Ultrastructure of Cells and Microanalysis in Malus domestica Borkh. ‘Szampion’ Fruit in Relation to Varied Calcium Foliar Feeding

Abstract

Calcium is one of the most poorly reutilized nutrients. Its deficiencies cause various physiological disturbances and, consequently, reduce the quantity and quality of yields. Reduced content of Ca2+ ions in cells leads to development of, e.g., bitter pit in apples. Efficient and instantaneous mitigation of Ca2+ deficiencies is provided by foliar feeding. There are no detailed data on the effect of foliar feeding with various calcium forms on the cell structure or on the microanalysis and mapping of this element in apple fruit cells. Therefore, we carried out comparative studies of the ultrastructure of epidermis and hypodermis cells, to assess the content and distribution of calcium in the cell wall, cytoplasmic membrane, cytoplasm, and precipitates of Malus domestica Borkh. ‘Szampion’ fruit exposed to four Ca treatments, including the control with no additional Ca supplementation (I) and foliar applications of Ca(NO3)2 (II), CaCl2 (III), and Ca chelated with EDTA (IV). Light and transmission electron microscopy and an X-ray microanalyzer were used and showed a beneficial effect of calcium preparations on the ultrastructure of fruit epidermis and hypodermis cells, manifested in the presence of a normally developed cell wall with a regular middle lamella, preserved continuity of cytoplasmic membranes, and stabilized cell structure. In the selected elements of apical epidermis cells, the highest level of Ca2+ ions was detected in the middle lamella, cell wall, plasmalemma, and cytoplasm. The highest increase in the Ca2+ content in these cell constituents was recorded in treatment IV, whereas the lowest value of the parameters was noted in variant III.

Transcriptomics Reveals the ERF2-bHLH2-CML5 Module Responses to H2S and ROS in Postharvest Calcium Deficiency Apples

“…In addition, compared to calcium-sufficient peels, calcium-deficient peels produced less H 2 S ( Figure 1 C–E), significantly increased O 2 •− , MDA, total phenol and flavonoid contents, and PPO activity, and decreased POD activity ( Figure 2 ). The increase in ROS and antioxidants such as total phenol and flavonoid in calcium-deficient peels may be caused by bitter pit disorder due to calcium deficiency, which was also consistent with previous reports [ 5 , 6 , 7 ]. The result of PCA shows that calcium content, ROS, and H 2 S production were main factors between calcium-deficient and calcium-sufficient apple peels.…”

“…It not only determines the yield and quality of agricultural crops, but also plays a pivotal role in maintaining plant cell structure, resistance to adverse stress and signal transduction [ 1 , 2 , 3 , 4 ]. Calcium can mitigate stress conditions, for example, by neutralizing reactive oxygen species (ROS) produced in cells [ 5 , 6 , 7 ]. Calcium deficiency results in ROS accumulation and causes damage to membranes, reduces the cell wall, weakens tissue stiffness, and increases water loss, which in turn leads to leaf wilting and shortens the shelf life of harvested fruit [ 8 , 9 , 10 ].…”

“…Calcium deficiency results in ROS accumulation and causes damage to membranes, reduces the cell wall, weakens tissue stiffness, and increases water loss, which in turn leads to leaf wilting and shortens the shelf life of harvested fruit [ 8 , 9 , 10 ]. It also causes various physiological disorders, such as reduction in fruit size, low firmness and thin peel, tip burn, and oxidative stress [ 5 , 10 , 11 , 12 ]. It has also been reported that calcium deficiency causes bitter pit and decreases titratable acidity, total soluble solids, and vitamin C contents, resulting in poorer postharvest fruit quality [ 13 ].…”

Accumulation of Abnormal Amyloplasts in Pulp Cells Induces Bitter Pit in Malus domestica

“…The apple was treated with Ca(NO 3 ) 2 , CaCl 2 , and Ca chelated with EDTA, and the structure of epidermal and hypodermal cells of the fruit was observed ultramicroscopically. Ca 2+ contributes to the stability of cell structure ( Kowalik et al, 2020 ). The distribution of Ca 2+ in various cell compartments is affected by various types of stimulation; however, these changes can only be observed at the ultrastructural level ( Sedmíková et al, 2003 ; Kowalik et al, 2020 ).…”

“…Ca 2+ contributes to the stability of cell structure ( Kowalik et al, 2020 ). The distribution of Ca 2+ in various cell compartments is affected by various types of stimulation; however, these changes can only be observed at the ultrastructural level ( Sedmíková et al, 2003 ; Kowalik et al, 2020 ). In another study, the ultramicroscopic analysis of the pulp cells of apples with bitter pit revealed plasmolysis and cell membrane rupture ( de Freitas et al, 2010 ); however, the type and mechanism of cell death remain unclear.…”