ESTABLISHMENT OF A PLASTOCHRON INDEX FOR DIANTHUS CHINENSIS L.

Abstract

The plastochron index was used to determine which leaves of Dianthus chinensis are developmentally equivalent during vegetative growth of the shoot. Three conditions of the plastochron index had to be met in order for leaves to be defined as developmentally equivalent. The leaves had to be growing exponentially in their early stages, growing at the same rate, and initiated at equal intervals. Linear regression analysis was used to determine the goodness of fit of the exponential model and to calculate the relative rate of leaf elongation. Linear regression was also used to determine the relationship of leaf initiation to time. Both greenhouse‐grown (100 plants) and growth‐chamber‐grown (25 plants) D. chinensis were studied. Regression analysis of the greenhouse plants was performed only with values of averaged leaves. It was found that the greenhouse‐grown average leaves grow exponentially and are initiated at equal intervals, the plastochron equaling 4.55 days. The relative rates of leaf elongation are not constant, ranging from 0.05 to 0.16 cm cm−‐1 day−‐1. However, these rates are most likely the result of analyzing values of averaged leaves. Regression analysis of the growth‐chamber plants was performed with both average and individual leaves. The latter procedure provided a more accurate description of the data. It showed that the leaves of the growth‐chamber plants grow exponentially in their early stage, have the same relative rate of leaf elongation from Leaf 5 to Leaf 12 (0.23 ± 0.005 cm cm−‐1 day−‐1), and are initiated at equal intervals for Plastochrons 6–11 (3.68 ± 0.14 days). Therefore Leaves 6–12 of the growth‐chamber‐grown Dianthus chinensis meet the three criteria of the plastochron index and can be defined as developmentally equivalent from inception to maturation.