Sinks for photosynthetic electron flow in green petioles and pedicels of Zantedeschia aethiopica: evidence for innately high photorespiration and cyclic electron flow rates

Abstract

A combination of gas exchange and various chlorophyll fluorescence measurements under varying O(2) and CO(2) partial pressures were used to characterize photosynthesis in green, stomata-bearing petioles of Zantedeschia aethiopica (calla lily) while corresponding leaves served as controls. Compared to leaves, petioles displayed considerably lower CO(2) assimilation rates, limited by both stomatal and mesophyll components. Further analysis of mesophyll limitations indicated lower carboxylating efficiencies and insufficient RuBP regeneration but almost similar rates of linear electron transport. Accordingly, higher oxygenation/carboxylation ratios were assumed for petioles and confirmed by experiments under non-photorespiratory conditions. Higher photorespiration rates in petioles were accompanied by higher cyclic electron flow around PSI, the latter being possibly linked to limitations in electron transport from intermediate electron carriers to end acceptors and low contents of PSI. Based on chlorophyll fluorescence methods, similar conclusions can be drawn for green pedicels, although gas exchange in these organs could not be applied due to their bulky size. Since our test plants were not subjected to stress we argue that higher photorespiration and cyclic electron flow rates are innate attributes of photosynthesis in stalks of calla lily. Active nitrogen metabolism may be inferred, while increased cyclic electron flow may provide the additional ATP required for the enhanced photorespiratory activity in petiole and pedicel chloroplasts and/or the decarboxylation of malate ascending from roots.

O2 evolution and cyclic electron flow around photosystem I in long-term ground batch culture of Euglena gracilis

“…But Munekaga et al (2004) are of the opinion that CEF-PSI is essential in photosynthesis, this idea really gave a new insight into the role of CEF-PSI in photosynthesis. CEF-PSI has also been regarded to be an innate process which operated in normal conditions (Yiotis and Manetas, 2010). Accordingly, we suggest that the occurrence of CEF-PSI was indispensable in E. gracilis in this whole cultivation.…”

“…It has also been reported that CEF-PSI could contribute to the induction of NPQ by generating DpH across the thylakoid membrane and provide protection to PSII against photoinhibition (Golding and Johnson, 2003;Huang et al, 2012). Recent years, researchers have started to focus on the performance of CEF-PSI in normal conditions, and the occurrence of CEF-PSI was regarded to be essential and innate in the process of photosynthesis (Munekaga et al, 2004;Yiotis and Manetas, 2010).…”

Dianthus caryophyllus stems and Zantedeschia aethiopica petioles/pedicels show anatomical features indicating efficient photosynthesis

“…Given that stomata permit gas exchange between internal tissues and external atmosphere, a notable number of functional stomata on the stem epidermis indicates facilitation of a considerable, yet lower relatively to the leaves, atmospheric CO 2 uptake in Z. aethiopica petiolesas already recorded from experimental measurements (Yiotis and Manetas, 2010).…”

“…Yet, their overall performance is quite limited compared to carbon gain of the leaves, despite the fact that both pigment concentrations and maximum linear electron flow rates were found similar (Yiotis and Manetas, 2010). This inconsistency could be due to anatomical differences in the fine structure of the photosynthetic apparatus resulting in increased resistance along the CO 2 diffusion pathway.…”

Lycopene cyclase paralog CruP protects against reactive oxygen species in oxygenic photosynthetic organisms

“…In silico analysis revealed that A. thaliana cruP is up-regulated under chilling stress and dark anoxia (Tables 1 and 2). Cotyledons and pedicels, where CruP transcripts were shown to be elevated, have been shown to undergo photoinhibition stress and high singlet oxygen production under normal "nonphotoinhibitory" conditions, in comparison to true leaves (41,42). Chilling stress in plants causes a range of physiological effects similar to those observed under high light stress (e.g., 43,44).…”