Wednesday, August 8, 2007

PS 50-139: Meeting the carbon demands of sexual reproduction in Podophyllum peltatum (Mayapple): Phenological, structural, and physiological components

John V.H. Constable, California State University, Fresno

            In Mayapple vegetative rhizomes (Vr) possess single leaves, whereas reproductive rhizomes (Rr) possess two leaves.  This study hypothesized that to meet reproductive carbon demands of Rr leaves relative to Vr leaves would (i) initiate growth earlier, (ii) possess greater leaf area, and (iii) exhibit greater photosynthesis.  Rhizomes (Vr and Rr) were grown at ~550 µmol•m-2•s-1 illumination and measured (growth and gas exchange) weekly for ~100d.  A repeated measures ANOVA was used to analyze the effect of leaf type (Vr or Rr) and time on measured parameters.  Leaves of both types emerged on similar dates, but Rr leaves were 23% longer at emergence than Vr leaves (P=0.008).  Leaves of both types exhibited similar initial elongation rates and final leaf area.  Seasonally averaged, Vr leaves had a light-saturated photosynthetic rate (Amax) of 7.40±0.63 µmol•m-2•s-1, light saturation point (LSP) of 117±10 µmol•m-2•s-1, light compensation point (LCP) of 10.2±1.3 µmol•m-2•s-1, and an apparent quantum efficiency (QE) of 0.069±0.001 (unitless).  In contrast, Rr leaves had a 50% greater Amax (P<0.0001), greater LSP (+42%, P=0.0358) and QE (+8%, P=0.0283), but LCP (P=0.5063) was similar.  All parameters, except LSP, were affected by time and only LCP exhibited an interaction effect (P=0.0414).  Hypotheses (i) and (ii) were not supported, while (iii) was strongly supported.  The additional finding that Rr leaves senesced 13d later than Vr leaves (P=0.002) coupled to greater initial leaf length and photosynthetic characteristics resulted in an ~65% greater seasonal C gain by Rr leaves over Vr leaves that may contribute to successful sexual reproduction.

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