**1. Introduction**

[117] Yu, G-R., Wang, Q-F., Zhuang, J. (2004). Modeling the water use efficiency of soy‐ bean and maize plants under environmental stress: application of a synthetic model of photosynthesis-transpiration based on stomatal behavior. *J. Plant Physiol.* v. 161, p.

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

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There is evidence suggesting that in plants photosynthetic matter production is regulated by photosynthetic source-sink balance, i.e., the ratio of photosynthetic source organs (e.g., leaves) to non-photosynthetic sink organs (e.g., roots) and/or the balance of supply and de‐ mand of photosynthetic carbohydrate(s) within the plant (Kasai, 2008, 2011). Plant photo‐ synthetic dry matter production is the source of a variety of metabolic and structural compounds. Because of increasing population, shortages of energy and food may become more severe (von Caemmerer & Evans, 2010; Raines, 2011). Plant photosynthetic dry matter production is also essential for maintaing environmental quality. For example, a wellknown environmental problem is climatic warming of the earth, which mainly comes from deforestation (Brovvkin et al., 2004). Improvement of plant dry matter productivity may be an effective way for solving the problems of energy, foods and climatic warming. Thus, it is important to elucidate the mechanism(s) of regulation of plant photosynthetic matter pro‐ duction through photosynthetic source-sink balance.

Data from a number of studies including field investigations implicate that in plants, accu‐ mulation of photosynthetic carbohydrate(s) in leaves, which occurs when photosynthetic source capacity exceeds sink capacity, can regulate leaf photosynthetic rate (Sawada et al., 1999; Kasai, 2008, 2011; Kasai et al., 2012). In soybean a significant negative correlation exists between leaf photosynthetic carbohydrate (sucrose or starch) content and photosynthetic rate (Sawada et al., 1986, 2001; Kasai, 2008). There have also been findings of photosynthetic carbohydrate-mediated decrease in the activity or the amount of Rubisco, the CO2-fixing en‐ zyme in leaves (Sage et al., 1989; Xu et al., 1994; Martin et al., 2002; Paul & Pellny, 2003), al‐ though the detailed mechanism(s) is still unclear. To date, many studies have focused on photosynthetic carbohydrate-mediated inhibition of leaf photosynthesis to elucidate the

mechanism(s) of regulation of photosynthetic matter production through photosynthetic source-sink balance. However, in contrast, there is also evidence suggesting that leaf photo‐ synthetic rate is not necessarily affected by accumulated photosynthetic carbohydrate(s) in leaf (Nebauer et al., 2011). Apart from the regulation of leaf photosynthesis through levels of photosynthetic carbohydrate(s), it is important to examine the mechanism(s) of regulation of photosynthetic dry matter production through photosynthetic source-sink balance by focus‐ ing on new enzyme(s) thought to be important.

Data from recent studies implicate that in plants, activity(ies) of membrane H+ pump(s) such as tonoplast H+ pump(s) can be important in the regulation of photosynthetic dry matter production through photosynthetic source-sink balance (Kasai &Muto, 1990.; Schumacher et al., 1999; Li et al., 2005; Yang et al., 2007; Wang et al., 2011). However, the effect of photosyn‐ thetic source-sink balance on the activity(ies) of membrane H+ pump(s) has not been investi‐ gated. We show here experimental data of our recent study relating to this subject. We investigated in soybean plants how removal of pods, which decreases the ratio of sink to source organs, affects various characteristics related to photosynthetic dry matter produc‐ tion. Factors studied were leaf photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO2 concentration, initial and total activities of Rubisco, chlorophyll, total protein, inorganic phosphate, photosynthetic carbohydrates (sucrose and starch), and dry weights of source and sink organs. We also investigated the effect of pod removal on activi‐ ties of the H+ pumps of the leaf plasma membrane (H+ -ATPase) and tonoplast (H+ -ATPase and H+ -PPase). It is now well known that soybean is one of the most important crops grown in the world (Board & Kahlon, 2011; Ainsworth et al., 2012). On the basis of our experimen‐ tal data and the other relevant information, we also consider how membrane H+ pump(s) can be important in the regulation of photosynthetic dry matter production through photo‐ synthetic source-sink balance.
