Genetic variation in soybean photosynthetic electron transport capacity is related to plastocyanin concentration in the chloroplast

Abstract

Fifteen ancestral genotypes of United States soybean cultivars were screened for differences in photosynthetic electron transport capacity using isolated thylakoid membranes. Plants were grown in controlled environment chambers under high or low irradiance conditions. Thylakoid membranes were isolated from mature leaves. Photosynthetic electron transport was assayed as uncoupled Hill activity using 2,6-dichlorophenolindophenol (DCIP). Soybean electron transport activity was dependent on genotype and growth irradiance and ranged from 6 to 91 mmol DCIP reduced [mol chlorophyll](-1) s(-1). Soybean plastocyanin pool size ranged from 0.1 to 1.3 mol plastocyanin [mol Photosystem I](-1). In contrast, barley and spinach electron transport activities were 140 and 170 mmol DCIP reduced [mol chlorophyll](-1) s(-1), respectively, with plastocyanin pool sizes of 3 to 4 mol plastocyanin [mol Photosystem I](-1). No significant differences in the concentrations of Photosystem II, plastoquinone, cytochrome b6f complexes, or Photosystem I were observed. Thus, genetic differences in electron transport activity were correlated with plastocyanin pool size. The results suggested that plastocyanin pool size can vary significantly and may limit photosynthetic electron transport capacity in certain species such as soybean. Soybean plastocyanin consisted of two isoforms with apparent molecular masses of 14 and 11 kDa, whereas barley and spinach plastocyanins each consisted of single polypeptides of 8 and 12 kDa, respectively.

The Role of Plastocyanin in the Adjustment of the Photosynthetic Electron Transport to the Carbon Metabolism in Tobacco

“…The maximum PC to P 700 ratios in young wild-type leaves are in agreement with numbers previously published for spinach (Haehnel et al, 1989) and barley (Burkey, 1994). The minimum values for PC contents shown here for sinklimited leaves are comparable to those published for low-light acclimated barley leaves (Burkey, 1993) and in soybean genotypes with constitutively repressed PET (Burkey et al, 1996).…”

“…The ratio of PC:PSI decreases from 4 to 5 in leaves with high assimilation rates to values below 1 in leaves, whose assimilation is depressed. Although a general correlation between PC content and PET has already been reported for barley (Burkey, 1994) and soybean genotypes with constitutively depressed photosynthesis (Burkey et al, 1996), its role in flux control under physiological condition has not yet been established.…”

“…Instead, the PET capacity was adjusted to the assimilation rate . In barley (Hordeum vulgare; Burkey, 1994) and soybean (Glycine max; Burkey et al, 1996) genotypes with constitutively depressed assimilation, PET correlated with the PC content. While a number of information is available about the acclimation of thylakoids to light intensity (Anderson et al, 1988;Bailey et al, 2001) and quality (Chow et al, 1990;Kim et al, 1993), a consistent concept of a sink-control of PET does not yet exist.…”

Structural comparison of the poplar plastocyanin isoforms PCa and PCb sheds new light on the role of the copper site geometry in interactions with redox partners in oxygenic photosynthesis

“…Both have essentially identical molecular mass, 10.5 kDa, but differ by a replacement of 12 amino acids. A similar PC dimorphism was established in parsley [9], tobacco [10], soybean [11] and Arabidopsis thaliana [12]. In particular, the occurrence of twin PC dimorphism in the amphidiploid plant Nicotiana tabacum and further genetic analyses suggest that heterogeneity of PC is widespread among higher plants [10,12,13].…”

Dynamic photosynthesis under a fluctuating environment: a modelling-based analysis

“…The reason for a dedicated section is that although the kinetic properties of the different enzymes and protein complexes are expected to be conserved or to vary in a narrow range within the different taxa of C3 plants, the concentrations and maximum activities discussed in Section 5.2.9 vary with species (Albertsson et al, 1991;Chow et al, 1991;Wullschleger, 1993;Burkey et al, 1996) and growth conditions (Schöttler and Tóth, 2014). Given that no publication exists reporting all such values, it is especially important to have a consistent set of values.…”