Carbon Partitioning in Mature Leaves of Pepper: Effects of Transfer to High or Low Irradiance

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Abstract
Grange, R. I. 1987. Carbon partitioning in mature leaves of pepper: Effects of transfer to high or low irradiance.—J. exp. Bot. 38: 77–83. Pepper plants were grown at an irradiance of either 55 W m–2 or 90 W m–2PAR. Changes in net photosynthesis, carbon export, starch and sugar contents in a single mature leaf were measured at intervals for 8 d following transfer of plants between the two irradiances. On transfer from low to high irradiance, the net photosynthesis rate increased immediately but export rate increased only slowly, to a maximum after 3 d. While assimilation exceeded export more starch and sucrose accumulated in the day and remained in the leaf at the end of each night. Hexose contents at the end of night remained low and constant, but the daytime maximum rose during the first 2 d from transfer, thereafter returning to pre-transfer contents. Following transfer of leaves from high to low irradiance starch present in the leaf provided sufficient reserves to maintain the rate of export for one day. Subsequently, the sucrose content fell and the export rate declined to near that in leaves grown in low irradiance. Sucrose and hexose accumulation following transfer from low to high irradiance suggests a limitation to export ‘downstream’ from sucrose synthesis, probably in the loading step from mesophyll to phloem.