Allocation of Organ Biomass in Perfect and Imperfect Flowers

Abstract

Perianth MP, gynoecium MG, and androecium MA dry-weight biomass (in g) of 39 species of perfect flowers was measured. These data were pooled with published data from an additional 51 species and used to determine size-dependent variations in (MG and MA) in terms of the hypothesis that the quotient of MG and MA exceeds 1·0 for out-breeding (xenogamous) species and less than 1·0 for in-breeding (autogamous) species. Ordinary least square regression of the pooled data (n = 90) showed MG = 0·118 M0·916P (r2 = 0·884) and MA = 0·186 M0·975P (r2 = 0·865), indicating that the biomass of the gynoecium proportionally decrease as floral size increases. The exponents of these regressions indicate that the ratio of gynoecial to androecial biomass decreased with increasing floral size such that comparatively small flowers (MP < 0·0021 g) had MG/MA > 1·0 (predicted for 'out-breeders') while comparatively larger flowers (MP > 0·0021 g) had MG /MA < 1·0 (predicted for 'in-breeders'). Thus, on average, the type of breeding system was a size-dependent phenomenon.To test whether the biomass of a floral organ-type is a legitimate indicator of gender reproductive effort, the biomass (in g) of stamen filaments Mm and anther sacs MAS of 39 species was determined. Least square regression of these data showed MAS = 0·188 M0·854fil (r2 = 0·967), indicating that species with larger stamen filaments, on the average, bore proportionally smaller anther sacs and thereby cautioning against the uncritical use of the allocation of biomass to floral organ-type as a strict gauge of gender-function investment.To determine whether the loss of one gender-function results in proportional reallocation of biomass to the remaining gender-function, the size-dependency of androecial and gynoecial biomass was determined for a total of 33 perfect and imperfect flowers of Cucumis melo. Regression of the data obtained from perfect flowers yielded MA = 0·402 M1·47P (r2 = 0·898) and MG = 4·63 M1·36P (r2 = 0·842). Since MG/MA ∝ M0·11P , the biomass allocation to the gynoecium relative to the androecium decreased with increasing floral size. This result was consistent with the broad interpecific comparison based on 90 species with perfect flowers . Regression of the data for imperfect flowers yielded MA = 0·151 M1·02P (r2 = 0·675) and MG = 4·68 M1·47P (r2 = 0·996), indicating a near allometric relation for the androecium and a strong positive anisometry for the gynoecium. Thus, for flowers of comparable size, a loss of female gender obtains a modest to significant again in androecial biomass whereas the loss of male gender yields only a slight increase in gynoecial biomass.Collectively, the results of these studies indicate that biomass allocation patterns are size-dependent phenomena whose complexities have been largely ignored in the literature.