Photosynthesis and Photorespiration in Presenescent, Senescent, and Rejuvenated Soybean Cotyledons

Abstract

Various growth and physiological parameters were measured in germinating, presenescent, and senescing soybean (Glycine max [L.] Merr.) cotyledons and in cotyledons rejuvenated by epicotyl removal 18 days after planting. The maximal measured carbon dioxide exchange rates (CER) in the cotyledons were in the range of those reported for field-grown soybean leaves. Rejuvenated cotyledons accumulated total chlorophyll in excess of the maximum observed in presenescent cotyledons. When photosynthetic rates were expressed per cotyledon, the CER in rejuvenated tissue recovered to the maximal rates observed in presenescent cotyledons. Ribulose-1,5-bisphosphate carboxylase/oxygenase in rejuvenated cotyledons also recovered to the maximal amount seen in presenescent cotyledons so that CER appeared to be a function of ribulose-1,5-bisphosphate carboxylase/oxygenase content during most of the period studied. Observations of the postillumination outburst of CO2 and 14C label in glycine indicated that photorespiration was occurring in the cotyledons and that photorespiration relative to photosynthesis was different in rejuvenated compared with presenescent cotyledons.senescing, or rejuvenated cotyledons, although they did see quantitative differences in certain proteins. However, when proteins were extracted from cotyledons, specific proteins became prominent only in the rejuvenated cotyledons, suggesting that the rejuvenated state may be different from that of the presenescent cotyledon.The rejuvenated cotyledon has not been well characterized physiologically. Photosynthesis in soybean cotyledons has been reported in only three studies, none of which included rejuvenated cotyledons (1,4,5,9). The published data show that net photosynthesis in cotyledons is never much greater than dark respiration. Because soybean cotyledons can recover from senescence and survive for extended periods, they must be able to carry on net assimilation. The objective of this study was to characterize these cotyledons physiologically. Soybean (Glycine max [L.] Merr. cv Corsoy 79) was grown in flats of sterilized soil (1:1:1, soil:peat:perlite) in a greenhouse. The minimum temperature was always >18°C, and the maximum temperature was normally 22 to 24°C. Maximum daily irradiance was never less than 1200 ,mol photons m-2 s-'. Seeds were screened to uniform size before planting, and cotyledon age was measured as number of days after planting. Plants were watered twice weekly with doublestrength modified Hoagland solution (14) and on other days with tap water. Seedlings were thinned daily to eliminate plants not at the same developmental stage, as determined by visual morphological characteristics. For decapitation treatments, the stem, which included unifoliolate leaves, trifoliolates, and apical bud (hereafter referred to as the epicotyl), was removed 1 or 2 cm above the cotyledonary node. After decapitation, axillary buds were carefully removed as they expanded. MATERIALS AND METHODS PlantAs daylength, irradiance, and temperature varied throu...

ArabidopsisPhosphoglycerate Dehydrogenase1 of the Phosphoserine Pathway Is Essential for Development and Required for Ammonium Assimilation and Tryptophan Biosynthesis

“…Because cotyledons are autotrophic organs (Marek and Stewart, 1992), Ser will most likely be synthesized via photorespiration and transported to the SAM via the phloem. Taken together, Ser synthesized by either photorespiration or PS pathway is essential for proper leaf development in plants.…”

Varietal Difference in Early Vegetative Growth during Seedling Stage in Soybean

“…It is reported that soybean cotyledons senesce and fall off when the third trifoliate leaf unfolds (Peterman and Siedow, 1985;Harris et al, 1986;Marek and Stewart, 1992). There may be varietal differences in this characteristic.…”

“…In soybean, the green cotyledons play an important role after emergence because the cotyledons not only have a storage-mobilizing function but also assimilate energy through photosynthesis (Harris et al, 1986;Brown and Huber, 1987;Marek and Stewart, 1992;Ramana et al, 2003;Kitajima, 2003;Hanley and May, 2006;Zhang et al, 2008). Zheng et al (2011) insisted that the cotyledons provide a major proportion of the assimilation needed for seedling growth until the first true leaf becomes a significant exporter of photosynthate.…”

Changes in photosynthetic capacity and polypeptide patterns during natural senescence and rejuvenation of Cucurbita pepo L. (zucchini) cotyledons

“…Decapitation of the shoot above differentiated leaves or the entire epicotyl above the yellow cotyledons, thus leading to subsequent rejuvenation is an approach for studying reversibility of the senescence process (Van Staden and Carmi 1982;Marek and Stewart 1992;Ananieva et al 2004). Cotyledon natural senescence and rejuvenation have not been sufficiently studied (Biswal and Biswal 1984;Marek and Stewart 1992;La Rocca et al 1996).…”

“…Cotyledon natural senescence and rejuvenation have not been sufficiently studied (Biswal and Biswal 1984;Marek and Stewart 1992;La Rocca et al 1996). Changes in CO 2 exchange rates, Rubisco levels and photorespiration were reported for presenescent, senescing and rejuvenated soybean cotyledons (Marek and Stewart 1992).…”