Physio-Biochemical Responses of Sweet Cherry Leaf to Natural Cold Conditions.

Trees of the sweet cherry cultivar 'Grace Star' (Prunus avium L.) were exposed to low temperatures without frost for two consecutive nights under natural conditions 36 d after flowering, to study the effects on the physiological properties and metabolic status of leaves. The response was studied by measuring chlorophyll fluorescence and gas exchange parameters and by analyzing chloroplast pigments (i) immediately after exposure, (ii) 24 h and (iii) 48 h later. The first exposure at 2.4 (±0.2) °C and a minimum of 0.8 °C elicited more changes than the second exposure at 4.9 (±0.3) °C and a minimum of 2.4 °C. After the first exposure, the maximum quantum yield of PS II (Fv/Fm), effective quantum efficiency of PS II, net photosynthesis (PN), stomatal conductance (gs), transpiration, and intercellular CO2 concentration were significantly lower, and after the second exposure, the content of chlorophyll b, total chlorophyll, ß-carotene, and lutein were lower. The content of antheraxanthin and zeaxanthin was higher immediately after both exposures, and that of antheraxanthin was also higher 24 h later. Recovery took longer in trees that were exposed twice. Fv/Fm recovered within 48 h, but the de-epoxidation state of the xanthophyll cycle pool, PN, and gs did not reach the level of controls, indicating that the stress effect lasted several days which is probably sufficient to cause fruit drop and reduce yield.

Summer pruning of sweet cherry: a way to control sugar content in different organs.

BACKGROUND: Sweet cherry trees (Prunus avium L.) of the cultivar Grace Star were pruned either in dormancy or in summer. The response was studied by analyzing the sugar content in different organs (flower bud, leaf, and fruit) at three sections of the canopy (inner, outer, and upper) using high-performance liquid chromatography. The effect of summer pruning was evaluated by measuring photosynthetic photon flux density (PPFD) and leaf chlorophyll content (SPAD). RESULTS: In this study, the timing of pruning had a significant effect on sugar content in flower buds, leaves, and fruit. Trees pruned in summer had higher glucose, fructose, sorbitol, and sucrose content in flower buds, higher glucose and fructose contents in leaves, and lower fructose, sorbitol, and total sugar content in fruit than in trees pruned at dormancy. Higher average PPFD and lower SPAD values were measured in the inner canopy of trees pruned in summer. All measured parameters were influenced by position in the canopy. The lowest fructose and sorbitol contents in the flower bud, the lowest content of glucose, fructose, sorbitol, total sugars and the highest SPAD values in the leaf, while less dark and lighter fruit were measured in the inner part of the canopy. CONCLUSION: Summer pruning affects sugar distribution in the tree by altering irradiation conditions within the canopy. Our results suggest that summer pruning is an effective technological measure to improve sugar content in the buds. A strong, well nourished flower bud is a good indication of high fruit production next season. © 2021 Society of Chemical Industry.

The Effect of Water Supply on Sweet Cherry Phytochemicals in Bud, Leaf and Fruit.

The influence of a water supply on the content of phytochemicals (sugars, organic acids, hydroxycinnamic acids, flavonols, flavanols and anthocyanins) in the bud, leaf and fruit of sweet cherry (Prunus avium L.) was studied in two growing seasons. In addition, the shoot length, yield efficiency and fruit weight were determined. The trees of the cultivar 'Regina' on Weiroot 72 or Gisela 5 rootstocks were either irrigated or non-irrigated. Irrigated trees received, in addition to rainfall, an amount of water equal to 100% of evapotranspiration, while non-irrigated trees received only rainwater (40% less). An analysis of phytochemicals was performed using high-performance liquid chromatography combined with electrospray ionization mass spectrometry. Irrigated trees had a higher content of total sugars in leaf and bud, higher content of total organic acids in the fruit, and lower content of total hydroxycinnamic acids, total flavonols and flavanols in the leaf and fruit. Irrigated trees also had higher shoot length, fruit weight and lower yield efficiency. The content of phytochemicals in bud and leaf was not affected by rootstock, but the fruit phytochemical composition, shoot length and yield efficiency were. The content of phytochemicals in the bud and leaf was influenced by the presence or absence of fruits. Our results show that irrigation, rootstock and the presence of fruits had an influence on the composition of phytochemicals in sweet cherry.

Response of chloroplast pigments, sugars and phenolics of sweet cherry leaves to chilling.

The aim of the present study was to evaluate the effect of post-flowering chilling of sweet cherry (Prunus avium L.) on the content of biochemical parameters in the leaf (chloroplast pigments, sugars and phenolics). The effect of chilling was investigated in two experiments. Potted 2-year-old trees of cv. 'Grace Star' and 'Schneiders' were exposed to one, two or three consecutive overnight chillings at an average air temperature of 4.7 °C (Experiment I), but in the following year only trees of 'Grace Star' were chilled at 2.2 °C (Experiment II), 3 to 7 weeks after flowering. The analysis of the biochemical parameters was performed by high performance liquid chromatography combined with electrospray ionization mass spectrometry. Chilling at 4.7 °C caused little or no stress, while 2.2 °C induced more intense stress with increased zeaxanthin, sugar and phenolic content in leaves, while exposure of trees to higher temperatures and closer to flowering showed no changes. Two or three consecutive overnight chilling periods increased the phenolic content and enhanced the accumulation of zeaxanthin in the leaves. Sucrose, sorbitol, fructose, total sugar, and total flavonoid content in leaves increased within 48 h after chilling. Zeaxanthin epoxidized within 24 h after one and 48 h after one and two consecutive overnight chillings.