Light piping activates chlorophyll biosynthesis in the under-soil hypocotyl section of bean seedlings

• Light piping of bean shoot was measured with modified spectrofluorometer.
• Light piping of shoot activates chlorophyll biosynthesis down to 5 cm of soil.
• Chlorophyll emission bands of green leaves were found in under-soil shoot.
• Protopigments dominate in hypocotyl segments under 5 cm soil layer.

Protochlorophyllide (Pchlide), protochlorophyll (Pchl) and chlorophyll (Chl) contents, their distribution and native arrangements were studied in under-soil hypocotyl segments of 4-, 7- and 14-day-old bean (Phaseolus vulgaris L. cv. Magnum) seedlings. The plants were grown in general potting soil under natural illumination conditions in pots. For sample collection, the pots were transferred into dark-room where all manipulations were done under dim green light. The pigments were extracted with acetone; phase separation was used to identify the Pchl contents. Fluorescence microscopic studies were done and 77 K fluorescence emission spectra were recorded. Using a special setup of a spectrofluorometer, the vertical light piping properties of the above-soil shoots were measured. The segments in the 5–7 cm deep soil region contained Pchlide and Pchl in 4- and 7-day-old seedlings and the segments towards the soil surface contained Chl in increasing amounts. In parallel with the pith degradation of hypocotyls, the Chl content of elder seedlings increased in the deeper under-soil segments. These results prove that the tissue structure of the shoot ensures light piping thus greening process and chloroplast formation can take place even in under-soil organs not directly exposed to light.