Shoot apical meristem and plant body organization: a cross-species comparative study.

Abstract

The shoot apical meristem (SAM) is the key organizing element in the plant body and is responsible for the core of plant body organization and shape. Surprisingly, there are almost no comparative data that would show links between parameters of the SAM and whole-plant traits as drivers of the plant's response to the environment. Interspecific differences in SAM anatomy were examined in 104 perennial herbaceous angiosperms. There were differences in SAM parameters among individual species, their phylogenetic patterns, and how their variation is linked to variation in plant above-ground organs and hence species' environmental niches. SAM parameters were correlated with the size-related traits of leaf area, seed mass and stem diameter. Of the two key SAM parameters (cell size and number), variation in all organ traits was linked more strongly to cell number, with cell size being important only for seed mass. Some of these correlations were due to shared phylogenetic history (e.g. SAM diameter versus stem diameter), whereas others were due to parallel evolution (e.g. SAM cell size and seed mass). These findings show that SAM parameters provide a functional link among sizes and numbers of plant organs, constituting species' environmental responses.