Biology subjects

Arp, J. J.

Publications and source records attributed to Arp, J. J..

3 recordsLinked to original sources

bioRxiv2021

Developmental Effects on Relative Use of PEPCK and NADP-ME Pathways of C4 Photosynthesis in Maize

C4 photosynthesis is an adaptive photosynthetic pathway which concentrates CO2 around Rubisco in specialized bundle sheath cells to reduce photorespiration. Historically, the pathway has been characterized into three different subtypes based on the decarboxylase involved, although recent work has provided evidence that some plants can use multiple decarboxylases, with maize in particular using both the NADP-malic enzyme (NADP-ME) pathway and phosphoenolpyruvate carboxykinase (PEPCK) pathway. Parallel C4 pathways could be advantageous in balancing energy and reducing equivalents between bundle sheath and mesophyll cells, in decreasing the size of the metabolite gradients between cells and may better accommodate changing environmental conditions or source to sink demands on growth. The enzyme activity of C4 decarboxylases can fluctuate with different stages of leaf development, but it remains unclear if the pathway flexibility is an innate aspect of leaf development or an adaptation to the leaf microenvironment that is regulated by the plant. In this study, variation in the two C4 pathways in maize were characterized at nine plant ages throughout the life cycle. Two positions in the canopy were examined for variation in physiology, gene expression, metabolite concentration, and enzyme activity, with particular interest in asparagine as a potential regulator of C4 decarboxylase activity. Variation in C4 and C3 metabolism was observed for both leaf age and canopy position, reflecting the ability of C4 pathways to adapt to changing microenvironments. One Sentence SummaryThe proportion of the two C4 pathways in maize plants is dependent on canopy position and not the age of the leaf.

plant biology↗

bioRxiv2020

Temporal changes in metabolism late in seed development affect biomass composition in soybean

The inverse correlation between protein and oil production in soybeans is well-documented; however, it has been based primarily on the composition of mature seeds. Though this is the cumulative result of events over the course of soybean seed development, it does not convey information specific to metabolic fluctuations during developmental growth regimes. Maternal nutrient supply via seed coat exudate measurements and metabolite levels within the cotyledon were assessed across development to identify trends in the accumulation of central carbon and nitrogen metabolic intermediates. Active metabolic operation during late seed development was probed through transient labeling with 13C substrates. The results indicated: i) a drop in lipid during seed maturation with a concomitant increase in carbohydrates, ii) a transition from seed filling to maturation phase characterized by quantitatively balanced changes in the carbon use and CO2 release, iii) changes in measured carbon and nitrogen resources supplied maternally over development, iv) 13C metabolites processed through gluconeogenesis towards sustained carbohydrate accumulation as the maternal nutrient supply diminishes, and v) oligosaccharide biosynthetic metabolism during seed coat senescence at maturation. These results highlight temporal engineering targets for altering final biomass composition to increase the value of soybeans and a path to breaking the inverse seed protein and oil correlation. One-sentence summaryAssessment of temporal changes in metabolism during soybean seed development indicated that lipid turnover during maturation contributes carbon for gluconeogenic production of carbohydrates.

plant biology↗

bioRxiv2020

Shifting carbon flux from non-transient starch to lipid allows oil accumulation in transgenic tobacco leaves

Plant leaf biomass is composed predominantly of carbohydrate and protein with less than 5% dry weight allocated to lipid and less than 1% of total lipid in the form of triacylglycerols (TAGs). The combined overexpression of multiple genes involved in different aspects of TAG synthesis and stabilization can result in TAG accumulation to over 30% dry weight in tobacco leaves, presumably requiring many metabolic adjustments within plant cells. The metabolic consequences to the combined source and sink capacities of high oil accumulating transgenic tobacco leaves compared to wild-type were inspected across development and photoperiod by utilizing foliar biomass components and 13CO2 flux through central carbon intermediates. Lipid biosynthesis was investigated through assessment of acyl-acyl carrier protein (ACP) pools using a recently derived quantification method that was extended to accommodate isotopic labeling. Lipids accumulated stepwise over plant development in the high-oil leaves, with 13CO2-labeling studies confirming increased carbon flux to lipids. The large increase in lipid content was concurrent with a decrease in foliar starch, with limited contribution from non-sucrose soluble sugars, indicating a redirection of carbon from starch to lipids. Starch accumulated non-transiently with plant age in wild-type leaves, suggesting an inherent capacity for a developmentally-regulated carbon sink in tobacco leaves that may have enabled the programmed altered carbon partitioning to lipids in transgenics. These studies provide insight into the metabolic plasticity of dual source-sink leaves over development and may in part explain recent successful leaf lipid engineering efforts in tobacco. One sentence summaryEngineering high oil accumulation in tobacco leaves is enabled by inherent source-sink plasticity associated with non-transient foliar starch accumulation over development.

plant biology↗