Regulation and function of extracellular invertase from higher plants in relation to assimilate partitioning, stress responses and sugar signalling

Abstract

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999 Carbohydrates are synthesised in photosynthetically active source tissues and exported, in most species in the form of sucrose, to photosynthetically less active or inactive sink tissues. Sucrose hydrolysis at the site of utilisation contributes to phloem unloading. This phenomenon links sink metabolism with phloem transport to, and partitioning between, sinks. Invertases catalyse the irreversible hydrolysis of sucrose and thus are expected to contribute to carbohydrate partitioning. Different invertase isoenzymes may be distinguished based on their intracellular location, their isoelectric points and pH optima. Extracellular, cell-wall-bound invertase is uniquely positioned to supply carbohydrates to sink tissues via an apoplasmic pathway, and links the transport sugar sucrose to hexose transporters. A number of studies demonstrate an essential function of this invertase isoenzyme for phloem unloading, carbohydrate partitioning and growth of sink tissues. Extracellular invertases were shown to be specifically expressed under conditions that require a high carbohydrate supply to sink tissues. Further, their expression is upregulated by a number of stimuli that affect source–sink relations. Substrate and reaction products of invertases are not only nutri-ents, but also signal molecules. Like hormones and in combination with hormones and other stimuli, they can regu-late many aspects of plant development from gene expression to long-distance nutrient allocation. Based on studies in Chenopodium rubrum, tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum), the regulation of extracellular invertase and its function in assimilate partitioning, defence reactions and sugar signal transduction pathways are discussed.

Induction of male sterility in plants by metabolic engineering of the carbohydrate supply

“…This study strongly supports the importance of apoplastic cleavage of sucrose by extracellular invertase for supplying carbohydrates to sink tissues and for normal development of plants, which has been suggested by an increasing number of studies in recent years (42)(43)(44)(45). A number of studies have shown that cell wall invertases are sink tissue specifically expressed and up-regulated by stimuli that are associated with an increased demand for carbohydrates such as stress-related stimuli and growth-stimulating phytohormones (25). The specific involvement of invertases in anther development was suggested before for Lilium longiflorum (46,20), tomato (27), and potato (28).…”

“…Extracellular invertases of different species were shown to be encoded by small gene families with a differential regulation and expression pattern (25). Whereas most of the invertases characterized so far are not restricted to one specific plant organ, the extracellular invertase Nin88 of tobacco was shown to be characterized by a specific temporal and spatial expression pattern in anthers.…”

“…These key reactions create a localized concentration gradient, thus promoting phloem unloading via an apoplastic pathway and increasing the sink strength of the corresponding sink tissue. The importance of extracellular invertases for assimilate partitioning and source sink regulation has been suggested in recent years in a number of studies (24,25), and the functional coupling with hexose transporters is supported by a coordinated regulation (26). It has been shown that extracellular invertases are encoded by small gene families that show a highly differential sink tissue-specific expression pattern (27).…”

Foliar carbohydrates content and invertase activity in vines at São Francisco River Valley - Brazil

“…According to Hunter et al (1994) and Palliotti & Cartechini (2001), the hexoses (glucose and fructose) and the sucrose contents, as well as the activity of carbohydrate metabolizing enzymes in grapevine (Vitis vinifera L.) leaves, they are influenced by seasonal and phenological changes. Plant invertase gene expression and enzyme activity are both known to be influenced by a variety of intracellular and extra cellular factors (Tymowska-Lalanne & Kreis, 1998), such as environmental conditions, plant hormones and phenological stages (Roitsch et al, 2000(Roitsch et al, , 2003.…”

Isomaltulose Is Actively Metabolized in Plant Cells

“…This property is commonly exploited in physiological studies aimed at better understanding of the regulatory roles and transport of sugars. Extracellular isomaltulose appears to be differentially sensed by plants (Loreti et al, 2000;Roitsch et al, 2000;Sinha et al, 2002;Atanassova et al, 2003), but known Suc transporters distinguish between isomers and do not detectably bind or transport isomaltulose (Li et al, 1994;Sivitz et al, 2007;Sun et al, 2010).…”