Phytochrome effects on leaf growth and chlorophyll content in Petunia axilaris

Changes in the phytochrome status at the end of the daily photosynthetic period result in several plant responses. To understand the causal relations among these responses it is useful to investigate species or experimental conditions where the most common correlations among responses are broken. A step in this direction is presented here with Petunia axilaris, where FR‐treated plants showed low chlorophyll content and erect leaves, but‐ contrary to other species‐higher leaf area and plant dry weight. Differences in area expansion were related to the late phase of leaf growth and were due, at least in part, to larger cells in FR‐treated plants. Effects on length/width ratio, specific leaf area, net assimilation rate, shoot/root ratio and leaf number were small or non‐existent. It is suggested that the lower chlorophyll content in FR‐treated plants was not a consequence of scarcity of assimilates.