RESULTS OF COLD AND FROST IMPACT ON PHYSIOLOGICAL AND BIOCHEMICAL INDICATORS OF CAUCASIAN TEA CAMELLIA SINENSIS (L.) KUNTZE GENOTYPES

Cold and frost are two limiting factors that restrict the yield of many agricultural crops, including the tea plant (Camellia sinensis (L.) Kuntze). Its acclimatization from tropical and temperate regions has resulted in the emergence of unique germplasm with extremely frost-resistant genotypes in the northwestern Caucasus. This study assessed the physiological and biochemical parameters of the frost-resistant varietal population ‘Gruzinsky No. 7’ and the non-frost-resistant cultivar ‘Kolkhida’, which were treated with cold from 0 to +2 °C and frost (–6…–8 °C). When studying the morpho-anatomical structure of the leaf, it was found that the specific features for the genotype ‘Gruzinsky No. 7’ are: a large thickness of the parenchyma (298.57 ±10.89a μm), a small size of the stomata (108.0 ±5.66b mm2) and their low width (29.0 ±1.35a μm), which allows recognizing low-temperature stress and reacting to it at an early metabolic level. A significant difference between the two genotypes was observed in the thickness of the spongy and palisade parenchyma. In ‘Gruzinsky № 7’, both parenchyma layers were significantly thicker (141.07 ±11.82a μm and 121.18 ±2.28a μm, respectively) compared to the frost-sensitive ‘Kolkhida’ cultivar (113.17 ±7.94b μm and 86.01 ±2.70b μm, respectively). Cold treatment did not change the cell membrane stability indices, relative water content in leaves, or cell sap pH in both studied tea genotypes. However, frost treatment caused a significant decrease in these indices in the ‘Kolkhida’ cultivar, while no significant changes were observed in ‘Gruzinsky № 7’. Both cold and frost treatments increased water-soluble protein by 3–4 times without any significant differences between the two genotypes. During frost treatment, ‘Gruzinsky № 7’ had the highest content of soluble sugars. The content of proline increased in both genotypes, during induction by both cold and frost. Also, the sum of cations in the cell sap increased, prominent changes were observed in K+, Mg2+, Ca2+, which may be an important mechanism of frost resistance due to the stabilization of cell turgor and ion exchange. Under the influence of cold, the content of 6 amino acids increased in ‘Gruzinsky № 7’: serine – by 3.24 times, leucine and valine – by 3.3 and 3.7, glycine – by 4, threonine – by 4.8, methionine – by 5.3 times. In the ‘Kolkhida’ cultivar, only 2 amino acids increased: serine – by 3.3 and methionine – by 4 times. Under frost, the content of 5 amino acids increased in ‘Gruzinsky No. 7’: leucine, valine, serine – by 3.6–3.7 times, threonine – by 4.4, methionine – by 6.55 times. Under similar conditions, the content of 4 amino acids increased in the ‘Kolkhida’ cultivar: serine – 2.8 times, valine – 3.2, leucine – 3.8, methionine – 4.4 times. An important role in the cold and frost resistance of tea plants was established for six amino acids: leucine, methionine, valine, threonine, serine and glycine.