Seasonal Metabolic Investigation in Pomegranate (Punica granatum L.) Highlights the Role of Amino Acids in Genotype- and Organ-Specific Adaptive Responses to Freezing Stress

Every winter, temperate woody plants have to cope with freezing stress. Winter hardiness is of crucial importance for pomegranate survival and productivity. A comparative morphological and metabolic study was conducted on the stems and buds of 15 field-grown mature pomegranate genotypes in seven time-points during two developmental cycles. Seasonal changes of frost hardiness, as determined by electrolyte leakage method, and metabolite analysis by HPLC and GC revealed the variability in frost hardiness and metabolic contents result from genetic background and organ, as well as seasonal condition. Morphological adaptations, as well as metabolic remodeling, are the distinct features of the hardy genotypes. Larger buds with a greater number of compressed scales and the higher number of protective leaves, together with the higher number and content of changed metabolites, especially amino acids, seem to provide a higher frost resistance for those trees. We recorded two-times the change in metabolites and several-times accumulation of amino acids in the stem compared with buds. A better potential of stem for metabolome adjustment during the hardening period and a higher level of tolerance to stress is therefore suggested. High levels of arginine, proline, glutamine, and asparagine, and particularly the accumulation of alanine, tryptophan, and histidine are responsible for excellent tolerance of the stem of tolerant genotypes. With regard to the protective roles of amino acids, a relation between stress tolerance and the level of amino acids is proposed. This points both to the importance of amino acids in the winter survival of pomegranate trees, and to the evaluation of frost tolerance in other plants, by these specific markers.

Seasonal changes in carbohydrates and water content predict dynamics of frost hardiness in various temperate tree species

Predicting tree frost tolerance is critical to select adapted species according to both the current and predicted future climate. The relative change in water to carbohydrate ratio is a relevant trait to predict frost acclimation in branches from many tree species. The objective of this study is to demonstrate the interspecific genericity of this approach across nine tree species. In the studied angiosperm species, frost hardiness dynamics were best correlated to a decrease in water content at the early stage of acclimation (summer and early autumn). Subsequently, frost hardiness dynamics were more tightly correlated to soluble carbohydrate contents until spring growth resumption. Based on different model formalisms, we predicted frost hardiness at different clade levels (angiosperms, family, genus and species) with high to moderate accuracy (1.5–6.0°C RMSE) and robustness (2.8–6.1°C RMSEP). The TOT model, taking all soluble carbohydrate and polyols into account, was more effective and adapted for large scale studies aiming to explore frost hardiness across a wide range of species. The ISC model taking the individual contribution of each soluble carbohydrate molecule into account was more efficient at finer scale such as family or species. The ISC model performance also suggests that the role of solutes cannot be reduced to a 'bulk' osmotic effect as could be computed if all of them were located in a single, common, compartment. This study provides sets of parameters to predict frost hardiness in a wide range of species, and clues in targeting specific carbohydrate molecules to improve frost hardiness.

The study of multivariance in realization of the plum graft and rootstock combinations adaptivity systems to the changing conditions of environment in the Krasnodar region with the use of digital technologies

The study of rootstocks group, providing the average vigor of growth for the grafted fruit plants, discovered their significant influence on the frost hardiness of the “graft-rootstock” system. The adaptivity of the plum varieties in the different graft and rootstock combinations was studied according to the “frost hardiness” criterion in the stages of the winter and spring development of the flower buds. The computer maps of the plum efficient allocation were created on the studied rootstocks, permitting to lay down the plantings with the lesser risks in the terms of climate fluctuation. It was established, that in the south of Russia the climatic conditions to cultivate Stanley variety on PK SK 1 rootstock, as compared with the rootstock of cherry plum seedling, mostly often used in industrial plantings of plum are mostly favorable. The conducted research contributes to isolation and allocation of the most adaptive graft and rootstock combinations based on their frost hardiness and, consequently, regularity of fruit-bearing and yielding capacity.