**Author details**

zyme in the cell membrane, promoting the pumping back to the cell of electrolytes that were lost because of membrane damage caused by water deficit (Palta, 1990, Waraich et al., 2011).

A Comprehensive Survey of International Soybean Research - Genetics, Physiology, Agronomy and Nitrogen

In addition to the direct effects of K, P, and Ca on the maintenance of plant metabolism un‐ der water deficit conditions, balanced nutrition regarding all essential elements (both mac‐ ro- and micronutrients) can support plant development under limiting conditions by improving the initial steps of vegetative growth, such as leaf area expansion. This improved growth will allow the achievement of high photosynthetic rates and, hence, good root devel‐ opment, thereby improving the absorption of water into deeper layers and allowing the

Breeders and geneticists involved in soybean breeding are interested in consolidating the current knowledge about physiology and functional genomics to improve crop breeding programs (Manavalan et al., 2009), especially based on studies aimed at providing the infor‐ mation needed to improve the resistance / tolerance of cultivars to a multitude of stress fac‐ tors (Kulcheski et al., 2011, Makbul et al., 2011). Through proteomic analysis, 145 genes that are differentially expressed according to the imposition of water stress were identified in two soybean cultivars, MG/BR46 [Conquista] and BR 16, that are considered tolerant and sensitive to water deficits, respectively (Stolf-Moreira et al., 2011). These genes were classi‐ fied into nine functional categories: energy, transcription factors, metabolism, stress re‐ sponses, protein synthesis, cell communication, the cell cycle, cellular transport, and other unknown functions. Additionally, 11 micro-RNAs that show different expression patterns during the imposition of biotic and abiotic stress were identified in the cultivars 'Embrapa 48' (tolerant to drought stress) and 'BR 16' (sensitive to water stress) (Kulcheski et al., 2011), and the transcription of several other proteins related to oxidative damage, isoflavonoids and lignin synthesis was detected in soybean under water stress (Yamaguchi et al., 2010). Furthermore, Alam et al. (2010) reported that there are two enzymes involved in carbohy‐ drate metabolism (UDP-glucose pyrophosphorylase and 2.3-biphosphoglycerate independ‐ ent phosphoglyceratemutase) that are suppressed after exposure to a water deficit. The levels of these enzymes tended to revert to the basal level after rehydration of the plants, suggesting that the change in the allocation of carbon in soybean plants under drought may indicate an adaptive response. According to the authors of this report, the metabolism of carbohydrates is one of the processes that are most susceptible to water stress, after photo‐ synthesis. Other studies have identified several soybean wildtypes that can be specifically adapted to adverse conditions, such as wind, water logging, salinity and water deficits, and may be useful for identifying genes related to tolerance / resistance to a variety of biotic and abiotic stresses (Lee et al., 2010). Such studies are required because genetic diversity has been lost in the process of domestication of *G. max* (Hyten et al., 2006), and wildtype soy‐ bean have been useful for contributing new and unique genes to increase yields under dif‐

Moreover, as discussed in previous sections of this chapter, to improve soybean growth un‐ der water deficit conditions, the application of additional strategies is necessary, such as

plants to survive water deficit periods.

ferent worldwide crop conditions (Wang et al., 2004).

**4.4. Future directions**

Relationships

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Gustavo M. Souza1 , Tiago A. Catuchi2 , Suzana C. Bertolli1 and Rogerio P. Soratto2

1 Laboratório de Ecofisiologia Vegetal, Universidade do Oeste Paulista, Presidente Pru‐ dente, SP, Brazil

2 Departamento de Produção Vegetal, Faculdade de Ciências Agronômicas, Universidade Estadual Paulista, Botucatu, SP, Brazil
