Photoperiod Induced Change in Phyllotaxis in Xanthium

Abstract

Photoperiodic floral induction in Xanthium, achieved by subjecting the plants to two long nights, is accompanied by a transient change of the phyllotaxis from the (2, 3) contact parastichy pattern of vegetative plants, to a (3, 5) pattern during the transition. To specify the phyllotaxis, two parameters were estimated from transverse sections of apical buds of control and treated plants: the divergence angle, α, and the plastochron ratio, a. The plastochron ratio decreased progressively during transition from the vegetative to the reproductive state of growth, from a = 1.48 initially to a = 1.15 six days after the beginning of induction. The divergence angle was not altered during the transition. This change in phyllotaxis is interpreted as a change in the relative positioning of leaf primordia on the transitional apex. This transient change appears to be identical with the previously described long‐term change of the phyllotaxis of Xanthium brought about by treatment of plants with gibberellic acid.

Short‐Day‐GrownArabidopsis thalianaSatisfies the Assumptions of the Plastochron Index as a Time Variable in Development

“…3A, 3B). For Chrysanthemum (Schwabe 1957), Chenopodium rubrum (Cook 1976), X. pensylanicum (Erickson and Meicenheimer 1977), and Ranunculus repens (Meicenheimer 1979), the plastochron became shorter during the floral transition. In E. hirsutum, the plastochron shortened during the reproductive transition but stabilized immediately afterward (Meicenheimer 1982).…”

Sink development, phyllotaxy, and dry matter distribution in a large inflorescence

“…Both in cauliflowers and in other species this transition entails an abrupt increase in apical volume . The increase seems to carry with it, as an almost ineluctable consequence, a change in phyllotaxis [5,13,14,20,35,42,501 . In spite of a number of recent attempts to understand the `fluid dynamics' or 'kinematics' of three dimensional growth [16,17,44,49,58], we still do not understand what it is in the behaviour of the component cells that distinguishes a large apex from a small one or indeed an organised apex from a randomly dividing callus.…”

Floral Induction Does not Alter the Growth Parameters of Fuchsia

“…In plants with a determinate flowering habit, the onset of reproductive development results in a complete diversion from one morphological pathway to another. In a more recent investigation, Erickson and Meicenheimer (1977) found that photoperiodic induction of Xanthium, a short-day (SO), determinate, plant, caused a shift in phyllotactic pattern from a (2,3) contact parastichy to a (3,5) contact parastichy during the transition from the vegetative to the reproductive state. Chrysanthemums, for example, underwent an alteration of phyllotaxis and a reduction of plastochron duration (Schwabe, 1958).…”

“…), equivalent to "p" in Erickson and Michelini (1957), was calculated as the ratio of lengths of two successive leaves in their exponential phase of growth: night-interruption treatment was started 17 days after the plants were placed in the growth chamber and lasted 10 days. ), equivalent to "p" in Erickson and Michelini (1957), was calculated as the ratio of lengths of two successive leaves in their exponential phase of growth: night-interruption treatment was started 17 days after the plants were placed in the growth chamber and lasted 10 days.…”

“…Computation of PI-For Fuchsia, the plastochron was defined as the interval between initiation of successive leaf pairs (Erickson, 1976). Assuming that the two leaves in each pair had equal lengths, measurements were made on one leaf of the pair.…”