Calcium forms in leaves of muskmelon plants grown with different calcium compounds

Abstract

The time course trend of the various calcium (Ca) forms (soluble, bound, inorganic insoluble, and organic insoluble) was studied throughout the growing period in mature and young leaves of Cucumis melo L. cv. Revigal plants cultivated on rockwool under unfavorable conditions for Ca uptake. The following anions accompanying Ca were tested: NO₃ ^‐ as control, as well as EDTA²‐, Cl^‐ and SO₄ ^2‐ with two concentration levels equivalent to half and a quarter part of the Ca level of the control. The differences between mature and young leaves were very marked for all the forms. Generally, the inorganic insoluble Ca form was predominant in mature leaves, while the bound form showed the lowest levels. In young leaves, on the other hand, soluble Ca was usually the major form, whereas organic insoluble Ca was the least plentiful. The treatments with Ca‐EDTA (Ch‐#fr1/2> and Ch‐#fr1/4>) resulted in lower leaf Ca concentration than the other treatments. The ratios referring to the Ca contents of mature leaves/young leaves for the six Ca‐deficiency treatments varied from 5.0 to 18.5 (soluble Ca), 3.8 to 11.0 (bound Ca), 9.0 to 41.7 (inorganic insoluble Ca), and 9.0 to 47.7 (organic insoluble Ca). For the control, these ratios were 2.3 (soluble Ca), 1.6 (bound Ca), 22.3 (inorganic insoluble Ca), and 61.5 (organic insoluble Ca). The insoluble forms always showed higher ratios. For all treatments and sampling dates the total Ca level was approximately ten times higher in mature leaves than in young leaves and always in the following order: NO^‐>Cl^‐‐#fr1/2> ^∼ SO₄2‐#fr1/2>> Cl^‐‐#fr1/4> ^∼ SO₄ ^2‐‐#fr1/4>> Ch‐#fr1/2>>Ch‐#fr1/4>, which was the same order observed in the response as reflected by fruit and vegetative biomass production.