Photosynthetic acclimation ofTradescantia albiflorato growth irradiance: Lack of adjustment of light‐harvesting components and its consequences

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Abstract
The photosynthetic acclimation ofTradescantia albiflora(Kunth), a trailing ground species naturally occurring in the deep shade of rainforests, was studied in relation to growth irradiance (glasshouse; direct light and 1 to 4 layers of shade cloth, giving 100 to 1.4% relative growth irradiance). Contrary to other irradiance studies of higher plants grown in natural habitats or controlled light environments, the chlorophylla/bratios ofTradescantialeaves were low (∼2.2) and constant. Acclimation to growth irradiance caused no changes in the relative amounts of specific Chl‐proteins or the numbers of photosystem I (PSI) and PSII reaction centres on a chlorophyll basis, indicating that the light‐harvesting antenna sizes of PSII and PSI, as well as the photosystem stoichiometry, were independent of growth irradiance. However, the amount of cytochromefand ATP synthase on a chlorophyll basis increased with increasing the relative growth irradiance from 1.4 to 35%, showing acclimation of electron transport and photophosphorylation capacity. The photosynthetic capacity and ribulose 1, 5‐bisphosphate carboxylase (EC 4.1.1.39) activity also increased with increase of the growth irradiance to 35%. Beyond that, the inflexible PSII/PSI stoichiometry and shade‐type photosystem II/light‐harvesting units inTradescaniiaare a disadvantage for long‐term exposure to high irradiance since the leaves are more prone to photoinhibition.