Restoration of Photosynthesis in Pot-Bound Tobacco Plants

Premature senescence is observed in pot-bound tobacco plants (Nicotiana tabacum L. cv. xanthii) and this is shown to be accompanied by gross accumulation of leaf starch and a marked decline in photosynthesis, ribulose- 1, 5-bisphosphate (RuBP) carboxylase activity, and soluble protein content. Starch content, uptake of CO2 by leaf discs, and the activity of RuBP carboxylase in whole leaf extracts were measured daily following transfer of restricted plants to larger pots. Starch declined rapidly, whilst photosynthetic activity was fully restored within a period of several days, and frequently exceeded the maximum rates measured in non-restricted plants. This overcompensation, which could be related to availability of carbohydrates accumulated as starch, is discussed in relation to the well-established horticultural practice of ‘potting on’.