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THE FORM, DISTRIBUTION AND SEASONAL ACCUMULATION OF CALCIUM IN KIWIFRUIT LEAVES
C J Clark1, G S Smith1, G D Walker2
1Ruakura Soil and Plant Research Station, Ministry of Agriculture and Fisheries, Private Bag, Hamilton, New Zealand.
The New Phytologist
|April 20, 2021
Summary
Kiwifruit leaves accumulate calcium and magnesium throughout the season, primarily as calcium oxalate. Magnesium is mostly soluble, while calcium oxalate forms distinct crystalline structures in mature leaves.
Area of Science:
- Plant Physiology
- Plant Nutrition
- Biochemistry
Background:
- Understanding mineral nutrient dynamics in fruit crops like kiwifruit is crucial for optimizing yield and quality.
- Calcium (Ca) and Magnesium (Mg) play vital roles in plant cell structure, enzyme activity, and overall plant health.
- Seasonal variations in nutrient content can impact physiological processes and fruit development.
Purpose of the Study:
- To investigate the seasonal changes in calcium and magnesium content and their chemical forms in kiwifruit (Actinidia deliciosa) leaves.
- To identify the specific crystalline structures of calcium oxalate in mature kiwifruit leaves.
- To differentiate between physiologically active and bound forms of calcium within the leaf tissue.
Main Methods:
- Sequential fractionation using acetic acid, hydrochloric acid, and residual extraction to determine Ca and Mg distribution.
- Analysis of total Ca and Mg concentrations over the growing season.
- Scanning electron microscopy (SEM) and X-ray microanalysis for morphological and elemental characterization of crystalline deposits.
- X-ray diffraction (XRD) for crystalline structure identification.
Main Results:
- Total Ca and Mg concentrations increased linearly after the initial growth phase, peaking at leaf fall.
- Calcium oxalate was the predominant Ca fraction, decreasing from 79% to 42% of total Ca from early to late season.
- Physiologically active (acetic acid-soluble) Ca ranged from 15% to 41% seasonally.
- Magnesium was predominantly extracted by acetic acid (89-96%), indicating high solubility.
- SEM and X-ray microanalysis revealed two distinct crystalline Ca-rich forms: styloids and raphides, identified as calcium oxalate monohydrate (whewellite).
Conclusions:
- Kiwifruit leaves exhibit significant seasonal accumulation of Ca and Mg, with distinct fractionation patterns.
- Calcium oxalate is a major storage form of calcium in kiwifruit leaves, with its proportion decreasing as the season progresses.
- The identification of specific calcium oxalate crystal morphologies (styloids and raphides) provides insights into Ca deposition and potential roles in leaf structure or defense.
- The high solubility of Mg suggests its ready availability for physiological functions throughout the season.
Keywords:
Kiwifruit (Actinidia deliciosa)calcium and magnesium fractionationcalcium oxalate crystalsscanning electron microscopyseasonal trendsMore Related Videos
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