Comparison of photomixotrophic and heterotrophic callus and suspension cultures of Pinus elliottii. 1. Photosynthetic properties and ultrastructural evidence for coexistence of starch granules and secondary metabolites

Abstract

Photomixotrophic callus and suspension cultures of slash pine (Pmus elliottii var. elliottii Engelm.) have been established. Callus tissues contained up to 2.76/ag chlorophyll mg-t dry wt and suspensions 2.98/~g chlorophyll mg-~ dry wt. Maximum photosynthetic oxygen evolution was 25-32 /~mol O., h -~ mg -~ chlorophyll for callus and 35-39/amol 02 h-~ mg-t chlorophyll for suspension, respectively. Photomixotrophic callus was friable with a high moisture content during early and exponential growth, but evolved into a compact and dense tissue during the latter stage of growth. Compact photomixotrophic callus accumulated and deposited secondary metabolites in the central vacuole and developed large starch granules in the chloroplasts. Secondary metabolites were not observed in photomixotrophic suspensions or in heterotrophic calli and suspensions. Photomixotrophic callus contained numerous mitochondria closely associated with well-developed chloroplasts containing 2-6 thylakoids per granum Heterotrophic callus was characterized by a poorly developed cytoplasm and cup-shaped mitochondria.

Plant Heterotrophic Cultures: No Food, No Growth

“…The ability to assimilate an exogenous substrate as a preferred carbon source is one of the most important properties of cells in heterotrophic conditions. The transfer of suspension cultures to heterotrophic conditions can lead to the loss of chlorophyll and a decrease in photosynthetic activity [ 71 , 73 , 74 ]. Moving bleached cultures grown in darkness under light, at times, induces the restoration of the photosynthetic apparatus.…”

“…Perhaps its properties allow it to be easily metabolized and therefore widely used as a substrate [ 45 , 66 , 83 ]. Cell cultures obtained from plant organisms of various systematic positions—both gymnosperms [ 73 ] and numerous angiosperms—have the ability to grow on sucrose-containing medium. These include cell cultures obtained for both monocotyledonous and dicotyledonous [ 45 , 66 , 84 , 85 ] plants, including such model objects as A. thaliana [ 85 , 86 ] and N. tabacum [ 15 ].…”