Long-term anoxia tolerance in leaves of three wetland species : (Acorus calamus L., Iris pseudacorus L., Vaccinium macrocarpon AIT)

Anoxia tolerance of Acorus calamus. Iris pseudacorus and Vaccinium macrocarpon has been investigated by incubating whole plants under anaerobic conditions in the dark. Long-term survival of rhizomes under anoxia has been described in previous studies, but this study has shown that green leaves can also endure anoxia for prolonged periods. Leaves of A. calamus, I.pseudacorus and V.macrocarpon remained green and turgid under anoxia for up to 75d, 60d and 45d respectively. All growth processes ceased in leaves under anoxia. Anaerobic energy production via ethanol fermentation was active in all investigated plant organs as shown by the accumulation of ethanol. Low rates of anaerobic CO2 production indicated however, that the overall metabolic activity in the leaves was low under prolonged anoxia. The leaves seemed to adapt to the anaerobic conditions by an overall reduction of energy consumption rather than acceleration of the glycolytic rate. The demands for fermentable substrate were met by the mobilisation of internal carbohydrate reserves in leaves of V.macrocarpon. A.calamus and I.pseudacorus leaves contained only small amounts of carbohydrates, and these leaves possibly received carbohydrates from the stores in the rhizome. Prolonged anoxia considerably affected the leaf capacity for respiration and photosynthesis. After 28d of anoxia, respiratory capacity was reduced in A.calamus and V.macrocarpon by 80%, and in I.pseudacorus by 90-95%; this corresponded with a decline in the activity of the cytochrome c oxidase. The photosynthetic capacity of leaves was decreased after 28d of anoxia by 83% in A.calamus, by 97% in I.pseudacorus and by 80% in V.macrocarpon. The reduction in the photosynthetic capacity was accompanied by alterations in the chlorophyll fluorescence pattern indicating damage to the PSII reaction centre and the subsequent electron transport; only minor changes occurred in the chlorophyll content of anaerobic leaves. On return to air and light, recovery of respiration and photosynthesis occurred in the leaves, but species-specific differences were observed in the speed of recovery. Among the three investigated species, A.calamus leaves endured the anoxic conditions longer than leaves of the other two species; and on return to air, A.calamus leaves showed the most rapid recovery. A.calamus was characterised by efficient carbohydrate utilisation under anoxia. Cellular membranes and organelle ultrastructure appeared to be stable in A.calamus leaves for at least 28d of anoxia

Photosynthesis in C3-C4 intermediate Moricandia species.

Evolution of C4 photosynthesis is not distributed evenly in the plant kingdom. Particularly interesting is the situation in the Brassicaceae, because the family contains no C4 species, but several C3-C4 intermediates, mainly in the genus Moricandia Investigation of leaf anatomy, gas exchange parameters, the metabolome, and the transcriptome of two C3-C4 intermediate Moricandia species, M. arvensis and M. suffruticosa, and their close C3 relative M. moricandioides enabled us to unravel the specific C3-C4 characteristics in these Moricandia lines. Reduced CO2 compensation points in these lines were accompanied by anatomical adjustments, such as centripetal concentration of organelles in the bundle sheath, and metabolic adjustments, such as the balancing of C and N metabolism between mesophyll and bundle sheath cells by multiple pathways. Evolution from C3 to C3-C4 intermediacy was probably facilitated first by loss of one copy of the glycine decarboxylase P-protein, followed by dominant activity of a bundle sheath-specific element in its promoter. In contrast to recent models, installation of the C3-C4 pathway was not accompanied by enhanced activity of the C4 cycle. Our results indicate that metabolic limitations connected to N metabolism or anatomical limitations connected to vein density could have constrained evolution of C4 in Moricandia

Transport Proteins Enabling Plant Photorespiratory Metabolism

Kuhnert F, Schlüter U, Linka N, Eisenhut M. Transport Proteins Enabling Plant Photorespiratory Metabolism. Plants. 2021;10(5): 880.Photorespiration (PR) is a metabolic repair pathway that acts in oxygenic photosynthetic organisms to degrade a toxic product of oxygen fixation generated by the enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase. Within the metabolic pathway, energy is consumed and carbon dioxide released. Consequently, PR is seen as a wasteful process making it a promising target for engineering to enhance plant productivity. Transport and channel proteins connect the organelles accomplishing the PR pathway—chloroplast, peroxisome, and mitochondrion—and thus enable efficient flux of PR metabolites. Although the pathway and the enzymes catalyzing the biochemical reactions have been the focus of research for the last several decades, the knowledge about transport proteins involved in PR is still limited. This review presents a timely state of knowledge with regard to metabolite channeling in PR and the participating proteins. The significance of transporters for implementation of synthetic bypasses to PR is highlighted. As an excursion, the physiological contribution of transport proteins that are involved in C4 metabolism is discussed

Flowering Time-Regulated Genes in Maize Include the Transcription Factor ZmMADS1

Flowering time (FTi) control is well examined in the long-day plant Arabidopsis (Arabidopsis thaliana), and increasing knowledge is available for the short-day plant rice (Oryza sativa). In contrast, little is known in the day-neutral and agronomically important crop plant maize (Zea mays). To learn more about FTi and to identify novel regulators in this species, we first compared the time points of floral transition of almost 30 maize inbred lines and show that tropical lines exhibit a delay in flowering transition of more than 3 weeks under long-day conditions compared with European flint lines adapted to temperate climate zones. We further analyzed the leaf transcriptomes of four lines that exhibit strong differences in flowering transition to identify new key players of the flowering control network in maize. We found strong differences among regulated genes between these lines and thus assume that the regulation of FTi is very complex in maize. Especially genes encoding MADS box transcriptional regulators are up-regulated in leaves during the meristem transition. ZmMADS1 was selected for functional studies. We demonstrate that it represents a functional ortholog of the central FTi integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) of Arabidopsis. RNA interference-mediated down-regulation of ZmMADS1 resulted in a delay of FTi in maize, while strong overexpression caused an early-flowering phenotype, indicating its role as a flowering activator. Taken together, we report that ZmMADS1 represents a positive FTi regulator that shares an evolutionarily conserved function with SOC1 and may now serve as an ideal stating point to study the integration and variation of FTi pathways also in maize

Chapter Identification and Application of Phenotypic and Molecular Markers for Abiotic Stress Tolerance in Soybean

Neurology & clinical neurophysiolog