Sugar signalling in plants

Plants frequently face unfavourable growth conditions like drought, salinity, chilling, freezing and so on. Drought affects the physiology of plants at the cellular and metabolite levels. Levels of various compounds increase to offer osmoprotective functions, prevent degradation of enzymes and to reduce the amount of reactive oxygen species. One of these metabolite/compounds is sugar. Carbohydrates or sugars are produced as the end products of photosynthesis and are required for the normal metabolism and growth of plants. Under drought stress, levels of various sugar molecules, such as mono-, di- and oligosaccharides, escalate to provide osmoregulation. Another approach to osmoregulation is by balancing the low molecular sugars by phloem transport and sucrose metabolism. Other than osmoregulation, soluble sugars also act as signalling molecules to modulate the sensitivity of plants and thus help in cell responses. The sensor proteins are needed for sensing the level of sugars in cells and lead to signal transduction cascades. The exogenous application of various sugar molecules (trehalose, mannitol, sorbitol etc.) has been found to be an effective approach to increase the resistance against various abiotic stresses including drought stress. This book chapter reviews the metabolism of sugar as well as its role as in stress signalling. The role of exogenous application of sugars under drought stress is also studied here.