Effect of Rate of Photosynthesis on the Pattern of Assimilate Distribution in the Graminaceous Plant

Abstract

Infrared gas analysis and a quantitative radiocarbon tracer technique were used to measure photosynthesis and the distribution of ¹⁴C-labelled assimilate in Lolium temulentum and a uniculm barley exposed continuously or intermittently to contrasting light intensities. Plants grown for 10–20 d in low light (−2 of visible light) exported a greater proportion of their assimilate to growing leaves at the terminal meristem and a smaller proportion to their roots and tillers than equivalent plants in high light (150 W m⁻²). A single day's exposure (8.4 h photoperiod) to a contrasting light regime elicited a change in the pattern of assimilate distribution in the same diurnal period, but 2–3 d exposure was required for a substantial shift in the pattern of supply of assimilate to meristems. The data indicated that in terms of assimilate distribution complete adaption to a new light regime is attained in about 7 d.