Transcript expression of Mg-chelatase and H+-ATPase isogenes in Vicia faba leaves as influenced by root and foliar magnesium supply

Background Magnesium deficiency results in a loss of yield and quality of crop plants. Foliar application of magnesium is under discussion with regard to the amelioration of magnesium deficiency. We have tested the effect of magnesium foliar application on the leaf photosynthesis rate and on the transcript abundance of two enzymes that depend upon the supply of magnesium. Methods Vicia faba L. were grown under controlled environmental conditions in nutrient solution. Plants growing in low-magnesium solution were treated with foliar applications of 0, 50 or 200 mM MgSO4. Results and conclusions Photosynthesis rate and chlorophyll concentration increased following magnesium leaf application in magnesium-deficient plants but did not reach the levels of plants sufficiently supplied with magnesium via the roots. Under magnesium deficiency, foliar application had its greatest effect on magnesium concentration, photosynthesis and chlorophyll concentration in older leaves but had only minor effects on younger leaves. However, foliar application increased the transcript levels of plasma-membrane ATPase in younger leaves but not in older leaves. The transcript levels of Mg-chelatase remained unchanged. The appearance of chlorosis is associated to aggravated loss of magnesium, in contrast a reduction in Mg chelatase transcript abundance is already measurable before the occurrence of visible symptoms as in the young leaves and might therefore represent a sensitive indicator of Mg deficiency.