Plant respiratory metabolism: A special focus on the physiology of beetroot (beta vulgaris L.) mitochondria

Abstract

Mitochondria are important organelles for cellular energy. Apart from orchestrating cellular energy balance, mitochondria involve themselves in various processes such as synthesis of vitamins and lipids and production of reactive oxygen and nitrogen species. Understanding mitochondrial metabolism is crucial for understanding complete cellular metabolism, which is directly or indirectly involved in the biosynthesis of food and pharmaceutical products. Respiration, the chief function occurring in mitochondria, is divided into glycolysis, tricarboxylic acid (TCA) cycle, and electron transport chain. In addition to the classic operation of the pathways, mitochondria have various alternative pathways that are involved in plant responses to various stresses. Respiratory metabolism in green tissues is different from that occurring in roots, and more so in bulky tissues such as beetroots, because such storage organs have to cope with very low cellular oxygen concentrations. Bulky tissue organs like beetroots store sucrose as their storage carbohydrate. Therefore the cellular respiration in beetroots is different, especially during the storage period and sprouting period in comparison with the normal roots. Here respiratory metabolism and its association with various other metabolic pathways are described, with a special focus on beetroot, in which various alternative pathways such as NAD(P)H dehydrogenases or alternative oxidase pathways are discussed. Understanding respiratory metabolism has bearing on engineering beetroot for higher yields as well as prevention of storage losses.