Allometry of stem growth in lettuce plants

Abstract

Lettuce plants were grown in naturally-lit glasshouses maintained at either 25/20°C or 20/15°C to elucidate the relationship between stem elongation and flower initiation. The first sign of inflorescence initiation, i.e., dome-shaped apices, could be detected 28 days after sowing (DAS) at 25/20°C and 39 DAS at 20/15°C. Plants went into the bolting stage without head formation at 25/20°C, but plants exhibited head formation at 20/15°C. Stems elongated exponentially with time, irrespective of temperatures. Log-linear relationships could be found between stem length and diameter until the first sign of inflorescence initiation, but thereafter the relationships deviated from linearity at both temperatures. The allometric exponents for the vegetative shoots were close to unity at both temperatures. Likewise, log-linear relationships were found between stem length and stem dry mass and between stem dry mass and leaf dry mass until the first sign of inflorescence initiation. These results show that vegetative shoots can be discerned from flower stalks by their shapes independent of whether the plants formed heads or not.