Sink feedback regulation of photosynthesis in vines: measurements and a model

Abstract

An experimental and modelling study of source-sink interactions in Vitis vinifera L., cv. Cabernet Sauvignon, rooted cuttings under non-limiting environmental conditions with a 12 h photoperiod is presented here. After 4 h, measured photosynthesis, stomatal conductance and leaf carbohydrate content reached maximum values. Over the remainder of the photoperiod, photosynthesis and stomatal conductance decreased continuously, whereas leaf carbohydrate content remained relatively constant. Because the experiment took place in a non-limiting environment, the results suggest that stomatal regulation of photosynthesis was mediated by an internal factor, possibly related to sink activity. A simple 1-source, 2-sink model was developed to examine the extent to which the data could be explained by a hypothetical sink-to-source feedback mechanism mediated by carbohydrate levels in either the mesophyll, the source phloem or the phloem of one of the two sinks. Model simulations reproduced the data well under the hypothesis of a phloem-based feedback signal, although the data were insufficient to elucidate the detailed nature of such a signal. In a sensitivity analysis, the steady-state response of photosynthesis to sink activity was explored and predictions made for the partitioning of photosynthate between the two sinks. The analysis highlights the effectiveness of a phloem-based feedback signal in regulating the balance between source and sink activities. However, other mechanisms for the observed decline in photosynthesis, such as photoinhibition, endogenous circadian rhythms or hydraulic signals in the leaf cannot be excluded. Nevertheless, it is concluded that the phloem-based feedback model developed here may provide a useful working hypothesis for incorporation into plant growth models and for further development and testing.

Impacts of using polyethylene sleeves and wavelength selective mulch in vineyards. II. Effects on growth, leaf gas exchange, yield components and fruit quality of Vitis vinifera cv. Merlot

“…A, g s and g m declined for leaves in open-top sleeves at Vin 1 and Paradise, and for leaves that had sleeves removed at Vin 1. Declining A after midday has been found previously in several studies of non-stressed grapevines (Chaves et al 1987;Edson et al 1993;Lang et al 1998;Williams et al 2000;Quereix et al 2001;Gomez-del-Campo 2002;Patakas et al 2002) and may result from sink feedback regulation which reduces g s and maintains a constant C i (Chaves et al 1987) and/or leaf carbohydrate content (Quereix et al 2001). The constant leaf C i levels found over the measurement period at Vin 1 and Paradise support this idea.…”

Drought-induced changes in development and function of grapevine (Vitis spp.) organs and in their hydraulic and non-hydraulic interactions at the whole-plant level: a physiological and molecular update

“…However, stomatal closure is not the only cause of decreased photosynthesis during the midday depression. The depression involves both stomatal and non-stomatal factors, as reflected by lower photosynthesis during the afternoon than in the morning at any given stomatal conductance (Cuevas et al 2006) or substomatal CO 2 concentration (Downton et al 1987;Quereix et al 2001). In addition, g s in the afternoon is less sensitive to ABA and more sensitive to CO 2 than during the morning, also supporting the idea that reduced photosynthesis is limiting g s in the afternoon and not vice versa (Düring 1991;Correia et al 1995).…”

Evidence That Sucrose Loaded into the Phloem of a Poplar Leaf Is Used Directly by Sucrose Synthase Associated with Various β-Glucan Synthases in the Stem

“…Fru-6-P º Glc-6-P º Glc-1-P). Fru buildup may be prevented during UDPGlc channeling, not only because a high concentration of Fru inhibits the activity of SuSy (Doehlert, 1987), but also because Fru buildup in this sink tissue may be coupled with a negative signaling related to photosynthesis (Quereix et al, 2001). Nevertheless, the Fru recycling system for cellulose synthesis at the plasma membrane may be different from that for xyloglucan synthesis in the Golgi network, possibly because the UDP-[ 3 H]Glc formed in the Golgi could be interconverted to UDP-3 H-sugars for the synthesis of heterogenous polysaccharides, whereas the Glc nucleotide formed at the plasma membrane is predominantly destined for the synthesis of cellulose.…”