The photoprotective role of epidermal anthocyanins and surface pubescence in young leaves of grapevine (Vitis vinifera)

BACKGROUND AND AIMS: Depending on cultivar, surfaces of young leaves of Vitis vinifera may be glabrous-green ('Soultanina') or transiently have anthocyanins ('Siriki') or pubescence ('Athiri'). A test is made of the hypothesis that anthocyanins and pubescence act as light screens affording a photoprotective advantage to the corresponding leaves, and an assessment is made of the magnitude of their effect. METHODS: Measurements were made on young leaves of the three cultivars in spring under field conditions. Photosynthetic gas-exchange and in vivo chlorophyll fluorescence were measured. Photosynthetic and photoprotective pigments were analysed by HPLC. KEY RESULTS: Compared with glabrous-green leaves, both anthocyanic and pubescent leaves had greater dark-adapted PSII photochemical efficiency and net photosynthesis. In leaves possessing either anthocyanins or pubescence, the ratio of xanthophyll cycle components to total chlorophyll, and mid-day de-epoxidation state of the xanthophyll cycle were considerably smaller, than in glabrous-green leaves. These differences were more evident in pubescent leaves, probably indicating that trichomes were more effective in decreasing light stress than anthocyanins in the epidermis. CONCLUSIONS: Light screens, especially in the form of pubescence, decrease the risk of photoinhibition whilst allowing leaves to maintain a smaller content of xanthophyll cycle components and depend less on xanthophyll cycle energy dissipation. This combination of photoprotective features, i.e. decreased photon flux to the photosynthetic apparatus and lower xanthophyll cycle utilization rates may be particularly advantageous under stressful conditions.     

Quantitative relationships between boron and mannitol concentrations in phloem exudates of Olea europaea leaves under contrasting boron supply conditions

Root exudates are implicated in the chemical defense of plants, but testing such hypotheses has been hindered by the difficulties of quantifying allelochemical concentrations in soil. Here we describe a new, simple method to quantify the dynamics of non-polar root exudates in soil. Novel soil probes were constructed using stainless steel wire inserted into polydimethylsiloxane (PDMS) tubing. Probes were inserted into soil for 24 h, removed and extracted, and analyzed by HPLC. Lipophilic thiophenes produced by roots of Tagetes and Rudbeckia species were chosen as candidate compounds to test the method. Probes recovered microgram quantities of the highly phytotoxic thiophenes 5-(3-buten-1-ynyl)-2,2′-bithienyl (BBT) and α-terthienyl per probe per day from the root zone of Tagetes patula, and distribution of thiophenes beneath plants was spatially and temporally heterogeneous. Flux-proportional sampling of soil provides a means to test hypotheses about the role of root exudates in plant–plant and other interactions.