Engineering Germination Fitness for Sub-Physiological Temperatures in Plants

Abstract

Abstract-Germination is a key event in plant life cycle and imbibition temperature is an important factor for the major reorganization processes in the germinating seeds. Sub-physiological temperature at this stage affects virtually all aspects of cellular function including protein folding, kinetic parameters of membrane fluidity, protein assembly, and general metabolic processes. In this article we will review the research which has been carried out to decipher the basic mechanisms of low temperature (LT) stress with special emphasis on germination. With the better understanding of LT tolerance in some plant species we will also discuss how these attributes can be transferred in the important food crops to attain better germination stamina at sub-physiological temperatures. At germination stage, the cellular machinery in the embryo is not at its proper place and is going through reorganisation and any environmental severity has devastating effects on the fragile plant. But LT resistant species have evolved the ability to acclimatise, with the remodelling of cell and tissue structures and the reprogramming of metabolism and gene expression. Metabolic networks are redirected towards the synthesis of cryoprotectant molecules, which in association with other proteins bring about physical and biochemical restructuring of cell membranes through changes in the lipid composition and induction of other non-enzymatic proteins that alter the freezing point of water. Genetic engineering of crops for enhanced seed germination performance will certainly help to achieve optimum agricultural yields.. Germination physiology in low temperatureAll environmental stresses disrupt the normal functioning of a living system. To re-establish metabolic homeostasis, living systems require an adjustment of metabolic pathways in a process usually referred to as acclimation. For temperate plants, low temperature (LT) is a major non-living element of the environmental that affects water and nutrient uptake, membrane fluidity and protein and nucleic acid conformation, drastically influencing cellular metabolism directly by reducing the rates of biochemical reactions [1], accompanied by changes in the transcriptome, proteome and metabolome [2]. Chilling temperatures (0 to 15°C) frequently occur in nature and affect many species of plants, especially those of tropical origin (such as rice, corn, tomato and soybean), by causing wilting, chlorosis, or necrosis, thus restricting their growth and development. Metabolic rates are lowered which create energy imbalance. Freezing (0°C and below) temperatures cause membrane injury [3], decrease the respiration rate and ATP content [4], resulting in poor germination, reduced seedling emergence, decreased seedling vigour, and ultimately severe loss in yield of the food crops of tropical and subtropical origins [5][6][7][8][9]. Embryos, excised from seed coats of soybeans, leak profusely during the first minutes of imbibition. In the embryos imbibed at 10°C or lower, disproportionately more solutes leak ...