A metabolic comparison between progressive and monocarpic senescence of soybean

Secor, Jacob; Shibles, Richard; Stewart, Cecil R.

doi:10.1139/b84-117

Cited by 24 publications

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“…18) and were greater than those reported in other studies of soybean cotyledon photosynthesis (1,4,5,9). Rates reported here were clearly in excess of dark respiration even in young cotyledons that showed high dark respiration rates.…”

Section: A' C-)contrasting

confidence: 70%

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

Marek

Stewart²

1992

Plant Physiol.

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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...

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Section: A' C-)contrasting

confidence: 70%

“…The amount of enzyme increased until day 6 and then decreased steadily until decapitation at day 18 (Fig. 2).…”

Section: Rubiscomentioning

confidence: 91%

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

Marek

Stewart²

1992

Plant Physiol.

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“…Two types of senescence have been described for soybean under field conditions: progressive senescence of lower leaves before reproductive growth and monocarpic senescence of the remaining leaves during the pod fill phase of reproductive growth (28). Wells (32) showed that the loss of lower canopy leaves was not closely associated with light interception subsequent to canopy closure, an indication that the shaded leaves do not contribute significantly to whole plant photosynthesis.…”

Section: Discussionmentioning

confidence: 99%

Response of Soybean Photosynthesis and Chloroplast Membrane Function to Canopy Development and Mutual Shading

Burkey

Wells²

1991

Plant Physiol.

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The effect of natural shading on photosynthetic capacity and chloroplast thylakoid membrane function was examined in soybean (Glycine max. cv Young) under field conditions using a randomized complete block design. Seedlings were thinned to 15 plants per square meter at 20 days after planting. Leaves destined to function in the shaded regions of the canopy were tagged during early expansion at 40 days after planting. To investigate the response of shaded leaves to an increase in available light, plants were removed from certain plots at 29 or 37 days after tagging to reduce the population from 15 to three plants per square meter and alter the irradiance and spectral quality of light. During the transition from a sun to a shade environment, maximum photosynthesis and chloroplast electron transport of control leaves decreased by two-to threefold over a period of 40 days followed by rapid senescence and abscission. Senescence and abscission of tagged leaves were delayed by more than 4 weeks in plots where plant populations were reduced to three plants per square meter. Maximum photosynthesis and chloroplast electron transport activity were stabilized or elevated in response to increased light when plant populations were reduced from 15 to three plants per square meter. Several chloroplast thylakoid membrane components were affected by light environment. Cytochrome f and coupling factor protein decreased by 40% and 80%, respectively, as control leaves became shaded and then increased when shaded leaves acclimated to high light. The concentrations of photosystem I (PSI) and photosystem 11 (PSII) reaction centers were not affected by light environment or leaf age in field grown plants, resulting in a constant PSII/PSI ratio of 1.6 ± 0.3. Analysis of the chlorophyll-protein composition revealed a shift in chlorophyll from PSI to PSII as leaves became shaded and a reversal of this process when shaded leaves were provided with increased light. These results were in contrast to those of soybeans grown in a growth chamber where the PSII/ PSI ratio as well as cytochrome f and coupling factor protein levels were dependent on growth irradiance. To summarize, light environment regulated both the photosynthetic characteristics and the timing of senescence in soybean leaves grown under field conditions. ' Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture or the North Carolina Agricultural Research Service and does not imply its approval to the exclusion of other products that may also be suitable.Both light quantity and light quality regulate the photosynthetic properties of higher plants by controlling the activity and the composition of the photosynthetic apparatus (2, 5, 29). Thus, light environment plays a critical role during leaf expansion in determining the photosynthetic properties of the mature leaf. More recently, controlled environment studies with a number of species have shown that fully expanded leaves reta...

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“…First, extreme shade conditions can induce rapid senescence of lower canopy leaves several weeks in advance of monocarpic senescence of the whole plant (Secor et al 1984;Burkey and Wells 1991;Wells 1991). During the development of a closed soybean canopy, many leaves expand under full sun and later function in extreme shade following the development of leaves at higher nodes.…”

Section: Introductionmentioning

confidence: 99%

Effects of natural shade on soybean thylakoid membrane composition

Burkey

Wells

1996

Photosynth Res

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The effect of natural shade on chloroplast thylakoid membrane activity and composition was examined for soybean (Glycine Max. cv. Young) grown under field conditions. Plots with high (10 plants m(-1) row) or low (1 plant m(-1) row) plant density were established. Expanding leaves were tagged at 50, 58 and 65 days after planting (DAP). At 92 DAP, tagged leaves were used as reference points to characterize canopy light environments and isolate thylakoid membranes. Light environments ranged from a photosynthetic photon flux density (PPFD) of 87% of full sun to a PPFD of 10% of full sun. The decline in PPFD was accompanied by an increase in the far-red/red (735 nm/645 nm) ratio from 0.9 to approximately six. The major effects of shade on chloroplast thylakoid membranes were a reduction in chloroplast coupling factor and a shift in light-harvesting capacity from Photosystem I to Photosystem II. Photosynthetic electron transport capacity was not affected by differences in PPFD, but was 20 to 30% higher in the 1 plant m(-1) row treatment. The plant density effect on electron transport was associated with differences in plastocyanin concentration, suggesting that plastocyanin is a limiting factor in soybean. Shade did not have a significant effect on the concentration of Photosystem II, Cyt b6f, or Photosystem I complexes.

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A metabolic comparison between progressive and monocarpic senescence of soybean

Cited by 24 publications

References 0 publications

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

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

Response of Soybean Photosynthesis and Chloroplast Membrane Function to Canopy Development and Mutual Shading

Effects of natural shade on soybean thylakoid membrane composition

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