rhythm are discussed.

A special group of ultradian oscillations.

Based on results from our studies, including those on leaf movements, circummutations of shoots, levels of enzyme activity, and metabolites, and from an extensive review of the literature, we have identified a special group of ultradian oscillations. Collectively, these oscillations have periods that range from approximately 30 to 240 min. Their patterns seldom exhibit strict periodicity or constant waveform. They have been observed in various animals, human beings, plants, and microorganisms. These oscillations appear to be a ubiquitous phenomenon, present at various levels of organization, e.g., biochemical to behavioral, and provide a unifying paradigm for exploring biological dynamics.

Two types of high frequency oscillations in Glycine max (L.) Merr.

Movements of the first trifoliolated leaf of Glycine max (L.) Merr. plants were monitored continuously for several weeks in a study that included 14 individual plants. Two types of high frequency oscillations that had periods of 1 hr or less were superimposed on the circadian profile of eight of the 14 plants. The first type of leaf movement was found to be an ultradian oscillation having periods that ranged from 45 to 62 min. These oscillations started 2 to 5 hr after the beginning of the 15-hr light span. Analysis by double complex demodulation revealed a progressive period elongation during the light span. The second type of leaf movement had a more complicated pattern with fast and irregular amplitude variations and appeared in the last 5-hr portion of the light span.

Cold sensitivity oscillations of young soybean plants.

Every 4 hr, a different group of soybean seedlings (Glycine max [L.] Merr. cv. Corsoy), maintained in a controlled environment chamber (LD 16:8), were briefly subjected to cold (-10 degrees C for 4 min). Ten days after the beginning of the cold treatment, plants were harvested, weighed, and their cotyledons assayed for chlorophyll. In other experiments, potassium levels of the foliage were monitored. Both the sensitivity of plants to cold and the potassium content of unifoliolate leaves not subjected to cold displayed a significant 24-hr oscillation. Less injury and the lowest level of potassium occurred near the end of the light span. Cotyledon chlorophyll levels again were shown to be a good indicator of injury, with the highest levels in the most severely injured plants.

Stomatal aperture oscillations of Abutilon theophrasti Medic. and Hordeum vulgare L. examined by three techniques.

Temporal fluctuations of stomatal aperture are important to water use efficiency. Techniques that use point measurements widely spaced in time such as diffusive resistance porometry (DRP) or pot weighing (PW) may not provide a complete description of changes in stomatal aperture. Three techniques, DRP, PW, and continuous flow porometry (CFP), were used to examine stomatal aperture changes in Hordeum vulgare L. and Abutilon theophrasti Medic. Plants maintained in controlled environment chambers at 23 degrees C under LD 12:12 were monitored during 2 days of continuous illumination (LL) and a subsequent LD cycle. Oscillations with periods of about 24 hr were observed in both leaf surfaces in the two species. In addition, during LL, high-frequency fluctuations were sometimes superimposed on the 24-hr oscillation. There was better agreement between the results of CFP and DRP in Abutilon than in Hordeum. The reason for this difference is unclear. CFP revealed rapid fluctuations in stomatal aperture that were not observed with the other techniques.

Chronophytopathology.

Studies on the chronobiology of plant diseases are sparse. To date three papers can be cited, and two more by the present authors are in press. A vast literature on phytopathology indicates neglect of this potentially important feature of pathogenisis, i.e., progress and outcome of parasitic and abiotic disease of economic plants. Neither the host nor the pathogen has been an object of observation by researchers in phytopathology relative to temporal organization prior to or during host-parasite interactions. We point out the present state of information on the chronobiology of diseased plants and some efforts in progress; we also propose research that would elucidate the phenomenon and that perhaps would be useful in interpreting certain discrepancies in the literature.

Daily variations in the sensitivity of soybean seedlings to low temperature.

Every 4 hr during a time span of 32 hr and of 76 hr a different group of soybean seedlings [Glycine max (L.) Merr., cv. Corsoy] maintained under a regime of 16 hr of light followed by 8 hr of darkness was exposed to -10 degrees C for 4 min. Extent of sensitivity to low temperature was evaluated approximately 10 days after exposure to freezing temperature by determining the weight of the plants and chlorophyll content of the cotyledons. The amount of sensitivity to low temperature was related to the time of exposure and displayed a significant 24-hr oscillation. Plants appeared to be least sensitive to cold injury during the late portions of the light span. Plants subjected to water stress were less sensitive to cold and no significant 24-hr oscillation in response to low temperature could be detected by the cosinor method of analysis.

Characteristics of the circadian rhythm in diffusive resistance of Abutilon theophrasti leaves in humid and dry environments.

Diffusive resistance of the upper and lower leaf surfaces of Abutilon theophrasti Medic, was measured with an automatic diffusive resistance meter. Plants were maintained in growth chambers under 4 different environments: 1. high humidity, well-watered, 2. high humidity, dry, 3. low humidity, well-watered, 4. low humidity, dry. Diffusive resistance measurements were obtained every 4 h for up to 3 days when the plants were subjected to either daily regimes consisting of 15 h of light followed by 9 h of darkness or to continuous illumination. Leaf movements were also monitored. Diffusive resistance was rhythmic (circadian) under all the environmental conditions examined. The pattern of diffusive resistance was the same regardless of whether the humidity and/or soil moisture were high or low. The rhythms of diffusive resistance of the upper and lower leaf surfaces differed, however, in amplitude and in the phase at which the minimum value was reached. Diffusive resistance of the leaf was highest (peak of the rhythm) when the leaf blade was in a nearly horizontal position.

Circadian Rhythmicity in the Activities of Phenylalanine Ammonia-Lyase from Lemna perpusilla and Spirodela polyrhiza.

The oscillations in phenylalanine ammonia-lyase activity from Spirodela polyrhiza and phenylalanine ammonia-lyase and tyrosine ammonia-lyase activities from Lemna perpusilla displayed a circadian rhythm under continuous light. Rhythmicity in enzymic activity could not be detected in continuous darkness since under this condition phenylalanine ammonia-lyase activity remains at a fairly constantly low level. Results from our studies of the oscillatory pattern of the respective activities of phenylalanine and tyrosine ammonia-lyase support their "inseparability."

Circadian periodic response of Phaseolus vulgaris l. to 2,4-dichlorophenoxyacetic acid.

The susceptibility of bean plants, Phaseolus vulgaris L., cv. Executive, to 2,4-dichlorophentoxyacetic acid (2,4-D) appeared to depend upon the time of application. Oscillations in response to 2,4-D were evident in plants subjected to conditions of alternating light and dark spans, continuous illumination or darkness. The fresh and dry weight of plant material was generally less when 2,4-D was applied to plants near the later portions of the light span.

Quantifying Rhythmic Movements of Albizzia julibrissin Pinnules.

The cosinor technique, previously applied to studies of animal rhythms, is used to assess the circadian rhythm in pinnule movement of Albizzia julibrissin. The method provides a quantitative approach for studying rhythm properties of either intact or excised pinnules. Phase shifting in A. julibrissin, as compared to the usually slower phase shifts of various circadian phenomena in the insect, bird, and mammal, occurs within 1 day or two. Rhythm adjustment in the pinnules takes place more rapidly when the lighting regiment is advanced than when it is delayed.