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- Title
Photoperiod and the Determination of Potential Seed Number in Chenopodium rubrum L.
- Authors
COOK, R. E.
- Abstract
Individuals from two latitudinal populations of , a short-day annual, were induced in two inductive photoperiods, 15 h and 12 h, to examine the dynamics of reproductive development that determine the potential number of seeds produced. The northern population (50° N) is induced in both photoperiods, while the southern population (34° N) is induced only in the 12 h photoperiod. Individuals were given either 2, 6, 10 or continuous inductive cycles and dissected at intervals after the start of inductive treatments to determine the rates of initiation and differentiation of primordia on the main axis and selected axillary buds. Initial reproductive data indicated that the duration of reproductive development among individuals of the northern population, when grown in the longer photoperiod, was 25 per cent greater, but the number of seeds was increased by a factor of 46. Likewise the duration of reproductive development among individuals of the southern population, when grown in the same photoperiod as the northern population, was 50 per cent longer and the number of seeds was increased by a factor of 66. Dissection of reproductively-developing individuals revealed that induction leads to a stimulation in the rate of initiation of primordia followed by a complete inhibition coincident with the differentiation of terminal floral structures. The timing of this stimulation-inhibition process on each axillary bud depends upon its age relative to the timing of induction. Thus certain primordia on individuals prematurely removed from inductive treatments escape floral differentiation and remain vegetative. The total number of floral primordia (potential number of seeds) is determined early in reproductive development by (1) the number of axillary buds at the start of induction, (2) the stimulated rate of initiation of primordia after induction, and (3) the rate of differentiation of induced primordia. Among individuals of the northern population, the longer inductive photoperiod leads to a greater stimulation in the rate of primordial initiation and a decrease in the rate of floral differentiation, which together lead to the production of more primordia. Likewise among individuals of the southern population in the shorter photoperiod, the rate of organ initiation is similar to that of the northern population in the same photoperiod, but the rate of floral differentiation is lower, leading to the initiation of many more primordia. The effects of photoperiod on seed number are discussed in terms of physiological and ecological criteria of optimality. Since natural induction occurs in the longest, physiologically-'sub-optimar photoperiods possible, and this leads to the greatest production of seeds, it is suggested that the critical photoperiod is a more meaningful focus of interpretation than the physiologically ‘optimal’ photoperiod. Of the factors influencing potential seed number, the most significant difference between the two latitudinal populations is the response of the rate of floral differentiation to the photoperiod of induction. Thus potential seed number in natural populations is intimately related to the prevailing photoperiods through the rates of developmental events. Selection for changes in or maintenance of a particular reproductive ecology must be mediated through developmental responses. Limitations on the potential growth rate of plants are discussed in terms of the ratio of meristematic cells to the total cell population in the plant. Thus the number of growing axillary buds greatly contributes to the potential growth rate, and the degree of correlative inhibition is interpreted as a cost of selection for vertical growth among terrestrial plants competing for light. By means of a simple model the cost of correlative inhibition is also discussed in terms of potential seed number. Reproduction is seen as a release from the developmental constraints required by plant form and a stimulation of ...
- Publication
Annals of Botany, 1976, Vol 40, Issue 5, p1085
- ISSN
0305-7364
- Publication type
Article