Regulation of assimilation and senescence by the fruit in monocarpic plants

Abstract

For most monocarpic species studied, blocking fruit development prevents or at least delays the death of the plants. However, it usually does not prevent the decline in photosynthetic rate, while it may or may not maintain the photosynthetic components (machinery) such as chlorophyll and ribulose 1,5‐bisphosphate carboxylase. Since sink demand influences photosynthetic rate and the fruit‐less plants have limited sink capacity, their reduced photosynthesis may represent a metabolic adjustment but not senescence. The exact causes of the variable decreases in photosynthetic components in fruit‐less plants are uncertain. The causes of metabolic decline may be different in reproductive‐phase monocarpic plants with and without fruit. In any case, assimilation rate, i.e. photosynthesis, may not always provide a reliable index of senescence. Whether or not the developing fruits of monocarpic plants actually control the early and intermediate decline of metabolism is not clear; however, at least in soybean under non‐stress conditions, they cause the final decrease and death.

Characterization of Cytoplasmic and Nuclear Mutations Affecting Chlorophyll and Chlorophyll-Binding Proteins during Senescence in Soybean

“…By contrast, the stay-green genotypes retained Chl to various degrees; at TPF, the leaves retained 34, 64, and 87% oftheir peak Chl levels in cytG, did2, and Gdjd2, respectively, as compared to only 7 to 8% in Clark. Earlier, Caro and Hadley (3) reported that Chl decreased more rapidly in djd2 than in cytG, but these were field-grown plants and the Chl loss may have been driven by stress (16).…”

“…Developing soybean embryos, seed coats, pod walls, and leaves normally are green but turn yellow during seed maturation (4,18). Seed development is correlated with the yellowing of both the pod walls and the leaves (16,18), which is part of a syndrome termed monocarpic senescence (14,15 …”

Correlation of Xylem Sap Cytokinin Levels with Monocarpic Senescence in Soybean

“…Flower or fruit removal are known to delay leaf senescence and death in monocarpic plants (19,20). Defruiting or deflowering appears to increase the levels of CK activity in root bleeding sap or xylem sap from a wide range of species (3,31,33).…”

“…A wide variety of studies have shown that leaf senescence is usually correlated with a decrease in CK activity levels in the leaves and have implicated roots as the major sources of CKs in mature leaves (30). These root-produced CKs are carried through the xylem into the leaves with the transpiration stream.In soybean, the developing pods, specifically the seeds, cause the plant to degenerate (monocarpic senescence) and die (14,15,19,20). Removal of the pods before, but not during, late podfill can prevent the dramatic yellowing and death of the plant (15, 19).…”

“…cause the plant to degenerate (monocarpic senescence) and die (14,15,19,20). Removal of the pods before, but not during, late podfill can prevent the dramatic yellowing and death of the plant (15,19).…”