Chapter 11 - 2 Photosynthesis : Photoinhibition

In high light intensities, chlorophyll can be damaged by the enhanced activity of electrons beyond that which it can process. This results in photoinhibition by decreasing the photosynthetic capacity. In tracheophytes, this is particularly pronounced in dehydrated plants, but in bryophytes, it seems the pattern is quite different. Seel et al. (1992) compared the desiccation-tolerant moss Syntrichia ruralis var. arenicola (=Tortula ruraliformis) (Figure 2) with the desiccation-intolerant moss Dicranella palustris (Figure 2). It appeared that desiccation in the dark had no effect on total concentrations of chlorophylls or carotenoids in either moss, but in D. palustris it resulted in loss of protein and accumulation of TBA, suggesting lipid peroxidation. Dicranella palustris was unable to recover its photosynthesis during rehydration, whereas photosynthesis of Syntrichia ruralis var. arenicola had only marginal depression in photosynthesis upon rehydration, and only at the highest irradiance. In the light, D. palustris likewise lost not only protein, but also chlorophyll and carotenoids, while lipid peroxidation increased. Again, S. ruralis var. arenicola suffered little damage. Greater damage occurred to this species when hydrated and exposed to high irradiance. Thus we can include that desiccation tolerance affords some protection to the chlorophyll in the presence of high light intensities, at least in some bryophyte species.