Tissue Partitioning During Leaf Development in Ornamentally-grown Frithia pulchra (Mesembryanthemaceae), a ‘Window Plant’

Abstract

The carbon economy of clonal plants of white clover (Trifolium repens L.) supporting ten mature leaves on the main stolon, or defoliated to leave just one mature leaf on the entire plant, was quantified and compared. Short-term, additive responses, such as greater rates of net photosynthesis by, and greater export of carbon (C) from residual leaves following defoliation increased the net amount of C available for utilization by sinks by 40% (when older leaves remained after defoliation) to 150% (when younger leaves remained) on a per-leaf basis. However, defoliation reduced the total available pool of C derived by current assimilation of leaves on the main stolon by 80-90%. When alterations in C allocation patterns following defoliation were accounted for, considerable compensation of high-priority sinks (such as the main stolon apex) for loss of C supply was evident. For example, when the second-youngest unfolded leaf on the stolon was considered, the total net flux of C from this single leaf to the main stolon apex was estimated to be 17 μmol−1 following defoliation; this equated to 77% of the total C moving to the apex from all ten main-stolon leaves on undefoliated plants. Compared to young leaves, older leaves showed less ability to boost C supply to the main stolon apex after other leaves were removed; instead, older leaves tended to provide greater C support for defoliated branches. The movement of current assimilate to stolon tissue was virtually eliminated following defoliation (approx. 1 μmol−1 in defoliated plants compared to >40 μmol−1 in undefoliated plants). Over 100 mg of reserve material was estimated to have been mobilized from the main stolon to support growth and respiration of the whole plant in the 4 d following defoliation. This equates to 3% of the mean total weight of undefoliated plants, or the weight of three mature leaves. Large amounts of reserves were also probably mobilized from roots. Stored energy sources were clearly a significant contributor to the C economy of plants immediately following defoliation.