Effects of Static Magnetic Field on the Ultradian Lateral Leaflet Movement Rhythm in Desmodium gyrans

The rhythmic leaflet movements of the plant Desmodium gyrans (L.f.) DC slow down in the presence of a static magnetic field. The leaflet positions were digitally retrieved from sequential CCD camera images of the moving leaflets. The experiments were performed under constant light (ca. 500 lux) and temperature (about 20 °C) conditions. The period of the leaflet was then around 5 min. Leaflets moving up and down in a magnetic field of approximately 50 mT flux density increased the period by about 10% due to a slower motion in the “up” position. Since during this position a rapid change of the extracellular potentials of the pulvinus occurs, it is proposed that the effects are mediated via the electric processes in the pulvinus tissue.

Nonlinear Dynamics in the Ultradian Rhythm of Desmodium motorium

The dynamics of the lateral leaflet movement of Desmodium motorium is studied. Simple periodic, quasiperiodic and aperiodic time series are observed. The long-scale dynamics may either be uniform or composed of several prototypic oscillations (one of them reminiscent of homoclinic chaos). Diffusively coupled nonlinear oscillators may account for the variety of ultradian rhythms.

Comparative leaf development of conventional and semileafless peas (Pisum sativum)

Comparative leaf development of conventional (cv. Improved Laxton's Progress) and semileafless (cv. Curly) peas was studied three-dimensionally, from initiation to maturity. The pattern of initiation of leaf primordia, stipules, and the pairs of lateral leaflet and tendril primordia is the same for both cultivars. However, their respective developmental pathways diverge by the time four pairs of lateral primordia have formed. In the conventional cultivar, the basal lateral primordia become increasingly dorsiventral as they develop into leaflets. Distal lateral primordia retain a cylindrical form and develop into tendrils. In contrast, basal first-order lateral primordia of the semileafless cultivar retain a cylindrical form and initiate second-order primordia, first in pairs, then in an alternate pattern. These second-order primordia develop into tendrils. Distal lateral primordium initiation and development are the same in both cultivars. Macroscopic development was subdivided into three stages based on tendril function. Stage I is an elongation phase during which the coiling response is not yet exhibited. During stage II, the tendrils are thigmotropic and retain their capacity to elongate. By stage III the tendrils have completed coiling and they no longer respond to thigmotropic stimuli. Stage I lasts an average of 1.4 ± 0.1 days in 'Improved Laxton's Progress' and 2.1 ± 0.1 days in 'Curly' from emergence from the stipule. Stage II may last up to 8 days, with an average of 6.4 ± 0.2 and 6.9 ± 0.3 days for 'Improved Laxton's Progress' and 'Curly', respectively, under greenhouse conditions for both cultivars. Key words: peas, Pisum sativum, leaf development, tendrils, afila.

Heteroblastic seedlings of green ash. II. Early development of simple and compound leaves

Simple and compound leaf primordia of green ash seedlings differ in shape from initiation. Simple leaf primordia are flattened until their lamina margins grow out at a primordial length of 150 μm. Compound leaf primordia are rounded and peglike at initiation and lateral leaflet buttresses appear when primordia are 150 μm long. Terminal leaflet margins appear when compound leaf primordia are 200 μm long. At initiation both types of leaf primordia are composed of densely cytoplasmic cells. Vacuolation proceeds so that densely cytoplasmic cells remain only in areas developing blades and leaflets and in procambium. Because simple and compound leaves of green ash differ from initiation, neither leaf type can be considered to result from a change in the ontogeny of the other.

Rachis vascularization and leaflet venation in developing leaves of Fraxinus pennsylvanica

Leaves of Fraxinus pennsylvanica are served by a double trace that exits the stem vasculature through a single gap. During embryonic leaf development, the leaf traces subdivide in the node to produce subsidiary bundles that differentiate acropetally in the leaf base and basipetally in the stem. The acropetal bundles converge distally in the node to form a rachis vasculature consisting of a semicircular arc joined by a ventral chord. Each lateral leaflet is vascularized by bundles contributed by both the semicircular arc and the ventral chord of the rachis. One rachis ridge bundle divides to form two leaflet ridge bundles and a new rachis ridge bundle diverges from the ventral chord. The leaflet ridge bundles diverge as basal veins and subsequent secondary veins diverge from the midvein in an approximate right–left sequence. Green ash has odd pinnate leaves; the terminal leaflet is vascularized by the rachis residual following departure of the last leaflet pair. Secondary veins extend to the lamina margins and then curve upward to initiate the marginal loops of the brochidodromous venation. Periclinal divisions occur in close association with secondary veins in the prospective plate meristem region. Anticlinal divisions occur in subepidermal layers of the internal ridge points in the prospective palisade mesophyll region.The latter divisions probably contribute both to lamina extension and to spreading of the conduplicately folded lamina wings.