**5. Conclusion**

example, in a study using *Arabidopsis* plants, overexpression of tonoplast H+

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

pression of tonoplast H+

pumps (H+

decrease in activities of H+

lation of activities of tonoplast H+

plants, changes in activity(ies) of membrane H+

at least in the regulation of activities of tonoplast H+

plast H+

Relationships

308

manipulation increasing tonoplast H+


shown to result in an increase in whole plant growth, in particular, growth of sink organ roots (Li et al., 2005). In another study using *Arabidopsis* plants, it was shown that overex‐

fold increase in shoot dry weight (Yang et al., 2007). There is also a report that transgenic

et al., 2011). In a study using rye plants, increases of root/shoot ratio and activities of tono‐

inducing deficiency of mineral nutrients (Kasai et al., 1998). Whereas conditions inducing deficiency of mineral nutrients can increase abscisic acid level in plant cells, it can also de‐ crease cytokinin level (Salama & Wareing, 1979; Mizrahi & Richmond, 1972; Battal et al., 2003). In a recent study using *Arabidopsis* plants, transgenic manipulation decreasing cytoki‐ nin level was shown to enhance root/shoot ratio (Werner et al., 2003). In plant cells, levels of abscisic acid and cytokinin can also be affected by levels of photosynthetic carbohydrates, which can interact with the levels of mineral nutrients (Rolland et al., 2002). Interestingly, a more recent study using *Arabidopsis* plants showed that overexpression of tonoplast H+

PPase resulted in an increase in cell abscisic acid level and a decrease in cell cytokinin (bio‐ logically active cytokinin) level (Gonzalez et al., 2010). In the other study using *Arabidopsis*

morphology resembling cytokinin-treated plants (Schumacher et al., 1999). As already men‐

tokinin had opposite effects antagonizing the effects of abscisic acid in barley (Kasai et al., 1993; Fukuda & Tanaka, 2006). In our pod removal study using soybean plants, decreasing the ratio of sink to source organs by conducting pod removal was shown to result in a large

characteristics such as leaf photosynthetic rate related to photosynthetic dry matter produc‐ tion were not analyzed in the above studies other than our study, information from these studies and the other information of our data from pod removal study implicate that in

regulation of photosynthetic matter production through photosynthetic source-sink balance. It is suggested from experimental evidence that abscisic acid and cytokinin can be involved

exists, data from more recent studies let us suppose that now well-known 2C-type protein phosphatase and salt-overly-sensitive 2 protein kinase may be involved (in part) in the regu‐

lated to be symbolic biomolecules that are able to induce or respond to a variety of internal and external environmental changes that cause the regulation of photosynthetic dry matter production through photosynthetic source-sink balance. Many experimental data suggest that interaction actually exists between environmental change and cell abscisic acid and cy‐

and environmental change and photosynthetic matter production and environmental change and photosynthetic source-sink balance (Board & Kahlon, 2011; Peleg & Blumwald,

tokinin levels and environmental change and, for example, activities of tonoplast H+

plants, it was shown that a mutant losing about 60% of tonoplast H+

tioned, abscisic acid had stimulatory effects on activities of tonoplast H+

Huertas et al., 2012). In plants, abscisic acid, cytokinin and membrane H+




pumps of the leaf plasma membrane and tonoplast. Although

pumps by abscisic acid and cytokinin (Batelli et al., 2007;

pump(s) can actually play key roles in the

pumps. Although no direct evidence




pumps, whereas cy‐

pump(s) are specu‐

pumps

Data from recent studies implicate that in plants, activity(ies) of membrane H+ pump(s) can be important in regulation of photosynthetic dry matter production through photosynthetic source-sink balance. However, the effect of photosynthetic source-sink balance on the activi‐ ty(ies) of membrane H+ pump(s) has not been investigated. In our recent study, we investi‐ gated in soybean plants how pod removal, which decreases the ratio of sink to source organs, affects various characteristics related to photosynthetic matter production. We also investigated, for the first time, the effect of pod removal on activities of H+ pumps of leaf plasma membrane and tonoplast. From the data obtained and the other relevant informa‐ tion, it was concluded that in plants, changes in activity(ies) of membrane H+ pump(s) can actually play key roles in the regulation of photosynthetic dry matter production through photosynthetic source-sink balance, and that hormones abscisic acid and cytokinin may be involved in regulation of activities of tonoplast H+ pumps. Plant photosynthetic dry matter

production is essential for all living organisms and is also essential for creating sound envi‐ ronments. Therefore, further studies are important to elucidate the detailed mechanism(s) of how membrane H+ pump(s) are involved in the regulation of photosynthetic dry matter pro‐ duction through photosynthetic source-sink balance.
